阅读说明：本技术 Q切换的激光器系统 (Q-switched laser system ) 是由 萨勒曼·诺施 乌齐耶·沙因托普 埃坦·摩西·佩雷斯 于 2019-05-22 设计创作，主要内容包括：一种激光器系统,包括激光器腔、定位在激光器腔内的增益介质、光耦合至增益介质的泵浦源、定位在激光器腔的第一端处的输入反射镜、定位在激光器腔的第二端处的输出耦合器、定位在激光器腔内的第一标准具和定位在激光器腔内的q切换元件,其中,激光器系统被配置为提供在1700nm至3000nm范围内的选定波长下具有至少10nm的可调谐光谱范围的激光束。还公开了一种用于使用例如用于产生脉冲激光束的激光器系统的方法。(A laser system comprising a laser cavity, a gain medium positioned within the laser cavity, a pump source optically coupled to the gain medium, an input mirror positioned at a first end of the laser cavity, an output coupler positioned at a second end of the laser cavity, a first etalon positioned within the laser cavity, and a q-switching element positioned within the laser cavity, wherein the laser system is configured to provide a laser beam having a tunable spectral range of at least 10nm at a selected wavelength in the range of 1700nm to 3000 nm. A method for using a laser system, for example for generating a pulsed laser beam, is also disclosed.)

1. A laser system, comprising:

a laser cavity;

a gain medium positioned within the laser cavity;

a pump source optically coupled to the gain medium;

an input mirror positioned at a first end of the laser cavity;

an output coupler positioned at a second end of the laser cavity;

a first etalon positioned within the laser cavity;

and a q-switching element positioned within the laser cavity;

wherein the content of the first and second substances,

the laser system is configured to provide a pulsed laser beam having a tunable spectral range of at least 10nm at a selected wavelength in the range 1700nm to 3000 nm;

the q-switching element provides pulsed switching of the laser beam;

and wherein the gain medium, the pump source, the input mirror, the output coupler, the first etalon, and the q-switching element are at an optical path of the pulsed laser beam.

2. The laser system of claim 1, further comprising a second etalon in the optical path of the pulsed laser beam and positioned proximate to the first etalon.

3. The laser system of any of claims 1 and 2, wherein the first etalon and/or the second etalon comprises yttrium aluminum garnet Y₃Al₅O₁₂(YAG)。

4. The laser system according to any of claims 2 and 3, wherein the second etalon is characterized by a thickness of 100 μm to 600 μm.

5. The laser system according to any of claims 1 to 4, wherein the first etalon is characterized by a thickness of 10 μm to 100 μm.

6. The laser system of any of claims 1 to 5, wherein the gain medium comprises YAlO selected from the group consisting of YAG, YAG-Al perovskite YAlO₃(YAP), lutetium lithium fluoride (LiLuF) and lithium yttrium fluoride (YLF).

7. The laser system according to any of claims 1 to 6, wherein the host crystal is doped with a rare earth element selected from the group consisting of thulium (Tm), holmium (Ho), chromium (Cr), erbium (Er) or any combination thereof.

8. The laser system of any of claims 1 to 7, wherein the gain medium comprises YAP and/or YLF host crystals doped with Tm.

9. The laser system of any of claims 1 to 8, wherein the pulsed laser beam is characterized by a wavelength in a range of 1800nm to 2100 nm.

10. The laser system of any of claims 1-9, wherein the pulsed laser beam has a spectral bandwidth of less than 1 nm.

11. The laser system of any of claims 1 to 10, wherein said q-switching element is selected from an active q-switching element and a passive q-switching element.

12. The laser system of any of claims 1 to 11, wherein the passive q-switching element comprises a saturable absorber configured to provide passive pulsed switching of a laser beam.

13. The laser system according to any of claims 1 to 12, wherein the saturable absorber comprises Cr: ZnS or Cr: ZnSe.

14. The laser system of any of claims 1 to 13, wherein the active q-switching element comprises an acousto-optic modulator (AOM) configured to provide active pulse switching of a laser beam.

15. The laser system of any of claims 1 to 14, further comprising one or more lenses that allow optical coupling of the pump source to the gain medium.

16. A method for generating a pulsed laser beam, the method comprising:

(i) providing a laser system, the laser system comprising:

a laser cavity;

a gain medium positioned within the laser cavity;

a pump source optically coupled to the gain medium;

an input mirror positioned at a first end of the laser cavity;

an output coupler positioned at a second end of the laser cavity;

a first etalon positioned within the laser cavity;

and a q-switching element positioned within the laser cavity; wherein the gain medium, the pump source, the input mirror, the output coupler, the first etalon, and the q-switching element are at an optical path of the pulsed laser beam;

(ii) supplying electrical power to the pump source to energize the gain medium, thereby generating the pulsed laser beam having a tunable spectral range of at least 10nm at a selected wavelength in a range from 1700nm to 3000 nm.

17. The method of claim 16, wherein the laser system further comprises a second etalon positioned proximate to the first etalon at an optical path of the pulsed laser beam.

18. The method of any of claims 16 and 17, wherein the pulsed laser beam is characterized by a pulse energy of at least 0.8 mJ.

19. The method of any of claims 16 to 18, wherein the pulsed laser beam is characterized by a wavelength in the range of 1800nm to 2100 nm.

20. The method of any of claims 16-19, wherein the pulsed laser beam is characterized by a tunable spectral range of at least 10 nm.

Technical Field

The invention relates to the field of laser Q-switching.

Background

Diode pumped solid state lasers are generally considered to be the most practical source of laser radiation for applications requiring high efficiency and compact, lightweight and robust packaging. The laser diode pump source has high electrical-to-optical conversion efficiency, and the narrow-band spectral output of the laser diode can be selected to closely match the absorption band of the solid-state laser material.

Q-switching provides short duration optical pulses required for laser ranging, nonlinear studies, medical and other important applications.

Lasers operating in the 2 μm region that are safe for the human eye have various applications in the fields of medical microsurgery, infrared neurostimulation, plastic material processing, gas spectroscopy, remote sensing, and are well established as pump sources for lasers in the mid-Infrared (IR) region.

Some of these applications require laser sources having one or more characteristics, such as: tunability, narrow spectral bandwidth, near diffraction limited beams and pulsed radiation. In particular, there is a desirable need in lasers combining spectral tunability and pulsed operation, so that laser parameters are controlled more precisely.

The above examples of related art and limitations related thereto are intended to be illustrative, not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.

Disclosure of Invention

The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools, and methods which are meant to be exemplary and illustrative, not limiting in scope.

According to an embodiment, there is provided a laser system comprising a laser cavity, a gain medium positioned within the laser cavity, a pump source optically coupled to the gain medium, an input mirror positioned at a first end of the laser cavity, an output coupler positioned at a second end of the laser cavity, a first etalon positioned within the laser cavity, and a q-switching element positioned within the laser cavity; wherein the laser system is configured to provide a pulsed laser beam having a tunable spectral range of at least 10nm at a selected wavelength in the range 1700nm to 3000 nm; the gain medium, the pumping source, the input reflector, the output coupler, the first etalon and the q-switching element are positioned at the optical path of the pulse laser beam; and wherein the q-switching element provides pulsed switching of the laser beam.

In some embodiments, the laser system further comprises a second etalon positioned proximate to the first etalon at an optical path of the pulsed laser beam.

In some embodiments, the second etalon is characterized by a thickness of 100 μm to 600 μm.

In some embodiments, the first etalon is characterized by a thickness of 10 μm to 100 μm.

In some embodiments, the gain medium comprises at least one matrix crystal selected from the group consisting of YAG, yttrium aluminum perovskite YAlO3(YAP), lithium lutetium fluoride (LiLuF), and Yttrium Lithium Fluoride (YLF).

In some embodiments, the host crystal is doped with a rare earth element selected from the group consisting of thulium (Tm), holmium (Ho), chromium (Cr), erbium (Er), or any combination thereof.

In some embodiments, the gain medium comprises a matrix crystal of YAP and/or YLF doped with Tm.

In some embodiments, the laser beam is characterized by a wavelength in the range of 1800nm to 2100 nm.

In some embodiments, the laser beam has a spectral bandwidth of less than 1 nm.

In some embodiments, the q-switching element is selected from the group consisting of an active q-switching element and a passive q-switching element.

In some embodiments, the passive q-switching element comprises a saturable absorber configured to provide passive pulsed switching of the laser beam.

In some embodiments, the saturable absorber comprises Cr: ZnS or Cr: ZnSe.

In some embodiments, the active q-switching element comprises an acousto-optic modulator (AOM) configured to provide active pulsed switching of the laser beam.

In some embodiments, the laser system includes one or more lenses to allow optical coupling of the pump source to the gain medium.

According to an embodiment, there is provided a method for generating a pulsed laser beam, the method comprising: (i) providing a laser system comprising a laser cavity, a gain medium positioned within the laser cavity, a pump source optically coupled to the gain medium, an input mirror positioned at a first end of the laser cavity, an output coupler positioned at a second end of the laser cavity, a first etalon positioned within the laser cavity, and a q-switching element positioned within the laser cavity; and wherein the gain medium, the pump source, the input mirror, the output coupler, the first etalon, and the q-switch element are at an optical path of the pulsed laser beam; (ii) electrical power is supplied to a pump source to energize the gain medium, thereby generating a pulsed laser beam at a selected wavelength in the range of 1700nm to 3000nm and having a tunable spectral range of at least 10 nm.

In some embodiments, the laser system further comprises a second etalon positioned proximate to the first etalon at an optical path of the pulsed laser beam.

In some embodiments, the pulsed laser beam is characterized by a pulse energy of at least 0.8 mJ.

In some embodiments, the pulsed laser beam is characterized by a wavelength in the range of 1800nm to 2100 nm.

In some embodiments, the pulsed laser beam is characterized by a tunable spectral range of at least 10 nm.

Unless defined otherwise, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, exemplary methods and/or materials are described below. In case of conflict, the present patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be necessarily limiting.

Drawings

Exemplary embodiments are shown in the referenced figures. The dimensions of the components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. These figures are listed below.

Fig. 1 is a schematic illustration of an exemplary laser system, according to certain exemplary embodiments of the present subject matter.

Fig. 2 is a schematic illustration of an exemplary laser system, according to certain exemplary embodiments of the present subject matter.

Fig. 3A and 3B present graphs showing Tm: YLF output power with and without etalon plates in continuous wave mode (CW) (fig. 3A) and pulsed mode (fig. 3B).

Fig. 4A and 4B present graphs showing the tunable performance of the laser; YLF spectral tuning at CW (FIG. 4A) and Tm in pulsed mode (FIG. 4B).

Fig. 5A and 5B present graphs showing the Tm: YLF spectral bandwidth without (fig. 5A) and with (fig. 5B) etalon plates.

Fig. 6A-6F present graphs showing laser performance in pulse mode (energy pulse-fig. 6A, 6D; pulse duration-fig. 6B, 6E; peak power-fig. 6C, 6F) with and without an etalon plate (fig. 6A, 6B, 6C).

Fig. 7 presents a graph showing the free spectral transmission range (solid line) superimposed by a pair of 25 μm and 500 μm etalon thicknesses compared to the transmission (dashed line) of a single 25 μm etalon plate, where the angle of the 25 μm etalon is optimal for a λ 1935nm laser.

Fig. 8A to 8C present graphs showing the performance of AQS Tm: YAP lasers (AOM frequency l kHZ, λ 1935nm, spectral bandwidth 0.15nm) with and without etalon plates. Fig. 8A presents a graph showing pulse energy as a function of absorbed pump power. Fig. 8B presents a graph showing pulse duration as a function of absorbed pump power. Fig. 8C presents a graph showing peak power as a function of absorbed pump power.

FIGS. 9A and 9B present tunable performance of AQS Tm: YAP lasers (FIG. 9A)

And spectral width (fig. 9B).

Fig. 10A and 10B present graphs showing the performance of a PQS Tm: YAP laser including an Output Coupler (OC) with 70% or 80% reflection. Fig. 10A presents a graph showing the laser average power (λ 1934nm, repetition rate 280Hz-1660 Hz, pulse duration: 24ns, 29ns for 70% and 85% OC, respectively). Fig. 10B presents a graph showing the laser peak energy (λ 1935nm, repetition rate 280Hz-1660 Hz, pulse duration: 24ns for 70% OC).

Fig. 11 presents a graph showing tunable performance of a PQS Tm: YAP laser comprising a saturable absorber with 89% transmission and an output coupler with 70% or 80% reflection.

FIG. 12 presents a graph showing Tm for different wavelengths for continuous mode (CW) and PQS modes, the threshold for absorbed pump power for YAP lasers.

Fig. 13 shows an exemplary laser system coupled to a multimode optical fiber.

FIG. 14 shows a flow diagram of an exemplary method for generating a pulsed laser beam, according to some non-limiting embodiments of the present invention.

FIG. 15 shows a flow diagram of an exemplary method for generating a pulsed laser beam, according to some non-limiting embodiments of the present invention.

Detailed Description

According to certain example embodiments, tunable Q-switched lasers are disclosed herein.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details set forth in the following description or illustrated in the examples thereof. The invention is capable of other embodiments or of being practiced or carried out in various ways.

A laser system, for example, a laser that generates light having a wavelength in the micrometer range is disclosed herein. In some embodiments, the laser is a pulsed laser that may be used in a variety of applications, such as surgery, military applications, material processing, optical communications, light detection and ranging (LIDAR).

Optionally, the system is capable of generating high energy pulses with pulse energies in the mJ range.

In some embodiments, the system may further include at least one etalon (also referred to as: "etalon plate"). Optionally, the etalon allows for tuning of the spectral bandwidth of the laser. Optionally, the etalon allows for tunability (e.g., free spectral range) of adjusting the wavelength of the emitted light.

Alternatively, the etalon may be an optical device having a desired reflectivity. Alternatively, the etalon may comprise Yttrium Aluminum Garnet (YAG). Alternatively, the etalon is modified by depositing a dielectric multilayer film on one or both surfaces. Alternatively, the spectral bandwidth of the laser may be adjusted by the reflectivity, thickness or refractive index of the etalon, for example, by limiting the transmitted wavelength band of the laser as it passes through the etalon.

Alternatively, etalons having different thicknesses may be used to adjust the spectral bandwidth and provide tunability of the spectral range. Alternatively, the spectral bandwidth and/or spectral range tunability of the laser light can be varied by adjusting the thickness of the etalon.

Optionally, by "at least one etalon" is meant at least two etalon plates. Optionally, the system comprises a pair of etalon plates.

Referring now to fig. 1, fig. 1 shows a schematic diagram of an exemplary laser system, according to certain exemplary embodiments of the present subject matter. Fig. 2 and 11 illustrate another exemplary laser system according to some exemplary embodiments of the present subject matter. According to one aspect of the present invention, a laser system 100 is provided. The laser system 100 may include a pump source (e.g., pump diode) 110. The pump source may generate particle number reversals within the gain medium, resulting in spontaneous emission.

Non-limiting exemplary elements of the pump source are: continuous lamps, flash lamps and lasers.

The pump diodes 110 may be optically coupled to the optical fiber 115, for example, by one or more optical elements (e.g., lens 120) to generate the gain of the laser. The pump diodes 110 may operate in a continuous wave mode or a quasi-continuous wave mode.

The pump diodes 110 may be tuned to provide an optical beam having a wavelength that matches a corresponding absorption wavelength corresponding to a transition from a ground state to an excited state of the gain medium as described below. There are various pumping schemes and pumping configurations known in the art, some of which may be applied to the application of the present disclosure. The pump diodes 110 may comprise direct pumps and the pump diodes may be fed into the optical fiber 115. Alternatively, the pump diode 110 configuration may include side pumping and end pumping.

The laser system 100 may include a gain medium 135. Gain medium 135 may be positioned within laser cavity 127. A non-limiting example gain medium 135 is selected from rare earth element doped materials (also referred to as "laser crystals"). Optionally, the material includes yttrium aluminum garnet Y selected from, but not limited to₃Al₅O₁₂("YAG"), yttrium lithium fluoride ("YLF"), lithium aluminum fluoride (LiLuF), and yttrium aluminum perovskite YAlO₃(a "YAP") as a matrix crystal. Optionally, the host crystal is doped with a rare earth element. Non-limiting exemplaryThe rare elements are selected from chromium (Cr), thulium (Tm), holmium (Ho), erbium (Er) or any combination thereof.

Alternatively, the matrix crystal may be any acceptable crystalline matrix such as, but not limited to: YAlO₃(YALO)、Y₃Al₅O₁₂(YAG), LuAG, YLF and Y₃(Sc_xAl_2-x)Al₃O₁₂(YSAG)。

Alternatively, the matrix crystal may be Tm³⁺-doped crystals. Optionally, the Tm-doped crystal ions include Tm: YAP and Tm: YLF crystals, allowing generation of laser light emitting light in the 2 μm range.

Additional non-limiting exemplary gain media 135 are selected from: tm is YAG, Tm is YVO4, Tm is YLF, Tm is YAP or Tm is LuAG. Alternatively, Tm in the host crystal material of the laser crystal³⁺The concentration of the dopant is inversely proportional to the length of the laser crystal. Alternatively, Tm³⁺The concentration of the dopant is between about 0.2% to about 8% by weight. Alternatively, the laser crystal has a size ranging from 1 × 1 × 1mm to 10 × 10 × 20mm, from 2 × 2 × 10mm to 4 × 4 × 10 mm. Alternatively, the gain medium may be Tm: YAP or Tm: YLF.

The laser system 100 may include a first optical element 130 (e.g., an input mirror). Optionally, the laser system 100 may include one or more lenses that may allow the pump source 110 to be optically coupled to the gain medium 135. Optionally, such a lens may focus the beam emitted from pump source 110, allowing for a minimum spot size (e.g., 100 μm to 500 μm) inside gain medium 135. Optionally, the laser system 100 may include a first collimating lens 120 and a second focusing lens 125.

The optical element 130 may be selected from a lens, a mirror such as a convex mirror, and a prism. The optical element 130 may be positioned in the optical path of the laser beam, for example, generally along the longitudinal axis 190 of the laser system 100. One or more of optical element 130, first collimating lens 120, and second focusing lens 125 may optically couple pump source 110 to gain medium 135. Optionally, the optical element 130, the first collimating lens 120, and the second focusing lens 125 may be positioned in the optical path of the laser beam.

Optionally, an input mirror 130 may be located at the first end of the laser cavity 127. Alternatively, input mirror 130 may be configured to act as a diverging optical element; either as a reflective convex surface, as a plano-optic element or as a plano-concave optical element. Light striking the input mirror may diverge as it reflects back toward the gain medium. In some cavities, depending on the gain medium, it may be beneficial to place an aperture adjacent to the input mirror to prevent high divergence light from re-entering the gain (lasing) medium, for example, due to waveguide effects.

Optionally, the input mirror 130 may include a first surface 122 and a second surface 123. Second surface 123 may be substantially facing laser cavity 127 and gain medium 135. Optionally, the second surface 123 may be coated with silver, a dielectric, or some similar coating to provide high reflective properties, for example, to serve as an input mirror. The first surface 122 may be characterized by a high transmission ("HT") of the optical beam received from the pump source 110. Alternatively, surface 123 can be characterized as having a high reflection ("HR") for wavelengths in the Infrared (IR) range (e.g., 1500nm-3500nm, such as 1800nm-2200 nm). Alternatively, the surface 123 may be characterized as having HT to the wavelength of the pump source 110 (e.g., 700nm-800 nm).

The laser system 100 may have one or more etalons (e.g., two) 140A and 140B positioned in the optical path of the laser beam. Optionally, the one or more etalons include a first etalon 140A and a second etalon 140B. Optionally, the second etalon 140B is positioned proximate to the first etalon 140A such that the first etalon and the second etalon are positioned in the optical path of the laser beam.

As used herein, "immediately adjacent" means that the second etalon is positioned next to the first etalon such that the generated laser beam is transmitted through the first etalon and subsequently transmitted through the second etalon. Further, it should be clarified that the laser system is not provided with any element between the first etalon and the second etalon. Optionally, etalons 140A and 140B are positioned along a horizontal axis 190 that includes gain medium 135. In some embodiments, the horizontal axis 190 may be defined as up to ± 60 degrees from the longitudinal axis.

Optionally, etalons 140A and 140B provide a tunable spectral range and narrow spectral bandwidth of the laser. Alternatively, the transmission wavelength bandwidth of the laser is determined by the reflectivity, thickness, and refractive index of the etalons 140A and 140B, and the pulse width thereof is adjusted accordingly. Optionally, the tunability range is at least 10nm, at least 14nm, at least 20nm, at least 25nm, at least 30nm, at least 35 nm. Optionally, the tunability range is from 8nm to 50nm, or in some embodiments from 8nm to 15nm, or in some embodiments from 10nm to 15nm, or in some embodiments from 15nm to 20nm, or in some embodiments from 20nm to 30nm, or in some embodiments from 30nm to 35nm, or in some embodiments from 35nm to 40 nm.

The tunability range may depend on the wavelength of the emitted light. Optionally, the tunability range may depend on the reflectivity of the output coupler and/or the transmissivity of the saturable absorber.

Optionally, etalon 140A is thinner than etalon 140B. Optionally, the etalon 140A has a thickness of 1 μm to 100 μm, or in some embodiments, 10 μm to 40 μm, or in some embodiments, 20 μm to 30 μm, or in some embodiments, 30 μm to 40 μm, or in some embodiments, 40 μm to 60 μm, or in some embodiments, 60 μm to 100 μm. In some embodiments, the etalon 140A has a thickness of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm, including any values and ranges therebetween.

Optionally, the etalon 140B has a thickness of 100 μm to 600 μm, or in some embodiments, 200 μm to 600 μm, or in some embodiments, 300 μm to 600 μm. Alternatively, the etalon 140B has a thickness of 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm, or 600 μm, including any values and ranges therebetween.

Optionally, the thickness ratio of etalon 140A to etalon 140B is 1:5 to 1:40, respectively. Optionally, the thickness ratio of etalon 140A to etalon 140B is 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, or 1:40, respectively, including any values and ranges therebetween.

Without being bound to any particular theory or mechanism, it is assumed that thinner etalons allow tunability of the spectral range. The thinner the etalon thickness, the wider the spectral range tunability. Further, the tunability range matches the amplification curve of the gain medium. Further, and without being bound by any particular theory or mechanism, it is assumed that a thicker etalon is responsive to spectral bandwidth narrowing, with the maximum thickness limited to avoid the occurrence of two spatially adjacent modes. In summary, the use of two etalons provides two features of spectral range tunability and spectral bandwidth narrowing.

Alternatively, etalon 140A or etalon 140B may comprise a fully or partially reflective material, e.g., in the form of a coating 145, such as described below under "exemplary configurations".

Optionally, the laser system 100 may have a Q-switching element 150 that allows the laser system 100 to be operated in a pulsed mode. The Q-switching element 150 may be a passive Q-switching element, or alternatively, an active Q-switching element.

The active Q-switching element may optionally be an optical modulation unit, optionally positioned within the resonator. Alternatively, an acousto-optic modulator (AOM), an electro-optic modulator (EOM), or an acousto-optic tunable filter (AOTF) may be included in the light modulation unit as the light modulator.

Optionally, the laser system 100 may have a Q-switching element, such as an acousto-optic modulator (AOM) 150. The AOM 150 may be positioned in the optical path of the laser beam, for example, approximately along the longitudinal axis of the laser system 100. In one exemplary configuration, the AOM 150 may be positioned at a second end of the laser cavity 127 between the etalon 140B and the OC 160. In other exemplary configurations, AOM 150 may be positioned between gain medium 135 and etalon 140A. Alternatively, the length of the laser cavity 127 may be in the range of 1mm-500mm, for example, about 100mm to 250 mm.

The AOM 150 may be configured to receive and modulate a seed laser beam. Alternatively, the laser beam may be arranged to be incident to the AOM 150 generally at a bragg angle. The AOM 150 may allow for the generation of a pulsed output beam. Further, the AOM 150 may control the time at which pulses are released from the seed laser.

In another configuration, laser system 100 has passive Q-switching elements instead of AOM 150. The passive Q-switching element may be configured to provide passive pulsed switching of the laser beam.

Optionally, the passive Q-switching element is a Saturable Absorber (SA). Such lasers provided with passive Q-switching elements can be a wide range of technologies that generate short pulse laser beams.

Optionally, the SA comprises a semiconductor. Optionally, the SA comprises quantum dots. Optionally, the SA comprises doped crystals. Non-limiting exemplary doped crystals are selected from: chromium (II) -doped zinc selenide (Cr: ZnSe) and chromium (II) -doped zinc sulfide (Cr: ZnS). Optionally, the w/w (weight/weight) concentration of the Cr2+ dopant in the doped crystal is between about 1% to about 20%, or alternatively 9% to 13%. In some cases, Cr: ZnSe and Cr: ZnS SA may have relatively high absorption cross sections, and thus, do not require a focusing mode for a small region on the SA. This may provide more flexibility with respect to the resonator. Alternatively, Cr: ZnSe and Cr: znsa have low saturable strength, which may result in a reduced risk of damage during Q-switching operation. Alternatively, the Cr: ZnS crystal SA can be applied to several passive Q-switched ("PQS") lasers, e.g., Ho: YAG, Tm: KY (WO)₄)、Tm:KLu(WO₄) And the like.

The laser system 100 may have an Output Coupler (OC) 160. OC 160 may be positioned at a second end of laser cavity 127. Alternatively, the OC may be positioned in the optical path of the laser beam. The OC 160 may transmit a portion of the optical power in an intra-cavity beam 170 outside the laser cavity to form an output beam. The OC 160 may be a component of an optical resonator that allows a portion of the light to be extracted from the intra-cavity beam of the laser. The OC 160 may have a Partially Reflective (PR) coating that allows some portion of the intra-cavity beam to transmit through. The OC may have a PR coating for wavelengths in the range 1800nm-2200 nm. Optionally, the PR coating has a reflectivity in the range of 50% -90%.

Optionally, gain medium 135, pump source 110, input mirror 130, output coupler 160, first etalon 140A, second etalon 140B and q-switching element 150 are in the optical path of the laser beam.

Alternatively, the OC can be a plano-concave mirror. Alternatively, the radius of curvature of the plano-concave mirror may range from 100mm to 400mm, from 150mm to 250 mm. Alternatively, the laser system 100 may have a housing. The housing may be made of a rigid, durable material such as, but not limited to, aluminum, stainless steel, hard polymers, and the like. The housing may have a cylindrical, conical, rectangular or any other suitable shape. The housing may prevent unwanted foreign elements from entering therein.

Exemplary configuration

In certain embodiments, the laser system 100 may be monitored by a monitoring system. The monitoring system may provide a means for monitoring and obtaining experimental data from the laser system 100 based on its output. The monitoring system may include an optical filter that may be optically connected to the laser cavity 127 that propagates at least partially through free-space light.

In some exemplary embodiments of the present subject matter, the pump diode 110 consists of a 793nm fiber coupled laser diode with a 105 μm core diameter (numerical aperture of 0.22). For a Tm-doped gain medium, the emitted wavelength may be tuned to correspond to³H₆→³H₄The absorption peak of the transition (e.g., when Tm: YLF is used for the gain medium). Alternatively, the emission wavelength of the pump source may be tuned to correspond to that of the gain medium³H₆→³F₄The absorption wavelength of the transition (e.g., when Tm: YAP is used for the gain medium). Alternatively, the emission wavelength of the pump source may be temperature tuned.

YLF crystals (9mm long and 3X 3mm cross section) with a 3.5% doping of Tm was used as gain medium 135. The laser crystal is anti-reflection (AR) coated at both the pump 110 and the laser wavelength. The crystal 135 is wrapped in indium foil and secured in an aluminum holder cooled by a cooler water at 18 ℃.

A pair of anti-reflection (AR) coated at the 650nm-1050nm biconvex first collimating lens 120 is used to deliver and focus the pump beam in the laser crystal Tm: YLF crystal (gain medium 135). The spot size obtained inside the Tm: YLF crystals was about 250 μm in diameter. YLF crystals can absorb about 67% of the pump power. An end-pumped architecture is implemented for the cavity 127. The optical element (input mirror) 130 is a back cavity mirror with an AR coating at the pump wavelength and a High Reflectivity (HR) coating for 1850nm-2000 nm.

Additional non-limiting embodiments of the input mirror 130, the first surface 122, and the second surface 123 are described above.

The OC 160 may be a plano-concave mirror having a 200mm radius of curvature. OC is Partially Reflective (PR) coated with 70% reflectivity between 1850nm-2000 nm. The distance between the two mirrors (first mirror and OC) is 200 mm.

For pulsed operation, a water-cooled AOM 150 made of 45mm long fused silica was used as the active Q-switch and operated at a radio frequency of 68 MHz.

The two etalons 140A and 140B comprise uncoated Yttrium Aluminum Garnet (YAG), with a thickness of 500 μm (140B) and 25 μm (140A) fixed on an intracavity rotary stage. The transmission of the etalon is based on fresnel reflection (8.2% from each surface). The transmission is wavelength dependent, varying over a spectrum between 72% and 100% for each of the etalons 140A and 140B. The use of two etalon plates allows a narrow spectral bandwidth to be achieved without reducing the tunability range. A thinner etalon 140A may be responsible for a wide tuning range due to its Free Spectral Range (FSR) of 39nm, while a thicker etalon may define the spectral bandwidth.

The transmission spectrum may vary inversely with the angle of the etalon to determine which wavelength will have the greatest transmission. Spectral loss can be controlled by rotating the 25 μm etalon 140A. After filtering out the remaining pump power, the output power can be measured using a power meter (Ophir, L50(150) A-35). The laser spectrum may be obtained by a spectrum analyzer OSA (Thorlabs, OSA 205C). The pulse energy can be measured using an energy meter (Ophir, PE 50-C). Pulse time characterization can be obtained using a 12.5GHz extended InGaAs photodetector (EOT, ET-5000) and a 100MHz oscilloscope (Agilent, DSO-X2012A).

Method

In some embodiments, a method of generating a pulsed laser beam is provided.

Referring now to fig. 14, an alternative flow diagram of a method for generating a pulsed laser beam is shown, according to some embodiments of the present invention.

In some embodiments, the method comprises the steps of:

(i) providing the above laser system, the laser system comprising:

a laser cavity;

an input mirror positioned at a first end of the laser cavity;

an output coupler positioned at a second end of the laser cavity;

a gain medium positioned within the laser cavity;

a pump source optically coupled to the gain medium;

a first etalon positioned within the laser cavity;

a q-switching element positioned within the laser cavity;

and optionally a second etalon positioned within the laser cavity, wherein the gain medium, the pump source, the input mirror, the output coupler, the first etalon, the q-switch element, and optionally the second etalon are in the optical path of the laser beam (step 700);

power (e.g., electrical power) is supplied to the pump source to energize the gain medium (step 702).

In some embodiments, the system includes two etalons, wherein the first etalon is positioned between the gain medium and the second etalon, and the second etalon is positioned between the first etalon and the q-switching element. In some embodiments, the q-switching element is positioned between the second etalon and an Output Coupler (OC).

When supplying power:

a laser beam may be generated through the gain medium (step 704); the laser beam then passes through the first etalon and optionally through the second etalon (step 706); and thereafter the laser beam is transmitted through the active or passive q-switching element (step 708).

The pulse mode of the laser can be obtained by passive q-switching elements, optionally within the resonator, or by active q-switching elements (e.g. optical modulation cells). An acousto-optic modulator (AOM), an electro-optic modulator (EOM), or an acousto-optic tunable filter (AOTF) may be included in the light modulation unit as the light modulator.

The laser beam may then pass through the OC (step 710), thereby outputting a pulsed laser beam from the laser cavity (step 712).

In some embodiments, the pump source is in operable communication with the input mirror.

Referring now to fig. 15, another alternative flow diagram of a method for generating a pulsed laser beam is shown, in accordance with some embodiments of the present invention.

In some embodiments, the method comprises the steps of:

(i) providing the above laser system, the laser system comprising:

a laser cavity;

an input mirror positioned at a first end of the laser cavity;

an output coupler positioned at a second end of the laser cavity;

a gain medium positioned within the laser cavity;

a pump source optically coupled to the gain medium;

a first etalon positioned within the laser cavity;

a q-switching element positioned within the laser cavity;

and optionally a second etalon positioned within the laser cavity, wherein the gain medium, the pump source, the input mirror, the output coupler, the first etalon, the q-switch element, and optionally the second etalon are in the optical path of the laser beam (step 700);

power (e.g., electrical power) is supplied to the pump source to energize the gain medium (step 702).

In some embodiments, the q-switch element is positioned between the gain medium and the first etalon, the first etalon is positioned between the q-switch element and the second etalon, and the second etalon is positioned between the first etalon and the OC.

When supplying power:

a laser beam may be generated through the gain medium (step 704); and thereafter the laser beam is transmitted through the active or passive q-switching element (step 706); and through the first etalon and then through the second etalon (step 708).

The pulse mode of the laser can be obtained by passive q-switching elements, optionally within the resonator, or by active q-switching elements (e.g. optical modulation cells). An acousto-optic modulator (AOM), an electro-optic modulator (EOM), or an acousto-optic tunable filter (AOTF) may be included in the light modulation unit as the light modulator.

The laser beam may then pass through the OC (step 710), thereby outputting a pulsed laser beam from the laser cavity (step 712).

In some embodiments, the pump source is in operable communication with the input mirror.

In some embodiments, the laser beam is further optically coupled to an optical fiber to enable fiber optic delivery of the laser beam (fig. 13). There are various optical fibers known in the art, some of which may be applied to the present application.

In some embodiments, the laser beam is characterized by a wavelength, such as the Infrared (IR) spectrum. Without being limited by any particular mechanism, the wavelength range may depend on the active ions on the gain medium. For example, but not limiting of, for Tm doped media, the range may vary from 1700nm to 2100 nm; for Ho-doped media, this range can vary from 2000nm to 2200 nm; for Cr-doped media, this range can vary from 2200nm to 2700nm or from 2700nm to 3000nm, for example for Er-doped media.

In some embodiments, the laser beam is characterized by a wavelength in a range from 1800nm to 2100nm, from 1900nm to 2000 nm.

In some embodiments, the pulsed laser beam is characterized by an energy of at least 0.8 mJ. In some embodiments, the pulsed laser beam is characterized by an energy of at least 1 mJ. In some embodiments, the pulsed laser beam is characterized by an energy of at least 2 mJ. In some embodiments, the pulsed laser beam is characterized by an energy of at least 3 mJ. In some embodiments, the pulsed laser beam is characterized by an energy of at least 4 mJ. In some embodiments, the pulsed laser beam is characterized by an energy of at least 4.5 mJ.

In some embodiments, the pulsed laser beam energy is in the range of 1mJ to 10 mJ. In some embodiments, the pulsed laser beam energy is 1mJ, 2mJ, 3mJ, 4mJ, 5mJ, 6mJ, 7mJ, 8mJ, 9mJ, or 10mJ, including any value and range therebetween.

In some embodiments, the pulses of the laser beam are characterized by: the duration is 5 to 10 nanoseconds, 10 to 20 nanoseconds, 20 to 30 nanoseconds, 30 to 40 nanoseconds or 30 to 50 nanoseconds at a total pulse energy of 1 to 10 millijoules and a wavelength of 1800 to 2000 nm.

In some embodiments, the laser spectral bandwidth is from 0.1nm to 0.5nm FWHM, such as 0.1nm, 0.2nm, 0.3nm, 0.4nm, or 0.5nm FWHM, including any values and ranges therebetween.

In some embodiments, the electrical power is supplied at 1 watt to 50 watts. In some embodiments, the electrical power is supplied at 1 watt to 40 watts. In some embodiments, the electrical power is supplied at 1 watt to 30 watts. In some embodiments, the electrical power is supplied at 2 watts to 30 watts. In some embodiments, the electrical power is supplied at 3 watts to 30 watts. In some embodiments, the electrical power is supplied at 1 watt, 5 watts, 10 watts, 15 watts, 20 watts, 25 watts, 30 watts, 35 watts, 40 watts, 45 watts, or 50 watts, including any values and ranges therebetween.

The present invention may be a system, method and/or computer program product. The computer program product may include a computer-readable storage medium (or multiple computer-readable storage media) having computer-readable program instructions thereon for causing a processor to perform various aspects of the present invention.

The computer readable storage medium may be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic memory device, a magnetic memory device, an optical memory device, an electromagnetic memory device, a semiconductor memory device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer-readable storage medium includes the following: a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a Static Random Access Memory (SRAM), a portable compact disc read-only memory (CD-ROM), a Digital Versatile Disc (DVD), a memory stick, a floppy disk, a mechanical encoding device having instructions recorded thereon, and any suitable combination of the foregoing. A computer-readable storage medium as used herein should not be interpreted as a transitory signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., optical pulses through a fiber optic cable), or an electrical signal transmitted through a wire. Rather, the computer-readable storage medium is a non-transitory (i.e., non-volatile) medium.

The computer-readable program instructions described herein may be downloaded from a computer-readable storage medium to a corresponding computing/processing device or to an external computer or external storage device via a network, such as the internet, a local area network, a wide area network, and/or a wireless network. The network may include copper transmission cables, optical transmission fibers, wireless transmissions, routers, firewalls, switches, gateway computers and/or edge servers. The network adapter card or network interface in each computing/processing device receives computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in a computer-readable storage medium within the respective computing/processing device.

Computer-readable program instructions for carrying out operations of the present invention may be assembly instructions, Instruction Set Architecture (ISA) instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C + +, or the like, as well as conventional programming languages, such as the "C" programming language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partly on the user's computer as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider). In some embodiments, an electronic circuit comprising, for example, a programmable logic circuit, a Field Programmable Gate Array (FPGA), or a Programmable Logic Array (PLA), can personalize the electronic circuit by executing computer-readable program instructions with state information of the computer-readable program instructions in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions.

These computer-readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer-readable program instructions may also be stored in a computer-readable storage medium that can direct a computer, programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer-readable storage medium having stored therein the instructions comprises an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer, other programmable apparatus or other devices implement the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

The description of various embodiments of the present invention has been presented for purposes of illustration but is not intended to be exhaustive or limited to the disclosed embodiments. Various modifications and alterations may become apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application, or technical improvements of the technology found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

SUMMARY

In the present application, various embodiments of the present invention may be presented in a range format. It is to be understood that the description of the range format is for convenience and simplicity only and is not to be construed as an exhaustive limitation on the scope of the invention. Thus, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, a description of a range (such as 1 to 6) should be considered to have specifically disclosed sub-ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., as well as individual values within that range, e.g., 1, 2, 3, 4, 5, and 6. The same applies regardless of the breadth of the range.

Whenever a numerical range is expressed herein, it is meant to include any recited number (decimal or integer) within the expressed range. The phrases "a range between a first indicated number and a second indicated number" and "a range from" the first indicated number "to" the second indicated number "are used interchangeably herein and are intended to include both the first indicated number and the second indicated number as well as all decimal and integer numbers therebetween.

In the description and claims of this application, the words "comprise," "include," and "have," and forms thereof, are not necessarily each limited to members of a list that may be associated with the words. Further, in the event of an inconsistency between the present application and any of the documents incorporated by reference, the present application is hereby intended to control.

Various embodiments and aspects of the present invention described above and claimed in the appended claims section find experimental support in the following examples.

Examples

Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non-limiting fashion.

In some exemplary procedures describing Tm: YLF lasers, a laser system as described above in the "exemplary configuration" is used. In some exemplary procedures describing Tm: YAP lasers, a laser configuration as described in fig. 2 is used.

In an alternative configuration, an exemplary embodiment of the present invention is shown that provides a Tm: YLF based laser system (as illustrated by fig. 1). The Tm for Continuous Wave (CW) operation, YLF laser performance as a function of absorbed pump power, without the intracavity etalon can be seen in fig. 3A. An absorbed pump power at a laser threshold of 1.9W is obtained. The maximum output power of 4.57W was measured at an absorbed pump power of 11.9W, corresponding to an optical-to-optical conversion of 23.3% and a slope efficiency of 42.9%.

The measured laser wavelength was 1885nm with a spectral width at full width at half maximum (FWHM) of 1.4 nm. After inserting the etalon pair into the laser cavity, the laser achieves a maximum output power of 4.05W corresponding to a 20.6% light-to-light conversion, and a slope efficiency of 38% at 1879nm laser wavelength of fig. 4A.

In the CW setting, the laser wavelength is tuned from 1873nm to 1908nm, as shown in fig. 4A, achieving a continuous tuning range of 35 nm. As shown in fig. 4A, the measured output power does not drop from 2.9W at an absorbed pump power of 11.9W throughout the tuning range.

For this narrowed bandwidth tuning operation, a maximum output power of 4.05W is achieved at a wavelength of 1879 nm. In the active Q-switch (AQS) mode, a repetition rate of 1KHz is selected. The average output power of the laser for free-running (without etalon) pulse operation is shown in fig. 3B.

The lasing threshold occurs at an absorbed pump power of 3W. A maximum average output power of 2.25W is achieved at an absorbed pump power of 8W corresponding to an optical-to-optical conversion of 18.3% and a slope efficiency of 44%. As shown in FIG. 5A, the measured emission wavelength was 1985nm with a spectral width of 1.4nm FWHM. A maximum output energy of 2.25mJ was measured, with a pulse duration of 40ns, corresponding to a peak power of 56.2Kw shown in fig. 6A to 6E. After inserting the etalon pair inside the laser cavity, the laser was operated with an absorbing pump power threshold of 3.6W, resulting in a maximum average output power of 1.97W at an absorbing pump power of 9.2W, as shown in fig. 3B, corresponding to an energy output of 1.97mJ to 13.7% of light conversion, and a slope efficiency of 36%. The pulse duration obtained was 37 nanoseconds, corresponding to a maximum peak power of 53.2 KW.

The laser energy, pulse duration and peak power for the two modes of operation are shown in fig. 6A-6E. The laser spectral bandwidth was narrowed to 0.15nm FWHM. This bandwidth is achieved along the entire tunable spectrum for CW and active Q-switched lasers, as shown in fig. 4B. The spectral tuning range in pulsed operation is slightly narrower compared to CW operation, from 35nm in CW to 33nm in pulsed mode, and in the range 1873nm to 1906 nm. As shown in fig. 7, the tuning range achieved in both cases closely coincides with the calculated Free Spectral Range (FSR) of 39nm for a 25 μm thick etalon plate. This means that the tuning range of the measurement is mainly limited by the etalon and that a wider spectral range can be obtained by selecting a thicker etalon. Along the entire spectral range, the measured output energy does not drop from 0.83mJ for a constant maximum absorbed pump power of 8.6W, as shown in fig. 4B.

The Tm for Continuous Wave (CW) operation without an intracavity etalon can be seen in fig. 3A: YLF laser performance as a function of absorbed pump power. An absorbed pump power at a laser threshold of 1.9W is obtained. The maximum output power of 4.57W was measured at an absorbed pump power of 11.9W, corresponding to an optical-to-optical conversion of 23.3% and a slope efficiency of 42.9%.

The measured laser wavelength was 1885nm with a spectral width at full width at half maximum (FWHM) of 1.4 nm.

In another alternative configuration, an exemplary embodiment of the present invention is shown that provides a Tm: YAP based laser system (as illustrated by fig. 2).

The Tm: yap (aqs) laser setup is shown in fig. 2. The pump source (110) is a fiber coupled (115) laser diode emitting up to 15.8W at 793nm, with a core diameter of 105 μm and a N.A. of 0.22. Tuning the emitted wavelength temperature to correspond to³H6→³Absorption peak of the F4 transition. A pair of anti-reflection (ARs) coated at 650nm-1050nm lenticular lenses (120, 125) is used to focus the pump beam on the Tm: YAP crystal (135), allowing a minimum spot size of about 260um within the Tm: YAP crystal. The pump is delivered through a planar-planar back cavity input mirror (130) having an AR coating for the pump wavelength and a High Reflectivity (HR) coating for 1850nm-2000 nm. We use a plano-concave mirror with a ROC of 200mm as the Output Coupler (OC) 160. For 1850nm-2000nm, the OC 160 is Partially Reflective (PR) coated with a reflectivity of 70%. The total cavity length (127) was 220 mm. YAP crystals (135) were 10mm long with a cross section of 3X 3 mm. Coating a laser crystal (135) AR at the pump wavelength and the laser wavelength, wrapping in indium foil and fasteningInto an aluminum holder cooled by a water cooler at a steady 18 ℃. Active pulse switching is achieved by inserting an AOM (150) into the laser cavity (127). Two uncoated YAG etalon plates with thicknesses of 500um (140B) and 25um (140A) are fixed on a rotating stage chamber and placed between AOM (150) and OC 160.

The Tm for AQS operation with and without an intracavity etalon can be seen in fig. 8, YAP laser performance as a function of absorbed pump power. As shown in fig. 8A to 8C, a maximum pulse energy of 2.25mJ was measured at an absorbed pump power of 8W, with a pulse duration of 40ns and a peak power of about 80 KW. Laser performance was measured at a wavelength of 1935nm and an AOM frequency of 1 KHz.

The laser wavelength was measured at 1935nm with a spectral width at half-peak width (FWHM) of 150pm (FIG. 9B). As shown in fig. 9A, the laser wavelength is tuned from 1925nm to 1960nm in AQS mode, achieving a continuous tuning range of 35 nm. As shown in fig. 9A, the measured pulse energy does not drop from below 0.83mJ along the entire tuning range.

YAP Passive Q-switched (PQS) laser systems are configured as described for AQS Tm: YAP lasers, where a passive Q-switched SA (Cr: ZnS crystal, 2 × 4 × 4mm, 89% transmission) replaces the AOM.

The Tm: YAP laser performance for PQS operation using OCs with 70% and 85% reflection as a function of absorbed pump power can be seen in fig. 10.

The laser average output power is shown in fig. 10A.

A maximum average output power of 1.6W for 70% OC and a maximum average output power of 0.9W for 85% OC were achieved at a pump power of 16W. The measured emission wavelength was 1934nm and the pulse durations were 24ns, 29ns for 70% and 85% of the OCs, respectively (fig. 10A). As shown in FIG. 10B, the maximum pulse energy of 70% of the OC was measured to be 1.22mJ, and the maximum pulse energy of 85% of the OC was measured to be 1.5 mJ. The repetition rate is in the range of 280Hz-1660 Hz. When using an OC with 85% reflectivity, the pulse energy and repetition rate are almost unchanged. When using an OC with 70% reflectivity, the pulse energy and repetition rate increase almost linearly.

As shown in fig. 11, the tunability range in the PQS mode is 11nm using 70% OC, and can be increased to 14nm by using 85% OC. As shown in fig. 11, for 85% OC, the laser wavelength was tuned from 1930nm to 1944nm, achieving a continuous tuning range. At an absorbed pump power of 12W, the maximum pulse energy is 1.22mJ at 1.5 kHz. As shown in fig. 11, the measured pulse energy does not drop from 0.85mJ along the entire tuning range.

FIG. 12 shows Tm for YAP laser absorption pump power threshold at different wavelengths in continuous mode (CW) and PQS mode. The absorbed pump power in PQS mode is almost constant in the operating wavelength range, whereas in CW mode the pump power shows a strong dependence on wavelength (fig. 12).

Fig. 13 shows an exemplary configuration of a Tm: YLF laser coupled to an optical fiber. As shown in fig. 13, a coupling efficiency of about 75% can be achieved. The focusing of the laser light into the fiber is achieved by using a collimating lens and a coupling lens to achieve coupling. The emission wavelength was 1885nm, the peak power measured was 40kW, and the input power was 4W. The fiber used in this experiment was a multimode silica core (low OH content) glass clad fiber.

During the tuning measurement for the pulse setting, the maximum pump power is reduced in order to reduce the probability of damaging the laser components.

Further, in one exemplary configuration presented herein, during tuning, the laser output power exhibits a significant variation as a function of the emission wavelength. These power variations are mainly caused by the wavelength dependent gain spectrum. For Tm: YLF gain media, the emission cross section is strongly wavelength dependent. In particular, when there is a significant drop in the gain cross section between the emission peaks at 1880nm and 1908 nm. These slight deviations can be explained by adding heat at lower laser levels for shorter wavelengths (typically for a quasi-tertiary laser). Furthermore, the emission polarization of the presented laser strongly depends on the laser wavelength. Emissions up to 1890nm are p-polarized, while longer wavelengths are s-polarized. YLF has excellent agreement with the reported Tm, luminescence, because the gain cross-section is different for both polarization directions.

However, in another exemplary configuration including a laser system having a Tm: YAP crystal as the gain medium, the wavelength-dependent variation in laser output power is less pronounced.

Although this output power is dependent on the laser wavelength, the laser configuration shown here allows for millijoule-level pulsed lasers over the entire tuning range, which is limited only by the etalon spectral transmission. By optimizing the etalon parameters, a wider tuning range can be expected.

In one exemplary embodiment of the present disclosure, a tunable pulse Tm: YLF laser is shown, up to mJ level energy pulses and a tunability range of 33nm between 1873nm and 1906 nm. A maximum peak power of 53.2KW was obtained at a laser wavelength of 1879 nm. The use of an etalon plate also allows laser emission to achieve a narrow spectral bandwidth of 0.15nm over the entire tunability range.

In another exemplary embodiment of the present disclosure, a tunable pulsed Tm YAP laser is presented, reaching mJ level energy pulses and a tunability range of 35nm between 1925nm-1960nm (for AQS mode of operation) and 11nm between 1930nm-1941nm (for PQS mode of operation). The tunability range of the PQS mode can also be increased to about 20nm by using SA with 93% transmission. A maximum peak power of about 80KW is obtained at the 1935nm laser wavelength (for AQS mode of operation). The use of an etalon plate also allows laser emission to achieve a narrow spectral bandwidth of 0.15nm over the entire tunability range. To our knowledge, for the first time a useful combination of high energy pulses with broad spectral tunability and narrow frequency lasing is presented in lasers based on Tm doped gain media in the 2 μm range. These unique characteristics significantly enhance the versatility of this type of laser system by allowing both pulse energy and emission wavelength to be tailored simultaneously and making this laser a promising tool in the rapidly evolving 2 μm laser application field.

While the present invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the spirit and broad scope of the appended claims.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.