阅读说明：本技术 稳定的uv激光器 (Stabilized UV laser ) 是由 罗宁一 黄日昌 于 2020-03-11 设计创作，主要内容包括：本申请示出和/或描述了UV激光装置、系统和方法。包括一种用于VECSEL和MECSEL激光器的方法、装置或系统,激光器包括势垒泵浦和井内泵浦激光器。还公开了制造用于激光器的增益芯片的方法、激光器的布置以及对用于器件的适当的非线性晶体(NLC)的选择。(UV laser apparatus, systems, and methods are shown and/or described herein. A method, apparatus or system is included for VECSEL and MECSEL lasers, including barrier pumped and borehole pumped lasers. Also disclosed are methods of fabricating gain chips for lasers, the arrangement of lasers, and the selection of an appropriate nonlinear crystal (NLC) for the device.)

1. A method, apparatus or system as described herein.

2. The method, apparatus or system of claim 1, comprising a UV laser comprising:

a gain chip having one or more quantum wells or one or more quantum dots; and

one or more mirrors.

3. The method, apparatus or system of claim 1 or 2, further comprising one or more of:

the one or more mirrors are highly reflective;

the one or more quantum wells are a semiconductor gain medium for the laser;

the gain chip has one or more laser cavities and the one or more quantum wells are enclosed within the one or more laser cavities;

the gain chip has one or more semiconductor thin disk laser cavities, in particular VECSEL or MECSEL cavities; and/or

The one or more mirrors are arranged to extract light from the one or more cavities.

4. The method, apparatus or system of any of claims 1-3, wherein the one or more quantum wells are one or more of:

electrically pumped quantum wells, or

The quantum wells are optically pumped with a pump,

including fibre-coupled diode lasers, or

A free space diode laser.

5. The method, apparatus or system of any of claims 1-4, further comprising one or more of:

the visible light power intensity is at least 10 times larger than the power of the visible light power intensity outside the cavity mirror;

when the one or more cavity mirrors are highly reflective, the magnification factor is between about 40 and about 100;

sufficient visible high intensity light is provided to provide the high intensity visible light stable over time necessary for a UV laser.

6. The method, apparatus or system of any of claims 1-5, wherein the laser is or includes one or more of:

VECSEL gain chip and

MECSEL gain chip.

7. The method, apparatus or system of any of claims 1-6, wherein the laser is or includes one or more of:

VECSEL；

VECSEL having the following VECSEL configuration: the one or more mirrors are at least one mirror operably disposed with respect to the gain chip;

MECSEL; and

MECSEL having the following MECSEL configuration: the one or more mirrors are at least two mirrors operatively disposed with respect to the gain chip.

8. The method, apparatus or system of any of claims 1-7, comprising a UV laser that enables efficient and/or temporally stable UV light generation by or using one or both of:

A) by a visible wavelength laser light source (VWLS), and by using a laser cavity supporting multiple frequencies of VWLS; and

B) doubling the visible frequency within the laser cavity to UV light using length optimized nonlinear optics.

9. A method, apparatus or system according to any of claims 1-8, wherein VECSEL and MECSEL lasers are used comprising one or both of barrier pump lasers or borehole pump lasers.

10. The method, apparatus or system of any of claims 1-9, comprising one or more of:

a gain chip for use in the laser is fabricated,

arranging a laser, and

a suitable nonlinear crystal (NLC) for use in the device is selected.

11. The method, apparatus or system of any of claims 1-10, comprising one or more of:

(A) temporally stable high intensity visible light, an

(B) Suitable nonlinear crystals or periodically poled materials to convert the visible light to UV light.

12. The method, apparatus or system of any of claims 1-11, comprising one or both of a VECSEL gain chip or a MECSEL gain chip; either or both of the VECSEL gain chip or the MECSELEL gain chip has:

one or more quantum wells ("QWs" or "VECSEL QWs") or quantum dots ("QDs").

13. The method, apparatus or system of any of claims 1-12, wherein the VECSEL gain chip or the MECSEL gain chip is a semiconductor gain medium for the laser.

14. The method, apparatus or system of any of claims 1-13, comprising one or more of:

enclosing the QW or QD within a laser cavity:

extracting several watts of visible light power from the cavity by using one or more partially reflective cavity mirrors;

electrically or optically pumping the VECSEL QW or QD or MECSELEL QW or QD to produce an output;

between the cavity mirrors, the intensity of the visible light power is at least 10 or more times greater than its power outside the cavity mirrors;

when all cavity mirrors are highly reflective, the magnification factor is between about 40 and about 100;

semiconductor thin disk laser cavities, particularly VECSEL or MECSEL cavities, provide the necessary visible high intensity light to provide the temporally stable high intensity visible light for UV lasers.

15. The method, apparatus or system of any of claims 1-14, comprising one or more nonlinear crystals (NLCs) for the apparatus.

16. The method, apparatus or system of claims 1-15, comprising one or more of:

cooling for high power operation;

the gain regions of the VECSEL gain chip and the MECSELEL gain chip have one or both of a layered structure or a layered arrangement for cooling; and

one or more of a heat sink and a reflector are laminated or sandwiched around the QW structure.

17. The method, apparatus or system of any of claims 1-16, comprising one or more of the gain chips, the gain chips comprising:

a heat spreader as a first layer thereof;

a heat spreader as a first layer, the heat spreader being selected from the following materials or components: diamond, SiC, GaAs or a high thermal conductive optical material for the cooling layer;

a second layer that is or includes the one or more quantum wells or quantum dots; and/or

A third layer that is or includes a Distributed Bragg Reflector (DBR).

18. The method, apparatus or system of claim 17, wherein the gain chip is one of:

VECSEL gain chip, and

MECSEL gain chip.

19. The method, apparatus or system of claim 18, wherein the gain chip is a MECSEL gain chip and has one or more of:

the MECSEL gain chip has one or more additional heat sinks;

the MECSEL gain chip sandwiches the MECSEL QW structure between two cooling devices or heat sinks,

the MECSEL gain chip does not have a DBR structure.

20. The method, apparatus or system of any of claims 1-19, comprising one or more of:

a method of manufacturing a VECSEL gain chip or a MECSEL gain chip, wherein the QW or QD structure is:

first growing the QW or QD structure on a desired substrate or wafer, such as GaAs; depending on the diameter of the wafer, the substrate typically has a thickness of 0.2-0.5mm,

optically bonding a heat sink such as SiC to the QW-GaAs wafer; the optical bonding includes mating one wafer to another to maintain good optical and thermal contact.

21. The method, apparatus or system of any of claims 1-20, comprising one or more of the following features:

the QW-GaAs or QD-GaAs wafer is made to be more flexible;

reducing the QW-GaAs or QD-GaAs wafer thickness from the GaAs side to about 0.1mm or less;

surface activation of SiC wafers and thin or reduced thickness QW-GaAs or QD-GaAs wafers; bonding or pressing the SiC wafer and the thin or reduced thickness QW-GaAs or QD-GaAs wafer together;

bonding or pressing the SiC wafer and the thin or reduced thickness QW-GaAs or QD-GaAs wafer together under ultra-high vacuum conditions; and

VECSEL gain chip with DBR at the end.

22. The method, apparatus or system of any of claims 1-21, comprising one or more of:

forming SiC-QW-GaAs or SiC-QD-GaAs into a monolithic wafer of partial MECSEL QW wafer assemblies according to one or more of claims 1-21;

immersing a portion of the MECSEL QW wafer assembly in an acidic solution, such as H, to selectively remove GaAs₂SO₄：H₂O₂：H₂O, or concentrated sulfuric acid or NH₄OH：H₂O₂An etchant;

after pickling, only a thin QW or QD layer remains on the SiC wafer; activating the second SiC wafer; and

pressing the second SiC wafer to the SiC-QW or SiC-QD using a bonding process in a standard optical bonder under high or ultra-high vacuum conditions;

resulting in the formation of a monolithic SiC-QW-SiC or SiC-QD-SiC wafer.

23. The method, apparatus or system of any of claims 1-22, comprising one or more of:

further processing the SiC-QW-GaAs or SiC-QD-GaAs (VECSEL) wafer and the SiC-QW-SiC or SiC-QD-SiC (MECSEL) wafer; and creating one or both of a single or monolithic SiC-QW-GaAs or SiC-QD-GaAs (vecsel) gain chip and a single or monolithic SiC-QW-SiC or SiC-QD-SiC (mecsel) gain chip by laser scribing and separation.

24. The method, apparatus or system of any of claims 1-23; including one or more of the following:

laser scribing by forming a grid with vertical and horizontal scribes, and

the gain chip of each cell is separated from the large pattern or array of gain chips.

25. The method, apparatus or system of any of claims 1-24, comprising one or more of:

adding a thin layer of dielectric material such as CN or SiN to the surface of the heat spreader and the QW or QD,

adding a thin layer of dielectric material such as CN or SiN to the surfaces of the heat spreader and the QW to reduce bonding resistance and aid in bonding of the surfaces of the heat spreader and the QW; depending on material compatibility, the heat sink and the surface of the QW may have some resistance and/or difficulty in forming a robust and complete optical joint;

selecting a thickness of the film to minimize optical reflectivity between the heat spreader and the QW or QD;

selecting a film thickness for film thickness versus reflectivity relationship to minimize optical reflectivity between the heat sink and the QW to have a refractive index of n-1.7;

the thickness of the film is chosen to minimize the optical reflectivity between the heat sink and the QW, which is approximately 200 nm.

26. The method, apparatus or system of any of claims 1-25, comprising one or more of:

a semiconductor material, the semiconductor material comprising:

a conduction band, and

the valence band.

27. The method, apparatus or system of any of claims 1-26, comprising one or more of:

a quantum well that is a recess in one or both of the conduction band and the valence band;

increasing the quantum efficiency of a barrier pumped laser by:

the photons of the pump are transmitted,

pushing electrons from the valence band of the bulk into the conduction band;

the quantum efficiency in the barrier pumped laser is maximized, and the QW of the barrier pumped laser absorbs pump light with a photon energy difference between the pump wavelength and the lasing wavelength of approximately 6%;

using 640nm as pump light to generate 680nm light;

the difference between 640nm and 680nm used is about 6%,

the difference in photon energy between the pump wavelength and the lasing wavelength used is about 28%.

28. The method, apparatus or system of any of claims 1-27, comprising one or more of:

increasing quantum efficiency for a pump laser in a well;

increasing quantum efficiency for a pump laser in a well; wherein the pump light is absorbed only in the quantum wells;

increasing quantum efficiency for a pump laser in a well; wherein the pump photon lifts an electron from a level in a valence band of the quantum well to a conduction band;

improving the quantum efficiency of a pump laser used in a well; wherein the pump photons lift electrons from a level in the valence band of the quantum well to the conduction band, the QW absorbing light with a photon energy difference between the pump wavelength and the lasing wavelength of approximately 3%;

improving the quantum efficiency of a pump laser used in a well; wherein the pump photon lifts an electron from a level in a valence band of the quantum well to a conduction band; for the pump laser, the pump wavelength is 680nm, and the lasing wavelength is 660 nm;

improving the quantum efficiency of a pump laser used in a well; wherein the pump photon lifts an electron from a level in a valence band of the quantum well to a conduction band; the generated visible light power is maximized by combining SiC contact cooling and pumping in the well.

29. The method, apparatus or system of any of claims 1-28, wherein the barrier pumped laser comprises one or more of:

the pump photons are pumped into the potential barrier of the conduction band; the pump photons are pumped into the potential barrier such that electron-hole pairs are generated in the potential barrier; the electron-hole pairs migrate to one of the one or more quantum wells and recombine to produce a laser photon.

30. A method, apparatus or system according to any of claims 1-28, wherein the downhole pump laser comprises one or more of:

the pump photons are pumped into a well of the conduction band; the pump photon is absorbed in one of the one or more quantum wells, creating an electron-hole pair in the quantum well,

relaxing to a ground state and recombining into laser photons; the energy difference between the pump photons and the laser photons, i.e. the quantum defects, is deposited in the heat sink in the form of heat.

31. The method, apparatus or system of any of claims 1-30, wherein the UV laser comprises one or more of:

MECSEL, comprising:

a MECSEL gain chip further having one or more MECSEL quantum wells, the MECSEL gain chip arranged at a Brewster angle θ relative to the optical path_BOr an angle of polarization;

a MECSEL gain chip further having one or more MECSEL quantum wells, the MECSEL gain chip arranged at a Brewster angle θ relative to the optical path_BOr polarization angle, to eliminate the addition of a visible wavelength laser source on the gain chip of the MECSELA clear coating layer;

a MECSEL gain chip further having one or more MECSEL quantum wells, the MECSEL gain chip arranged at a Brewster angle θ relative to the optical path_BOr polarization angle, that reduces optical loss due to defective coatings on the gain chip.

32. The method, apparatus or system of any of claims 1-31, wherein the UV laser comprises one or more of:

a VECSEL gain chip having one or more quantum wells ("QW" or "VECSEL QW" or QD) that are semiconductor gain media for a laser;

the VECSEL gain chip is an electrically or optically pumped semiconductor thin disk gain medium and is also a first cavity mirror;

an NLC disposed in an output path or light path, the NLC producing UV light when output passes through the NLC;

the UV light travels through and passes through a partially reflective cavity mirror;

the gain chip comprises an intracavity SiC heat sink with a thin layer of CN or SiN coating between the heat sink and the GaAs wafer.

33. The method, apparatus or system of any of claims 1-32, wherein the UV laser comprises one or more of:

a VECSEL having a cavity containing a VECSEL gain chip having one or more quantum wells and an NLC disposed within the cavity; and a BFP arranged in an output path or optical path, and a first dedicated mirror arranged behind the BFP corresponding to the optical path;

the inner surface of the first special reflector is coated to reflect VWL and transmit UV with high efficiency to extract UV light;

the first dedicated mirror is angled to reflect the output through the NLC and toward a second dedicated mirror;

the inner surface of the second special reflector is coated to reflect VWL and UV wavelengths; and

the second dedicated mirror reflects UV laser output two through the NLC and back through the first dedicated mirror.

34. A method, apparatus or system according to any of claims 1-33 wherein the UV laser comprises one or more of:

a MECSEL having a cavity containing a MECSEL gain chip having one or more quantum wells and an NLC disposed within the cavity; and a BFP disposed in the output path or optical path; the first reflector is arranged behind the BFP and corresponds to the optical path;

the first mirror is dedicated and has an inner surface coated with a coating to reflect VWL and transmit UV to extract UV light;

the first dedicated mirror is angled to reflect output through the NLC and toward a second dedicated mirror;

the inner surface of the second special reflector is coated to reflect VWL and UV wavelengths; and

the second dedicated mirror reflects UV laser output through the NLC and back through the first dedicated mirror;

a third mirror disposed behind a gain chip of the MECSEL to reflect back to the VWL.

35. The method, apparatus or system of any of claims 1-34, wherein the UV laser comprises one or more of:

a VECSEL comprising a VECSEL gain chip having one or more quantum wells ("QW" or "VECSEL QW" or QD) that provide an electrically or optically pumped semiconductor gain medium for a laser; the semiconductor thin disk gain medium or gain chip is also used as a first cavity mirror;

an NLC disposed in an output path or light path, the NLC producing UV light as the output passes through the NLC, the UV light then traveling through a partially reflective cavity mirror;

the gain chip contains an intracavity SiC heat spreader with a thin layer of CN or SiN coating between the heat spreader and the GaAs wafer.

36. The method, apparatus or system of any of claims 1-35, wherein the UV laser comprises one or more of:

a downhole pumped MECSEL comprising a MECSEL assembly comprising one or more SiC heatsinks, optionally with a CN or SiN film layer;

pump light optics arranged around the MECSEL to assist in-well pumping;

a laser cavity enclosing a well-pumped MECSEL located within the laser cavity, the laser cavity configured to extract several watts of visible light power from the cavity by using one or more cavity mirrors;

an NLC disposed in an output path or optical path to convert VWL to stable UV light;

a second cavity mirror located at an end of the cavity opposite the first cavity mirror;

providing a downhole pumped MECSEL, wherein the MECSEL QW is sandwiched between CTE compatible heat sinks to support multiple frequencies of high intensity VWL output;

red pumping to pump the MECSEL QW;

an appropriate length of NLC PPLT/PPLST or PP-LBGO is used to convert the multi-frequency output to stable UV light.

37. The method, apparatus or system of any of claims 1-36, wherein the UV laser comprises one or more of:

a VECSEL arrangement providing a wide range of UV power output by using additional optics;

providing a VECSEL comprising a VECSEL gain chip having one or more quantum wells ("QW" or "VECSEL QW" or QD) that provide an electrically or optically pumped semiconductor gain medium for a laser; an electrically or optically pumped semiconductor thin disk gain medium or gain chip is also used as the first cavity mirror;

an NLC arranged in an output path or light path for generating UV light when output passes through the NLC, which then travels through a partially reflective cavity or end mirror;

the gain chip comprises an intracavity SiC heat spreader and has a thin layer of CN or SiN coating between the heat spreader and a GaAs wafer;

a focusing lens is provided.

38. The method, apparatus or system of any of claims 1-37, wherein the UV laser comprises one or more of:

an additional element to increase the power output of the UV laser;

additional optics and/or

A focusing lens.

39. A method, apparatus or system according to any of claims 1-38, wherein the UV laser comprises one or more of:

a focusing lens having a focal length F1;

an end mirror having a radius of curvature R2;

distance: d1, D2 and D3;

d1 is the distance between the surface of the gain chip and the focusing lens;

d2 is the distance between the focusing lens and the NLC; and

d3 is the distance between the NLC and the end mirror.

40. The method, apparatus or system of claim 39, wherein the UV laser comprises one or more of:

operating the laser can operate over a wide range of power levels;

operating the laser can be achieved by operating over a wide range of power levels:

the UV power output is adjusted by setting F1/R2 to be approximately equal to 1 and the value of D1/(D2+ D3) to be approximately equal to 2.

41. A method, apparatus or system according to any of claims 1-40 wherein the UV laser comprises one or more of:

a downhole pumped MECSEL including a MECSEL assembly, the MECSEL assembly comprising:

one or more SiC heatsinks, optionally with a CN or SiN film layer;

pump light optics arranged around the MECSEL for downhole pumping;

extracting visible light power from the cavity by means of using one or more cavity mirrors by enclosing the downhole pumped MECSEL within a laser cavity;

wavelength selection and limiting optics are arranged in the output path or optical path to select and limit the VWF output.

42. The method, apparatus or system of any of claims 1-41, wherein UV laser comprises one or more of:

a second cavity mirror located at an opposite end of the cavity from the first cavity mirror;

the second cavity reflects the VWF output through the NLC to convert the multi-frequency output to UV light;

reflecting the UV light back through the third cavity mirror as UV output;

providing a downhole pumped MECSEL, wherein one or more MECSEL QWs or QDs are sandwiched between CTE compatible heat sinks to support multiple frequencies of high intensity VWL output;

red pumping to pump the one or more MECSEL QWs or QDs;

the NLC is one or more of PPLT/PPLST or PP-LBGO of suitable length to convert the multi-frequency output to stable UV light.

43. The method, apparatus or system of any of claims 1-42, wherein UV laser comprises one or more of:

eliminating feedback loops related to power stability with efficient multi-mode operation;

an STDL having a bandwidth greater than several nm, the bandwidth including a plurality of frequencies;

STDL, providing stable VWLS at about 1nm bandwidth;

bandwidth is controlled by adding wavelength limiting optics such as Birefringent Filter Plates (BFPs) according to bandwidth requirements;

providing a high intensity VWLS that is stable over time using efficient multimode operation;

the problem of mode shooting is avoided, and single-mode operation with unstable power caused by the change of the cavity length along with the temperature is also avoided;

power stability is maintained using efficient multi-mode operation to avoid complex feedback systems.

44. The method, apparatus or system of any of claims 1-43, wherein UV laser comprises one or more of:

selecting an appropriate NLC for use in a UV laser apparatus;

selecting an appropriate NLC for use in a UV laser device having one or more of:

(1) transparent to the corresponding VWL and UV wavelengths;

(2) a high non-linear coefficient;

(3) large bandwidth to support multiple frequencies simultaneously; and

(4) a minimum walk-off angle;

selecting an appropriate NLC for use in a UV laser apparatus comprising one or more of:

an exemplary NLC that provides one or more of:

(a) periodically poled crystals, such as lithium tantalate (PPLT or PPSLT); and/or the presence of a gas in the gas,

(b) periodically polarized LaBGeO₅(PPLBGO)；

For PPLT and PPLBGO, first, second or higher order can be used;

selecting an appropriate NLC for use in a UV laser apparatus; having one or more of the following:

bandwidth requirements have a limit on the maximum length of the NLC;

a cavity length of 60mm has a mode spacing of 2.5GHz (about 0.004nm at 680 nm);

a 1.6mm long PPSLT has a bandwidth of full width at half maximum (FWHM) of 0.1nm, which allows about 25 frequencies to oscillate within the cavity;

bandwidth and UV conversion efficiency at two NLC lengths at similar VWLS power density;

NLC length, which is determined by the bandwidth requirement of FWHM.

45. The method, apparatus or system of any of claims 1-44, wherein UV laser comprises one or more of:

walk away to compensate NLC, in order to meet the minimum walk away requirement;

a pair of beta-Barium Boroxide (BBO) optics having substantially the same or similar phase matching angles, the beta-barium boroxide optics being arranged in opposite directions to return the deflected light beam (2 ω) to the center again; reducing the separation between the two BBOs to about zero or in optical contact.

46. The method, apparatus or system of claims 1-45, comprising:

a cavity;

at least one external energy source configured to provide electrical or optical pumping energy;

a semiconductor thin disk gain medium enclosed within the cavity, the semiconductor thin disk gain medium having one or more quantum wells configured to: receiving and converting electrical or optical pumping energy from the external energy source and generating multi-frequency high-intensity visible wavelength laser;

a heat sink;

a nonlinear crystal configured to convert the visible wavelength light into ultraviolet light;

and one or more mirrors.

47. The method, apparatus or system of claims 1-46, wherein the external energy source is red light.

48. The method, apparatus or system of claims 1-47, wherein said semiconductor thin disk gain media further comprises a cavity mirror.

49. The method, apparatus or system of claims 1-48, wherein a thin layer of CN or SiN is laminated between said heat spreader and said quantum well.

50. The method apparatus or system of claims 1-49, wherein a mirror is placed opposite said semiconductor thin disk gain medium.

51. The method, apparatus or system of claims 1-50, wherein an inner surface of said mirror disposed opposite said semiconductor thin disk gain medium has a highly reflective coating for visible wavelength light and a high transmittance for ultraviolet light.

52. The method, apparatus or system of claims 1-51, comprising:

a cavity;

at least one external energy source configured to provide electrical or optical pumping energy;

a semiconductor thin disk gain medium enclosed within the cavity, the semiconductor thin disk gain medium having one or more quantum wells configured to: receiving and converting electrical or optical pumping energy from the external energy source and generating multi-frequency high intensity visible wavelength laser light;

a heat sink;

a nonlinear crystal configured to convert visible wavelength light to ultraviolet light;

and one or more mirrors.

53. The method, apparatus or system of claims 1-52, wherein said thin disk gain media is selected from MECSEL or VECSEL.

54. A method, apparatus or system according to claims 1-53 wherein the MECSEL or VECSEL is excited by barrier pumping or downhole pumping.

55. The method, apparatus or system of claims 1-54 wherein said nonlinear crystal is selected from the group consisting of periodically poled lithium tantalate, periodically poled stoichiometric lithium tantalate and periodically poled LaBGeO₅。

56. The method, apparatus or system of claims 1-55, further comprising pump light optics disposed in said cavity to increase the intensity of pump light from said external source.

57. The method, apparatus or system of claims 1-56, further comprising a focusing lens.

58. The method, apparatus or system of claims 1-57 further comprising selecting a focusing lens having a focal length of F1, selecting an end mirror having a radius of curvature of R2, wherein F1/R2 is about equal to 1.

59. The method, apparatus or system of claims 1-58, further comprising: setting the distance between the surface of the VECSEL or MECSELL gain chip and the focusing lens to D1; setting a distance between the focusing lens and the NLC to D2; the distance between the NLC and the end mirror is set to D3 and the value of D1/(D2+ D3) is made to be approximately equal to 2.

Technical Field

The present invention relates to an apparatus and method for generating temporally stable Ultraviolet (UV) light. In many embodiments, methods, systems and/or apparatus may include and/or involve, among other things, the use of a Semiconductor Thin film Laser (STDL) as a Visible Wavelength Laser Light Source (VWLS) and frequency doubling optics, such as Nonlinear Crystal (NLC) or periodically poled materials, to convert Visible Light to UV Light.

Background

The apparatus and/or method of such a stabilized-like UV light source may be used in various applications including, but not limited to, scanning, spectroscopy, telecommunications applications and/or medical applications. UV lasers are well suited for applications requiring high quality micro-dimensions. Furthermore, UV lasers may be used in a variety of commercial and industrial applications, including but not limited to: micro-scale machining, engraving precision tools for stamping or micro-spark erosion, marking glass and its composites (so that the surface does not change in structure or chemical composition), drilling small holes in various materials such as diesel injectors, and precisely cleaning surfaces such as artwork. Because there are a wide range of applications for UV lasers, examples and applications of these UV lasers are only examples.

Several desirable solutions for producing temporally stable high intensity visible light are described herein (e.g., from Vertical External Cavity Surface Emitting Lasers (VECSELs) or thin film External Cavity Surface Emitting lasers (MECSELs)). Furthermore, several possible/alternative embodiments and arrangements relating to one or more Quantum Wells (QWs) or one or more Quantum Dots (QDs), formation and fabrication of the QWs and QDs, barrier-pumped lasers, in-Well pumped lasers and cooling of the QWs/QDs are provided. In addition, several embodiments and material choices related to the material and length of the NLC are also clearly described.

Disclosure of Invention

UV or frequency conversion laser apparatus, systems, and/or methods are shown and/or described herein. Methods, systems and/or apparatus that use a Semiconductor Thin film Laser (STDL) as a Visible Wavelength Laser Light Source (VWLS) and frequency doubling optics, such as Nonlinear Crystal (NLC) or periodically poled materials, to convert Visible Light to UV Light are included. As described further herein, the STDL is electrically or optically pumped to generate visible laser light. Visible Light (VWL) is also referred to herein as Visible Light (VIS), which also represents an intermediate output that can produce a final UV output when directed through the NLC.

The present application provides VECSEL-based UV lasers and may include a VECSEL quantum well (VECSEL QW or QW) gain chip or QD gain chip, a Birefringent Filter Plate (BFP) and/or etalon, a nonlinear crystal (NLC) and one or more mirrors, e.g. cavity mirrors. The VECSEL gain chip produces laser photons or output when electrically or optically pumped. The laser photons travel along the optical path, through the BFP and contact the first cavity mirror. The first cavity mirror reflects the laser photons or VWL through the NLC crystal with appropriate length and material and converts VWL into stable UV light. The second mirror is located on the other, opposite side of the NLC and nearly parallel to the first mirror, thus reflecting the stabilized UV light back toward the first mirror and ultimately toward a target outside the cavity.

The present application also provides a MECSEL-based UV laser and includes a similar structure to the VECSEL described above; however, the MECSEL can utilize the third mirror as a cavity mirror, since the MECSEL is centrally arranged, while the VECSEL is arranged at the end or at the outside.

Embodiments of a VECSEL QW or QD gain chip and a MECSELL QW or QD gain chip are described. The gain chips may be assembled under certain conditions to ensure that appropriate optical bonding is achieved between and among the various layers of the respective VECSEL QW or QD and MECSEL QW or QD gain chips. The layers and arrangement of the heat sink are discussed as providing adequate cooling during high power operation.

In other features, laser systems employing barrier pumping and downhole pumping are described. Both techniques and arrangements may have certain features which may in some cases be employed in some preferred embodiments of the inventive extension.

Drawings

For a detailed description of an exemplary embodiment of the expansion, reference will now be made to the accompanying drawings in which:

FIG. 1A shows a schematic diagram of a VECSEL according to some embodiments of the present invention;

FIG. 1B shows a schematic diagram of a MECSEL according to some embodiments of the present invention;

FIG. 2 provides a cross-sectional view of a multilayer structure of Quantum Wells (QWs) or QDs of a VECSEL gain chip (not drawn to scale) of the present invention;

FIG. 3 provides a cross-sectional view of a multilayer structure of a Quantum Well (QW) or QD of a Quantum Well (QW) or quantum well gain chip (not drawn to scale) of the present invention;

FIG. 4 provides a cross-sectional view of a multilayer structure of a Quantum Well (QW) of a MECSEL using SiC as a heat spreader (not drawn to scale);

FIG. 5A provides exemplary patterns associated with forming a wafer for VECSELs and/or MECSLs;

FIG. 5B illustrates an exemplary pattern for laser scribing and singulation to form a single gain chip for VECSEL and/or MECSEL;

FIG. 6 provides a graph of reflectance versus thickness of a film between a QW and SiC wafer;

FIG. 7 shows a schematic diagram of a MECSEL with the gain chip arranged at a Brewster angle with respect to the optical path;

fig. 8 shows a graph of relative intensity versus wavelength (bandwidth and UV conversion efficiency) for two nonlinear crystal (NLC) lengths, respectively, under similar visible wavelength laser light source (VWLS) conditions;

FIG. 9 provides a plot of Full Width at Half maximum (FWHM) versus the length of a periodic polarization Stoichiometric ratio Lithium Tantalate (PPSLT);

FIG. 10 provides a schematic diagram of a basic UV laser using VECSELs in accordance with at least some embodiments of the present invention;

FIG. 11 provides a schematic diagram of a basic UV laser using VECSELs in accordance with at least some embodiments of the present invention;

FIG. 12 provides a schematic diagram of a UV laser using MECSEL in accordance with at least some embodiments of the present invention;

FIG. 13 provides a schematic diagram of a walk-off compensated NLC (walk-off compensated NLC) in accordance with at least some embodiments of the present invention;

FIG. 14 provides a schematic of an electrically or optically pumped VECSEL of the present invention;

FIG. 15 shows a schematic of the downhole pumped MECSEL in a straight lumen of the present invention;

FIG. 16 provides a schematic diagram of some alternative additional optics and distances for an exemplary VECSEL in accordance with at least some embodiments of the present invention;

FIG. 17 provides a schematic of a MECSEL in a V-shaped cavity with a pump layout in the well;

figure 18A provides a side view of the valence and conduction bands of the quantum wells of an exemplary gain chip of the present invention;

FIG. 18B provides a side view of a barrier pumped laser of the present invention;

FIG. 18C provides a side view of the downhole pump laser of the present invention;

FIG. 19A provides a side view schematic of an alternative barrier pumped laser of the present invention; and

fig. 19B provides a side view schematic of an alternative downhole pump laser of the present invention.

Detailed Description

The following discussion is directed to various embodiments of the developments herein. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, or used to limit the scope of the disclosure, including the claims. Furthermore, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.

Various example embodiments relate to UV lasers, and more particularly to UV lasers as described below: by using a laser cavity supporting multiple frequencies for multiple VWLS and using length-optimized nonlinear optics to double the visible frequency within the laser cavity to UV light, the UV laser can provide efficient and time-stable generation of UV light by a visible wavelength laser light source (VWLS). This specification first introduces a high level overview of the UV laser in the example system.

As a first note, to achieve visible-to-UV conversion, two factors may need to be satisfied: (1) high visible light intensity that is stable over time, and (2) suitable nonlinear crystals or periodically poled materials to convert visible light to UV light.

Fig. 1A shows a simplified schematic of a VIS laser 100 (part of a UV laser), here a VECSEL110, according to the disclosure, and fig. 1B shows a simplified schematic of a VIS laser 100 (part of a UV laser), here a MECSEL 210. Various other forms of UV or VIS lasers, whether alternative VECSEL or MECSEL, or otherwise, may be adapted within the scope of the present invention, and are not intended to be limited to the embodiments shown, whether in fig. 1 limited only by the proper scope of the appended claims or otherwise limiting the invention.

Fig. 1A shows a VECSEL110 having a VECSEL gain chip 150 with one or more quantum wells 120 ("QWs" or "VECSEL QWs" or quantum dots "QDs"), which may then be the semiconductor gain medium of a laser. The gain chip may comprise one or more laser cavities, the QWs 120 may be arranged and/or enclosed within the respective laser cavities, and due to the enclosure, several watts of visible light power may be extracted from the cavities by using one or more partially or fully reflective cavity mirrors 130. The cavity mirror 130 may be a dielectric coated mirror or a Volume Bragg Grating (VBG) mirror. The VBG mirror may also be used as a wavelength selection and limiting device. The VECSEL QW120 may in turn generate an output 140. Note that the output or light 140 is VIS light inside the cavity mirror 130; and a further external output or light 141 is the VIS output external to the cavity mirror 130. Depending on the coating on the mirrors 130 and 230, the internal and external light intensities have a ratio. The VECSEL QW120 may be electrically or optically pumped for causing the VECSEL QW120 to produce an output 140. Between the cavity mirrors, the power intensity of the enclosed visible light 140 may be at least 10 or more times greater than its power 141 outside the cavity mirrors 130. When all cavity mirrors are highly reflective, a typical magnification factor is between 40 and 100. Thus, a semiconductor thin film laser cavity, in particular a VECSEL cavity, can provide the necessary visible high intensity light 140 to provide the high intensity visible light 141 required to be stable over time for a UV laser.

Alternatively, fig. 1B shows a UV or VIS laser 100 that can be arranged using a MECSEL 210. Here, MECSEL includes MECSEL gain chip 250, which further includes MECSEL quantum well 220("QW" or "MECSEL QW"), which in turn may be a semiconductor gain medium for a laser. Similar to the VECSEL setup described above with respect to fig. 1A, the gain chip may include one or more laser cavities, the QWs 220 may be arranged and/or enclosed within the respective laser cavities, and several watts of visible light power may be extracted from the cavities by using one or more partially or fully reflective cavity mirrors 230. MECSEL QW220 may be electrically or optically pumped such that MECSEL QW220 produces output 141. As described above with respect to fig. 1A, the power intensity of the confined visible light 140 may be at least 10 or more times greater than its power outside the cavity mirrors, and a magnification factor between 40 and 100 may typically be achieved when all cavity mirrors are highly reflective. In this way, the MECSEL cavity can provide the necessary visible high intensity light 140 to provide the high intensity visible light required by the UV laser to be stable over time.

The VECSEL QW of fig. 1A and the MECSEL QW of fig. 1B may require appropriate cooling to ensure high power operation. To ensure proper cooling of the QWs of the gain regions of both the VECSEL gain chip and the MECSEL gain chip, a layered structure or layered arrangement may be employed. In this technique, a heat sink and reflector having desired characteristics may be layered or sandwiched around the QW structure.

Thus, fig. 2 provides a cross-sectional view of the layers for the gain region 160 of the VECSEL gain chip 150. The heat sink 170 may be the first layer of the VECSEL structure. The material or composition used for heat spreader 170 may be selected from diamond, SiC, or any highly thermally conductive optic may be used as/for the cooling device. In some cases, using SiC instead of diamond as a heat spreader may provide some additional benefits, as discussed further below with respect to fig. 4. In fig. 2, the second layer is the VECSEL QW120 and the third layer is the Distributed Bragg Reflector (DBR) 172. One characteristic of DBRs is that DBRs can have a high thermal resistance and therefore will not contribute to the cooling of the VECSEL as the electrical or optical pump power is increased.

In addition, fig. 3 shows a cross-sectional view of the layers for the gain region 260 of the MECSEL gain chip 250. The heat spreader 170 may be the first layer of the MECSEL structure. Also, the material or composition for the heat spreader 170 may be selected from diamond, SiC, or any highly thermally conductive optic. In fig. 3, the second layer is MECSEL QW220, and the third layer is again heat sink 170. As shown, the QW layered structure of MECSEL has no DBR structure or layer; instead, additional cooling is achieved by sandwiching the MECSEL QW structure between two cooling devices or heat sinks.

As previously mentioned, the use Of SiC as a heat spreader, rather than diamond or other material, may provide some additional benefits, since SiC has a Coefficient Of Thermal Expansion (CTE) that is very similar to the CTE Of GaAs and QW materials. VECSELs and MECSELs are typically grown on gallium arsenide (GaAs) wafers, and thus using SiC as a heat sink may provide an effective heat removal material. Fig. 4 provides a cross-sectional view of gain region 260 for MECSEL gain chip 250. In this fig. 4, MECSEL QW220 is sandwiched or laminated between SiC layers 174. Followed byAs the pump power increases, more waste heat must be removed from the QW 220. In this embodiment, the SiC layer 174 serves as an efficient heat removal material. SiC has a thickness of about 4X 10^-6CTE of/K, which is closer to the CTE of QW (where the wafer is made of GaAs and the QW is GaInP/AIGnp/GaAs), which is larger than the CTE of diamond (about 1X 10)^-6/K) height of about 5X 10^-6and/K. At higher power operation, the temperature of the QW can be as high as 60 ℃, and large CTE differences (like those from diamond) can lead to device cracking or overheating and failure. Thus, SiC can avoid this problem because its CTE value is closer to that of GaAs/QW used in wafers of QWs.

In one embodiment, the inventive subject matter may provide a method of manufacturing a VECSEL gain chip or a MECSEL gain chip in which a QW structure is first grown on a desired substrate or wafer (such as GaAs). The GaAs substrate may typically have a thickness of 0.2-0.5mm, depending on the wafer diameter. After the QW is grown on the substrate, selected and/or designated heat sinks (such as SiC) are optically bonded to the QW-GaAs wafer. Optical bonding involves a wafer being mated to another wafer to maintain good optical and thermal contact. Note that SiC is a relatively hard material compared to GaAs, which is relatively soft and in some cases brittle. Therefore, to achieve optical bonding, it is advantageous to reduce the QW-GaAs wafer thickness from the GaAs side to about 0.1mm or less. This reduction in thickness makes the QW-GaAs wafer more flexible. The SiC wafers and thin or reduced thickness QW-GaAs wafers are surface activated and subjected to high vacuum conditions (such as 10) in a standard optical bonding machine (e.g., EVG500 series by EVP corporation)^-7Torr or higher) are pressed together using a bonding process. For a VECSEL QW gain chip, only one optical bond is required, since one side of the VECSEL gain chip is covered by the DBR, as shown in fig. 2.

For MECSEL QW gain chips, after the SiC-QW-GaAs is fabricated into a monolithic wafer assembly, the assembly is immersed in an acid solution (e.g., H)₂SO₄:H₂O₂:H₂O or concentrated sulfuric acid, or NH₄OH:H₂O₂) To selectively remove GaAs. After the acid-washing, the acid-washed,only a thin QW layer remains on the SiC wafer. The second SiC wafer is then activated and bonded to the SiC-QW using a bonding process in a standard optical bonder under high or ultra-high vacuum conditions, as described above. The result is a single SiC-QW-SiC wafer, as shown in fig. 3 and 4.

The patterns 180 of the SiC-QW-GaAs (VECSEL) wafer and the SiC-QW-SiC (MECSEL) wafer are further processed by applying an Anti-Reflection (AR) coating and metallization as shown in FIG. 5A. Then, a single or monolithic SiC-QW-GaAs (VECSEL) gain chip and a single or monolithic SiC-QW-SiC (MECSEL) gain chip are produced by laser scribing and separation, as shown in FIG. 5B. In particular, the vertical and horizontal scribe lines 190, 192 may form a grid and thus illustrate one exemplary way for laser scribing and how each individual gain chip may be separated from the large pattern or gain chip array 180.

Depending on material compatibility, the surfaces of the heat sink and QW may have some resistance and/or difficulty in forming a robust and complete optical joint. Adding a thin layer of dielectric material, such as CN or SiN, to the surface of the heat spreader and QW may help to mitigate bonding resistance and to facilitate surface bonding of the heat spreader and QW. The thickness of the film must be chosen appropriately to minimize the optical reflectivity between the heat sink and the QW. Fig. 6 provides a graph showing the relationship of reflectance to the thickness of the film, where the refractive index n is 1.7. Thus, in this case, the best choice for the thickness is 200 nm.

Fig. 18A provides a schematic illustration of a semiconductor including a conduction band 410 and a valence band 412. Quantum well 414 is a depression in the valence and conduction bands of the semiconductor. One embodiment of the invention may include increasing the quantum efficiency of the barrier pumped laser 430. In a barrier pumped laser 430 such as that shown in the schematic diagram of fig. 18B, the pump photons 418 push the electrons 416 from the valence band 412 of the bulk into the conduction band 410. In order to maximize quantum efficiency in a barrier pumped laser, its QW is designed to absorb pump light with a photon energy difference between the pump wavelength and the lasing wavelength of close to 6%. For example, in a development of the invention, one embodiment uses 640nm as pump light to generate light at 680 nm. The difference between 640nm and 680nm is about 6%, which by comparison is significantly smaller than other laser designs that use a 532nm pump wavelength to produce a 680nm lasing wavelength (the difference between the photon energy between the pump wavelength and the lasing wavelength is about 28%).

In another embodiment of the invention, the quantum efficiency can be further increased for a pump laser in a well. Pump lasers in a well refer to structures and methods used in lasers where the pump light is absorbed only in the quantum well. Fig. 18C provides a pump laser 440 in the well, where the pump photons 418 lift the electrons 416 from the level in the valence band 412 of the quantum well to the conduction band 410. In one embodiment of an extension of the invention, the QW is designed to absorb light with a photon energy difference between the pump wavelength and the lasing wavelength of approximately 3%. In one embodiment, for the downhole pump laser of the present invention, the pump wavelength is 660nm and the lasing wavelength is 680 nm. Furthermore, combining SiC contact cooling and downhole pumping can maximize the visible light power generated. Downhole Pumping structures, methods and techniques may be known to those skilled In the art and are also disclosed In several publications, for example, "Direct Pumping of Quantum Wells improvements Performance of Semiconductor Thin-Disk Lasers" Photonics Spectra (June2005) and "Enhanced Efficiency of AIGalnP Disk Laser by In-well Pumping" Optics Express, p2472 (2015).

Fig. 7 shows a schematic diagram of an alternative embodiment and arrangement of the MECSEL. In particular, fig. 7 shows a UV or VIS laser 100 where MECSEL210 includes a MECSEL gain chip 250 that further has one or more MECSEL quantum wells 220("QW" or "MECSEL QW") that may provide a semiconductor gain medium for the laser. Similar to the MECSEL described in fig. 1A, several watts of visible light power can be extracted from the cavity by enclosing the QWs 220 within the laser cavity, by using one (or more) partially reflective cavity mirror(s) 230. When electrically or optically pumped, MECSEL QW220 produces an output or VIS 140. Note that in this alternative embodiment, in order to eliminate the AR coating on the MECSEL gain chip for VWL, MECSEL gain chip 250 is arranged oppositeAt Brewster's angle theta in the optical path_B(or polarization angle). The brewster angle may help avoid some amount of optical loss due to defective coatings on the gain chip.

In the presently expanded embodiments that utilize efficient multi-mode operation, multi-mode operation may be included that may eliminate feedback loops related to power stability. STDL has a bandwidth greater than several nm, which contains multiple frequencies. STDL can provide stable VWLS at about 1nm bandwidth. Depending on the bandwidth requirements, the bandwidth can be further controlled by adding wavelength limiting optics such as Birefringent Filter Plate (BFP). Using the efficient multi-mode operation described above, this alternative embodiment is capable of providing a high intensity VWLS that is stable over time. This alternative feature can be extended to avoid mode bending problem (mode bending while also avoiding single mode operation, which may lead to power instability due to cavity length variation with temperature. Furthermore, by using efficient multimode operation, embodiments herein can also avoid complex feedback systems to maintain power stability, which is a desirable characteristic of UV lasers.

The selection of a suitable NLC for use in the UV laser apparatus of the present invention may require specific properties and characteristics to produce the desired UV light. These properties and characteristics may include, but are not limited to: (1) transparent to the corresponding VWL and UV wavelengths; (2) a high non-linear coefficient; (3) large bandwidth to support multiple frequencies simultaneously; and (4) minimum walk-off angle. Exemplary NLCs that provide desired characteristics may include: (a) periodically poled crystals, such as lithium tantalate (PPLT or PPSLT); and/or (b) periodically poled LaBGeO₅(PPLBGO). For PPLT and PPLBGO, first, second or higher order may be used.

Fig. 8 shows a graph of relative intensity versus wavelength (bandwidth and UV conversion efficiency) for two nonlinear crystal (NLC) lengths under similar visible wavelength laser light source (VWLS) conditions. Fig. 8 further demonstrates that the NLC length must be chosen appropriately and that the length of the NLC plays an important role in the preferred function of the UV laser. Longer crystals may provide higher conversion efficiency but limit bandwidth. Therefore, the bandwidth requirement has a limit on the maximum length of the NLC. A60 mm cavity length has a mode spacing of 2.5GHz (about 0.004nm at 680 nm). A 1.6mm long PPSLT has a bandwidth of full width at half maximum (FWHM) of 0.1nm, which allows about 25 frequencies to oscillate within such a cavity. Thus, fig. 8 shows the bandwidth and UV conversion efficiency at two NLC lengths at similar VWLS power densities. Further, fig. 9 shows a graph with NLC length determined by bandwidth requirements at FWHM as shown.

Fig. 10 provides a schematic diagram of an exemplary UV laser 101 (here VECSEL 110). The VECSEL110 includes a VECSEL gain chip 150, the VECSEL gain chip 150 having one or more quantum wells 120 ("QWs" or "VECSEL QWs") that may be semiconductor gain media of a laser. In this example, an electrically or optically pumped semiconductor thin disk gain medium or gain chip 150 is also used as the first cavity mirror. In fig. 10, NLC 270 is disposed between 120, 130 in output path or light path 140, where the NLC is used to generate UV light as the output or VIS 140 passes through the NLC. The UV light then travels through the UV transmissive cavity mirror 130, which is partially reflective or coated with a special coating. The gain chip 150 contains an intracavity SiC heat spreader with a thin layer of CN or SiN coating between the heat spreader and the GaAs wafer, as described in detail above.

Fig. 11 provides a further schematic diagram of an alternative embodiment of a UV laser 101, here a VECSEL 110. In this configuration, NLC 270 is disposed within a cavity containing VECSEL gain chip 150, which has one or more quantum wells 120. In this embodiment, BFP 280 is disposed in output path or optical path 140. In this embodiment, the first dedicated mirror 132 is disposed behind the BFP and corresponds to the optical path. The first special mirror 132 is unique in that its inner surface is coated to reflect VWL and transmit UV with high efficiency to extract UV light. The first dedicated mirror 132 is angled to reflect or direct the output or VIS 140 through the NLC 270 and toward the second dedicated mirror 134. The inner surface of the second special mirror 134 is coated to reflect VWL and UV wavelengths. The second dedicated mirror 134 reflects the UV laser output or beam 142 through the NLC 270 and back through the first dedicated mirror 132. Thus, UV light is generated in two directions, with the left UV light being reflected back by the second cavity mirror 134 to combine with the right UV light into a single UV output 142. In this way a stable VECSEL-based UV laser output 142 is achieved.

Fig. 12 provides yet another schematic of another embodiment of a UV laser 101 utilizing a MECSEL 210. In this embodiment, NLC 270 is disposed within a cavity containing MECSEL gain chip 250, which has one or more quantum wells 220. In this embodiment, BFP 280 is disposed in output 140 or optical path 140. The first mirror 132 is disposed behind the BFP but corresponds to the optical path. The first special mirror 132 is unique in that its inner surface is coated to reflect VWL and transmit UV with high efficiency to extract UV light. The first dedicated mirror 132 is angled to reflect or direct the output or VIS 140 through the NLC 270 and toward the second dedicated mirror 134. The inner surface of the second special mirror 134 is coated to reflect VWL and UV wavelengths. The second dedicated mirror 134 reflects the UV laser output through the NLC 270 and back through the first dedicated mirror 132. Thus, UV light is generated in two directions, with the left UV light being reflected back by the second cavity mirror 134 to combine with the right UV light into a single UV output 142. A third mirror 136 is arranged behind the gain chip 250 of the MECSEL to reflect back towards VWL. By using mirrors 136, 132 and 134 together, a stable VIS cavity is achieved. In this way a stable MECSEL-based UV laser is achieved.

Fig. 13 provides a schematic diagram of a walk-off compensating NLC, in accordance with at least some embodiments of the present invention. The minimum walk-off requirement can be met using a walk-off compensation NLC obtained from the crystal supplier. For example, fig. 13 provides a pair of Barium Boron Oxide (BBO) optics 300 with the same phase matching angle, arranged in opposite directions to return the deflected beam (2 ω)310 back to the center again. The separation between the two BBOs 300 may be reduced to zero or may be in optical contact.

Fig. 14 provides a UV laser 101 (here a VECSEL 110). The VECSEL110 includes a VECSEL gain chip 150, the VECSEL gain chip 150 having one or more quantum wells 120 ("QWs" or "VECSEL QWs") that can provide a semiconductor gain medium for the laser. In this example, an electrically or optically pumped semiconductor thin disk gain medium or gain chip 150 is also used as the first cavity mirror. In fig. 14, an NLC 270 is disposed in the output path or light path 140, where the NLC is used to generate UV light as the output or VIS passes through the NLC. The UV light then travels and passes through a partially reflective (highly reflective VIS and highly transmissive UV) cavity mirror 130, or coated with a special coating. As described above, the gain chip 150 comprises an intracavity SiC heat spreader with/without a thin layer of CN or SiN coating between the heat spreader and the GaAs wafer.

Fig. 15 provides a UV laser 101 (here a well pumped MESEL 400). MECSEL assembly 410 includes a SiC heat spreader 420 that may or may not have a CN or SiN film layer as described elsewhere in this disclosure. Pump light optics 430, 432, 434 are disposed at selected locations around the MECSEL to recycle unabsorbed pump light back to the MECSEL for multiple downhole pumping. By enclosing the downhole pumped MECSEL400 within a laser cavity, several watts of visible light power can be extracted from the cavity by using the cavity mirror(s) 230/440. The NLC 270 is positioned in the output 140 or optical path 140 to convert VWL into stable UV light 142. The second cavity mirror is located at the opposite end of the cavity from the first cavity mirror 442. Thus, fig. 15 provides a well pumped MECSEL400 with MECSEL QW220 sandwiched between CTE compatible heat sinks 420 to support multiple frequencies of high intensity VWL output 140. In this embodiment, MECSEL QW220 is pumped using red pump 450. In fig. 15, the meselQW220 may be pumped with a red pump 450. In fig. 15, NLCs 270 of appropriate length (such as PPLT/PPLST or PP-LBGO) may be utilized to convert the multi-frequency output 140 into stable UV light 142. Other variations and embodiments of this configuration may also be employed to generate the stabilized UV light 142, as further disclosed and described.

Fig. 16 provides a schematic diagram of an arrangement of VECSELs that can provide and achieve a wide range of UV power output by using additional optics. Fig. 16 provides a UV laser 101, (here VECSEL 110). The VECSEL110 includes a VECSEL gain chip 150 having one or more quantum wells 120 ("QWs" or "VECSEL QWs") that may be or provide a semiconductor gain medium for the laser. In this example, an electrically or optically pumped semiconductor thin disk gain medium or gain chip 150 is also used as the first cavity mirror. In fig. 16, NLC 270 is disposed in output path or light path 140, where NLC 270 is used to generate UV light 142 as the output VIS passes through NLC 270. The UV light 142 then travels through a partially reflective or special coated (high reflection VIS and high transmission UV) cavity or end mirror 138. As described above, the gain chip 150 comprises an intracavity SiC heat spreader with/without a thin layer of CN or SiN coating between the heat spreader and the GaAs wafer. Fig. 16 also provides or includes a focusing lens 290.

In fig. 16, additional optics such as a focusing lens 290 may be utilized to increase the power output of the UV laser. The focusing lens 290 may have a focal length F1. End mirror 138 may have a radius of curvature R2. The distance is also shown in fig. 16: dl, D2 and D3; where D1 represents the distance between the surface of the VECSEL gain chip 150 and the focusing lens 290; d2 denotes the distance between the focusing lens 290 and the NLC 270; and D3 represents the distance between NLC 270 and end mirror 137. In one aspect, the UV power output may be adjusted by setting F1/R2 to approximately equal 1 and setting the value of D1/(D2+ D3) to approximately equal 2. In this way, the laser can be operated at a wide range of power levels.

Fig. 17 provides yet another schematic view of the UV laser 101 (here a downhole pumped MECSEL 400). MECSEL assembly 410 includes a SiC heat spreader 420 that may or may not have a CN or SiN film layer as described elsewhere in this disclosure. Pump light optics 430, 432, 434 are disposed at selected locations around the MECSEL to recover unabsorbed pump light for multiple passes. By enclosing the well-pumped MESEL 400 within a laser cavity, several watts of visible light power can be extracted from the cavity by using the cavity mirror(s) 230/440. In this example, wavelength selection and limiting optics 292 are positioned in the output or VIS 140 or optical path to select and limit VWF output 140. The second cavity mirror 444 is located at the opposite end of the cavity from the first cavity mirror 440. VWF output 140 is reflected by the second cavity through NLC 270 to convert the multi-frequency output or VWF to UV light 142. UV light is generated in two directions and the left UV light is reflected back by the third mirror 134 to combine with the right UV light into a single UV output 1422. Thus, fig. 17 provides a well pumped MECSEL400 with MECSEL QW220 sandwiched between CTE compatible heat sinks 420 to support multiple frequencies of high intensity VWL output 140. In this embodiment, MECSEL QW220 is pumped using red pump 450. In FIG. 17, a NLC 270 of appropriate length (such as PPLT/PPLST or PP-LBGO) can be utilized to convert the multi-frequency output VIS 140 into stable UV light 142. Other variations and embodiments of this configuration may also be used to generate the stabilized UV light 142, as further disclosed and described.

Fig. 19A shows an example of a barrier pumped laser 500. In fig. 19A, a pump photon 502 is pumped into a potential barrier 504a of the conduction band 510. Pumping a pump photon 502 into the potential barrier 504 generates an electron-hole pair 520a, 520b in the potential barrier 505. The electron-hole pairs 520a, 520b migrate (as indicated by dashed lines 522a, 522 b) to one of the quantum wells 514 and recombine at the quantum well to produce a laser photon 524.

Fig. 19B shows an example of an in-well pump laser 600, in fig. 19B, pump photons 602 are pumped into a well 614 of the conduction band 610. The pump photon 602 is absorbed in the quantum well 614, which creates an electron-hole pair 620a, 620b in the quantum well 614. After relaxation (as shown by dashed lines 622a, 622 b) to the ground state, it recombines into laser photons 624. The energy difference between the pump photons and the laser photons, called quantum defects, is deposited in the heat sink in the form of heat, as shown in fig. 1A, 1B and 2.

The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations, substitutions and modifications of the basic concepts not described will become apparent to those skilled in the art once the above disclosure is fully appreciated. All such modifications and variations are intended to be included herein within the scope of the appended claims and their legal equivalents, and the scope of the invention is not limited to the examples given or their claims.