阅读说明：本技术 一种直接产生涡旋光束以及拍频的微片激光器 (Microchip laser for directly generating vortex light beam and beat frequency ) 是由 张子龙 贵崑 赵长明 张海洋 李亚弼 于 2020-05-26 设计创作，主要内容包括：本发明提供了一种直接产生涡旋光束以及拍频的微片激光器,能够直接产生涡旋光束的同时输出拍频,结构更加简单、紧凑,输出稳定。本发明采用具有圆对称性端面冷却结构的晶体外壳为双偏振微型激光腔提供圆对称的温度梯度场分布,能够直接产生涡旋光束；再利用微片双折射晶体将激光分裂为垂直偏振的双频激光,并且两个频率具有不同的横模模式,其中一个为LG<Sub>01</Sub>模,另一个为基横模。本发明不需要特殊的泵浦源与光束控制元件,可以直接产生涡旋光束,而且涡旋光与正交偏振的基横模可以产生稳定的拍频；具有微片结构的增益晶体和双折射晶体,横截面积与厚度都可以控制在毫米量级,极大的缩小了直接产生涡旋光的激光器的体积,有利于集成化的工业应用。(The invention provides a microchip laser capable of directly generating vortex beams and beat frequency, which can directly generate the vortex beams and output the beat frequency at the same time, and has the advantages of simpler and more compact structure and stable output. The crystal shell with the circular symmetry end face cooling structure is adopted to provide circular symmetry temperature gradient field distribution for the dual-polarization micro laser cavity, and vortex beams can be directly generated; and splitting the laser into vertically polarized dual-frequency laser by using a micro-slab birefringent crystal, wherein two frequencies have different transverse mode modes, and one of the two frequencies is LG 01 The other is a basic transverse mold. The invention does not need special pumping source and beam control element, can directly generate vortex beam, and the vortex rotation and the orthogonal polarization fundamental transverse mode can generate stable beat frequency; gain crystal and birefringent crystal with micro-slab structureThe cross-sectional area and the thickness of the laser can be controlled in millimeter magnitude, so that the volume of the laser directly generating vortex rotation is greatly reduced, and the industrial application of integration is facilitated.)

1. A microchip laser for directly generating vortex beams and beat frequency is characterized by comprising a pumping source, a birefringent crystal (1), a gain crystal (2), a first resonant cavity mirror (3), a second resonant cavity mirror (4) and a crystal shell (12);

wherein, the birefringent crystal (1) and the gain crystal (2) are jointed together to form a composite crystal, and both the birefringent crystal (1) and the gain crystal (2) adopt a micro-sheet structure;

one end of the composite crystal is coated with a film to form a first resonant cavity mirror (3), the other end of the composite crystal is coated with a film to form a second resonant cavity mirror (4), the first resonant cavity mirror (3) is highly transparent to pumping light and highly reflective to oscillation laser, and the second resonant cavity mirror (4) partially transmits the oscillation laser; the composite crystal is embedded into a crystal shell (12), the joint part of the crystal shell (12) and the end face of the composite crystal adopts a boss structure which is circularly and symmetrically distributed, a first light through hole (7) is formed in the center of the boss, a second light through hole (8) is formed in one side, opposite to the first light through hole (7), of the crystal shell (12), and output laser is output through the second light through hole (8);

the pump source is used for generating pump light, and the pump light passes through the center of the first light through hole (7) and is normally incident on the gain crystal (2) through a circular light spot; the birefringent crystal (1) is used to split laser light into vertically polarized dual frequency laser light.

2. The microchip laser for direct generation of vortex beam and beat frequency according to claim 1, wherein the crystal housing (12) has a groove (6) and a clip (5) therein, and the composite crystal is embedded in the groove (6) and fixed by the clip (5).

3. The microchip laser for directly generating vortex beam and beat frequency according to claim 1, wherein the crystal housing (12) is a metal housing, and heat is directly conducted from the end face of the composite crystal to the metal housing (12) by means of end-face-attached heat conduction.

4. The microchip laser for direct generation of a vortex beam and a beat frequency according to claim 1, 2 or 3, characterized in that the crystal housing (12) is connected to a temperature control device for controlling the temperature of the composite crystal.

Technical Field

The invention belongs to the technical field of double-frequency microchip lasers, and particularly relates to a microchip laser capable of directly generating vortex beams and beat frequency.

Background

Recent decades of research on the output characteristics of microchip lasers have helped us understand the physical properties of lasers more deeply, especially solid-state lasers. The output light of the double-frequency microchip laser carries microwave or terahertz wave components, and the double-frequency microchip laser has important application in the aspects of laser radar detection and optical communication.

In recent years, the direct generation of a vortex beam by a microchip laser has attracted much attention. There are two main ways of directly generating a vortex beam today: one is to use a ring pump source, and the other is to introduce low-order mode loss into the resonant cavity, wherein the former can be regarded as gain control, and the latter is loss control; however, the annular pump source has a complex structure, so that the overall structure of the laser is not compact enough; the introduction of low-order mode loss in the resonant cavity results in more laser devices, more complex structure and difficult guarantee of stability. The existing method for directly generating vortex beams is difficult to meet the requirements of miniaturization and high stability.

In addition, the vortex light beam is directly generated, meanwhile, the double-frequency beat frequency effect plays a unique application value in the field of double-frequency laser detection, the double-frequency difference can measure the distance and radial velocity information of a detected target, and the vortex light beam can measure the rotation angular velocity and even the tangential velocity information of the target. Therefore, the technology of fusing the dual-frequency laser and the vortex beam has great application value in the detection field, and is hopeful to become the mainstream of the next generation laser radar detection technology.

Disclosure of Invention

In view of this, the invention provides a microchip laser capable of directly generating vortex beams and beat frequencies, which can directly generate vortex beams and output beat frequencies at the same time, and has a simpler and more compact structure and stable output.

The invention provides a microchip laser for directly generating vortex beams and beat frequency, which comprises a pumping source, a birefringent crystal, a gain crystal, a first resonant cavity mirror, a second resonant cavity mirror and a crystal shell, wherein the first resonant cavity mirror is arranged on the upper surface of the birefringent crystal;

the double-refraction crystal and the gain crystal are attached together to form a composite crystal, and both the double-refraction crystal and the gain crystal adopt a micro-sheet structure;

one end of the composite crystal is coated with a film to form a first resonant cavity mirror, the other end of the composite crystal is coated with a film to form a second resonant cavity mirror, the first resonant cavity mirror is highly transparent to pumping light and highly reflective to oscillation laser, and the second resonant cavity mirror partially transmits the oscillation laser; the composite crystal is embedded into the crystal shell, the joint part of the crystal shell and the end face of the composite crystal adopts a boss structure which is circularly and symmetrically distributed, a first light through hole is formed in the center of the boss, a second light through hole is formed in one side, opposite to the first light through hole, of the crystal shell, and output laser is output through the second light through hole;

the pump source is used for generating pump light, and the pump light passes through the center of the first light through hole and is normally incident to the gain crystal through a circular light spot; the birefringent crystal is used to split the laser light into vertically polarized dual frequency laser light.

The crystal shell is internally provided with a groove and a clamping piece, and the composite crystal is embedded into the groove and is fixed through the clamping piece.

The crystal shell is a metal shell, and heat is directly conducted to the metal shell from the end face of the composite crystal by adopting an end face attaching heat conduction mode.

The crystal shell is connected with a temperature control device and used for controlling the temperature of the composite crystal.

Has the advantages that:

the crystal shell with the circular symmetry end face cooling structure is adopted to provide circular symmetry temperature gradient field distribution for the dual-polarization micro laser cavity, and vortex beams can be directly generated; and splitting the laser into vertically polarized dual-frequency laser by using a micro-slab birefringent crystal, wherein two frequencies have different transverse mode modes, one of the two frequencies hasIs LG₀₁The other is a basic transverse mold. The invention does not need special pumping source and beam control element, can directly generate vortex beam, and the vortex rotation and the orthogonal polarization fundamental transverse mode can generate stable beat frequency; the cross section area and the thickness of the gain crystal and the birefringent crystal with the microchip structure can be controlled in millimeter magnitude, the volume of the laser directly generating the vortex rotation is greatly reduced, and the industrial application of integration is facilitated.

Drawings

FIG. 1 is a block diagram of a laser resonator of the present invention;

wherein, 1-birefringent crystal; 2-gain crystal; 3-a first resonator cavity mirror; 4-second resonator cavity mirror.

FIG. 2 is a block diagram of a crystal enclosure of the present invention;

wherein, 5-clamping piece; 6-groove; 7-a first light through hole; 8-second light hole 2.

FIG. 3 is a schematic diagram of pump light incidence according to the present invention;

wherein, 9-tail fiber semiconductor laser; 10-pump light; 11-a lens group; 12-crystal shell.

Detailed Description

The invention is described in detail below by way of example with reference to the accompanying drawings.

The present invention is completely different from the two modes mentioned above, and the dual-polarization microchip laser of the present invention generates vortex beams and beat frequency signals by using the temperature gradient field control and the polarization control of the gain crystal 2. The method specifically comprises the following steps: the double-polarized microchip laser of the invention generates self-Q-switching effect, utilizes the pump light 10 of normal incidence circular facula and the crystal shell 12 with symmetrical structure to make the temperature gradient field of the gain crystal 2 distributed symmetrically, and can directly generate vortex Light (LG) with orbital angular momentum easily₀₁A mold); then, the polarization selection characteristic of the birefringent crystal 1 is utilized to obtain the cross polarization LG₀₁The mode and the fundamental transverse mode are simultaneously output, and a beat frequency signal with a GHz level can be output.

The resonant cavity of the dual-polarization microchip laser is formed by compounding a birefringent crystal 1 and a gain crystal 2, wherein the birefringent crystal 1 and the gain crystal 2 both adopt a microchip structure, the thickness is hundreds of microns, the cross section area is 1mm x 1mm, and the birefringent crystal 1 and the gain crystal are attached together in the form of optical cement to form a composite crystal. The end face of the gain crystal 2 which is not in contact with the birefringent crystal 1 is coated with a film to form a first resonant cavity mirror 3, and the first resonant cavity mirror 3 has high transmittance to the pump light and partially transmits the oscillation laser; the birefringent crystal 1 and the end face which is not in contact with the gain crystal 2 are coated with films to form a second resonant cavity mirror 4, and the second resonant cavity mirror 4 is highly reflective to laser; the gain crystal 2, the birefringent crystal 1, the first resonant cavity mirror 3 and the second resonant cavity mirror 4 form a resonant cavity with dual-polarization characteristics.

The composite crystal of the birefringent crystal 1 and the gain crystal 2 is embedded into a groove 6 of a crystal shell 12 and is fixed by a clamping piece 5; the crystal shell 12 is a metal shell, and a large-area end face attaching heat conduction mode is adopted, so that heat can be directly conducted to the metal shell 12 from the crystal end face, and the method is different from a traditional laser crystal side face cooling mode; the crystal shell 12 can also be connected with other temperature control devices to control the temperature of the composite crystal; the joint part of the crystal shell 12 and the end face of the composite crystal adopts a boss structure which is distributed in a circular symmetry manner, the joint part can be fully contacted with the composite crystal, a first light through hole 7 is reserved in the center of the boss, a second light through hole 8 is arranged on one side of the crystal shell 12 opposite to the first light through hole 7, and output laser is output through the second light through hole 8.

The tail fiber semiconductor laser 9 generates pump light 10, the pump light 10 is converged into a circular light spot through the lens group 11, and the circular light spot is normally incident on the gain crystal 2 through the center of the first light through hole 7. Because the crystal shell 12 and the pumping light spots are in a circular symmetrical structure, the temperature gradient field distribution in the gain crystal 2 is also in symmetrical distribution, and the LG can be directly generated₀₁Mode(s). After the laser light propagates into the birefringent crystal 1, because the birefringent crystal 1 has anisotropy, the laser light is split into two orthogonal linear polarization lights, different transverse mode modes are generated in the two orthogonal polarization directions, and the gain and the loss in the two polarization directions are different, so that the laser thresholds of the two laser lights are different. At low pump power, both modes are TEM₀₀Die, increase pumping powerAfter division, LG is first generated in one of the polarization directions₀₁Modulus, assuming that the direction is x, LG in the x-direction₀₁Die and TEM₀₀Mode competition occurs in the mode, and LG is realized under the condition of higher pumping power₀₁Mode dominance, TEM in x-direction₀₀The mode may not get enough gain and be extinguished; the other polarization direction is assumed to be y, y-direction TEM₀₀Mode and x-direction LG₀₁The frequency difference of the mode is large, the longitudinal hole burning effect is considered, and the TEM is arranged in the y direction₀₀Mode and x-direction LG₀₁Competition ratio between modes LG in x-direction₀₁Die and TEM₀₀The competition between the modes is weak. Thus, LG is taken in the x-direction₀₁Mold, TEM₀₀Modulo, y-direction TEM₀₀Under the mode co-competition mechanism, the dual-polarization microchip laser finally outputs LG in the x direction₀₁Mode and y-direction TEM₀₀And the laser of the mode is output through the second light through hole 8.

It can be seen that the present invention utilizes a dual-polarized microchip laser to generate a vertically polarized fundamental transverse mode (TEM)₀₀Mode) and laguerre-gaussian (LG) mode₀₁A mold); in particular, the crystal generates a symmetrical temperature gradient distribution field by using an axisymmetric crystal shell, and pumping light is normally incident to the gain crystal through a circular light spot to generate LG₀₁Molding; splitting laser into vertically polarized dual-frequency laser by utilizing a microchip birefringent crystal, wherein the two frequencies have different transverse mode modes; one of them is LG₀₁The other is a basic transverse mould; and the two modes are coherent, a stable beat frequency can be generated. In addition, the cross section area and the thickness of the gain crystal and the birefringent crystal with the microchip structure can be controlled in millimeter level, the volume of the vortex light laser is greatly reduced, integration is facilitated, the gain crystal and the birefringent crystal are simpler, and the structure is more compact and stable.

The invention fuses the direct generation of the dual-frequency laser and the vortex beam, directly generates two modes with different frequencies or wavelengths and vertical polarization through the laser resonant cavity, wherein one mode is the vortex beam, the other mode is the fundamental mode beam, and the two modes can be strictly coaxially transmitted. Due to the characteristic difference of the two modes in modes, polarization and light frequency, the two modes have unique application value in the field of dual-frequency laser detection.

In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.