Polarization-state-adjustable solid Raman laser and working method thereof

Abstract

The invention relates to a solid Raman laser with an adjustable polarization state and a working method thereof, and belongs to the technical field of lasers. The laser comprises an LD pumping source, a fundamental frequency light input mirror, a laser working substance, a Q-switched working substance, a fundamental frequency light output mirror, a Raman cavity input mirror, an a-cut anisotropic Raman crystal, a Raman cavity output mirror, a beam splitter, a polaroid and a power meter which are sequentially arranged along a light path, and an oscilloscope is arranged on one side of the beam splitter. By accurately controlling the orientation of the anisotropic Raman crystal, the elliptical polarization passive Q-switched Raman laser can be switched among different polarization states, and has the advantages of compact structure, easiness in integration and controllable Raman light polarization state.

Description

Technical Field

[0001] The invention relates to a solid Raman laser with adjustable polarization state and a working method thereof, belonging to the technical field of lasers. Background Art

[0002] In the development of high peak power passively Q-switched Raman lasers, manipulating the polarization state of the laser, such as the ellipticity and azimuth of elliptically polarized light, the output power and polarization angle of linearly polarized light, is crucial for many applications. These areas include material processing, molecular manipulation, and the use of lasers to capture and manipulate particles. Especially in biomedical imaging, due to the high scattering properties of biological tissues, precise control of the polarization state of the laser can significantly improve the imaging quality and diagnostic accuracy. The polarization of laser light is one of its basic physical properties, and together with spectrum and coherence, it plays a key role in the interaction between light and matter.

[0003] In elliptically polarized Raman lasers, crystal orientation has an important influence on the polarization state of the laser. The adjustment of crystal orientation is complex and it is difficult to achieve precise control of the elliptically polarized state. The refractive index and absorption coefficient of anisotropic crystals usually show differences in different crystal axis directions, which makes them show different absorption characteristics for light of different polarization states. For a-cut anisotropic crystals, the change of its output laser characteristics is greater. This influence includes the change of the intensity of stimulated Raman scattered light and the distribution of the spatial angle of non-axial Raman scattered light. In view of this characteristic, passive Q-switched Raman lasers with adjustable polarization pump laser characteristics have gradually become a research hotspot. For this reason, the present invention is proposed. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a solid Raman laser with adjustable polarization state and a working method thereof. By precisely controlling the orientation of the anisotropic Raman crystal, the elliptically polarized passively Q-switched Raman laser can switch between different polarization states, which has the advantages of compact structure, easy integration and controllable polarization state of Raman light.

[0005] The technical solution of the present invention is as follows:

[0006] A solid Raman laser with adjustable polarization state comprises an LD pump source, a fundamental frequency light input mirror, a laser working substance, a Q-switched working substance, a fundamental frequency light output mirror, a Raman cavity input mirror, an a-cut anisotropic Raman crystal, a Raman cavity output mirror, a beam splitter, a polarizer and a power meter, which are sequentially arranged along an optical path, and an oscilloscope is arranged on one side of the beam splitter;

[0007] The fundamental frequency light input mirror, the laser working material, the Q-switched working material and the fundamental frequency light output mirror constitute the fundamental frequency light resonant cavity, and the Raman cavity input mirror, the a-cut anisotropic Raman crystal and the Raman cavity output mirror constitute the Raman resonant cavity.

[0008] Preferably, the LD pump source is modulated by power supply, and the working pulse width and working cycle are adjustable. A coupling lens group is provided on the output side of the LD pump source to collimate and focus the pump light and adjust the pump light spot radius incident on the a-cut anisotropic Raman crystal. The coupling lens group is a common component in solid-state lasers.

[0009] Preferably, according to the present invention, both ends of the fundamental frequency light input mirror are coated with high transmittance to pump light and high reflectance to fundamental frequency light, and are used to transmit pump light and reflect laser light generated by a-cut anisotropic Raman crystal.

[0010] According to the preferred embodiment of the present invention, the laser working material is doped with Nd 3+ Particles or Yb 3+ The laser working material of the particles, such as Nd:YVO4, Nd:GdVO4 or Nd:YAP, will generate pulsed laser under the pumping of pump light and enhance the intensity of the laser light incident into the a-cut anisotropic Raman crystal.

[0011] Preferably according to the present invention, the Q-switched working material is a saturable absorber crystal, and can also be any Q-switched working material that can absorb the laser wavelength emitted by the laser working material to a certain extent. The Q-switched working material will increase the pump threshold. When the pump light power reaches a certain level, the pump threshold will be suddenly reduced, thereby forming a nanosecond / sub-nanosecond pulse train laser output.

[0012] Preferably, according to the present invention, a half-wave plate is provided between the fundamental frequency light output mirror and the Raman cavity input mirror for changing the polarization state of the fundamental frequency light, converting the linearly polarized fundamental frequency light into elliptically polarized light without changing other properties of the laser.

[0013] Preferably, according to the present invention, both ends of the Raman cavity input mirror are coated with high transmittance to fundamental frequency light and partial reflectance to Raman light, so as to transmit fundamental frequency light and reflect Raman light generated by a-cut anisotropic Raman crystal.

[0014] Preferably, according to the present invention, the a-cut anisotropic Raman crystal is a laser working material that generates Raman frequency shift, such as YVO4, Nd:YVO4, GdVO4 or diamond. The incident fundamental frequency light is stimulated by Raman through the a-cut anisotropic Raman crystal to form a Raman frequency shift, and the generated photon frequency is lower than the fundamental frequency photon frequency, and Raman light is output. A vertical rotation adjustment table is provided on the lower side of the a-cut anisotropic Raman crystal, and the angle φ between the axial direction of the a-cut anisotropic Raman crystal and the polarization state of the fundamental frequency light is changed by the vertical rotation adjustment table, so that its c-axis is along the light transmission direction, and the a-axis can be accurately rotated in the vertical direction, thereby achieving the purpose of outputting Raman light of different polarization states.

[0015] The angle φ between the axial direction of the a-cut anisotropic Raman crystal and the polarization state of the fundamental frequency light is expanded from 0° to 360°, and the polarization state of the generated Raman light changes regularly with the angle, thereby outputting linearly polarized Raman light with controllable angle, power and extinction ratio, and elliptically polarized fundamental frequency light outputting elliptically polarized Raman light with controllable ellipticity, azimuth angle and power, thereby realizing the control of the polarization state of the Raman light.

[0016] The working method of the above-mentioned polarization-adjustable solid Raman laser comprises the following steps:

[0017] (1) The LD pump source outputs pump light after power modulation, and the coupling lens group collimates and focuses the pump light. The focused pump light enters the fundamental frequency optical resonant cavity through the fundamental frequency light input mirror;

[0018] (2) In the fundamental frequency optical resonant cavity, the laser working material generates pulsed laser under the pumping of pump light, and the Q-switched working material increases the pumping threshold. When the pumping light power reaches a certain level, the pumping threshold is suddenly reduced, thereby forming a nanosecond / sub-nanosecond pulse train laser output;

[0019] (3) The fundamental frequency light output by the fundamental frequency optical resonant cavity enters the Raman resonant cavity. The incident fundamental frequency light passes through the a-cut anisotropic Raman crystal to form a Raman frequency shift. The generated photon frequency is lower than the fundamental frequency photon frequency, and the Raman light is output. During the operation of the Raman resonant cavity, the angle φ between the axial direction of the a-cut anisotropic Raman crystal and the polarization state of the fundamental frequency light is changed by the vertical rotation adjustment stage, so that its c-axis is along the light transmission direction, and the a-axis can be accurately rotated in the vertical direction, so as to achieve the purpose of outputting Raman light with different polarization states;

[0020] (4) The beam splitter splits the Raman light, one beam is used for oscilloscope measurement, and the other beam is used for power meter measurement. The polarizer measures the polarization state of the Raman light. By rotating the polarizer, light with a specific polarization direction is selectively transmitted. The power meter measures the power of the Raman light and records the regular changes in the power meter reading, thereby recording the polarization state of the Raman light.

[0021] Preferably according to the present invention, when the fundamental frequency light is linearly polarized light, the polarization state of the fundamental frequency light is changed by a half-wave plate to convert the linearly polarized fundamental frequency light into elliptically polarized light.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention has a compact structure, reasonable design, easy operation and integration. Compared with the actively Q-switched Raman laser, the passive Q-switched method of generating fundamental frequency light can obtain fundamental frequency light with narrower pulse width and higher efficiency.

[0024] 2. The present invention can output Raman light with different polarization characteristics in the same resonant cavity by finely adjusting the axial direction of the a-cut anisotropic Raman crystal. At the same time, the Raman crystal has a beam purification effect on the fundamental frequency light to obtain Raman light with a narrower pulse width.

[0025] 3. The present invention can maximize the efficiency of Raman scattering and improve the laser output power by precisely controlling the orientation and rotation of the a-cut anisotropic Raman crystal to match and optimize the polarization direction of the fundamental frequency light.

[0026] 4. The present invention optimizes polarization control and Raman gain, and this laser system can be more effectively used in a variety of applications, including material processing, biomedical imaging, and precision measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0029] In the figure, 1-LD pump source; 2-fundamental frequency light input mirror; 3-laser working material; 4-Q-switched working material; 5-fundamental frequency light output mirror; 6-Raman cavity input mirror; 7-a-cut anisotropic Raman crystal; 8-Raman cavity output mirror; 9-beam splitter; 10-oscilloscope; 11-polarizer; 12-power meter; 13-half-wave plate. DETAILED DESCRIPTION

[0030] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0031] Embodiment 1:

[0032] like Figure 1 As shown, this embodiment provides a solid Raman laser with adjustable polarization state, including an LD pump source 1, a fundamental frequency light input mirror 2, a laser working substance 3, a Q-switched working substance 4, a fundamental frequency light output mirror 5, a Raman cavity input mirror 6, an a-cut anisotropic Raman crystal 7, a Raman cavity output mirror 8, a beam splitter 9, a polarizer 11 and a power meter 12, which are sequentially arranged along the optical path, and an oscilloscope 10 is arranged on one side of the beam splitter 9;

[0033] The fundamental frequency light input mirror 2, the laser working material 3, the Q-switched working material 4 and the fundamental frequency light output mirror 5 constitute a fundamental frequency light resonant cavity, and the Raman cavity input mirror 6, the a-cut anisotropic Raman crystal 7 and the Raman cavity output mirror 8 constitute a Raman resonant cavity.

[0034] The LD pump source 1 is modulated by power supply, and the working pulse width and working cycle can be adjusted. A coupling lens group is provided on the output side of the LD pump source to collimate and focus the pump light and adjust the pump light spot radius incident on the a-cut anisotropic Raman crystal. The coupling lens group is a common component in solid-state lasers.

[0035] Both ends of the fundamental frequency light input mirror 2 are coated with high transmittance to the pump light and high reflectance to the fundamental frequency light, and are used to transmit the pump light and reflect the laser generated by the a-cut anisotropic Raman crystal.

[0036] Laser working material 3 is doped with Nd 3+ Particles or Yb 3+ The laser working material of the particles, such as Nd:YVO4, Nd:GdVO4 or Nd:YAP, will generate pulsed laser under the pumping of pump light and enhance the intensity of the laser light incident into the a-cut anisotropic Raman crystal.

[0037] The Q-switched working material 4 is a saturable absorber crystal, and can also be any Q-switched working material that can absorb the laser wavelength emitted by the laser working material to a certain extent. The Q-switched working material will increase the pump threshold. When the pump light power reaches a certain level, the pump threshold will be suddenly reduced, thereby forming a nanosecond / sub-nanosecond pulse train laser output.

[0038] Both ends of the Raman cavity input mirror 6 are coated with a film, which has high transmittance to the fundamental frequency light and partial reflectivity to the Raman light, and is used to transmit the fundamental frequency light and reflect the Raman light generated by the a-cut anisotropic Raman crystal.

[0039] The a-cut anisotropic Raman crystal 7 is a laser working material that generates Raman frequency shift, such as YVO4, Nd:YVO4, GdVO4 or diamond. The incident fundamental frequency light is stimulated by Raman through the a-cut anisotropic Raman crystal to form a Raman frequency shift, and the generated photon frequency is lower than the fundamental frequency photon frequency, and Raman light is output. A vertical rotation adjustment table is provided on the lower side of the a-cut anisotropic Raman crystal 7. The vertical rotation adjustment table is used to change the angle φ between the axial direction of the a-cut anisotropic Raman crystal and the polarization state of the fundamental frequency light, so that its c-axis is along the light transmission direction, and the a-axis can be accurately rotated in the vertical direction, thereby achieving the purpose of outputting Raman light with different polarization states.

[0040] The angle φ between the axial direction of the a-cut anisotropic Raman crystal and the polarization state of the fundamental frequency light is expanded from 0° to 360°, and the polarization state of the generated Raman light changes regularly with the angle, thereby outputting linearly polarized Raman light with controllable angle, power and extinction ratio, and elliptically polarized fundamental frequency light outputting elliptically polarized Raman light with controllable ellipticity, azimuth angle and power, thereby realizing the control of the polarization state of the Raman light.

[0041] The working method of the above-mentioned polarization-adjustable solid Raman laser comprises the following steps:

[0042] (1) LD pump source 1 outputs pump light after power modulation, and the coupling lens group collimates and focuses the pump light. The focused pump light enters the fundamental frequency optical resonant cavity through the fundamental frequency light input mirror;

[0043] (2) In the fundamental frequency optical resonant cavity, the laser working material generates pulsed laser under the pumping of pump light, and the Q-switched working material increases the pumping threshold. When the pumping light power reaches a certain level, the pumping threshold is suddenly reduced, thereby forming a nanosecond / sub-nanosecond pulse train laser output;

[0044] (3) The fundamental frequency light output by the fundamental frequency optical resonant cavity enters the Raman resonant cavity. The incident fundamental frequency light passes through the a-cut anisotropic Raman crystal to form a Raman frequency shift. The generated photon frequency is lower than the fundamental frequency photon frequency, and the Raman light is output. During the operation of the Raman resonant cavity, the angle φ between the axial direction of the a-cut anisotropic Raman crystal and the polarization state of the fundamental frequency light is changed by the vertical rotation adjustment stage, so that its c-axis is along the light transmission direction, and the a-axis can be accurately rotated in the vertical direction, so as to achieve the purpose of outputting Raman light with different polarization states;

[0045] (4) The beam splitter splits the Raman light, one beam is used for oscilloscope measurement, and the other beam is used for power meter measurement. The polarizer measures the polarization state of the Raman light. By rotating the polarizer, light with a specific polarization direction is selectively transmitted. The power meter measures the power of the Raman light and records the regular changes in the power meter reading, thereby recording the polarization state of the Raman light.

[0046] Embodiment 2:

[0047] A solid Raman laser with adjustable polarization state, as described in Example 1, except that a half-wave plate 13 is provided between the fundamental frequency light output mirror 5 and the Raman cavity input mirror 6, as shown in FIG. Figure 2 As shown, it is used to change the polarization state of the fundamental frequency light, converting the linearly polarized fundamental frequency light into elliptically polarized light without changing other properties of the laser.

[0048] When the fundamental frequency light is linearly polarized light, the polarization state of the fundamental frequency light is changed by a half-wave plate, and the linearly polarized fundamental frequency light is converted into elliptically polarized light.

[0049] The embodiments of the present invention are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A solid Raman laser with adjustable polarization state, characterized in that: It includes an LD pump source, a fundamental frequency light input mirror, a laser working substance, a Q-switched working substance, a fundamental frequency light output mirror, a Raman cavity input mirror, an a-cut anisotropic Raman crystal, a Raman cavity output mirror, a beam splitter, a polarizer and a power meter, which are sequentially arranged along the optical path. An oscilloscope is arranged on one side of the beam splitter. The fundamental frequency light input mirror, the laser working material, the Q-switched working material and the fundamental frequency light output mirror constitute the fundamental frequency light resonant cavity, and the Raman cavity input mirror, the a-cut anisotropic Raman crystal and the Raman cavity output mirror constitute the Raman resonant cavity.

2. The solid-state Raman laser with adjustable polarization state according to claim 1, characterized in that: A coupling lens group is provided on the output side of the LD pump source for collimating and focusing the pump light and adjusting the spot radius of the pump light incident on the a-cut anisotropic Raman crystal.

3. The solid-state Raman laser with adjustable polarization state as claimed in claim 2, characterized in that: Both ends of the fundamental frequency light input mirror are coated to transmit the pump light and reflect the laser light generated by the a-cut anisotropic Raman crystal.

4. The solid-state Raman laser with adjustable polarization state as claimed in claim 3, characterized in that: The laser working material is Nd:YVO4, Nd:GdVO4 or Nd:YAP.

5. The solid-state Raman laser with adjustable polarization state as claimed in claim 4, characterized in that: The Q-switching working material is a saturable absorber crystal.

6. The solid-state Raman laser with adjustable polarization state as claimed in claim 5, characterized in that: A half-wave plate is arranged between the fundamental frequency light output mirror and the Raman cavity input mirror.

7. The solid-state Raman laser with adjustable polarization state according to claim 6, characterized in that: The Raman cavity input mirror is coated at both ends to transmit the fundamental frequency light and reflect the Raman light generated by the a-cut anisotropic Raman crystal.

8. The polarization-adjustable solid Raman laser according to claim 7, characterized in that: The a-cut anisotropic Raman crystal is YVO4, Nd:YVO4, GdVO4 or diamond. A vertical rotation adjustment table is arranged at the lower side of the a-cut anisotropic Raman crystal, and the angle φ between the axial direction of the a-cut anisotropic Raman crystal and the polarization state of the fundamental frequency light is changed by the vertical rotation adjustment table.

9. The operating method of the polarization-adjustable solid Raman laser according to claim 8, characterized in that: Here are the steps: (1) The LD pump source outputs pump light after power modulation, and the coupling lens group collimates and focuses the pump light. The focused pump light enters the fundamental frequency optical resonant cavity through the fundamental frequency light input mirror; (2) In the fundamental frequency optical resonant cavity, the laser working material generates pulsed laser under the pumping of pump light, and the Q-switched working material increases the pumping threshold. When the pumping light power reaches a certain level, the pumping threshold is suddenly reduced, thereby forming a nanosecond / sub-nanosecond pulse train laser output; (3) The fundamental frequency light output by the fundamental frequency optical resonant cavity enters the Raman resonant cavity. The incident fundamental frequency light passes through the a-cut anisotropic Raman crystal to form a Raman frequency shift. The generated photon frequency is lower than the fundamental frequency photon frequency, and the Raman light is output. During the operation of the Raman resonant cavity, the angle φ between the axial direction of the a-cut anisotropic Raman crystal and the polarization state of the fundamental frequency light is changed by the vertical rotation adjustment stage, so that its c-axis is along the light transmission direction, and the a-axis can be accurately rotated in the vertical direction, so as to achieve the purpose of outputting Raman light with different polarization states; (4) The beam splitter splits the Raman light, one beam is used for oscilloscope measurement, and the other beam is used for power meter measurement. The polarizer measures the polarization state of the Raman light. By rotating the polarizer, light with a specific polarization direction is selectively transmitted. The power meter measures the power of the Raman light and records the regular changes in the power meter reading, thereby recording the polarization state of the Raman light.

10. The operating method of the polarization-adjustable solid Raman laser according to claim 9, characterized in that: When the fundamental frequency light is linearly polarized light, the polarization state of the fundamental frequency light is changed by a half-wave plate, and the linearly polarized fundamental frequency light is converted into elliptically polarized light.

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