Spatial light filter

Abstract

The invention discloses a spatial optical filter, which comprises a pump light supply device and a self-filtering laser amplification device, and is characterized in that the self-filtering laser amplification device is arranged on an emergent light path of the pump light supply device; a pump light absorption crystal is arranged in the self-filtering laser amplification device; the pump light supply device injects pump light distributed in a flat top mode into the self-filtering laser amplification device, filtered light beams pass through the pump light absorption crystal to obtain light beams separated from each other in the radial direction, and spatial light filtering is achieved. According to the 4f spatial light filter, the pump light absorption crystal plays a role of a diaphragm and is used for realizing spatial light filtering, and the problems that air is easy to ionize under high power of a traditional 4f spatial light filter and filtered fundamental mode light is relatively poor due to diffraction of a hard diaphragm are solved.

Description

Technical Field

[0001] The present application relates to the field of optical technology, and more specifically, to a spatial optical filter. Background Art

[0002] Lasers are important light sources for the development of modern science and technology. To meet the demand for higher power and greater energy lasers in the development of science and technology, lasers must work under the premise of high pumping. Lasers will produce serious optical distortion under high pumping, which will lead to the deterioration of laser beam quality. The most common is the generation of high-order Gaussian beam modes. In order to obtain the fundamental transverse mode Gaussian beam, it is necessary to filter out the high-order Gaussian beam mode through spatial filtering.

[0003] In addition, for the traveling wave amplification of the master oscillator in the laser field, when the number of amplification stages is large, the weak spontaneous emission noise light in the gain medium of the master oscillator and amplifier will be continuously amplified when passing through other gain media, making the gain extracted from the seed light less and less, and the amplified spontaneous emission light will be superimposed on the seed light, causing the seed light pulse width to become wider and background noise light to be around the light beam. Therefore, it is necessary to prevent the continuous amplification of spontaneous emission light by means of spatial optical filtering.

[0004] Although traditional 4f spatial optical filters are often used to improve the quality of laser beams, since such spatial optical filters form a very small light spot, it is very easy to make the power density of high-power lasers very large, which in turn causes the surrounding air to ionize, producing a sharp air breakdown sound, affecting the normal use of the laser. In addition, such spatial optical filters require a hard aperture (such as the edge of a lens, a frame, or a specially set perforated screen) to block high-order Gaussian mode lasers. If the power of the high-order mode laser is strong, the service life of the hard aperture will also be seriously reduced. At the same time, the hard aperture will also cause serious diffraction effects, resulting in the acquisition of poor fundamental mode light. Summary of the invention

[0005] The present application provides a spatial light filter. When a filtered light beam passes through a pump light absorbing crystal, due to the thermal lens effect, the focal length of the thermal lens in the pump region is the same, while the focal length of the thermal lens outside the pump region gradually decreases with the increase of the radial distance. Therefore, the light beams at different radial positions experience different lens focal lengths, so that the light beams after passing through the pump light absorbing crystal are separated in the radial direction. Therefore, the pump light absorbing crystal plays the role of an aperture to achieve spatial light filtering, avoiding the problems of easy ionization of air at high power in traditional 4f spatial light filters and the diffraction of the hard aperture that easily makes the fundamental mode light after filtering poor.

[0006] The present application provides a spatial optical filter, comprising a pump light providing device and a self-filtering laser amplifying device, wherein the self-filtering laser amplifying device is arranged on an outgoing optical path of the pump light providing device;

[0007] A pump light absorbing crystal is arranged in the self-filtering laser amplifier; a pump light providing device injects flat-top distributed pump light into the self-filtering laser amplifier, and the filtered light beams pass through the pump light absorbing crystal to obtain radially separated light beams, thereby realizing spatial light filtering.

[0008] Preferably, a beam diverging device is also provided in the self-filtering laser amplifying device.

[0009] Preferably, the self-filtering laser amplification device is a first laser resonant cavity.

[0010] Preferably, at least one first divergence filter component is provided in the first laser resonant cavity, and the first divergence filter component includes a first pump light absorption crystal and a first light beam divergence device.

[0011] Preferably, the self-filtering laser amplification device is a seed light injection amplifier.

[0012] Preferably, at least one second divergence filter component is provided in the second laser resonant cavity of the seed light injection amplifier, and the second divergence filter component includes a second pump light absorption crystal and a second light beam divergence device.

[0013] Preferably, the self-filtering laser amplification device is a traveling wave amplifier.

[0014] Preferably, the traveling wave amplifier includes a third beam diverging device and a traveling wave optical path, and the seed light enters the traveling wave optical path after being diverged by the third beam diverging device; a third pump light absorption crystal and at least one third diverging filter component are provided on the traveling wave optical path, and the third diverging filter component includes a fourth pump light absorption crystal and a fourth beam diverging device.

[0015] Preferably, the pump light providing device comprises a pump source and a beam coupling system, and the beam coupling system is an end-face pumping module.

[0016] Preferably, the beam diverging device is a plano-concave lens.

[0017] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0019] Figure 1A structural diagram of an embodiment of the spatial light filter provided by the present application;

[0020] Figure 2 A structural diagram of another embodiment of the spatial light filter provided by the present application;

[0021] Figure 3 This is a structural diagram of yet another embodiment of the spatial light filter provided in the present application.

[0022] The following are marked in the figure:

[0023] 1-first pump source; 2-first beam coupling system; 21-first convex lens; 22-second convex lens; 3-first laser resonant cavity; 31-first pump light absorption crystal; 32-first plane mirror; 33-second plane mirror; 34-third plane mirror; 35-fourth plane mirror; 4-first beam divergence device; 5-second pump source; 6-second beam coupling system; 61-third convex lens; 62-fourth convex lens; 7-second laser resonant cavity;

[0024] 71-second pump light absorption crystal; 72-fifth plane mirror; 73-sixth plane mirror;

[0025] 74-seventh plane mirror; 75-eighth plane mirror; 8-second beam diverging device; 9-isolator; 91-first polarization beam splitter prism; 92-second polarization beam splitter prism; 93-45°

[0026] Magneto-optical rotator; 10-first seed light; 11-third pump source; 12-fourth pump source; 13-third beam coupling system; 131-fifth convex lens; 132-sixth convex lens; 14-fourth beam coupling system; 141-seventh convex lens; 142-eighth convex lens; 15-ninth plane mirror; 16-third pump light absorption crystal; 17-tenth plane mirror; 18-eleventh plane mirror; 19-fourth pump light absorption crystal; 20-twelfth plane mirror; 25-third beam divergence device; 26-fourth beam divergence device; 23-seed light; 24-amplified output light. DETAILED DESCRIPTION

[0027] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0028] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0029] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0030] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0031] The present application provides a spatial light filter. When a filtered light beam passes through a pump light absorbing crystal, due to the thermal lens effect, the focal length of the thermal lens in the pump region is the same, while the focal length of the thermal lens outside the pump region gradually decreases with the increase of the radial distance. Therefore, the light beams at different radial positions experience different lens focal lengths, so that the light beams after passing through the pump light absorbing crystal are separated in the radial direction. Therefore, the pump light absorbing crystal plays the role of an aperture to achieve spatial light filtering, avoiding the problems of easy ionization of air at high power in traditional 4f spatial light filters and the diffraction of the hard aperture that easily makes the fundamental mode light after filtering poor. On the basis of the above, a beam divergence device is also provided in the self-filtering laser amplifying device. When the fundamental mode light part of the multi-mode oscillating light beam is the same size as the filtered light beam spot, the beam divergence device diverges the light beam to compensate for the focusing effect of the fundamental mode light part when it is subjected to the thermal lens effect. Subsequently, the fundamental mode light part will propagate as nearly parallel light after the thermal lens effect of the pump light absorbing crystal, while the high-order modes around the fundamental mode light part will aggravate the divergence, and finally the fundamental mode light and the high-order mode light will be completely separated, thereby improving the separation effect. Furthermore, by providing multiple divergence filter components in the self-filtering laser amplifying device to form a multi-stage amplification structure, the spontaneous radiation noise light carried in the light beam amplified by the upper-stage component is filtered out in the lower-stage component, thereby improving the quality of the output fundamental mode light.

[0032] The spatial optical filter provided in the present application comprises a pump light providing device and a self-filtering laser amplifying device, wherein the self-filtering laser amplifying device is arranged on the outgoing light path of the pump light providing device.

[0033] A pump light absorbing crystal is arranged in the self-filtering laser amplifying device. A pump light providing device injects a flat-top distributed pump light into the self-filtering laser amplifying device, and the filtered light beam in the self-filtering laser amplifying device passes through the pump light absorbing crystal to obtain radially separated light beams, thereby realizing spatial light filtering.

[0034] As an embodiment, the pump light providing device includes a pump source and a beam coupling system, wherein the beam coupling system is an end-face pump module to obtain a flat-top distributed pump light. The flat-top distributed pump light makes the thermal lens focal length of the pump area constant after the pump light absorbing crystal absorbs the pump light, while the thermal lens focal length outside the pump area decreases with the increase of radial distance, thereby facilitating the radial separation of the beam.

[0035] The refractive index change of the pump light absorbing crystal is determined by the intensity distribution of the pump light. Therefore, the pump light absorbing crystal can be matched according to the intensity distribution characteristics of the pump light, thereby achieving the effect of spatial light filtering.

[0036] Preferably, the spatial optical filtering effect is achieved by adjusting the spot size of the pump light, the spot size and divergence angle of the incident multimode signal light, etc. Specifically, the spot size of the pump light is adjusted by changing the focal length of the lens of the beam coupling system, and the spot size and divergence angle of the multimode signal light are adjusted by changing the focal length of the beam divergence device and the distance between the beam divergence device and the pump light absorption crystal.

[0037] The present application achieves good mode matching between the multimode light beam and the pump mode at the pump light absorbing crystal by optimizing and adjusting the light beam coupling system and the light beam divergence device. The size and distribution pattern of the thermal lens effect can be controlled by optimizing the pump light parameters to ensure the separation of the fundamental mode light beam and the higher-order modes.

[0038] As an embodiment, the pump source is a semiconductor laser with fiber-coupled output.

[0039] As an embodiment, the central wavelength of the pump source is 888 nm, the core diameter is 400 μm, and the numerical aperture is 0.22.

[0040] As an embodiment, the pump light absorbing crystal is a laser crystal, preferably a laser crystal with a rod-shaped structure.

[0041] As an embodiment, the pump light absorbing crystal is a Nd:YVO4 crystal with a crystal size of 3×3×20 mm. 3 .

[0042] On the basis of the above, preferably, a beam diverging device is also provided in the self-filtering laser amplifying device to diverge the light beam.

[0043] As an embodiment, the beam diverging device is a plano-concave lens.

[0044] Example 1

[0045] like Figure 1 In the illustrated embodiment, the self-filtering laser amplification device is the first laser resonant cavity 3 .

[0046] In this embodiment, the pump light providing device includes a first pump source 1 and a first beam coupling system 2. The first beam coupling system 2 includes a first convex lens 21 and a second convex lens 22. The focal lengths of the first convex lens 21 and the second convex lens 22 may be the same or different. The two convex lenses form a telescope beam expansion system, which is used to change the spot size of the pump light and inject the pump light into the self-filtering laser amplification device in an end-face pumping manner.

[0047] As an embodiment, the first laser resonant cavity 3 includes a first plane mirror 32, a second plane mirror 33, a third plane mirror 34 and a fourth plane mirror 35, and a first pump light absorption crystal 31 is provided between the first plane mirror 32 and the second plane mirror 33. It should be noted that, in this embodiment, the first pump light absorption crystal 31 can also be provided between other two adjacent plane mirrors.

[0048] In this embodiment, the pump source 1 is shaped into a flat-top distribution pump light through the beam coupling system 2. When the flat-top distribution pump light is incident on the first laser resonant cavity 3, it is absorbed by the first pump light absorbing crystal 31. After absorbing the pump light, the first pump light absorbing crystal 31 forms a thermal gradient distribution inside. Since the refractive index of the crystal is related to the temperature, the first pump light absorbing crystal 31 produces a thermal lens effect. Specifically, the focal length of the thermal lens in the pumping area of ​​the first pump light absorbing crystal 31 is the same. The thermal lens effect outside the pumping area will gradually decrease with the increase of radial distance due to heat transfer, so that the light beam emitted by the pump light absorbing crystal is separated in the radial direction, which plays the role of an aperture. The light beam emitted by the pump light absorbing crystal oscillates in the first laser resonant cavity 3 to generate a multi-mode oscillation light beam. When the multi-mode oscillating light beam passes through the first pump light absorbing crystal 31, due to the thermal lens effect of the first pump light absorbing crystal 31, the light beams at different radial positions experience different lens focal lengths, so that the multi-mode oscillating light beams after the thermal lens effect are separated in the radial direction, realizing spatial light filtering. The filtered light beam is output from the fourth plane mirror 35.

[0049] On the basis of the above, preferably, Figure 1 As shown, a first beam diverging device 4 is provided between the first pump light absorbing crystal 31 and the second plane mirror 33. It should be noted that the first beam diverging device 4 can also be provided at other positions of the first laser resonant cavity 3.

[0050] When the fundamental mode light portion in the multimode oscillation light beam in the first laser resonant cavity 3 is the same as the spot size of the filtered light beam, the first beam divergence device 4 diverges the multimode oscillation light beam to compensate for the focusing effect of the fundamental mode light portion when it is affected by the thermal lens effect, so that the fundamental mode light portion propagates as nearly parallel light after the thermal lens effect, while the high-order modes around the fundamental mode light portion will intensify the divergence, and finally the fundamental mode light and the high-order mode light will be completely separated, thereby improving the spatial filtering effect.

[0051] On the basis of the above, preferably, the first laser resonant cavity may include other numbers of plane mirrors. On this basis, at least one first divergent filter component is provided in the first laser resonant cavity, each first divergent filter component matches a set of pump light providing devices, and different pump light providing devices inject pump light from different plane mirrors of the first laser resonant cavity. Among them, each first divergent filter component includes a first pump light absorbing crystal and a first beam diverging device. In this preferred embodiment, the self-filtering laser amplifying device forms a multi-stage amplification structure, wherein each stage of the divergent filter component amplifies the light beam and carries spontaneous radiation noise light. When the spontaneous radiation noise light passes through the next stage of the divergent filter component, it will also be filtered out due to the thermal lens aperture of the first beam diverging device of the next stage of the divergent filter component and the first pump light absorbing crystal, thereby improving the quality of the output fundamental mode light.

[0052] Example 2

[0053] like Figure 2 In the illustrated embodiment, the self-filtering laser amplification device is a seed light injection amplifier.

[0054] In this embodiment, the pump light providing device includes a second pump source 5 and a second beam coupling system 6. The second beam coupling system 6 includes a third convex lens 61 and a fourth convex lens 62. The focal lengths of the third convex lens 61 and the fourth convex lens 62 may be the same or different. The two convex lenses form a telescope beam expansion system, which is used to change the spot size of the pump light and inject the pump light into the self-filtering laser amplifier device in an end-face pumping manner.

[0055] As an example, Figure 2 As shown, the seed light injection amplifier includes a second laser resonant cavity 7 and an isolator 9. The second laser resonant cavity 7 includes a fifth plane mirror 72, a sixth plane mirror 73, a seventh plane mirror 74 and an eighth plane mirror 75, and a second pump light absorption crystal 71 is provided between the fifth plane mirror 72 and the sixth plane mirror 73. The optical isolator 9 includes a first polarization beam splitter prism 91, a second polarization beam splitter prism 92 and a 45° magneto-optical rotator 93.

[0056] The polarization direction of the seed light 10 forms an angle of 45° with the polarization direction of the oscillating light in the cavity, and the bottom edge of the first polarization beam splitter prism 91 forms an angle of 90° with the polarization direction of the seed light 10. The seed light 10 is first reflected by the first polarization beam splitter prism 91, and then passes through the 45° magneto-rotator 93 and the second polarization beam splitter prism 92 in sequence, and then passes through the eighth plane mirror 75 to enter the second laser resonant cavity. The second pump light absorption crystal 71 absorbs the pump light and generates a thermal lens effect, so that the light beam emitted by the second pump light absorption crystal 71 is separated in the radial direction. The light beam emitted by the second pump light absorption crystal 71 oscillates in the second laser resonant cavity to form a multi-mode oscillation light beam.

[0057] In this embodiment, the filtered light beam is the seed light and the multi-mode oscillating light beam oscillating in the second laser resonant cavity 7. The thermal lens effect of the second pump light absorbing crystal 71 makes the thermal lens focal length in the pumping region of the second pump light absorbing crystal 71 the same, and the thermal lens effect outside the pumping region gradually decreases with the increase of radial distance due to heat transfer, so that the filtered light is separated in the radial direction after passing through the second pump light absorbing crystal 71, and the second pump light absorbing crystal 71 plays the role of an aperture.

[0058] On the basis of the above, preferably, Figure 2 As shown, a second beam diverging device 8 is provided between the second pump light absorbing crystal 71 and the sixth plane mirror 73. The spatial light filtering principle of the second beam diverging device 8 and the second pump light absorbing crystal 71 on the seed light and the multi-mode oscillation light beam is the same as the spatial light filtering principle of the first beam diverging device 4 and the first pump light absorbing crystal 31 on the multi-mode oscillation light beam in Example 1.

[0059] In the second laser resonant cavity, the high-order mode of the filtered light beam is filtered out after passing through the second beam diverging device 8 and the second pump light absorbing crystal 71, and the amplified fundamental mode light is output after passing through the optical isolator 9. The frequency and spectrum width of the output laser are determined by the seed light.

[0060] On the basis of the above, preferably, the second laser resonant cavity may include other number of plane mirrors. On this basis, at least one second divergent filter component is provided in the second laser resonant cavity, each second divergent filter component matches a set of pump light providing devices, and different pump light providing devices inject pump light from different plane mirrors of the second laser resonant cavity. Among them, each second divergent filter component includes a second pump light absorption crystal and a second beam divergence device. The multi-stage amplification principle of embodiment 2 is the same as that of embodiment 1, and will not be repeated here.

[0061] Example 3

[0062] like Figure 3 In the illustrated embodiment, the self-filtering laser amplification device is a traveling wave amplifier.

[0063] In this embodiment, the spatial light filter includes two pump light providing devices, one of which includes a third pump source 11 and a third beam coupling system 13. The third beam coupling system 13 includes a fifth convex lens 131 and a sixth convex lens 132. The other pump light providing device includes a fourth pump source 12 and a fourth beam coupling system 14. The fourth beam coupling system 14 includes a seventh convex lens 141 and an eighth convex lens 142.

[0064] The traveling wave amplifier comprises a third light beam diverging device 25 and a traveling wave optical path. The seed light 23 is diverged by the third light beam diverging device 25 and then injected into the traveling wave optical path.

[0065] A third pump light absorption crystal and at least one third divergence filter component are arranged on the traveling wave optical path, and the third divergence filter component includes a fourth pump light absorption crystal and a fourth light beam divergence device.

[0066] As an example, Figure 3 As shown, a third divergent filter component is provided on the traveling wave optical path. A ninth plane mirror 15, a tenth plane mirror 17, an eleventh plane mirror 18 and a twelfth plane mirror 20 are provided on the traveling wave optical path. A third pump light absorption crystal 16 is provided between the ninth plane mirror 15 and the tenth plane mirror 17, and a fourth pump light absorption crystal 19 and a fourth light beam divergent device 26 are provided between the eleventh plane mirror 18 and the twelfth plane mirror 20. Thus, the third light beam divergent device 25 and the third pump light absorption crystal 16 form a divergent filter component, which forms a two-stage amplification structure with the third divergent filter component.

[0067] In this embodiment, the light beam to be filtered is the seed light. Specifically, the third pump light absorbing crystal 16 generates a thermal lens effect after absorbing the pump light, so that the light beam emitted by the third pump light absorbing crystal 16 is separated in the radial direction. The seed light 23 diverges after passing through the third beam divergence device 25, and then enters the traveling wave optical path. After the diverged seed light is focused by the thermal lens of the third pump light absorbing crystal 16, the fundamental mode light part propagates in a nearly parallel light manner, while the high-order mode light around the fundamental mode light continues to diverge, thereby filtering out the high-order mode and achieving first-level amplification. The seed light after the first-level amplification will carry spontaneous radiation noise light. When the spontaneous radiation noise light passes through the third divergence filter component, it will also be filtered out due to the action of the thermal lens aperture of the fourth beam divergence device 26 and the fourth pump light absorbing crystal, thereby achieving the output of the fundamental mode light beam. The amplified fundamental mode light 24 is output through the twelfth plane mirror 20.

[0068] The present application realizes the function of spatial light filtering based on the thermal lens aperture. Specifically, the pump light absorbing crystal generates a thermal lens effect after absorbing the pump light, so that the pump light absorbing crystal has a constant thermal lens focal length in the pump region. As the radial distance outside the pump region gradually increases, the thermal lens focal length gradually decreases. Combined with the different spatial distribution characteristics of the fundamental mode light and the high-order mode light in the cross section, the fundamental mode light and the high-order mode light are separated due to the thermal lens effect of different focal lengths when passing through the pump light absorbing crystal, thereby achieving the purpose of spatial light filtering. The present application further uses a beam divergence device to aggravate the divergence of the high-order mode, thereby improving the separation effect and enhancing the spatial light filtering effect.

[0069] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A spatial optical filter, characterized in that: It comprises a pump light providing device and a self-filtering laser amplifying device, wherein the self-filtering laser amplifying device is arranged on the outgoing light path of the pump light providing device; A pump light absorbing crystal is arranged inside the self-filtering laser amplifying device; the pump light providing device injects flat-top distributed pump light into the self-filtering laser amplifying device, and the filtered light beams pass through the pump light absorbing crystal to obtain radially separated light beams, thereby realizing spatial light filtering.

2. The spatial light filter according to claim 1, characterized in that The self-filtering laser amplifying device is also provided with a beam diverging device.

3. The spatial light filter according to claim 2, characterized in that The self-filtering laser amplifying device is a first laser resonant cavity.

4. The spatial light filter according to claim 3, characterized in that At least one first divergence filter component is arranged in the first laser resonance cavity, and the first divergence filter component includes a first pump light absorption crystal and a first light beam divergence device.

5. The spatial light filter according to claim 2, characterized in that The self-filtering laser amplification device is a seed light injection amplifier.

6. The spatial light filter according to claim 5, characterized in that At least one second divergence filter component is arranged in the second laser resonance cavity of the seed light injection amplifier, and the second divergence filter component includes a second pump light absorption crystal and a second light beam divergence device.

7. The spatial light filter according to claim 2, characterized in that The self-filtering laser amplifying device is a traveling wave amplifier.

8. The spatial light filter according to claim 7, characterized in that The traveling wave amplifier includes a third light beam diverging device and a traveling wave optical path. The seed light enters the traveling wave optical path after being diverged by the third light beam diverging device. A third pump light absorption crystal and at least one third divergence filter component are provided on the traveling wave optical path. The third divergence filter component includes a fourth pump light absorption crystal and a fourth light beam diverging device.

9. The spatial light filter according to claim 1, characterized in that: The pump light providing device comprises a pump source and a beam coupling system, and the beam coupling system is an end face pump module.

10. The spatial light filter according to claim 2, characterized in that: The light beam diverging device is a plano-concave lens.

Images