Laser based on self-amplification and its control method

Abstract

The present application discloses a self-amplified laser and a control method thereof, wherein the laser is provided with a Q switch in the resonant cavity, and by adjusting the internal structure of the laser, the inversion particles stored in the energy level of the laser crystal are reused in the pulse output interval in a Q-switched manner, thereby improving the output energy of the pulsed laser in a self-amplified manner. Compared with the prior art, the present application improves the pulse output power of the laser through the above-mentioned method while optimizing the space occupation of the laser, reducing the volume, and saving the manufacturing cost.

Description

Technical Field

[0001] The present application relates to the field of pulsed lasers, and in particular to a self-amplified laser and a control method thereof. Background Art

[0002] Traditional lasers usually have a standing wave resonant cavity and a traveling wave amplifier structure, and these two structures are separate. The resonant cavity generates a signal, and the amplifier structure amplifies the signal light to the target parameters.

[0003] In the prior art, in order to output high peak power lasers, the pump power is usually increased, or the MOPA (Master Oscillator Power-Amplifier) ​​method is used, or the amplification structure adopts a multiple-pass method. Increasing the pump power will increase the thermal effect of the crystal, reduce the stable region of the resonant cavity, and deteriorate the spot mode; while the MOPA and multiple-pass amplification stage structure increase the volume of the laser, occupying more space while increasing the cost of the laser. For laser crystals with a fixed upper energy level lifetime, when the pulse interval time of the pulsed laser output is greater than the upper energy level lifetime, the number of inverted particles no longer increases. At this time, the pump light absorbed by the laser crystal will eventually be consumed in the form of heat energy, and this part of the consumed heat energy is wasted for the laser output power. Summary of the invention

[0004] The present application mainly provides a laser based on self-amplification and a control method thereof to solve the problem of low utilization rate of the added pump light in the above-mentioned pulse laser.

[0005] In order to solve the above technical problems, a technical solution adopted in the present application is: to provide a laser based on self-amplification, including a mirror group, a resonant cavity, a second reflector, a laser adjustment lens, a third reflector and a half-wave plate, wherein the resonant cavity includes a resonant cavity end mirror, a first polarizer, a laser crystal, a second polarizer, a Q switch, a first reflector, and a resonant cavity output mirror.

[0006] The mirror group is used to adjust the pump light to a collimated and focused beam that meets the preset requirements. After entering the resonant cavity, the collimated and focused beam passes through the resonant cavity end mirror and the first polarizer in sequence, and then enters and excites the laser crystal. The laser crystal reverses the particle number to perform pulse amplification on the resonant cavity. The amplified pulse laser passes through the second polarizer, the Q switch, the first reflector, and the resonant cavity output mirror in sequence, and then leaves the resonant cavity. After passing through the second reflector, the laser adjustment lens, the third reflector, and the half-wave plate in sequence, the polarization direction is twisted by the half-wave plate, and then enters the resonant cavity again, passes through the first polarizer and the laser crystal in sequence, and is reflected by the second polarizer and then output to the outside.

[0007] In a possible implementation, the mirror assembly includes a pump light collimating mirror and a pump light focusing mirror, and the pump light passes through the pump light collimating mirror and the pump light focusing mirror in sequence to form the collimated and focused light beam that meets the preset requirements.

[0008] In a possible implementation manner, both sides of the pump light collimating mirror and the pump light focusing mirror are coated with anti-reflection films having a design wavelength equal to the wavelength of the pump light.

[0009] In a possible implementation, the resonant cavity further includes a thermal lens compensation negative lens, and the thermal lens compensation negative lens is disposed between the resonant cavity end mirror and the first polarizer.

[0010] In a possible implementation manner, the first polarizer is coated with PBS films on both sides.

[0011] In a possible implementation manner, a reflective film is coated on the mirror surfaces of the first reflector, the second reflector, and the third reflector.

[0012] In a possible implementation, the laser adjustment lens includes a laser adjustment positive lens and a laser adjustment negative lens sequentially arranged along the optical path.

[0013] In order to solve the above technical problems, another technical solution adopted by the present application is: to provide a laser control method based on self-amplification, which is used for the laser based on self-amplification as described above, comprising:

[0014] Adjust the output position of the resonant cavity output mirror to the optical path of the laser crystal again L ,satisfy

[0015] ,

[0016] in c is the speed of light, F is the modulation frequency of the self-amplified laser, T is the upper level lifetime of the laser crystal, t 1 is the time taken for the Q switch to go from opening to a predetermined state, t 2 is the time taken for the Q switch to reach the predetermined state until the pulse is established, t 3 is the 3dB width of the pulse, t 4 is the time taken for the pulse to pass through the laser crystal.

[0017] In a possible implementation manner, the laser crystal length is l , the time it takes for the pulse to pass through the laser crystal t 4 Satisfaction

[0018] .

[0019] In a possible implementation manner, when the Q switch is in the predetermined state, the number of inversion particles reaches a maximum value.

[0020] The beneficial effect of the present application is as follows: Different from the prior art, the present application discloses a self-amplified laser and a control method thereof, which fully utilizes the upper energy level particles accumulated in the laser crystal by Q-switching and setting a circulating optical path, achieves a higher utilization rate of the resonant cavity structure, reduces space occupancy and costs, and improves output power. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0022] Figure 1 It is a schematic structural diagram of an embodiment of a self-amplified laser of the present application.

[0023] Description of main component symbols:

[0024] 100-laser based on self-amplification; 10-mirror group; 11-pump light collimator; 12-pump light focusing mirror; 20-first polarizer; 30-resonator end mirror; 31-thermal lens compensation negative lens; 32 laser crystal; 40-second polarizer; 50-Q switch; 61-first reflector; 62-second reflector; 63-third reflector; 70-resonator output mirror; 80-laser adjustment lens; 81-laser adjustment positive lens; 82-laser adjustment negative lens; 90-half-wave plate. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0026] The terms "first", "second", "third" in the embodiments of the present application are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first", "second", "third" can expressly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but optionally also includes steps or units that are not listed, or optionally also includes other steps or units inherent to these processes, methods, products or devices.

[0027] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0028] See also Figure 1 The embodiment of the present application provides a self-amplified laser 100, including a mirror group 10, a resonant cavity, a second reflector 62, a laser adjustment lens 80, a third reflector 63 and a half-wave plate 90. The resonant cavity includes a resonant cavity end mirror 30, a first polarizer 20, a laser crystal 32, a second polarizer 40, a Q switch 50, a first reflector 61, and a resonant cavity output mirror 70.

[0029] The mirror group 10 is used to adjust the pump light to a collimated and focused beam that meets the preset requirements. After entering the resonant cavity, the collimated and focused beam passes through the resonant cavity end mirror 30 and the first polarizer 20 once, and then enters and excites the laser crystal 32. The laser crystal 32 reverses the particle number to perform pulse amplification on the resonant cavity. The amplified pulse laser passes through the second polarizer 40, the Q switch 50, the first reflector 61, and the resonant cavity output mirror 70 in sequence, and then leaves the resonant cavity, and then passes through the second reflector 62, the laser adjustment lens 80, the third reflector 63, and the half-wave plate 90 in sequence. After the polarization direction is rotated by the half-wave plate 90, it enters the resonant cavity again, passes through the first polarizer 20 and the laser crystal 32 in sequence, and finally is reflected by the second polarizer 40 and output to the outside; wherein the laser adjustment lens 80 is used to adjust the divergence angle of the light beam.

[0030] See also Figure 1The external incident pump light beam enters from the mirror group 10. In this embodiment, an LD pump light source is used, and the mirror group 10 includes a pump light collimator 11 and a pump light focusing mirror 12. The pump light collimator 11 is used to convert the light beam from pump light into a collimated and focused light beam, and the pump light focusing mirror 12 is used to adjust the focal length of the light.

[0031] After passing through the lens group 10, the collimated focused light beam passes through the first polarizer 20. The first polarizer 20 reflects S polarized light and transmits P polarized light. However, the collimated focused light beam at this time will directly pass through the first polarizer 20 without changing the polarization direction. The first polarizer 20 is used to change the direction of the subsequent light beam. Then the collimated focused light beam enters and excites the laser crystal 32 again. The laser crystal 32 will amplify the resonant cavity output by inverting the particle number, and then passes through the second polarizer 40 and the Q switch 50 in sequence. The first reflector 61 changes the direction of the light beam, and then passes through the resonant cavity output mirror 70 and leaves the resonant cavity. The second polarizer 40 and the first polarizer 20 have the same polarization direction, which can make the light beam become P polarized light. After being pumped by the laser crystal, the pump light oscillates in the resonant cavity and is then output to the outside.

[0032] The light beam emitted from the resonant cavity output mirror 70 is redirected again by the second reflector 62 and enters the laser adjustment lens 80, which is used to adjust the divergence angle of the light beam so that it can enter the laser crystal 32 again with appropriate parameters to achieve re-amplification. The diameter ratio of the light spot of the light beam incident on the laser crystal 32 for the second time and the light spot of the light beam incident on the laser crystal 32 for the first time is 0.8:1, and the ratio of the divergence angle is also 0.8:1.

[0033] After the light beam is emitted from the laser adjustment lens 80, the direction is changed again by the third reflector 63, and after passing through the half-wave plate 90, it is emitted to the first polarizer 20 again. The half-wave plate 90 rotates the light beam from the P polarization direction to the S polarization direction. At this time, when the light beam in the S polarization direction is emitted to the first polarizer 20 again, since the polarization direction of the first polarizer 20 is the P direction, the light beam in the S polarization direction will be reflected and enter the laser crystal 32 again to be amplified, and contact the second polarizer 40 again, and is also reflected due to the different polarization directions, thereby changing the direction of the light beam and outputting it to the outside. In addition to changing the direction of the light path, the first polarizer 20 also avoids the formation of another resonant cavity structure between the resonant cavity output mirror 70 and the first polarizer 20, so as to improve the stability of the laser 100 based on self-amplification.

[0034] The first polarizer 20 , the first reflector 61 , the second reflector 62 and the third reflector 63 form a loop, ensuring that the light beam can enter the laser crystal 32 again after being amplified by the resonant cavity and twisted by the half-wave plate 90 . Figure 1 In the illustrated embodiment, the cyclic light path loop is rectangular, but this is only an example and not a limitation.

[0035] During the incident light beam, the Q-switched switch 50 adjusts the Q value of the resonant cavity and improves the storage capacity of the resonant cavity for photons. When the energy storage time is greater than the energy level lifetime of the laser crystal 32 during the interval of pulse laser output, the pulse laser is amplified to extract more inversion particles, thereby achieving an increase in the laser output power.

[0036] Considering the delay of acoustic wave transmission, it is necessary to adjust the distance between the second reflector 62 and the third reflector 63 so that the redundant inversion particles stored in the resonant cavity during the output interval of a Q-switched pulse are fully utilized instead of being consumed in the form of heat energy. The following conditions must be met:

[0037] .

[0038] in, L is the optical path from the emission position of the resonant cavity output mirror 70 to the re-incident laser crystal 32, c is the speed of light, F is the modulation frequency of the self-amplified laser 100, T is the upper energy level lifetime of the laser crystal 32, t 1 is the time taken for the Q switch 50 to go from opening to a predetermined state, t 2 is the time taken for the Q switch 50 to establish a pulse from a predetermined state, t 3 is the 3dB width of the pulse, t 4 is the time taken for the pulse to pass through the laser crystal 32. It should be explained that the predetermined state of the Q switch 50 refers to the fully working state or the fully output state of the Q switch 50. In this way, within a Q-switched pulse output interval, the excess inversion particle number stored in the energy level of the laser crystal 32 will be reused by the laser output pulse, thereby further amplifying the pulse output energy, and after the pulse passes through the laser crystal 32, before the Q switch 50 is fully opened again, the laser crystal 32 can still accumulate inversion particles again, thereby achieving a continuous self-amplification effect.

[0039] In one embodiment, the lens assembly 10 includes a pump light collimator 11 and a pump light focusing lens 12. The pump light passes through the pump light collimator 11 and the pump light focusing lens 12 in sequence to form a collimated and focused beam that meets the preset requirements. The pump light collimator 11 is used to convert the pump light into collimated light, and the pump light focusing lens 12 is used to adjust the focal length of the beam.

[0040] In one embodiment, a resonant cavity end mirror 30 is further included, and the resonant cavity end mirror 30 is disposed between the mirror assembly 10 and the first polarizer 20. In this embodiment, the resonant cavity end mirror 30 is coated with an anti-reflection film, and the design wavelength of the anti-reflection film on the side close to the external light source is the wavelength of the pump light emitted by the external light source, and the design wavelength of the anti-reflection film on the side close to the resonant cavity / laser crystal 32 is the output wavelength of the resonant cavity.

[0041] Figure 1 The shape of the resonant cavity is not clearly drawn, but it is easy to understand that the area surrounded by the necessary structures of the resonant cavity, such as the resonant cavity end mirror 30, the resonant cavity output mirror 70, and the laser crystal 32, can be considered to belong to the resonant cavity in the usual sense.

[0042] In one embodiment, a thermal lens compensation negative lens 31 is further included, and the thermal lens compensation negative lens 31 is disposed between the resonant cavity end mirror 30 and the first polarizer 20. The thermal lens compensation negative lens 31 is plated with an anti-reflection film with a design wavelength equal to the output wavelength of the resonant cavity, and the design equivalent focal length is determined according to needs to compensate for the thermal lens effect of the working state of the laser crystal 32, so that the resonant cavity can work stably.

[0043] In one embodiment, the first polarizer 20 is coated with PBS films on both sides to reflect S polarized light and transmit P polarized light. The resonant cavity in this embodiment resonates with P polarized light.

[0044] In one embodiment, the mirror surfaces of the first reflector 61 , the second reflector 62 , and the third reflector 63 are coated with a reflective film, and the design wavelength of the reflective film is the wavelength of the laser output.

[0045] In one embodiment, the laser adjustment lens 80 includes a laser adjustment positive lens 81 and a laser adjustment negative lens 82 arranged in sequence along the optical path, both of which are used to adjust the laser output from the resonant cavity so that the laser has a suitable divergence angle to re-enter the laser crystal 32.

[0046] This embodiment further discloses a control method of a laser 100 based on self-amplification, which is used for the above laser 100 based on self-amplification, and includes:

[0047] Adjust the output position of the resonant cavity output mirror 70 to the optical path of the incident laser crystal 32 again. L ,satisfy

[0048] .

[0049] in c is the speed of light, F is the modulation frequency of the self-amplified laser 100, T is the upper energy level lifetime of the laser crystal 32, t 1 is the time taken for the Q switch 50 to go from opening to a predetermined state, t 2 is the time taken for the Q switch 50 to reach the predetermined state until the pulse is established, t 3 is the 3dB width of the pulse, t4 is the time taken for the pulse to pass through the laser crystal 32. It should be explained that the predetermined state of the Q switch 50 refers to the fully working state or the fully output state of the Q switch 50. In this way, within a Q-switched pulse output interval, the excess inversion particle number stored in the energy level of the laser crystal 32 will be reused by the laser output pulse, thereby further amplifying the pulse output energy, and after the pulse passes through the laser crystal 32, before the Q switch 50 is fully opened again, the laser crystal 32 can still accumulate inversion particles again, thereby achieving a continuous self-amplification effect.

[0050] In one embodiment, the length of the laser crystal 32 is l , the time it takes for the pulse to pass through the laser crystal 32 t 4 Satisfaction:

[0051] .

[0052] The time it takes for the pulse to pass through the laser crystal 32 is calculated by the length of the laser crystal 32. t 4.

[0053] In one embodiment, when the Q switch 50 is in a predetermined state, the number of inverted particles reaches a maximum value, that is, the Q switch 50 is in a maximum working state.

[0054] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A laser based on self-amplification, characterized in that, The invention comprises a mirror group, a resonant cavity, a second reflector, a laser adjustment lens, a third reflector and a half-wave plate, wherein the resonant cavity comprises a resonant cavity end mirror, a first polarizer, a laser crystal, a second polarizer, a Q switch, a first reflector and a resonant cavity output mirror. The mirror group is used to adjust the pump light to a collimated and focused beam that meets the preset requirements. After entering the resonant cavity, the collimated and focused beam passes through the resonant cavity end mirror and the first polarizer in sequence, and then enters and excites the laser crystal. The laser crystal reverses the particle number to perform pulse amplification on the resonant cavity. The amplified pulse laser passes through the second polarizer, the Q switch, the first reflector, and the resonant cavity output mirror in sequence, and then leaves the resonant cavity. After passing through the second reflector, the laser adjustment lens, the third reflector, and the half-wave plate in sequence, the polarization direction is twisted by the half-wave plate, and then enters the resonant cavity again, passes through the first polarizer and the laser crystal in sequence, and is reflected by the second polarizer and then output to the outside. The optical path from the output position of the resonant cavity output mirror to the optical path of the laser crystal that is incident again L satisfy: ， in c is the speed of light, F is the modulation frequency of the self-amplified laser, T is the upper level lifetime of the laser crystal, t 1 is the time taken for the Q switch to go from opening to a predetermined state, t 2 is the time taken for the Q switch to reach the predetermined state until the pulse is established, t 3 is the 3dB width of the pulse, t 4 is the time taken for the pulse to pass through the laser crystal.

2. The self-amplified laser according to claim 1, characterized in that: The mirror group includes a pump light collimating mirror and a pump light focusing mirror. The pump light passes through the pump light collimating mirror and the pump light focusing mirror in sequence to form the collimated and focused light beam that meets the preset requirements.

3. The self-amplified laser according to claim 2, characterized in that The pump light collimating mirror and the pump light focusing mirror are coated with anti-reflection films with a design wavelength equal to the wavelength of the pump light on both sides.

4. The self-amplified laser according to claim 1, characterized in that The resonant cavity further comprises a thermal lens compensation negative lens, and the thermal lens compensation negative lens is arranged between the resonant cavity end mirror and the first polarizer.

5. The self-amplified laser according to claim 1, characterized in that: The first polarizer is coated with PBS films on both sides.

6. The self-amplified laser according to claim 1, characterized in that The mirror surfaces of the first reflector, the second reflector and the third reflector are coated with reflective films.

7. The self-amplified laser according to claim 1, characterized in that The laser adjustment lens comprises a laser adjustment positive lens and a laser adjustment negative lens which are sequentially arranged along the optical path.

8. A self-amplification-based laser control method, used for the self-amplification-based laser according to any one of claims 1 to 7, characterized in that: include: Adjust the output position of the resonant cavity output mirror to the optical path of the laser crystal again L ,satisfy ， in c is the speed of light, F is the modulation frequency of the self-amplified laser, T is the upper level lifetime of the laser crystal, t 1 is the time taken for the Q switch to go from opening to a predetermined state, t 2 is the time taken for the Q switch to reach the predetermined state until the pulse is established, t 3 is the 3dB width of the pulse, t 4 is the time taken for the pulse to pass through the laser crystal.

9. The laser control method based on self-amplification according to claim 8, characterized in that: The laser crystal length is l , the time it takes for the pulse to pass through the laser crystal t 4 Satisfaction 。 10. The laser control method based on self-amplification according to claim 8, characterized in that: When the Q switch is in the predetermined state, the number of inverted particles reaches a maximum value.

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