Sub-nanosecond laser output characteristic optimization apparatus and method

Abstract

The present disclosure provides a sub-nanosecond laser output characteristic optimization device and method, the device comprising: a pump source for generating pump light; a coupling lens system for obtaining focused pump light; a gain Q unit for absorbing the focused pump light to generate sub-nanosecond pulse laser, and for receiving sub-nanosecond auxiliary pulse laser, and under the action of the sub-nanosecond auxiliary pulse laser, the output characteristic of the sub-nanosecond pulse laser is optimized in each pulse period of the sub-nanosecond pulse laser; a mirror arranged on a displacement platform for reflecting the sub-nanosecond pulse laser to form the sub-nanosecond auxiliary pulse laser based on a predetermined transmission-reflection ratio; and a displacement platform for adjusting the distance between the mirror and the gain Q unit; based on the adjustment of the distance, the output characteristic of the sub-nanosecond pulse laser is observed in real time, so that the gain Q unit outputs sub-nanosecond laser with weakened high-order mode and no pulse tailing at a predetermined interval.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of solid-state lasers, and particularly relates to a sub-nanosecond laser output characteristic optimization device and method. BACKGROUND

[0002] Sub-nanosecond laser generally refers to pulsed laser with pulse duration between hundreds of picoseconds and nanoseconds, and can be generated by a passive Q-switched microchip laser. Compared with nanosecond pulsed laser, sub-nanosecond laser has narrower pulse width and higher peak power under the same single-pulse energy. Compared with picosecond laser and femtosecond laser, sub-nanosecond laser is easier to achieve high energy output. Based on the advantages of high peak power of ultra-short pulsed laser and large energy of nanosecond pulsed laser, sub-nanosecond laser can be applied to technical fields such as high-precision laser radar, laser ignition, material processing, nonlinear optical frequency conversion and laser-induced breakdown spectroscopy.

[0003] However, in the output process of sub-nanosecond laser, the opening of the saturable absorber is not complete, resulting in pulse tailing of the pulse time-domain waveform, increase of the waveform falling edge time, slow change of the waveform trailing edge, and widening of the pulse duration. The sub-nanosecond pulsed laser output under small spot end-pumping still inevitably exists high-order modes, which makes the beam quality worse and the divergence angle larger. SUMMARY

[0004] In view of the above problems, the present disclosure provides a sub-nanosecond laser output characteristic optimization device and method.

[0005] According to a first aspect of the present disclosure, a sub-nanosecond laser output characteristic optimization device is provided, comprising: a pump source 1 for generating pump light; a coupling lens system 2 for focusing the pump light to obtain focused pump light; a gain Q-switching unit 3 for absorbing the focused pump light to generate sub-nanosecond pulsed laser, and for receiving sub-nanosecond auxiliary pulsed laser, and under the action of the sub-nanosecond auxiliary pulsed laser, optimizing the output characteristic of the sub-nanosecond pulsed laser in each pulse period of the sub-nanosecond pulsed laser; a mirror 4 disposed on a displacement platform, for reflecting the sub-nanosecond pulsed laser based on a predetermined transmission-reflection ratio, and the reflected part of the sub-nanosecond pulsed laser forms the sub-nanosecond auxiliary pulsed laser; and a displacement platform 5 for adjusting the distance between the mirror and the gain Q-switching unit; based on the adjustment of the distance, the output characteristic of the sub-nanosecond pulsed laser is observed in real time, so that the gain Q-switching unit outputs sub-nanosecond laser with weakened high-order modes and no pulse tailing at a predetermined interval.

[0006] According to an embodiment of the present disclosure, the gain medium 31 comprises a laser crystal doped with Nd 3+ , and is configured to absorb the focused pump light and generate oscillation laser; and the saturable absorber 32 comprises a laser crystal doped with Cr 4+ , and is configured to adjust the oscillation time length of the oscillation laser, so as to realize the output of the sub-nanosecond pulse laser.

[0007] According to an embodiment of the present disclosure, the gain medium and the saturable absorber are bonded by thermal diffusion; an end surface of the gain medium close to the coupling lens system is coated with a first pump light anti-reflection film and a first oscillation laser high-reflection film, and an end surface of the saturable absorber close to the mirror is coated with a second pump light anti-reflection film and a first oscillation laser partial-transmission film.

[0008] According to an embodiment of the present disclosure, the gain medium and the saturable absorber are independently coaxially arranged; an end surface of the gain medium close to the coupling lens system is coated with a third pump light anti-reflection film and a second oscillation laser high-reflection film, the other end of the gain medium is coated with a first oscillation laser anti-reflection film, an end surface of the saturable absorber close to the mirror is coated with a fourth pump light anti-reflection film and a second oscillation laser partial-transmission film, and the other end of the saturable absorber is coated with a second oscillation laser anti-reflection film.

[0009] According to an embodiment of the present disclosure, the focused pump light is used for pumping the gain medium, so that the active particles in the gain medium absorb the focused light to realize particle number inversion; and the sub-nanosecond auxiliary pulse laser is used for auxiliary bleaching according to the bleaching characteristics of the saturable absorber.

[0010] According to an embodiment of the present disclosure, the displacement platform comprises an electrically controlled displacement platform and a manually controlled displacement platform.

[0011] According to an embodiment of the present disclosure, the mirror surface of the mirror comprises one of a planar mirror, a plano-concave mirror and a double-concave mirror; and a mirror surface of the mirror close to the gain Q-switching unit is coated with a sub-nanosecond pulse laser partial-reflection film.

[0012] According to an embodiment of the present disclosure, the pump source comprises a semiconductor laser; and the wavelength range of the pump light comprises 800-810 nm and 880-890 nm.

[0013] According to an embodiment of the present disclosure, the coupling lens system is coupled with the pump source through an energy transmission optical fiber, and is configured to focus the pump light to obtain the focused pump light; and the focal length ratio range comprises 1:0.5-1:4.

[0014] The second aspect of the present disclosure provides a sub-nanosecond laser output characteristic optimization method, comprising: focusing pump light generated by a pump source to obtain focused pump light; converting the focused pump light into sub-nanosecond pulse laser by a gain Q-switching unit; reflecting the sub-nanosecond pulse laser by a mirror based on a predetermined transmission-reflection ratio, and a part of the sub-nanosecond pulse laser reflected forms sub-nanosecond auxiliary pulse laser; adjusting the distance between the mirror and the gain Q-switching unit by a displacement platform; observing the output characteristic of the sub-nanosecond pulse laser in real time based on the adjustment of the distance; and outputting sub-nanosecond laser with weakened high-order mode and no pulse tailing under the action of the sub-nanosecond auxiliary pulse laser in each pulse period of generating the sub-nanosecond pulse laser by the gain Q-switching unit based on a predetermined interval.

[0015] According to the embodiments of the present disclosure, the sub-nanosecond auxiliary pulse laser is injected into the gain Q-switching unit by the mirror. The distance between the mirror and the gain Q-switching unit is adjusted by the displacement platform, so as to observe the output characteristic of the sub-nanosecond pulse laser in real time. Finally, at the predetermined interval, the gain Q-switching unit can output sub-nanosecond laser with weakened high-order mode and no pulse tailing under the action of the sub-nanosecond auxiliary pulse laser in each pulse period of generating the sub-nanosecond pulse laser. BRIEF DESCRIPTION OF DRAWINGS

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments of the present disclosure taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 A structure schematic diagram of a sub-nanosecond laser output characteristic optimization device according to an embodiment of the present disclosure is schematically shown;

[0018] Figure 2 A pulse timing diagram of a gain Q-switching unit output according to an embodiment of the present disclosure is schematically shown;

[0019] Figure 3 A sub-nanosecond pulse laser time-domain waveform diagram when not injecting sub-nanosecond auxiliary pulse laser according to an embodiment of the present disclosure is schematically shown;

[0020] Figure 4 A sub-nanosecond laser time-domain waveform diagram after injecting sub-nanosecond auxiliary pulse laser according to an embodiment of the present disclosure is schematically shown;

[0021] Figure 5 A sub-nanosecond pulse laser beam quality diagram when not injecting sub-nanosecond auxiliary pulse laser according to an embodiment of the present disclosure is schematically shown;

[0022] Figure 6 A sub-nanosecond laser beam quality diagram after injecting sub-nanosecond auxiliary pulse laser according to an embodiment of the present disclosure is schematically shown;

[0023] Figure 7 schematic diagram of a nanosecond pulse laser spot pattern at different distances between a mirror and a gain Q-switch unit according to an embodiment of the present disclosure; and

[0024] Figure 8 a flowchart of a method for optimizing nanosecond laser output characteristics according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It is to be understood, however, that the description is merely exemplary and is not intended to limit the scope of the present disclosure. In the following detailed description of the embodiments of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it would be apparent to those skilled in the art that the embodiments of the present disclosure can be practiced without these specific details. In other instances, well-known structures and functions have been omitted or simply referenced in order not to obscure the concept of the present disclosure.

[0026] The terms used herein are merely used to describe specific embodiments, and are not intended to limit the present disclosure. The terms "include", "comprise" and the like used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0027] All terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of the present specification, and should not be interpreted in an idealized or overly formal manner.

[0028] Q-switching technology is a technology that dynamically and real-time adjusts the quality factor (Q value) of an optical resonant cavity by some means. Through Q-switching technology, the continuous output of laser becomes intermittent pulse output. Q-switching technology, also known as Q-switching technology, is a technology that compresses the continuous laser energy of general output into a pulse with extremely narrow width, thereby increasing the peak power of the light source by several orders of magnitude. Active Q-switching technology is achieved by actively introducing or increasing a modulator in the laser resonant cavity. Passive Q-switching technology uses the saturation absorption effect of nonlinear optical materials to achieve rapid Q-switching. Passive Q-switching technology is relatively easy to design and use, generally does not require an external power supply, and is more stable and reliable.

[0029] The passive Q-switching technology utilizes the bleaching characteristics of the saturable absorber itself, i.e., the absorption coefficient is not a constant, and when under the action of strong laser, the absorption coefficient decreases with the increase of light intensity until saturation, and the saturable absorber presents a transparent characteristic to light. The specific physical process of the passive Q-switching laser: in the initial stage, the fluorescence generated by the gain medium in the resonant cavity is weak, the absorption coefficient of the saturable absorber is large, the light transmittance is low, and the resonant cavity is in a low Q value (high loss) state, and cannot form laser oscillation; with the continuous action of the pump light, the accumulation of the inversion population of the gain medium, the fluorescence in the resonant cavity gradually becomes strong, the absorption coefficient becomes small, and the transmittance gradually increases, when the saturable absorber reaches saturation, i.e., the absorption coefficient is at a minimum value, the saturable absorber is suddenly "bleached" and becomes transparent, the Q value of the resonant cavity increases suddenly, and a passive Q-switching laser pulse is generated.

[0030] The passive Q-switched microchip laser is designed based on the principle of passive Q-switched laser. The passive Q-switched microchip laser has the following disadvantages: due to incomplete opening of the saturable absorber during laser output, pulse tailing occurs in the pulse time domain waveform, the waveform falling edge time increases, the waveform trailing edge becomes slow, and the pulse duration is widened; under small spot end face pumping, subnanosecond pulse laser still inevitably exists high order mode, and the existence of high order mode makes the beam quality worse and the divergence angle larger. These two aspects greatly limit the utilization efficiency of subnanosecond pulse laser in many applications, and the pulse tailing of the pulse time domain waveform and the high order mode of the output spot lead to the dispersion distribution of subnanosecond laser energy in time domain and spatial domain, which will cause the decline of subnanosecond laser material processing precision and quality, the increase of subnanosecond laser radar signal noise and the reduction of time resolution, and the increase of nonlinear effect and the reduction of damage threshold in subnanosecond nonlinear frequency conversion process.

[0031] The related art usually optimizes the output characteristics of subnanosecond laser by the following way: using a fiber delay line or a free space seed cavity to construct an output light splitting structure to generate a self-injection auxiliary pulse, which is used to realize instantaneous bleaching of the saturable absorber, so as to achieve the purpose of optimizing the output characteristics of subnanosecond laser. Or using an electro-optic Q-switched laser or a semiconductor laser to generate a high beam quality and high stability auxiliary pulse, and using an externally built light splitting structure to inject the auxiliary pulse into the saturable absorber.

[0032] In the implementation of the present disclosure, the inventors have found that the related art has at least the following problems: the related art needs to additionally increase a complex external structure (e.g., a laser and a light splitting structure) to generate an auxiliary pulse, and the auxiliary pulse has problems of being difficult to regulate, low alignment sensitivity, and poor coupling efficiency. Moreover, the related art needs to add a complex pulse synchronization system to realize pulse synchronization or an injection time interval adjustable of a sub-nanosecond passive Q-switched laser and an electro-optical Q-switched laser or a semiconductor laser, and the overall structure is extremely complex, which makes a sub-nanosecond passive Q-switched microchip laser system originally integrable become complex, and causes an increase in the cost of the entire system, poor stability and flexibility, and reduced application applicability, and it is more difficult to be applied to various complex environments. In addition, the related art has no significant optimization effect on the sub-nanosecond laser output characteristics, and part of the sub-nanosecond laser still has a pulse tailing phenomenon, and high-order modes of a sub-nanosecond laser output spot are only partially eliminated, which still has a certain influence on the performance of the sub-nanosecond passive Q-switched laser.

[0033] Therefore, there is an urgent need to provide a sub-nanosecond laser output characteristic optimization device to optimize the output characteristics of the sub-nanosecond laser through a simple and compact structure.

[0034] Figure 1 An example of a structure of a sub-nanosecond laser output characteristic optimization device according to an embodiment of the present disclosure is shown schematically.

[0035] As shown in Figure 1 the device includes a pump source 1, a coupling lens group 2, a gain Q-switching unit 3, a mirror 4, and a displacement platform 5. The pump source 1 is configured to generate pump light; the coupling lens system 2 is configured to focus the pump light to obtain focused pump light; the gain Q-switching unit 3 is configured to absorb the focused pump light to generate sub-nanosecond pulse laser, and is also configured to receive sub-nanosecond auxiliary pulse laser, and under the action of the sub-nanosecond auxiliary pulse laser in each pulse period of the sub-nanosecond pulse laser, the output characteristics of the sub-nanosecond pulse laser are optimized; the mirror 4 is arranged on the displacement platform 5, and is configured to reflect the sub-nanosecond pulse laser based on a predetermined transmission-reflection ratio, and a part of the sub-nanosecond pulse laser reflected forms the sub-nanosecond auxiliary pulse laser; and the displacement platform 5 is configured to adjust the distance between the mirror 4 and the gain Q-switching unit 3; based on the adjustment of the distance, the output characteristics of the sub-nanosecond pulse laser are observed in real time, so that at a predetermined interval, the gain Q-switching unit 3 outputs sub-nanosecond laser with weakened high-order modes and no pulse tailing.

[0036] According to an embodiment of the present disclosure, after the sub-nanosecond pulse laser output by the gain Q-switching unit 3 is incident on the mirror 4, the mirror 4 reflects the sub-nanosecond pulse laser based on a predetermined transmission-reflection ratio, and the sub-nanosecond auxiliary pulse laser formed by the reflection is injected into the gain Q-switching unit 3, and the laser output by itself is used as injection seed light, that is, self-seeding injection.

[0037] According to an embodiment of the present disclosure, the mirror 4 can be mounted on the displacement platform 5, and the mounting manner can include but is not limited to detachable mounting and fixed mounting, and the present disclosure does not limit this.

[0038] According to an embodiment of the present disclosure, the displacement platform 5 can control the position movement of the mirror 4, and then adjust the distance between the mirror 4 and the gain-switched Q unit 3.

[0039] According to an embodiment of the present disclosure, the displacement platform 5 adjusts the distance between the mirror 4 and the gain-switched Q unit 3 at a predetermined interval, that is, at an optimal distance, and the gain-switched Q unit can output sub-nanosecond laser with weakened high-order mode and no pulse tailing. After that, the displacement platform 5 can be removed, and the most simple sub-nanosecond laser output characteristic optimization device can be obtained.

[0040] According to an embodiment of the present disclosure, the sub-nanosecond auxiliary pulse laser is injected into the gain-switched Q unit by using the mirror, and no external complex auxiliary pulse generation and light splitting structure and pulse synchronization system are needed, so that the sub-nanosecond laser output characteristic optimization device is simple and compact, and the cost of the sub-nanosecond laser output characteristic optimization device is reduced. The distance between the mirror and the gain-switched Q unit is adjusted by using the displacement platform, so as to facilitate real-time observation of the output characteristics of the sub-nanosecond pulse laser. Finally, at the predetermined interval, the gain-switched Q unit can output sub-nanosecond laser with weakened high-order mode and no pulse tailing under the action of the sub-nanosecond auxiliary pulse laser in each pulse period of the sub-nanosecond pulse laser, precise control of the laser characteristics is realized, and the flexibility of the sub-nanosecond laser output device is improved.

[0041] According to an embodiment of the present disclosure, in each pulse period of the sub-nanosecond pulse laser, the injection of the sub-nanosecond auxiliary pulse laser plays a role in the output characteristics of the sub-nanosecond pulse laser, can weaken the influence of the high-order mode in the sub-nanosecond pulse laser, and at the same time eliminate the pulse tailing phenomenon of the sub-nanosecond pulse laser.

[0042] Figure 2 The pulse timing diagram of the output of the gain-switched Q unit according to an embodiment of the present disclosure is schematically shown.

[0043] As shown in Figure 2 , before the sub-nanosecond auxiliary pulse laser is injected into the gain-switched Q unit, in the case that the sub-nanosecond pulse laser is not optimized, the timing diagram of the output of the sub-nanosecond pulse laser is shown in Figure 2 (B); after the sub-nanosecond auxiliary pulse laser is injected into the gain-switched Q unit, in the case that the sub-nanosecond pulse laser is optimized, the pulse timing diagram of the output of the sub-nanosecond laser is shown in Figure 2 (A); and Figure 2In the diagram, (C) represents the timing diagram of a sub-nanosecond assisted pulsed laser. L represents the predetermined distance between the mirror and the Q-switching unit, and c is the speed of light. This indicates the injection time of the sub-nanosecond assisted pulse laser.

[0044] like Figure 2 As shown in (B), the sub-nanosecond pulsed laser includes a pulse leading edge and a pulse trailing edge. When the sub-nanosecond auxiliary pulsed laser is not injected into the gain-Q-switching unit, the pulse trailing edge of the sub-nanosecond pulsed laser output by the gain-Q-switching unit exhibits a pulse tailing phenomenon.

[0045] like Figure 2 As shown in (A), when a sub-nanosecond auxiliary pulse laser is injected into the gain-Q-switching unit, the sub-nanosecond auxiliary pulse laser optimizes the output characteristics of the sub-nanosecond pulse laser, and the sub-nanosecond laser output by the gain-Q-switching unit does not exhibit pulse tailing.

[0046] like Figure 2 As shown, within the same pulse period, the sub-nanosecond auxiliary pulse laser should be injected during the time period from after the formation of the normal sub-nanosecond pulse laser to before the formation of the pulse tail. Based on the adjustment of the distance between the reflector and the gain Q-switching unit, by observing and analyzing the output characteristics of the sub-nanosecond pulse laser, the injection time corresponding to the predetermined spacing can be obtained as 2L / c, that is, the time from the formation of the sub-nanosecond auxiliary pulse laser to its entry into the saturable absorber. The injection time is consistent with the formation time of the pulse leading edge of the sub-nanosecond pulse laser, indicating that the sub-nanosecond auxiliary pulse laser is injected after the formation of the pulse leading edge of the sub-nanosecond pulse laser. Therefore, the pulse leading edges of the sub-nanosecond pulse laser and the sub-nanosecond laser are basically consistent. In other words, the optimization effect of the sub-nanosecond auxiliary pulse laser mainly targets the pulse trailing edge of the sub-nanosecond pulse laser.

[0047] like Figure 1 As shown, within each pulse cycle of the sub-nanosecond pulsed laser, the output characteristics of the sub-nanosecond pulsed laser are optimized under the action of the sub-nanosecond auxiliary pulsed laser, and the gain-Q-switching unit outputs a sub-nanosecond laser without pulse tailing. Figure 3 As shown, the gain-Q-switching unit 3 includes a gain medium 31 and a saturable absorber 32.

[0048] According to embodiments of this disclosure, the gain medium 31 includes Nd-doped material. 3+ Laser crystals, such as Nd:YAG crystals or Nd:YVO4 crystals, are used to absorb focused light and generate oscillating lasers.

[0049] For example, the gain medium 31 is an Nd:YAG crystal with dimensions of 3mm × 3mm × 6mm, along... <111> It is oriented and cut, Nd 3+The doping concentration is 1.1 at. %.

[0050] According to an embodiment of the present disclosure, the saturable absorber 32 comprises a Q-switched crystal doped with Cr 4+ for adjusting the oscillation length of the oscillation laser, adjusting the loss of the resonant cavity under the action of the oscillation laser, so as to realize the output of the sub-nanosecond pulse laser.

[0051] For example, the saturable absorber 32 is a Cr:YAG crystal with a size of 3mm×3mm×3mm, which is cut along the <110> direction and has an initial transmittance of 50%.

[0052] According to an embodiment of the present disclosure, the two end surfaces of the gain Q-switching unit 3 form a resonant cavity after being coated.

[0053] According to an embodiment of the present disclosure, the gain medium 31 and the saturable absorber 32 are combined together by means of thermal diffusion bonding. Thermal diffusion bonding, also known as thermal bonding, tightly bonds two precisely processed crystals after a series of surface treatments, and then performs heat treatment on the crystals to form a permanent bond.

[0054] According to an embodiment of the present disclosure, the end surface of the gain medium 31 close to the coupling lens system is coated with a first pump light anti-reflection film and a first oscillation laser high-reflection film, and the end surface of the saturable absorber 32 close to the mirror is coated with a second pump light anti-reflection film and a first oscillation laser partial-transmission film.

[0055] According to an embodiment of the present disclosure, the second pump light anti-reflection film is an 808nm anti-reflection film.

[0056] According to an embodiment of the present disclosure, the gain medium and the saturable absorber can be integrated by means of thermal bonding technology, thereby forming a gain Q-switching unit, and a resonant cavity with a length of less than 10mm can be formed by coating the two ends, so as to output sub-nanosecond laser.

[0057] According to an embodiment of the present disclosure, the gain medium 31 and the saturable absorber 32 are independently arranged coaxially;

[0058] The end surface of the gain medium 31 close to the coupling lens system is coated with a third pump light anti-reflection film and a second oscillation laser high-reflection film, the other end of the gain medium 31 is coated with a first oscillation laser anti-reflection film, the end surface of the saturable absorber 32 close to the mirror is coated with a fourth pump light anti-reflection film and a second oscillation laser partial-transmission film, and the other end of the saturable absorber 32 is coated with a second oscillation laser anti-reflection film.

[0059] According to an embodiment of the present disclosure, the third pump light anti-reflection film allows the pump light to transmit, the second oscillation laser high-reflection film is used for high reflection of the oscillation laser, and the second oscillation laser partial transmission film allows the oscillation laser to partially transmit, and the transmission ratio includes 10% to 90%, for example, the transmission ratio is 10%, the transmission ratio is 50%, and the transmission ratio is 90%.

[0060] For example, the third pump light anti-reflection film is an 808 nm anti-reflection film, the second oscillation laser high-reflection film is a 1064 nm high-reflection film, the first oscillation laser anti-reflection film is an 808 nm anti-reflection film, the fourth pump light anti-reflection film is an 808 nm anti-reflection film, and the second oscillation laser partial transmission film is a 1064 nm and 50% transmission ratio partial transmission film.

[0061] According to an embodiment of the present disclosure, the focused pump light is used for pumping the gain medium 31, so that the active particles in the gain medium 31 absorb the focused light to realize particle number inversion.

[0062] According to an embodiment of the present disclosure, the gain medium 31 absorbs the focused pump light, the active particles in the Nd:YAG crystal of the gain medium 31 are transitioned from the ground state to the excited state, and the pump light energy is stored in the upper energy level of the laser. When the Cr:YAG Q-switching crystal of the saturable absorber 32 is not bleached, that is, the resonant cavity is in a closed state, the upper energy level particle number continuously accumulates and a large number of inverted particle numbers are generated. When the Cr:YAG crystal is bleached, that is, the Q-switch of the resonant cavity is opened, the gain in the resonant cavity exceeds the loss, the laser oscillation condition is met, and the stimulated radiation amplification is rapidly realized through the feedback of the resonant cavity. The laser oscillation is established in the resonant cavity, and finally the laser is output. In this case, the switch of the saturable absorber 32 is not completely opened, resulting in a phenomenon of pulse tailing of the obtained sub-nanosecond pulse laser.

[0063] According to an embodiment of the present disclosure, the sub-nanosecond auxiliary pulse laser is used for auxiliary bleaching according to the bleaching characteristics of the saturable absorber 32, so as to optimize the output characteristics of the sub-nanosecond pulse laser.

[0064] According to an embodiment of the present disclosure, the change of the output characteristics of the sub-nanosecond pulse laser with and without injection of the sub-nanosecond auxiliary pulse laser is observed. The output characteristics of the sub-nanosecond pulse laser include the pulse waveform in the time domain and the beam quality in the spatial domain. For example, the change of the sub-nanosecond pulse laser spot can be observed by using a beam analyzer. For example, the change of the time-domain waveform of the sub-nanosecond pulse laser can be observed by using a digital oscilloscope.

[0065] According to an embodiment of the present disclosure, the sub-nanosecond auxiliary pulse laser has extremely high peak power and extremely steep rising edge waveform, and is injected into the saturable absorber 32, such as a Cr:YAG crystal, to provide a large number of bleaching photons in the saturable absorber instantaneously, so that the Cr:YAG crystal is bleached within a set time and is in a fully open state within the output time of the sub-nanosecond pulse laser, and the pulse tail phenomenon is basically not generated, the waveform falling edge time of the sub-nanosecond pulse laser is shortened, the waveform trailing edge is steepened, and the pulse time-domain waveform of the sub-nanosecond pulse laser is optimized.

[0066] According to an embodiment of the present disclosure, the sub-nanosecond auxiliary pulse laser is injected after the pulse front edge of the sub-nanosecond pulse laser, and the optimization of the sub-nanosecond auxiliary pulse laser is mainly for the pulse trailing edge of the sub-nanosecond pulse laser. Without the injection of the sub-nanosecond auxiliary pulse laser, when the Q-switch of the saturable absorber is opened, the transmittance of the saturable absorber starts to gradually decrease after the pulse front edge of the sub-nanosecond pulse laser is output, and the state of incomplete opening of the switch is presented, and the pulse trailing edge of the output sub-nanosecond pulse laser forms a pulse tail phenomenon; in the case of injecting the sub-nanosecond auxiliary pulse laser, in each pulse period, the sub-nanosecond auxiliary pulse laser is injected into the saturable absorber after the pulse front edge of the sub-nanosecond pulse laser is formed, so that the saturable absorber is always in a state of complete opening of the switch, and the output sub-nanosecond laser after optimization is a smooth pulse trailing edge.

[0067] Figure 3 The time-domain waveform diagram of the sub-nanosecond pulse laser without injecting the sub-nanosecond auxiliary pulse laser according to an embodiment of the present disclosure is schematically shown.

[0068] As shown in Figure 4 , the abscissa time represents the time, and the ordinate intensity represents the pulse intensity of the sub-nanosecond pulse laser. Without injecting the sub-nanosecond auxiliary pulse laser, that is, before injecting the seed, due to the incomplete opening of the saturable absorber during the output of the sub-nanosecond pulse laser, the pulse tail appears in the time-domain waveform of the sub-nanosecond pulse laser, the waveform falling edge time increases, the waveform trailing edge becomes slow, and the pulse duration is widened.

[0069] Figure 4 The time-domain waveform diagram of the sub-nanosecond laser after injecting the sub-nanosecond auxiliary pulse laser according to an embodiment of the present disclosure is schematically shown.

[0070] As shown in Figure 5As shown, the horizontal axis represents time, and the vertical axis represents the pulse intensity of the sub-nanosecond laser. The distance between the reflector and the Q-switching unit can be set to a predetermined spacing. Due to the injection of the sub-nanosecond auxiliary pulse laser, the saturable absorber remains fully open throughout the entire sub-nanosecond pulse laser output time, virtually eliminating pulse tailing. The sub-nanosecond laser output from the Q-switching unit exhibits no pulse tailing, a shorter falling edge time, and a steeper trailing edge. Therefore, the pulse time-domain waveform of the sub-nanosecond laser is optimized compared to the sub-nanosecond pulse laser without the injection of the sub-nanosecond auxiliary pulse laser.

[0071] According to embodiments of this disclosure, the sub-nanosecond pulsed laser beam profile has good symmetry and conforms to a Gaussian distribution. The sub-nanosecond auxiliary pulsed laser reflected by the mirror to the gain-Q-switching unit also conforms to a Gaussian distribution. The spot size of the reflected sub-nanosecond auxiliary pulsed laser is slightly larger or smaller than the spot size of the sub-nanosecond pulsed laser output from the output end face of the gain-Q-switching unit. When the self-injected seed with a Gaussian-distributed spot is incident on the saturable absorber, the relatively concentrated and higher energy distribution in the central part causes the original fundamental mode distribution in the saturable absorber to be instantaneously bleached, entering a fully open state. The relatively dispersed and lower energy distribution at the edges has little or no bleaching effect on the original higher-order mode distribution in the saturable absorber. This makes the fundamental mode dominant over the higher-order modes in the mode competition of the sub-nanosecond pulsed laser oscillation output. In the spatial domain, most higher-order modes are suppressed, improving beam quality and directionality, thus optimizing the beam quality of the sub-nanosecond pulsed laser. The gain-Q-switching unit can output sub-nanosecond lasers with weakened higher-order modes.

[0072] Figure 6 The diagram illustrates the beam quality of a sub-nanosecond pulsed laser without the injection of a sub-nanosecond auxiliary pulsed laser according to an embodiment of the present disclosure.

[0073] Figure 5 The diagram schematically illustrates the sub-nanosecond laser beam quality after injection of a sub-nanosecond auxiliary pulse laser according to an embodiment of the present disclosure.

[0074] According to embodiments of this disclosure, the laser beam quality is evaluated using the knife-edge method, where the beam quality factor M is... 2 The beam quality factor is a parameter used to evaluate the quality of a laser beam. The closer the beam quality factor is to 1, the better the beam quality.

[0075] like Figure 6 , Figure 5 As shown, the horizontal axis represents the experimental distance of the light spot measured by the knife-edge method, and the vertical axis represents the distance of the light spot measured by the knife-edge method. 2This represents the square of the spot radius corresponding to the experimental distance measured by the knife-edge method. The figure shows a fitted parabola obtained from the experimental data, from which the beam quality factor M in two orthogonal directions is derived. 2 .

[0076] like Figure 5 As shown, the spot pattern illustration represents the spot of the sub-nanosecond pulsed laser without the injection of sub-nanosecond auxiliary pulsed laser, i.e., before self-seed injection. The beam quality factors in the two orthogonal directions, measured using the knife-edge method, are respectively... and Even without the injection of sub-nanosecond auxiliary pulsed laser, the sub-nanosecond pulsed laser output from the small spot end-pump inevitably still contains higher-order modes. For example... Figure 6 As shown in the light spot illustration, the presence of higher-order modes degrades the beam quality.

[0077] like Figure 6 As shown, the spot pattern in the case of sub-nanosecond assisted pulsed laser injection, i.e., self-seed injection, represents the spot of the sub-nanosecond laser. The beam quality factors in the two orthogonal directions, measured using the knife-edge method, are respectively... and Subnanosecond-assisted pulsed lasers with a Gaussian distribution instantaneously bleach the portion of the original fundamental mode distribution in a saturable absorber, while the bleaching effect on the portion of the original higher-order mode distribution is insignificant or nonexistent, and the fundamental mode dominates over the higher-order modes. For example... Figure 7 As shown in the inset of the light spot, the beam quality of the sub-nanosecond laser is optimized compared to the sub-nanosecond pulsed laser without the injection of sub-nanosecond auxiliary pulsed laser.

[0078] According to embodiments of this disclosure, the displacement platform 5 can be an electrically controlled displacement platform or a manually controlled displacement platform.

[0079] According to embodiments of this disclosure, the distance between the reflector 5 and the gain-Q-switching unit 3 is adjusted using an electrically controlled displacement platform. Based on the adjustment of the distance, the characteristics of the laser beam when the sub-nanosecond assisted pulse laser is injected into the gain-Q-switching unit 3 can be adjusted, such as the injection time, the spot size during injection, and the injection energy density.

[0080] According to embodiments of this disclosure, the sub-nanosecond assisted pulsed laser needs to be injected before the pulse tail of the sub-nanosecond pulsed laser is formed, that is, a suitable injection time needs to be met. At the same time, the sub-nanosecond assisted pulsed laser needs a high energy density to assist in the bleaching of the saturable absorber 32, that is, a suitable injection energy and spot size need to be met.

[0081] According to an embodiment of the present disclosure, by adjusting the distance between the mirror and the gain-switched Q-switching unit, the laser beam characteristics when the sub-nanosecond auxiliary pulse laser is injected into the gain-switched Q-switching unit can be adjusted. By adjusting the laser beam characteristics when the sub-nanosecond auxiliary pulse laser is injected into the gain-switched Q-switching unit, the output characteristics of the sub-nanosecond pulse laser can be optimized. In the case where the distance between the mirror 4 and the gain-switched Q-switching unit 3 is a predetermined interval, the injection energy, the spot size and the injection time of the appropriate sub-nanosecond auxiliary pulse laser are obtained. The output characteristics of the sub-nanosecond pulse laser can be observed in real time based on the adjustment of the distance.

[0082] For example, the change of the sub-nanosecond pulse laser spot can be observed by a beam profiler. For example, the change of the time-domain waveform of the sub-nanosecond pulse laser can be observed by a digital oscilloscope.

[0083] Figure 7 The sub-nanosecond pulse laser spot diagrams at different distances between the mirror and the gain-switched Q-switching unit according to an embodiment of the present disclosure are schematically shown.

[0084] According to an embodiment of the present disclosure, the sub-nanosecond pulse laser spot can be observed in the case where the distance between the mirror and the gain-switched Q-switching unit is 11 cm, 9 cm, 7 cm, 5 cm, 3 cm and 1 cm respectively, and the sub-nanosecond auxiliary pulse laser having a fixed time sequence relationship with the sub-nanosecond pulse laser is injected into the gain-switched Q-switching unit to optimize the output characteristics of the sub-nanosecond pulse laser.

[0085] As shown in (A) of FIG. 11, Figure 7 the sub-nanosecond pulse laser spot is observed in the case where the distance between the mirror and the gain-switched Q-switching unit is 11 cm.

[0086] As shown in (B) of FIG. 11, Figure 7 the sub-nanosecond pulse laser spot is observed in the case where the distance between the mirror and the gain-switched Q-switching unit is 9 cm.

[0087] As shown in (C) of FIG. 11, Figure 7 the sub-nanosecond pulse laser spot is observed in the case where the distance between the mirror and the gain-switched Q-switching unit is 7 cm.

[0088] As shown in (D) of FIG. 11, Figure 7 the sub-nanosecond pulse laser spot is observed in the case where the distance between the mirror and the gain-switched Q-switching unit is 5 cm.

[0089] As shown in (E) of FIG. 11, Figure 7 the sub-nanosecond pulse laser spot is observed in the case where the distance between the mirror and the gain-switched Q-switching unit is 3 cm.

[0090] As shown in (F) of FIG. 11,Figure 7 As shown in (F), the sub-nanosecond pulsed laser spot was observed with a distance of 1 cm between the reflector and the Q-switching unit.

[0091] like Figure 7 As shown in (E), the difference between the injection time and the initial output time of the sub-nanosecond assisted pulse laser can be 200±5 ps, the spot size of the sub-nanosecond assisted pulse laser can be 0.237±0.05 mm, and the corresponding peak power can be 24.12±0.05 MW / cm². 2 Subnanosecond-assisted pulsed lasers with a Gaussian distribution instantaneously bleach the portion of the original fundamental mode distribution in a saturable absorber, while the bleaching effect on the portion of the original higher-order mode distribution is not obvious or non-bleaching. The fundamental mode dominates over the higher-order modes, thus optimizing the beam quality of the subnanosecond-pulsed laser.

[0092] like Figure 8 As shown in (F), due to the small distance between the reflector and the Q-switching unit, the sub-nanosecond auxiliary pulse laser injection time is too early and the peak power density is too high, resulting in a deterioration of the sub-nanosecond auxiliary pulse laser spot. However, compared to the case without sub-nanosecond auxiliary pulse laser injection, the sub-nanosecond pulse laser spot is still improved.

[0093] like Figure 8 As shown, as the distance between the mirror and the Q-switching unit gradually decreases, higher-order modes in the sub-nanosecond pulsed laser tend to be eliminated, with the fundamental mode becoming dominant. For example, using an electric displacement platform with a maximum displacement of 12 cm and a displacement accuracy of 1 μm, and adjusting the distance between the mirror and the Q-switching unit to between 1 and 11 cm, the optimal distance between the mirror and the Q-switching unit is found to be between 2.5 cm and 3.5 cm. Specifically, when the distance between the mirror and the Q-switching unit is adjusted to 11 cm, 9 cm, 7 cm, 5 cm, 3 cm, and 1 cm, the optimal distance is 3 cm, where the fundamental mode dominates over the higher-order modes, thus optimizing the beam quality of the sub-nanosecond pulsed laser.

[0094] It should be noted that the optimal distance varies depending on the choice of different gain media and / or saturable absorber materials; similarly, the optimal distance also varies depending on the choice of different mirror surface profiles and coatings.

[0095] According to embodiments of this disclosure, the surface of the reflector 4 includes one of the following: a plane mirror, a plano-concave mirror, and a biconcave mirror; the mirror surface of the reflector near the gain-Q-switching unit 3 is coated with a sub-nanosecond pulsed laser partial reflective film.

[0096] According to an embodiment of the present disclosure, both sides of the mirror 4 can be coated with an 808 nm band pump light anti-reflection film.

[0097] According to an embodiment of the present disclosure, the mirror surface of the mirror 4 close to the gain Q-switching unit 3 can be coated with a 10%-50% reflectivity sub-nanosecond pulse laser partial reflection film, for example, a 10% reflectivity, a 15% reflectivity, and a 50% reflectivity. The base material of the mirror 4 is K9 glass material. The other side of the mirror 4 can be coated with a 1064 nm band sub-nanosecond pulse laser anti-reflection film.

[0098] For example, the mirror surface of the mirror 4 close to the gain Q-switching unit 3 is coated with a 15% reflectivity sub-nanosecond pulse laser partial reflection film, and the gain Q-switching unit 3 outputs a sub-nanosecond laser with a wavelength of 1064.39 nm and a power of 268 mW before the sub-nanosecond auxiliary laser is injected. After passing through the 15% reflectivity sub-nanosecond pulse laser partial reflection film, 40 mW of the sub-nanosecond laser is reflected, and the remaining 228 mW of the sub-nanosecond laser can be normally output. The 40 mW of the sub-nanosecond laser is reflected into the saturable absorber 32 of the gain Q-switching unit 3 to form a self-injected sub-nanosecond auxiliary laser, which optimizes the time-domain waveform, beam quality, and other output characteristics of the sub-nanosecond laser under the action of the sub-nanosecond auxiliary laser assisting bleaching of the saturable absorber 32.

[0099] According to an embodiment of the present disclosure, by changing the size and structure of the mirror, such as a plane mirror, a plane-concave mirror with different focal lengths, or a double-concave mirror, the characteristics of the laser beam assisted by the sub-nanosecond auxiliary laser can also be changed, thereby having different effects on the time-domain waveform, beam quality, and other output characteristics of the sub-nanosecond laser.

[0100] According to an embodiment of the present disclosure, the pump source includes a semiconductor laser, which can be a fiber-coupled output semiconductor laser. The wavelength range of the pump light includes 800-810 nm and 880-890 nm. By changing the working temperature of the pump source inside the semiconductor pump source, the wavelength of the pump laser can be adjusted.

[0101] For example, at room temperature, the center wavelength of the pump light emitted by the pump source is 806 nm. By changing the working temperature of the pump source, the wavelength of the pump laser emitted by the pump source can be adjusted in the range of 804-809 nm.

[0102] According to an embodiment of the present disclosure, the coupling lens system can be a fiber output focusing mirror coupled with the pump source through an energy transmission fiber for focusing the pump light to obtain focused light. The focal length ratio range includes 1:0.5-1:4, for example: the focal length ratio is 1:0.5, the focal length ratio is 1:0.8, the focal length ratio is 1:1, the focal length ratio is 1:4, and the focal length ratio can be continuously adjustable.

[0103] According to an embodiment of the present disclosure, the core diameter of the energy transmission fiber can be 400 μm, and the numerical aperture can be 0.22.

[0104] For example, the energy transmission fiber transmits pump laser, and the coupling lens system focuses the pump laser into pump light, when the focal ratio is 1:1, the spot diameter of the pump light is 400 μm, and the pump light is incident into the gain medium of the gain Q unit, and the focal point is located at 1 mm from the inner surface of the gain medium.

[0105] ​ A flow chart of the sub-nanosecond laser output characteristic optimization method according to an embodiment of the present disclosure is schematically shown.

[0106] As shown in ​ , the sub-nanosecond laser output characteristic optimization method includes operations S810-S860.

[0107] In operation S810, the pump light generated by the pump source is focused to obtain focused pump light.

[0108] In operation S820, the focused pump light is converted into sub-nanosecond pulse laser by the gain Q unit.

[0109] In operation S830, based on a predetermined transmission-reflection ratio, the sub-nanosecond pulse laser is reflected by the mirror, and the reflected part of the sub-nanosecond pulse laser forms sub-nanosecond auxiliary pulse laser.

[0110] In operation S840, the distance between the mirror and the gain Q unit is adjusted by the displacement platform.

[0111] In operation S850, based on the adjustment of the distance, the output characteristic of the sub-nanosecond pulse laser is observed in real time.

[0112] In operation S860, based on a predetermined interval, the gain Q unit outputs sub-nanosecond laser with weakened high-order mode and no pulse tailing under the action of the sub-nanosecond auxiliary pulse laser in each pulse period of the sub-nanosecond pulse laser.

[0113] It should be noted that the sub-nanosecond laser output characteristic optimization method part in the embodiments of the present disclosure corresponds to the sub-nanosecond laser output characteristic optimization device part in the embodiments of the present disclosure, and the description of the sub-nanosecond laser output characteristic optimization method part is specifically referred to the sub-nanosecond laser output characteristic optimization device part, which will not be repeated here.

[0114] The present disclosure utilizes a mirror to generate sub-nanosecond auxiliary pulse laser to assist the bleaching of a saturable absorber in a self-injection manner, and realizes the optimization of the output characteristics such as the time-domain waveform and the beam quality of the sub-nanosecond pulse laser. The sub-nanosecond pulse laser itself has extremely high peak power and extremely steep rising edge waveform, so that the optimization effect of the sub-nanosecond auxiliary pulse laser on the output characteristics of the sub-nanosecond laser is remarkable: the pulse tail of the sub-nanosecond pulse laser disappears in the time domain, the waveform falling edge time is shortened, the waveform trailing edge becomes steep, and the pulse duration is narrowed; in the spatial domain, most of the high-order modes are suppressed, and the beam quality and directionality are improved. The sub-nanosecond laser output characteristic optimization device has an extremely simple and compact structure, and can meet the integration needs of the sub-nanosecond passive Q-switched microchip laser in various complex application scenarios. Thus, the applicability of the sub-nanosecond passive Q-switched microchip laser is increased, and the utilization efficiency of the sub-nanosecond laser in many applications is improved.

[0115] In the embodiments of the present disclosure, the gain medium, the type of saturable absorber, the doping concentration or the size can be selected according to actual needs, and the size, the radius of curvature, the film coating index and other parameters of the mirror can be selected according to the type of saturable absorber, the initial transmittance and the size, and the sub-nanosecond output characteristic optimization effect.

[0116] The flowcharts and block diagrams in the drawings illustrate the possible implementation architectures, functions and operations of the apparatuses, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowcharts or block diagrams can represent a module, a program segment or a part of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks can occur in different orders from those shown in the drawings. For example, two blocks indicated in succession can actually be executed substantially in parallel, and sometimes they can be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams or flowcharts, and the combination of blocks in the block diagrams or flowcharts, can be implemented by a dedicated hardware-based system that performs the specified functions or operations, or can be implemented by a combination of dedicated hardware and computer instructions.

[0117] Those skilled in the art can understand that the features described in various embodiments of the present disclosure can be combined and / or integrated in various combinations, even if such combinations or integrations are not explicitly described in the present disclosure. In particular, the features described in various embodiments of the present disclosure can be combined and / or integrated in various combinations without departing from the spirit and teachings of the present disclosure. All these combinations and / or integrations fall within the scope of the present disclosure.

[0118] The above describes embodiments of the present disclosure. However, these embodiments are merely for illustrative purposes, and are not intended to limit the scope of the present disclosure. Although each embodiment is described above separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Those skilled in the art can make various substitutions and modifications without departing from the scope of the present disclosure, and these substitutions and modifications should all fall within the scope of the present disclosure.

Claims

1. An apparatus for optimizing sub-nanosecond laser output characteristics, comprising: The device comprises: a pump source (1) for generating pump light; a coupling lens system (2) for focusing the pump light to obtain focused pump light; a gain Q-switching unit (3) for absorbing the focused pump light to generate sub-nanosecond pulse laser, and for receiving sub-nanosecond auxiliary pulse laser, and for optimizing the output characteristics of the sub-nanosecond pulse laser under the action of the sub-nanosecond auxiliary pulse laser in each pulse period of the sub-nanosecond pulse laser; a mirror (4) disposed on a displacement platform, for reflecting the sub-nanosecond pulse laser based on a predetermined transmission-reflection ratio, and for forming the sub-nanosecond auxiliary pulse laser by reflecting part of the sub-nanosecond pulse laser; and a displacement platform (5) for adjusting the distance between the mirror and the gain Q-switching unit, and for observing the output characteristics of the sub-nanosecond pulse laser in real time based on the adjustment of the distance, so that the gain Q-switching unit outputs sub-nanosecond laser with weakened high-order mode and no pulse tailing at a predetermined interval. The gain Q-switching unit comprises:

2. The apparatus of claim 1, wherein, the gain medium and the saturable absorber are bonded by thermal diffusion; a gain medium (31) comprising a laser crystal doped with Nd 3+ for absorbing the focused pump light and generating an oscillation laser; and A saturable absorber (32) including a Cr-doped 4+ laser crystal for adjusting the oscillation length of the oscillating laser to achieve the output of the sub-nanosecond pulse laser.

3. The apparatus of claim 2, wherein, the end face of the gain medium close to the coupling lens system is coated with a first pump light anti-reflection film and a first oscillation laser high-reflection film, and the end face of the saturable absorber close to the mirror is coated with a second pump light anti-reflection film and a first oscillation laser partial-transmission film. The gain medium and the saturable absorber are independently arranged coaxially; 4. The apparatus of claim 2, wherein, the end face of the gain medium close to the coupling lens system is coated with a third pump light anti-reflection film and a second oscillation laser high-reflection film, the other end of the gain medium is coated with a first oscillation laser anti-reflection film, the end face of the saturable absorber close to the mirror is coated with a fourth pump light anti-reflection film and a second oscillation laser partial-transmission film, and the other end of the saturable absorber is coated with a second oscillation laser anti-reflection film.

5. The device according to claim 2, wherein: the focused pump light is used for pumping the gain medium, so that the active particles in the gain medium absorb the focused light to achieve particle number inversion; the sub-nanosecond auxiliary pulse laser is used for auxiliary bleaching according to the bleaching characteristics of the saturable absorber. The displacement platform comprises an electrically controlled displacement platform and a manually controlled displacement platform.

6. The apparatus of any one of claims 1-4, wherein, The profile of the mirror comprises one of a plane mirror, a plano-concave mirror and a double-concave mirror, and the mirror surface of the mirror close to the gain Q-switching unit is coated with a sub-nanosecond pulse laser partial-reflection film.

7. The apparatus of any one of claims 1-4, wherein, The pump source comprises a semiconductor laser, and the wavelength range of the pump light comprises 800-810 nm and 880-890 nm.

8. The apparatus of any one of claims 1-4, wherein, The coupling lens system is coupled with the pump source through an energy transmission optical fiber, and is used for focusing the pump light to obtain the focused pump light, and the focal length ratio range comprises 1:0.5-1:

4.

9. The apparatus of any one of claims 1-4, wherein, The device comprises:

10. A method of optimizing sub-nanosecond laser output characteristics, characterized by, focusing pump light generated by a pump source to obtain focused pump light; converting the focused pump light into sub-nanosecond pulse laser by a gain Q-switching unit; ​ Reflecting the sub-nanosecond pulse laser by a mirror based on a predetermined transmission-reflection ratio, a part of the sub-nanosecond pulse laser being reflected forms a sub-nanosecond auxiliary pulse laser; Adjusting a distance between the mirror and the gain Q-switching unit by a displacement platform; Observing output characteristics of the sub-nanosecond pulse laser in real time based on the adjustment of the distance; Based on a predetermined interval, the gain Q-switching unit outputs sub-nanosecond laser with weakened high-order mode and no pulse tailing under the action of the sub-nanosecond auxiliary pulse laser in each pulse period of the sub-nanosecond pulse laser.

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