A picosecond pulse source based on harmonic self-mode-locked semiconductor surface-emitting laser

Abstract

The application provides a picosecond pulse source based on harmonic self-mode-locking semiconductor surface-emitting laser, comprising an optical pumping assembly and a V-cavity resonant cavity assembly, the optical pumping assembly comprises a semiconductor bar laser and a collimating and focusing lens optical coupling assembly, and the V-cavity resonant cavity assembly comprises a microcavity gain structure and an external cavity structure; wherein the pump laser emitted by the semiconductor bar laser is focused and coupled by the collimating and focusing lens optical coupling assembly to output a light spot, the light spot is absorbed and gain-processed by the microcavity gain structure, and then the resonant laser is output by the external cavity structure through feedback resonance; and when the resonant laser and the light spot are matched in the external cavity structure, the external cavity structure outputs the mode-locked pulse after adjustment through spatiotemporal dynamics calculation. The picosecond pulse source realizes harmonic mode-locked pulse output with a pulse width of hundreds of picoseconds and a repetition frequency of hundreds of MHz.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of picosecond pulse laser, in particular to a picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser. BACKGROUND

[0002] Picosecond pulse lasers have advantages of small heat-affected zone, fast processing speed and high processing quality in the field of laser processing compared with nanosecond pulse lasers. They also have wide commercial applications in the fields of signal processing, material processing and free space communication. High power picosecond pulse lasers used in industry usually require single pulse energy as high as microjoule or even sub-joule. These systems use mode-locked seed lasers, single pulse selection and multi-stage amplification to achieve high single pulse energy output in the range of hundreds of picoseconds. The mode-locked picosecond pulse source used is a key component of the picosecond pulse laser, which usually works at a repetition frequency of hundreds of MHz and has a pulse width of hundreds of picoseconds.

[0003] At present, picosecond pulse lasers mainly include mode-locked solid-state lasers, mode-locked fiber lasers and mode-locked semiconductor lasers. The solid-state pulse seed laser source has problems of limited emission wavelength, complex structure, high cost and poor stability. The mode-locked fiber laser has a limited wavelength range and relies on a saturable absorber mirror or a ring cavity structure. Due to the limitation of the length of the fiber, the repetition frequency is usually limited to kilohertz. In contrast, mode-locked semiconductor lasers have attracted great attention in the research of picosecond pulse sources. They have many advantages, including wavelength flexibility, compact size, long service life and low cost. When used in combination with a suitable external cavity, i.e. a mode-locked vertical external cavity surface emitting laser (VECSEL), the output pulse characteristics can be more easily manipulated to achieve the desired performance results, such as near-diffraction-limited beam quality, high output power and arbitrary radiation wavelength. More importantly, VECSEL can generate self-mode-locked (SML) pulses without the participation of SESAM, unlike fiber seed lasers and solid-state mode-locked picosecond pulse sources, which do not require the participation of a saturable absorber, thereby avoiding the design of saturable absorber-specific parameters such as output wavelength, saturation flux and modulation depth. SUMMARY

[0004] (1) Technical problems to be solved

[0005] In view of the above problems, the main purpose of the present application is to provide a picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser, which solves the problems of wavelength limitation, complex structure, high cost and poor stability of solid-state pulse seed source, and the problems of length limitation of MHz repetition frequency, narrow wavelength selection range and the need for complex design of saturable absorber in fiber seed source, and obtains the output of picosecond pulse width and MHz pulse width.

[0006] (II) Technical Solution

[0007] In order to achieve the above object, the application provides a picosecond pulse source based on harmonic self-mode-locking semiconductor surface-emitting laser, which comprises an optical pumping assembly and a V-cavity resonant cavity assembly, the optical pumping assembly comprises a semiconductor bar laser and a collimating and focusing lens optical coupling assembly, and the V-cavity resonant cavity assembly comprises a microcavity gain structure and an external cavity structure; wherein the pump laser emitted by the semiconductor bar laser is focused and coupled by the collimating and focusing lens optical coupling assembly to output a light spot, the light spot is absorbed and gain-processed by the microcavity gain structure, and then the resonant laser is output by the external cavity structure through feedback resonance; and when the resonant laser in the external cavity structure matches the light spot, the external cavity structure outputs the mode-locked pulse after adjustment through spatiotemporal dynamics calculation.

[0008] In the above scheme, the microcavity gain structure comprises a semiconductor gain chip, a heat dissipation heat sink and an air interface on the surface of the semiconductor gain chip; wherein the semiconductor gain chip is bonded on the heat dissipation heat sink through Au-In solid-liquid interdiffusion.

[0009] In the above scheme, the semiconductor gain chip comprises, in the first direction, a substrate, a barrier layer, a bottom DBR mirror, an active region multi-quantum well layer and a surface cap layer which are sequentially stacked from bottom to top; wherein the semiconductor gain chip is bonded on the heat dissipation heat sink through Au-In solid-liquid interdiffusion after the substrate and the barrier layer are removed.

[0010] In the above scheme, the absorption wavelength range of the quantum well in the active region multi-quantum well layer covers the pump laser.

[0011] In the above scheme, the material of the bottom DBR mirror is lattice matched with the material of the substrate; the bottom DBR mirror is obtained by alternately growing two materials with a refractive index difference exceeding a preset refractive index threshold; and the center wavelength of the bottom DBR mirror is consistent with the design wavelength of the active region.

[0012] In the above scheme, the microcavity gain structure is a resonant periodic gain structure, and the standing wave antinode of the microcavity gain structure is located above the active region multi-quantum well layer of the semiconductor gain chip for gain maximization processing.

[0013] In the above scheme, the external cavity structure is a laser resonant cavity, which comprises a bottom DBR mirror, a first mirror and a second mirror; wherein the first mirror is a coupling mirror with a curvature radius, and the reflectivity of the first mirror is higher than a preset reflectivity threshold; and the second mirror is a plane output mirror.

[0014] In the above scheme, the first mirror is used to control the matching of the resonant laser in the external cavity structure and the light spot.

[0015] In the above scheme, the electric field intensity of all the locked transverse electromagnetic modes is obtained after the calculation adjustment of the spatiotemporal dynamics of the external cavity structure, and the mode locking consistent with the calculation of the empty dynamics is obtained by controlling the external cavity structure, so that the output of the mode-locked pulse is realized.

[0016] In the above scheme, when the round trip time of the resonant laser through the external cavity structure is higher than the carrier lifetime of the semiconductor gain chip by 2 times or more, the external cavity structure outputs the harmonic mode-locked.

[0017] (Three) beneficial effects

[0018] The technical scheme of the embodiment of the application has at least the following beneficial effects:

[0019] (1) The picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser has flexible emission wavelength, high beam quality, long service life and low generation cost.

[0020] (2) The picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser utilizes the advantages of semiconductor laser materials, realizes picosecond pulse output by self-mode-locking, and has the characteristics of stability and reliability, simple technical structure, and no insert element in the cavity.

[0021] (3) The picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser has a flexible external cavity structure, which is convenient for flexible design of the pulse repetition frequency according to the requirements, and meets the wider application requirements.

[0022] (4) The external cavity structure of the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser is also convenient for inserting other optical elements, such as nonlinear frequency conversion elements, to realize frequency conversion and obtain other wavelength, high beam quality, base transverse mode, self-mode-locked picosecond pulse output. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The overall structure diagram of the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser according to the embodiment of the application is schematically shown;

[0024] Figure 2 The optical pumping assembly structure diagram of the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser according to the embodiment of the application is schematically shown;

[0025] Figure 3 The semiconductor gain chip structure diagram of the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser according to the embodiment of the application is schematically shown;

[0026] Figure 4A thermal management semiconductor gain chip structure diagram of a picosecond pulse source based on a harmonic self-mode-locked semiconductor surface-emitting laser according to an embodiment of the present application is schematically shown;

[0027] Figure 5 A pulse sequence result diagram of a picosecond pulse source based on a harmonic self-mode-locked semiconductor surface-emitting laser according to an embodiment of the present application is schematically shown;

[0028] Figure 6 A pulse width result diagram of a picosecond pulse source based on a harmonic self-mode-locked semiconductor surface-emitting laser according to an embodiment of the present application is schematically shown. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application is further described in detail below with reference to specific embodiments and accompanying drawings.

[0030] Figure 1 A whole structure diagram of a picosecond pulse source based on a harmonic self-mode-locked semiconductor surface-emitting laser according to an embodiment of the present application is schematically shown. Figure 2 A light pumping assembly structure diagram of a picosecond pulse source based on a harmonic self-mode-locked semiconductor surface-emitting laser according to an embodiment of the present application is schematically shown.

[0031] As shown in Figure 1 the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser includes a light pumping assembly 1 and a V-cavity resonant cavity assembly 2. The light pumping assembly 1 includes a semiconductor bar laser 11 and a collimating and focusing lens optical coupling assembly 12. The V-cavity resonant cavity assembly 2 includes a microcavity gain structure 21 and an external cavity structure 22. The pump laser emitted by the semiconductor bar laser 11 is focused and coupled by the collimating and focusing lens optical coupling assembly 12 to output a light spot. The light spot is absorbed and gain-processed by the microcavity gain structure 21, and then the resonant laser is output by the external cavity structure 22 through feedback resonance. When the resonant laser and the light spot in the external cavity structure 22 are matched, the external cavity structure 22 outputs the mode-locked pulse after adjustment through spatiotemporal dynamics calculation.

[0032] Specifically, as shown in Figure 2 the light pumping assembly 1 includes the semiconductor bar laser 11 and the collimating and focusing lens optical coupling assembly 12. For example, the pump laser output by the semiconductor bar laser 11 has a wavelength of 808 nm and an output power of 50 W. The laser fiber has a core diameter of 200 μm and a numerical aperture of 0.22. The collimating and focusing lens optical coupling assembly 12 focuses the pump laser output by the laser fiber through a 1:3 optical coupling system, and the focused light spot has a diameter of 600 μm.

[0033] Figure 3A semiconductor gain chip structure of a picosecond pulse source based on a harmonic self-mode-locked semiconductor surface-emitting laser according to an embodiment of the present application is schematically shown. Figure 4 A thermally managed semiconductor gain chip structure of a picosecond pulse source based on a harmonic self-mode-locked semiconductor surface-emitting laser according to an embodiment of the present application is schematically shown.

[0034] In an embodiment of the present application, as shown in Figure 1 The microcavity gain structure 21 includes a semiconductor gain chip 211, a heat dissipation heat sink 212, and an air interface on the surface of the semiconductor gain chip 211, wherein the semiconductor gain chip 211 is bonded on the heat dissipation heat sink 212 through Au-In solid-liquid interdiffusion.

[0035] Further, as shown in Figure 3 The semiconductor gain chip 211 includes, in order from bottom to top along the first direction X1, a substrate 35, a barrier layer 34, a bottom DBR mirror 33, an active region multi-quantum well layer 32, and a surface cap layer 31.

[0036] Specifically, the semiconductor gain chip 211 is grown by metal organic chemical vapor deposition (MOCVD), and the barrier layer 34, the bottom DBR mirror 33, the active region multi-quantum well layer 32, and the surface cap layer 31 are etched in order from bottom to top along the first direction X1 on the substrate 35.

[0037] Preferably, the semiconductor gain chip 211 is made of III-V semiconductor material.

[0038] Preferably, the substrate 35 is made of GaAs material, and the barrier layer 34 is made of InGaP material.

[0039] In an embodiment of the present application, the semiconductor gain chip 211 is bonded on the heat dissipation heat sink 212 through Au-In solid-liquid interdiffusion after the substrate 35 and the barrier layer 34 are removed.

[0040] Specifically, the semiconductor gain chip 211 is subjected to substrate 35 and barrier layer 34 removal and heat dissipation treatment. First, the substrate 35 of the semiconductor gain chip 211 is removed by chemical wet etching, wherein the etching solution is preferably a solution of ammonia and hydrogen peroxide, which can quickly etch, shorten the etching time, and improve the flatness of the etching. After the substrate 35 is removed, the barrier layer 34 is removed. As shown in Figure 4 The semiconductor gain chip 211 after the substrate 35 and the barrier layer 34 are removed is bonded on the heat dissipation heat sink 212 through Au-In solid-liquid interdiffusion, that is, the bottom DBR mirror 33 is bonded on the heat dissipation heat sink 212 through Au-In solid-liquid interdiffusion.

[0041] Preferably, the heat sink 212 is made of a material with high thermal conductivity and a surface roughness as low as possible, for example, the heat sink 212 can be made of a high flatness copper heat sink.

[0042] In the embodiment of the present application, the material of the bottom DBR mirror 33 is lattice matched with the material of the substrate 35; and the bottom DBR mirror 33 is formed by alternately growing two materials with a refractive index difference exceeding a preset refractive index threshold; and the center wavelength of the bottom DBR mirror 33 is consistent with the design wavelength of the active region.

[0043] Specifically, the center wavelength of the bottom DBR mirror 33 is consistent with the design wavelength of the active region, the reflection bandwidth should be as wide as possible > 100 nm, and the reflectivity should be as high as possible > 99.9%. The bottom DBR mirror 33 should be formed by alternately growing two materials with a lattice matched with the GaAs substrate and a large refractive index difference, and preferably GaAs / AlGaAs materials are used.

[0044] For example, the center wavelength of the bottom DBR mirror 33 is 1064 nm, the reflection bandwidth is 100 nm, and the periodic structure is formed by alternately growing GaAs and AlGaAs materials, and the number of pairs of the periodic structure of the bottom DBR mirror 33 is 27.5 pairs.

[0045] In the embodiment of the present application, the absorption wavelength range of the quantum well in the active region multi-quantum well layer 32 covers the pump laser.

[0046] For example, the wavelength of the pump laser and the absorption wavelength of the quantum well in the active region multi-quantum well layer 32 can be consistent, both being 808 nm.

[0047] Preferably, the active region multi-quantum well layer 32 is a "sandwich" structure of InGaAs / GaAs / GaAsP materials. For example, the active region multi-quantum well layer 32 is composed of 11 pairs of InGaAs / GaAs material quantum wells, and the barrier layer material can be GaAsP; the center wavelength of the active region multi-quantum well layer 32 structure is 1064 nm, and the optical thickness is half of the center wavelength.

[0048] For example, the surface cap layer 31 is a high barrier layer, which prevents the leakage of carriers to the surface of the gain chip to cause non-radiative recombination, and also plays a protective role. Preferably, the material of the surface cap layer 31 can be GaAs material.

[0049] In the embodiment of the present application, the pump laser emitted by the semiconductor bar laser 11 is focused and coupled by the collimating and focusing lens optical coupling assembly 12, and the output spot is absorbed and gain-processed by the microcavity gain structure 21, and then the resonant laser is output by the external cavity structure 22.

[0050] Please continue to refer to Figure 1 In the embodiment of the present application, the microcavity gain structure 21 is a resonant periodic gain structure, and the standing wave antinode of the microcavity gain structure 21 is located above the active region multi-quantum well layer 32 of the semiconductor gain chip 211, for gain maximization processing.

[0051] For example, the microcavity gain structure 21 is a resonant periodic gain structure, and the standing wave antinode of the microcavity gain structure 21 is located directly above the active region multi-quantum well layer 32 in the gain chip, so as to maximize the gain of the light spot.

[0052] As shown in Figure 1 The external cavity structure 22 is V-shaped, and the external cavity structure 22 is a laser resonant cavity, which includes a bottom DBR mirror 33, a first mirror 221, a second mirror 222, and the distance between the bottom DBR mirror 33, the first mirror 221, and the second mirror 222; wherein the first mirror 221 is a coupling mirror with a curvature radius, and the reflectivity of the first mirror 221 is higher than a preset reflectivity threshold; the second mirror 222 is a plane output mirror.

[0053] In the embodiment of the present application, the first mirror 221 is used to control the matching of the resonant laser and the light spot in the external cavity structure 22.

[0054] For example, the first mirror 221 is a high-reflectivity R>99.9% coupling mirror with a curvature radius, and the curvature radius R=1000mm, which is used to control the matching of the resonant laser and the light spot in the external cavity structure 22.

[0055] For example, the second mirror 222 is a plane output mirror, and the transmittance T=0.6%.

[0056] In the embodiment of the present application, when the resonant laser and the light spot in the external cavity structure 22 are matched, the external cavity structure 22 outputs the mode-locked pulse after the adjustment of the spatiotemporal dynamics calculation.

[0057] Figure 5 The pulse sequence result diagram of the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser according to the embodiment of the present application is schematically shown. Figure 6 The pulse width result diagram of the pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser according to the embodiment of the present application is schematically shown.

[0058] It can be understood that the electric field intensity of all the locked transverse electromagnetic modes is obtained after the adjustment of the spatiotemporal dynamics calculation of the external cavity structure 22; and the mode locking consistent with the spatiotemporal dynamics calculation is obtained by controlling the external cavity structure 22, so as to realize the output of the mode-locked pulse.

[0059] For example, the length of the external cavity structure 22 corresponds to a repetition frequency of 80 MHz. The beam waist of the surface light beam of the gain chip is calculated by the ABCD transfer matrix to be 346 μm in the sagittal plane and 401 μm in the tangential plane. By calculating the time-space dynamics of the external cavity structure, the coupling coefficients of all TEM lmn Electric field intensity of transverse electromagnetic mode locking.

[0060] Further, when the round-trip time of the resonant laser through the external cavity structure 22 is higher than 2 times the carrier lifetime of the semiconductor gain chip 211, the external cavity structure 22 outputs harmonic mode locking.

[0061] It can be understood that when the round-trip time of the resonant laser through the external cavity structure 22 is much higher than the carrier lifetime of the gain chip, harmonic mode locking can be obtained. Preferably, the round-trip time of the resonant laser through the external cavity structure 22 is about 3 to 4 times the carrier lifetime of the gain chip.

[0062] The coupling coefficients of the high-order transverse modes obtained by calculation promote the stability of mode locking, and the coupling coefficients of the high-order transverse modes and the corresponding cavity structure are determined when the mode locking is stable. For example, the relationship between the transverse modes is calculated to be 1*TEM 00 +0.5*TEM 01 +0.1*TEM 02 Stable harmonic mode-locked pulse output is obtained. As shown in Figure 5 , the pulse sequence of the picosecond pulse source is measured by using a photodiode, and the mode-locked repetition frequency is 340 MHz, which is 4 times the frequency of the resonant cavity, i.e., the frequency of the external cavity structure. As shown in Figure 6 , the pulse width of the pulse source is 352 ps.

[0063] Through the embodiment of the present application, the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser realizes a wavelength of 1064 nm, a pulse repetition frequency of 340 MHz, and a pulse width of 352 ps by using the gain chip and the external multiple passive optical elements to form a resonant cavity for self-mode-locking. In addition, the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface-emitting laser realizes a pulse output with a pulse width of hundreds of ps and a repetition frequency of hundreds of MHz by fine-tuning the coupling coefficients of the high-order transverse modes in the external cavity structure 22, without the participation of other nonlinear elements such as SESAM, without being limited by the bandwidth of SESAM, and with the characteristics of simple structure.

[0064] It should be noted that the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface emitting laser can also be combined with other experiments, for example, combined with a frequency-doubled VECSEL, to obtain a pulse source of other wavelengths on the basis of the device. It can be seen that the external cavity structure of the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface emitting laser is also convenient for inserting other optical elements to realize frequency conversion and obtain a self-mode-locked picosecond pulse output of other wavelengths and beam quality TEM00.

[0065] Through the embodiments of the present application, the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface emitting laser can set the size of the pump spot incident on the gain chip by calculating the spatiotemporal dynamics of the external cavity structure, control the modes existing in the resonant cavity structure, and promote the self-mode-locked stability of the semiconductor surface emitting laser by combining the nonlinear Kerr effect determined by the semiconductor material inside the gain chip, to realize harmonic mode-locked pulse output of hundreds of picoseconds pulse width and hundreds of MHz repetition frequency, and solve the difficulty of realizing kilohertz repetition rate of a fiber laser. In addition, the picosecond pulse source based on the harmonic self-mode-locked semiconductor surface emitting laser has good practicability and operability, compact structure, is suitable for repeated production and assembly, is suitable for mass production, has low cost, unidirectional laser output, high repetition frequency, high stability, and high beam quality, and the like.

[0066] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the present application, and it should be understood that the above are only specific embodiments of the present application and are not used to limit the present application, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A picosecond pulsed source based on a harmonic self-mode-locked semiconductor surface-emitting laser, characterized in that, The application relates to a semiconductor laser device, which comprises a light pumping assembly (1) and a V-cavity resonant cavity assembly (2), wherein the light pumping assembly (1) comprises a semiconductor bar laser (11) and a collimating and focusing lens optical coupling assembly (12), and the V-cavity resonant cavity assembly (2) comprises a microcavity gain structure (21) and an external cavity structure (22). The semiconductor bar laser (11) emits pumping laser, which is focused and coupled by the collimating and focusing lens optical coupling assembly (12) to output a light spot, the light spot is absorbed and gain-processed by the microcavity gain structure (21), and then the resonant laser is output by the external cavity structure (22) through feedback resonance. When the resonant laser matches the light spot in the external cavity structure (22), the external cavity structure (22) is adjusted through space-time dynamics calculation to output a mode-locked pulse. After the space-time dynamics calculation of the external cavity structure (22), the electric field intensity of all the locked transverse electromagnetic modes is obtained. The mode locking consistent with the space-time dynamics calculation is obtained by controlling the external cavity structure (22), so that the mode-locked pulse is output.

2. The picosecond pulse source based on harmonic self-mode-locked semiconductor surface-emitting laser according to claim 1, characterized in that, The microcavity gain structure (21) comprises a semiconductor gain chip (211), a heat dissipation heat sink (212) and an air interface on the surface of the semiconductor gain chip (211). The semiconductor gain chip (211) is bonded on the heat dissipation heat sink (212) through Au-In solid-liquid interdiffusion.

3. Picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser according to claim 1 or 2, characterized in that, The semiconductor gain chip (211) comprises, from bottom to top along a first direction, a substrate (35), a barrier layer (34), a bottom DBR mirror (33), an active region multi-quantum well layer (32) and a surface cap layer (31). After the substrate (35) and the barrier layer (34) are removed, the semiconductor gain chip (211) is bonded on the heat dissipation heat sink (212) through Au-In solid-liquid interdiffusion.

4. The picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser according to claim 3, characterized in that, The absorption wavelength range of the quantum well in the active region multi-quantum well layer (32) covers the pumping laser.

5. The picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser according to claim 3, characterized in that, The material of the bottom DBR mirror (33) is lattice matched with the material of the substrate (35); and The bottom DBR mirror (33) is obtained by alternately growing two materials with a refractive index difference exceeding a preset refractive index threshold. The center wavelength of the bottom DBR mirror (33) is consistent with the design wavelength of the active region.

6. The picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser according to claim 3, characterized in that, The microcavity gain structure (21) is a resonant period gain structure, and the standing wave antinode of the microcavity gain structure (21) is located above the active region multi-quantum well layer (32) of the semiconductor gain chip (211) for gain maximization processing.

7. The picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser according to claim 3, characterized in that, The external cavity structure (22) is a laser resonant cavity, which comprises the bottom DBR mirror (33), a first mirror (221) and a second mirror (222). The first mirror (221) is a coupling mirror with a curvature radius, and the reflectivity of the first mirror (221) is higher than a preset reflectivity threshold. The second mirror (222) is a plane output mirror.

8. Picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser according to claim 1 or 7, characterized in that, The first mirror (221) is used for controlling the matching of the resonant laser and the light spot in the external cavity structure (22).

9. The picosecond pulse source based on harmonic self-mode-locked semiconductor surface emitting laser according to claim 1, characterized in that, When the round-trip time of the external cavity structure (22) is higher than 2 times of the carrier lifetime of the semiconductor gain chip (211), the external cavity structure (22) outputs harmonic mode-locking.

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