WO2023174034A1 - 高亮度皮秒激光系统 - Google Patents

高亮度皮秒激光系统 Download PDF

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Publication number
WO2023174034A1
WO2023174034A1 PCT/CN2023/078203 CN2023078203W WO2023174034A1 WO 2023174034 A1 WO2023174034 A1 WO 2023174034A1 CN 2023078203 W CN2023078203 W CN 2023078203W WO 2023174034 A1 WO2023174034 A1 WO 2023174034A1
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Prior art keywords
laser
picosecond
crystal
picosecond laser
traveling wave
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PCT/CN2023/078203
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English (en)
French (fr)
Inventor
刘民哲
赵坤
翟瑞占
贾中青
刘梦霖
王丽莎
闫炜
尹晓琴
王巍
李欢欣
张明山
孙丽媛
张振振
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山东省科学院激光研究所
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Publication of WO2023174034A1 publication Critical patent/WO2023174034A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/139—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media

Definitions

  • the present disclosure belongs to the field of ultrafast laser technology, and particularly relates to high-brightness picosecond laser systems.
  • high-brightness picosecond lasers have found important applications in fields such as micromachining, precision ranging, medicine and spectroscopy due to their advantages of high spectral purity and high peak power.
  • the fiber laser system can exhibit very high gain and low threshold.
  • high peak power often causes optical damage and obvious nonlinear effects.
  • solid-state lasers have advantages, usually including end-pumping and side-pumping.
  • end-pump laser systems can achieve high gains with short gain medium lengths, the crystals that constitute the gain medium cannot withstand excessive High power affects the power of the final output laser; while the side-pumped laser system faces severe thermally induced spherical aberration effects, making it difficult to control the beam quality and affecting the brightness of the final output laser.
  • a high-brightness picosecond laser system includes a fully polarization-maintaining fiber picosecond seed laser, a fiber collimator, a spatial isolator, a polarizing beam splitter prism, a first-level solid traveling wave amplifier, and a second-level solid state sequentially arranged along the optical path direction. Traveling wave amplifiers and three-stage solid traveling wave amplifiers;
  • Fully polarization-maintaining fiber picosecond seed laser used to emit picosecond seed laser with spectral width ⁇ 0.3nm and linear polarization state;
  • Fiber collimator connected to the fully polarization-maintaining fiber picosecond seed laser through a pigtail, used to collimate the picosecond seed laser;
  • Spatial isolator used to isolate the picosecond laser returned in the subsequent optical path
  • Polarizing beam splitter prism used to transmit the picosecond seed laser to the first-stage solid traveling wave amplifier
  • the first-level solid traveling wave amplifier is used to amplify the power of the picosecond seed laser for the first time to form the first picosecond laser, and return the first picosecond laser to the polarizing beam splitting prism;
  • Polarizing beam splitter prism also used to reflect the first picosecond laser to the secondary solid traveling wave amplifier
  • the two-stage solid traveling wave amplifier is used to amplify the power of the first picosecond laser for the second time to form the second picosecond laser;
  • the three-stage solid traveling wave amplifier is used to amplify the power of the second picosecond laser for the third time to form a third picosecond laser, which is emitted to the designated area.
  • the first-stage solid traveling wave amplifier includes: a Faraday rotator arranged sequentially along the optical path direction, a first half-wave plate, a first 45° dichroic mirror, a first laser crystal and a first 0° full-wave amplifier. a mirror, as well as a first laser diode and a first lens group arranged sequentially in the propagation direction of the first pump light;
  • Faraday rotator used to rotate the polarization state of the picosecond seed laser by 45° and shoot it to the first half-wave plate
  • the first half-wave plate is a half-wave plate, used in conjunction with the Faraday rotator to adjust the polarization state of the picosecond seed laser to a horizontal polarization state and emit it to the first 45° dichroic mirror;
  • the first laser diode is used to emit the first pump light to the first 45° dichroic mirror;
  • the first lens group is used to collimate and focus the first pump light on the first laser crystal
  • the first 45° dichroic mirror is used to reflect the picosecond seed laser to the first laser crystal and transmit the first pump light to the first laser crystal;
  • the first laser crystal is used to amplify the power of the passing picosecond seed laser, obtain the amplified fourth picosecond laser, and direct the fourth picosecond laser to the first 0° total reflection mirror;
  • the first 0° total reflection mirror is used to return the fourth picosecond laser to the first laser crystal
  • the first laser crystal is used to continue to amplify the power of the returned fourth picosecond laser to obtain the first picosecond laser, and shoot the first picosecond laser toward the first 45° dichroic mirror;
  • the first 45° dichroic mirror is also used to return the first picosecond laser to the polarizing beam splitter along the first half-wave plate and the Faraday rotator.
  • the first picosecond laser passes through the first half-wave plate and the Faraday rotator. When the rotator is rotated, the horizontal polarization state of the first picosecond laser light changes to the vertical polarization state.
  • the two-stage solid traveling wave amplifier includes a second laser crystal, a second 45° dichroic mirror, a first lens and a second half-wave plate arranged sequentially along the optical path transmission direction, and a second pump A second laser diode and a second lens group are arranged sequentially in the light propagation direction.
  • the second laser crystal is used to amplify the power of the passing first picosecond laser, and shoot the amplified first picosecond laser to the second 45° dichroic mirror;
  • a second laser diode used to emit the second pump light to the second lens group
  • a second lens group used to collimate and focus the second pump light
  • the second 45° dichroic mirror is used to reflect the power-amplified first picosecond laser and transmit the second pump light to form a second picosecond laser directed toward the first lens;
  • the first lens is used to collimate the second picosecond laser and emit it to the second half-wave plate;
  • the second half-wave plate is used to adjust the vertical polarization state of the second picosecond laser to a horizontal polarization state and emit it to the three-stage solid traveling wave amplifier.
  • the three-stage solid traveling wave amplifier includes a third 45° dichroic mirror, a first 56° polarizer, a first side pump module, a 90° rotator, and 4f arranged sequentially along the optical path transmission direction. system, a second side pump module, a quarter wave plate, a second 0° total reflection mirror, and a second 56° polarizer that adjusts the reflected light path of the first 56° polarizer;
  • the third 45° dichroic mirror is used to reflect the second picosecond laser in the horizontal polarization state to the first 56° polarizer;
  • the first 56° polarizer is used to filter out the vertically polarized laser in the second picosecond laser and emit it to the first side pump module;
  • the first side pump module is used to provide the third pump light and the third laser crystal.
  • the third pump light provides energy for the second picosecond laser through the third laser crystal, so as to amplify the power of the second picosecond laser to form
  • the fifth picosecond laser shoots towards the 90° polarizer;
  • the second side pump module is used to provide the fourth pump light and the fourth laser crystal.
  • the fourth pump light provides energy for the fifth picosecond laser through the fourth laser crystal, amplifying the power of the fifth picosecond laser to form The sixth picosecond laser shoots towards the 1/4 wave plate;
  • 1/4 wave plate used to adjust the polarization direction of the sixth picosecond laser and shoot it to the second 0° total reflection mirror;
  • the second 0° total reflection mirror is used to reflect the sixth picosecond laser so that the sixth picosecond laser returns along the optical path to the second side pump module;
  • the second side pump module and the first side pump module are also used for the sixth picosecond of the second 0° total reflection mirror return.
  • the laser power is amplified to form the third picosecond laser, which is directed towards the first 56° polarizer;
  • the first 56° polarizing plate is also used to reflect the third picosecond laser and direct the third picosecond laser to the second 56° polarizing plate;
  • the second 56° polarizer is used to reflect the third picosecond laser to the designated area.
  • the optical path downstream of the three-stage solid traveling wave amplifier also includes a frequency doubling module.
  • the frequency doubling module includes a second lens, a frequency doubling crystal, a third lens, a fourth 45° second lens, and a second lens arranged sequentially along the output direction of the optical path.
  • the second lens is used to focus the third picosecond laser onto the frequency doubling crystal
  • the frequency doubling crystal is used to double the frequency of the third picosecond laser to form a seventh picosecond laser, which is directed to the third lens;
  • the third lens is used to collimate the seventh picosecond laser and shoot it to the fourth 45° dichroic mirror;
  • the fourth 45° dichroic mirror is used to transmit the frequency doubled seventh picosecond laser to the designated area, and to reflect the unfrequency doubled seventh picosecond laser to the laser absorber;
  • Laser absorber is used to absorb the unfrequency-multiplied seventh picosecond laser.
  • both the first laser crystal and the second laser crystal have a cuboid structure, and the materials are bonded Nd:YVO 4 crystals.
  • the input and output laser end faces of the first laser crystal and the second laser crystal are both 4mm*4mm square, length 35mm.
  • the frequency doubling crystal has a cuboid structure, a square end face, and a geometric parameter of 6 mm. *6mm*16mm.
  • Some possible implementation methods also include:
  • the 45° total reflection mirror is installed downstream of the optical path of the spatial isolator to reflect the collimated picosecond seed laser to the polarizing beam splitter prism.
  • a fully polarization-maintaining fiber picosecond seed laser is used to generate a picosecond pulse laser with a wavelength of 1064 nm, a pulse width of ⁇ 10ps, a maximum single pulse energy of >100nJ, and a repetition frequency adjustment range of 1Hz-20MHz.
  • the filling factor in the first-stage solid traveling wave amplifier ranges from 0.7 to 0.9; the filling factor in the second-stage solid traveling wave amplifier is 0.85.
  • Figure 1 is a schematic diagram of the present disclosure according to some embodiments of the present disclosure.
  • Figure 2 is a schematic structural diagram of a first-stage solid traveling wave amplifier according to some embodiments of the present disclosure
  • Figure 3 is a schematic structural diagram of a two-stage solid traveling wave amplifier according to some embodiments of the present disclosure
  • Figure 4 is a schematic structural diagram of a three-stage solid traveling wave amplifier according to some embodiments of the present disclosure
  • Figure 5 is a schematic diagram of the present disclosure with a frequency doubling module according to some embodiments of the present disclosure
  • Figure 6 is a schematic structural diagram of a frequency multiplication module according to some embodiments of the present disclosure.
  • Figure 7 is a graph showing the output 1064nm laser wavelength test results of the present disclosure according to some embodiments of the present disclosure.
  • Figure 8 shows the 1064nm laser output power and stability test results of the present disclosure according to some embodiments of the present disclosure
  • Figure 9 is a graph showing the output 1064nm laser beam quality test results of the present disclosure according to some embodiments of the present disclosure.
  • Figure 10 is a graph showing the output 1064nm laser pulse width test results of the present disclosure according to some embodiments of the present disclosure.
  • Figure 11 is a graph showing the output 532nm laser wavelength test results of the present disclosure according to some embodiments of the present disclosure.
  • Figure 12 shows the 532nm laser output power and stability test results of the present disclosure according to some embodiments of the present disclosure.
  • High-brightness picosecond lasers are not only used in fields such as micromachining, precision ranging, medicine, and spectroscopy, but are also commonly used as pump light sources in nonlinear optical frequency conversion applications.
  • the short duration of the interaction between the picosecond pulse and the material can avoid the effects of laser linear absorption, energy transfer and diffusion, thereby achieving "cold processing" of materials.
  • All-solid-state lasers based on semiconductor pumping have novel structural gain media that can effectively improve thermo-optical performance.
  • Thin-sheet lasers use gain media hundreds of microns thick for single-sided heat dissipation. Excellent thermal management capabilities can ensure good beam quality and obtain high-power laser output at the same time.
  • the sheet-shaped laser crystal has low single-pass gain and complex multi-pass structure, which greatly increases the complexity of the system.
  • slab lasers have advantages in technical complexity, but due to their special pump structure, additional coupling and shaping technologies are required, which limits their further development.
  • the pump power density of the end pump is high, which can achieve good mode matching between the pump light and the oscillation light, and can achieve high gain under a short gain medium length.
  • Representative crystals include Nd:YVO 4 and Nd:GdVO 4.
  • the disadvantage is that the crystal It cannot withstand excessive power and requires a multi-stage amplifier structure, which increases the complexity of the system.
  • the advantage of the side pump module is that it will not explode easily during high-power pumping.
  • the water-cooling power of the module can reach several kilowatts.
  • the present disclosure provides a high-brightness picosecond laser system, including a fully polarization-maintaining fiber picosecond seed laser 1, a fiber collimator 2, a spatial isolator 3, and a polarization splitter that are sequentially arranged along the laser output direction.
  • Prism 5 polarization beam splitter, PBS for short
  • first-level solid traveling wave amplifier 6 second-level solid traveling wave amplifier 7
  • the fully polarization-maintaining fiber picosecond seed laser 1 is used to emit picosecond seed laser with spectral width ⁇ 0.3nm and linear polarization state.
  • the fully polarization-maintaining fiber picosecond seed laser 1 is specifically used to generate a picosecond pulse laser with a wavelength of 1064 nm, a spectral width of ⁇ 0.3 nm, a pulse width of ⁇ 10 ps, a maximum single pulse energy of >100 nJ, and a repetition frequency adjustment range of 1 Hz. -20MHz.
  • the fully polarization-maintaining fiber picosecond seed laser 1 has the advantages of simple structure, stable performance, easy maintenance, etc., and can be suitable for use in different external environments.
  • the pigtail of the fiber collimator 2 is connected to the output end of the fully polarization-maintaining fiber picosecond seed laser 1, and the fiber collimator 2 is used to collimate the picosecond seed laser.
  • the horizontal polarization or vertical polarization output of the picosecond pulse laser is achieved, and the horizontal polarization state is used here.
  • the working distance of the fiber collimator 2 is 1 m
  • the output laser spot diameter of the fiber collimator 2 is set to D1.
  • the spatial isolator 3 is arranged downstream of the optical path of the optical fiber collimator 2 and is used to isolate the laser light returned from the subsequent first-stage solid traveling wave amplifier, second-stage solid traveling wave amplifier and third-stage solid traveling wave amplifier.
  • the spatial isolator 3 can prevent the returned picosecond laser from causing damage to the components of the fully polarization-maintaining fiber picosecond seed laser.
  • the space isolator 3 handles 30W of power.
  • the polarization beam splitter prism 5 is arranged downstream of the optical path of the spatial isolator 3 and is used to transmit the picosecond seed laser in the horizontal polarization state and reflect the picosecond seed laser in the vertical polarization state.
  • the extinction ratio of the polarizing beam splitter prism 5 is >1000:1, and for a 1064nm laser with a pulse width of 10ps, the damage threshold of the coating is >1J/cm 2 .
  • the first-stage solid traveling wave amplifier 6 is provided downstream of the polarization beam splitter 5 to amplify the power of the picosecond seed laser for the first time to form the first picosecond laser and return the first picosecond laser to the polarization beam splitter prism 5 .
  • the first-stage solid traveling wave amplifier 6 is located on the transmitted light side of the polarizing beam splitter prism 5 .
  • the first-stage solid traveling wave amplifier 6 includes a Faraday rotator 61, a first half-wave plate 62, and a first 45° dichroic mirror 63 arranged sequentially along the transmission direction of the optical path.
  • the first laser crystal 64 and the first 0° total reflection mirror 65, as well as the first laser diode 67 and the first lens group 66 are arranged in sequence in the propagation direction of the first pump light.
  • Each of the above devices is placed independently of each other in space, and the height of the geometric center is consistent, which facilitates adjustment and improves efficiency.
  • the Faraday rotator 61 is disposed on the downstream optical path of the polarization beam splitter and is used to rotate the polarization state of the picosecond seed laser by 45°.
  • Faraday rotator 61 corresponds to the wavelength of 1064nm and can withstand power >30W. After the picosecond seed laser passes through the Faraday rotator 61, the polarization state of the picosecond seed laser is non-reciprocally rotated 45° along the polarization plane of the Faraday rotator 61, thereby realizing the 45° rotation of the polarization state of the picosecond seed laser.
  • the first half-wave plate 62 is a half-wave plate, which is disposed on the downstream optical path of the Faraday rotator 61 and is used to cooperate with the Faraday rotator 61 to convert the polarization state of the picosecond seed laser into a horizontal polarization state.
  • the first half-wave plate 62 corresponds to a center wavelength of 1064 nm.
  • the Faraday rotator 61, the first half-wave plate 62 and the polarizing beam splitter prism 5 can form a spatial isolator.
  • the spatial isolator can isolate the laser light returned in the subsequent optical path, thereby achieving full polarization-maintaining fiber picosecond seed laser 1 protection of.
  • the first 45° dichroic mirror 63 is disposed on the downstream optical path of the first half-wave plate 62 for reflecting the picosecond seed laser to the first laser crystal 64 .
  • the coating parameters of the first 45° dichroic mirror 63 are >98.5% transmittance for 888nm pump light, and >99% for 1064nm laser reflectivity.
  • the first laser diode 67 is disposed on the upstream optical path of the first 45° dichroic mirror 63 and is used to emit the first pump light to the first 45° dichroic mirror 63 .
  • the first pump light emitted by the first laser diode 67 has a lower quantum loss, which can greatly reduce the thermal effect of the laser crystal and help achieve better beam quality.
  • the first 45° dichroic mirror 63 When the first pump light is directed to the first 45° dichroic mirror 63, the first 45° dichroic mirror 63 is also used to transmit the first pump light to the first laser crystal 64, so that the first 45° dichroic mirror 63 is A pump light and the picosecond seed laser are coupled in the first laser crystal 64 .
  • the first lens group 66 is disposed on the downstream optical path of the first laser diode 67 for collimating the first pump light and focusing it on the first laser crystal 64 .
  • the first lens group 66 consists of a first coated lens and a second coated lens group.
  • the first coated lens and the second coated lens are sequentially disposed on the downstream optical path of the first laser diode 67 , and the first coated lens is adjacent to the first laser diode 67 . That is to say, the first coated lens is used to collimate the first pump light emitted from the first laser diode 67 ; the second coated lens is used to focus the collimated first pump light onto the first laser crystal 64 .
  • the diameter of the light spot focused on the first laser crystal 64 is D2.
  • the coating requirements for the two coated lenses are: transmittance of the first pump light >99.9%.
  • D1/D2 constitute the filling factor.
  • the focal length of the first coated lens in the first lens group 66 can be set to 30 mm, and the focal length of the second coated lens can be set to 45 mm.
  • the first lens group 66 composed of lenses with focal lengths of 30 mm and 45 mm, the first lens group 66 can expand the first pump light by 1.5 times, and the focused spot diameter is 600 ⁇ m.
  • the spot diameter of the first lens group 66 focusing the first pump light on the first laser crystal 64 is D2, and the filling factor of D1/D2 is 0.7-0.9. In this way, a fill factor of 0.7-0.9 can achieve higher extraction efficiency of the first picosecond laser while ensuring better beam quality.
  • the first laser crystal 64 is disposed on the downstream optical path of the first 45° dichroic mirror 63 to provide a gain medium for amplifying the passing laser power.
  • the power of the picosecond seed laser can be amplified to obtain a fourth picosecond laser, and then the fourth picosecond laser is emitted to To the first 0° total mirror 65.
  • first laser crystal 64 is a bonded Nd:YVO 4 crystal. It can be a single-end bonded crystal (Nd:YVO 4 —YVO 4 ) or a double-end bonded crystal (YVO 4 —Nd:YVO 4 —YVO 4 ).
  • the doping concentration of Nd 3+ ions is 0.4%.
  • the input and output laser end faces of the first laser crystal 64 are both 4mm*4mm square, with a length of 35mm. Among them, the length of the Nd:YVO 4 crystal doped with Nd 3+ ions is 33 mm, and the length of the YVO 4 crystal not doped with Nd 3+ ions is 2 mm.
  • the first laser crystal 64 can greatly reduce the thermal effect of the crystal, which is beneficial to the control of beam quality.
  • the first laser crystal 64 needs to be water-cooled for heat dissipation, and the water-cooling temperature range is 18-25°C. During the working process, the first laser crystal 64 absorbs the first pump light to produce a thermal lens effect, which is equivalent to a thermal lens.
  • the first 0° total reflection mirror 65 is disposed on the downstream optical path of the first laser crystal 64 for returning the fourth picosecond laser light to the first laser crystal 64 .
  • the first laser crystal 64 can amplify the power of the fourth picosecond laser again, thereby obtaining the first picosecond laser.
  • the first 0° total reflection mirror 65 has a reflectivity of >99.9% for 1064 nm laser light.
  • the first 0° total reflection mirror 65 is placed at the focus of the thermal lens formed by the first laser crystal 64 .
  • the first 45° dichroic mirror 63, the first laser crystal 64 and the first 0° total reflection mirror 65 form a double-pass amplification structure to amplify the picosecond seed laser that passes twice. After the first amplification, the fourth picosecond laser is obtained, and after the second amplification, the first picosecond laser is obtained, thereby achieving double-pass amplification and improving gain and extraction efficiency.
  • the two-pass amplification structure can also compensate for the positive spherical aberration generated in the amplification stage and prevent the deterioration of the beam quality.
  • the double-pass amplified first picosecond laser passes through the first half-wave plate 62 and the Faraday rotator 61, it becomes the first picosecond laser in a vertical linear polarization state. Next, it is reflected by the polarizing beam splitter prism 5 and enters the secondary solid traveling wave amplifier 7 for subsequent power amplification.
  • the first 45° dichroic mirror 63 After receiving the first picosecond laser, the first 45° dichroic mirror 63 reflects the first picosecond laser to the first half-wave plate 62 . After the first picosecond laser passes through the first half-wave plate 62 and the Faraday rotator 61 in sequence, it is emitted to the polarizing beam splitter prism 5. During this process, when the first picosecond laser passes through the first half-wave plate and the Faraday rotator, The horizontal polarization state of the laser light changes to the vertical polarization state within one picosecond.
  • the picosecond laser power of 20mW and 100nJ can be amplified to >16W.
  • the two-stage solid traveling wave amplifier 7 is located on the reflected light side of the polarizing beam splitter prism 5 .
  • the two-level solid traveling wave amplifier 7 includes a second laser crystal 71, a second 45° dichroic mirror 72, a first lens 75 and a second half-wave plate 76 arranged sequentially along the optical path transmission direction, and the second pump light propagation
  • the second laser is set sequentially in the direction of the second pole tube 74 and the second lens group 73 .
  • the second laser crystal 71 is disposed downstream of the polarization beam splitter prism 5 and is used to amplify the power of the first picosecond laser reflected by the polarization beam splitter prism 5 passing through.
  • the second laser crystal 71 can use the same structure and material as the first laser crystal 64 , and the second laser diode 74 can output a maximum average power of pump light >120W.
  • the second laser crystals 71 all have a cuboid structure, the material is bonded Nd:YVO 4 crystal, and the doping concentration of Nd 3+ ions is 0.4%.
  • the input and output laser end faces of the crystal are 4mm*4mm square and the length is 35mm. Among them, the length of the Nd:YVO 4 crystal doped with Nd 3+ ions is 33 mm, and the length of the YVO 4 crystal not doped with Nd 3+ ions is 2 mm.
  • the second 45° dichroic mirror 72 is disposed on the downstream optical path of the second laser crystal 71 for reflecting the first picosecond laser light passing through the second laser crystal 71 .
  • the coating parameters of the second 45° dichroic mirror 72 are >98.5% transmittance for the second pump light and >99% for the 1064nm laser reflectivity.
  • the second laser diode 74 is disposed on the upstream optical path of the second lens group 73 and is used to emit the second pump light to the second lens group 73 .
  • the second laser diode 74 can emit pump light with a wavelength of 888 nm, and can also emit pump light with a wavelength of 878 nm or 880 nm.
  • the maximum average output power of the second laser diode 74 is >120W.
  • the second lens group 73 is disposed on the upstream optical path of the second 45° dichroic mirror 72 to collimate the second pump light emitted by the second laser diode 74 and focus it on the second laser crystal 71 .
  • the second lens group 73 is composed of two coated lenses. The functions of the second lens group 73 are the same as those of the first lens group 66 and will not be described again here.
  • the second 45° dichroic mirror 72 is also used to transmit the second pump light focused by the second lens group 73 to the second laser crystal 71 .
  • the second 45° dichroic mirror 72 also reflects the first picosecond laser, the first picosecond laser and the pump light are coupled at the second laser crystal 71 to generate the second picosecond laser.
  • the first lens 75 is disposed on the downstream optical path of the second 45° dichroic mirror 72 .
  • the first lens 75 is used to collimate the second picosecond laser and emit it to the second half-wave plate 76 .
  • the second half-wave plate 76 is disposed on the downstream optical path of the first lens 75 .
  • the second half-wave plate 76 is used to adjust the polarization state of the second picosecond laser to a horizontal polarization state and emit it to the three-stage solid traveling wave amplifier 8 .
  • the spot diameter is D3.
  • the second laser crystal 71 performs power amplification on the second picosecond laser.
  • the focused spot diameter is D4
  • the fill factor (D3/D4) in the second-stage solid traveling wave amplifier 7 is designed to be 0.85. , thereby ensuring beam quality and laser extraction efficiency.
  • the second 45° dichroic mirror 72 shoots the second picosecond laser to the first lens 75 , and then collimates it through the first lens 75 before entering the three-stage solid traveling wave amplifier 8 .
  • the 16W laser power output by the first-stage solid traveling wave amplifier 6 can be amplified to more than 50W.
  • the three-stage solid traveling wave amplifier 8 includes a third 45° dichroic mirror 81, a first 56° polarizer 82, and a first side pump sequentially arranged along the optical path transmission direction.
  • the third 45° dichroic mirror 81 is arranged on the downstream optical path of the two-stage solid traveling wave amplifier 7 .
  • the third 45° dichroic mirror 81 is used to reflect the second picosecond laser in the horizontal polarization state to the first 56° polarizer 82 .
  • the first 56° polarizer 82 is disposed on the downstream optical path of the third 45° dichroic mirror 81 .
  • the first 56° polarizer 82 is used to filter out the vertically polarized laser in the second picosecond laser, and radiate the second horizontally polarized picosecond laser to the first side pump.
  • Module 83 is used to filter out the vertically polarized laser in the second picosecond laser, and radiate the second horizontally polarized picosecond laser to the first side pump.
  • the first side pump module 83 is disposed on the downstream optical path of the first 56° polarizing plate 82 .
  • the first side pump module 83 is used to provide the third pump light and the third laser crystal 801.
  • the third pump light provides energy for the second picosecond laser through the third laser crystal 801, so as to amplify the power of the second picosecond laser. , forming the fifth picosecond laser, and shooting to the 90° optical rotator 84.
  • the second side pump module 86 is disposed on the downstream optical path of the first side pump module 83 .
  • the second side pump module 86 is used to provide the fourth pump light and the fourth laser crystal 802.
  • the fourth pump light passes through the fourth laser crystal 802 to provide energy for the fifth picosecond laser to amplify the power of the fifth picosecond laser. , forming the sixth picosecond laser.
  • the first side pump module 83 and the second side pump module 86 are composed of multiple bar arrays, and the wavelength is 808 nm.
  • the third laser crystal 801 and the fourth laser crystal 802 are respectively provided in the first side pump module 83 and the second side pump module 86, wherein the fourth laser crystal 802 and the third laser crystal 801 are both Nd:YAG crystals. .
  • the third laser crystal 801 is placed in the first side pump module 83, and the fourth laser crystal 802 is placed in the second side pump module 86 and uses water cooling for heat dissipation.
  • the water cooling temperature range is 18-22°C.
  • the 90° optical rotator 84 and the 4f system 85 are sequentially arranged in the first side pump module 83 on the downstream optical path and is arranged between the first side pump module 83 and the second side pump module 86 .
  • the 90° optical rotator and 4f system are used to compensate for the thermally induced birefringence effect of the third laser crystal 801 and the fourth laser crystal 802 in the first side pump module 83 and the second side pump module 86, thereby improving the beam quality. .
  • the 1/4 wave plate 87 is disposed on the downstream optical path of the second side pump module 86 .
  • the 1/4 wave plate 87 is used to adjust the polarization direction of the sixth picosecond laser.
  • the second 0° total reflection mirror 88 is disposed on the downstream optical path of the quarter wave plate 87 , and the second 0° total reflection mirror 88 is placed at the focus of the thermal lens formed by the third laser crystal 801 .
  • the second 0° total reflection mirror 88 is used to reflect the sixth picosecond laser so that the sixth picosecond laser returns along the original optical path.
  • the coating parameters of the second 0° total reflection mirror 88 are >98.5% for the fourth pump light transmittance and >99% for the 1064nm laser reflectivity.
  • the second side pump module 86 and the first side pump module 83 are also used to amplify the sixth picosecond laser power returned by the second 0° total reflection mirror 88 to form a third picosecond laser, which is emitted to the first 56° polarizer 82;
  • the first 56° polarizing plate 82 is also used to reflect the third picosecond laser and direct the third picosecond laser to the second 56° polarizing plate 89;
  • the second 56° polarizing plate 82 is used to reflect the third picosecond laser to a designated area.
  • the three-stage solid traveling wave amplifier 8 receives the second picosecond laser of horizontally polarized light output by the two-stage solid traveling wave amplifier 7, and passes through the third 45° dichroic mirror 81 and the first 56° polarizer in sequence. After 82, it passes through the first side pump module 83 and the second side pump module 86 in sequence.
  • the second picosecond laser passes through the first side pump module 83, the second picosecond laser is amplified to form a fifth picosecond laser.
  • the fifth picosecond laser then enters the second side pump module 86 and is amplified by the second side pump module 86 to form the sixth picosecond laser.
  • the 1/4 wave plate 87 changes the polarization direction of the sixth picosecond laser.
  • the sixth picosecond laser that undergoes single amplification through the first side pump module 83 and the second side pump module 86 is totally reflected by the second 0° total reflection mirror 88 .
  • the sixth picosecond laser returns along the original optical path, and sequentially passes through the second side pump module 86 and the first side pump module 83 for secondary amplification to form a third picosecond laser, thereby achieving dual control of the picosecond laser.
  • Pass amplification In the two-pass amplification process, a 90° rotator and a 4f system are installed between the optical paths of the first side pump module 83 and the second side pump module 86 to compensate for the thermally induced birefringence effect of the pump module and ensure beam quality. .
  • the first-level solid traveling wave amplifier 8 adopts two first side pump modules 83 and second side pump modules 86 with average power >200W, which can amplify the 50W laser power output by the second-level solid traveling wave amplifier 7 to more than one hundred watts. , while controlling the beam quality factor M 2 ⁇ 1.3.
  • the high-brightness picosecond laser system also includes a 45° total reflection mirror 4.
  • the 45° total reflection mirror 4 is provided downstream of the optical path of the spatial isolator 3 and is used to reflect the collimated picosecond seed laser toward Polarizing beam splitter prism 5.
  • the use of 45° total mirror 4 can effectively reduce the overall length of the high-brightness picosecond laser system and improve the applicability of practical applications.
  • the first-stage solid traveling wave amplifier, the second-stage solid traveling wave amplifier and the third-stage solid traveling wave amplifier in the present disclosure are all traveling wave amplifiers that use a combination of direct end pumping technology and side pumping technology.
  • the three-stage amplifier can increase the brightness of the picosecond 1064nm output laser to more than 5.7*10 9 W ⁇ cm -2 ⁇ Sr. It not only maintains the advantages of high gain and high extraction efficiency under end pumping, but also can increase the maximum laser power due to the high damage threshold of the side pump.
  • the first laser diode and the second laser diode are used to replace the traditional multi-stage end-pump traveling wave amplifier, which simplifies the laser structure, facilitates integration, improves the operating stability of the laser, and extends the service life.
  • a first laser crystal and a second laser crystal are respectively provided on the downstream optical paths of the first laser diode and the second laser diode, thereby achieving spherical aberration compensation.
  • the first 0° total reflection mirror and the second 0° total reflection mirror are placed correspondingly at the focus of the first laser crystal and the second laser crystal, and at the same time Adjust the fill factor to ultimately improve beam quality.
  • the two-stage solid hybrid amplification method of using LD double end-pumped solid laser amplifier and LD side-pumped solid laser amplifier can only achieve The smaller power 1064nm laser output corresponds to a beam quality of 1.3, and the brightness is usually ⁇ 1.47*10 9 W ⁇ cm -2 ⁇ Sr.
  • a three-stage solid traveling wave amplifier structure consisting of a first-stage solid traveling wave amplifier, a second-stage solid traveling wave amplifier, and a third-stage solid traveling wave amplifier can achieve high average power 1064 nm laser output.
  • the laser system using the Nd:YVO 4 crystal solid amplifier as the amplification stage can only achieve a part of the power of the present disclosure.
  • the laser system using the Nd:YVO 4 crystal solid amplifier as the amplification stage can achieve a maximum of 27.65W.
  • the average power of the 1064nm laser output is only 25.6% of the average power of the present disclosure.
  • This disclosure can achieve 103.24W high average power 1064nm laser output, while the beam quality is controlled at ⁇ 1.27, and the laser brightness reaches 5.74*10 9 W ⁇ cm -2 ⁇ Sr.
  • the Nd:YVO 4 crystal will reach gain saturation and the output power will still be insufficient. Reaching the power of this disclosure, or even continuing to increase the output power, will cause the higher pump power to be unabsorbed and converted into heat, causing damage to the crystal and coating.
  • the final laser output power will be significantly lower than the achieved 27.65W laser output. That is, the present disclosure focuses on increasing picosecond laser brightness using a three-stage solid traveling wave amplifier structure. When only a part of the power of the present disclosure is achieved, a solid traveling wave amplifier structure needs to be added to achieve the picosecond laser brightness to be achieved by the present disclosure.
  • the spectral width parameters of the fully polarization-maintaining fiber picosecond seed laser need to be limited. That is to say, only when the spectral width of the fully polarization-maintaining fiber picosecond seed laser is ⁇ 0.3nm can the high average power 1064nm laser output of the present disclosure such as 103.24W be achieved, and this will help improve the working efficiency of the back-end solid amplifier.
  • the optical path downstream of the three-stage solid traveling wave amplifier 8 also includes a frequency doubling module 9.
  • the frequency doubling module 9 includes a second lens 91 , a frequency doubling crystal 921 , a third lens 93 , and a fourth 45° dichroic mirror 94 arranged sequentially along the output direction of the optical path; and the fourth 45° dichroic mirror 94 is provided for reflection.
  • the second lens 91 is disposed on the downstream optical path of the three-stage solid traveling wave amplifier 8 .
  • the second lens 91 is used to focus the third picosecond laser light onto the frequency doubling crystal 921 .
  • the frequency doubling crystal 921 is disposed on the downstream optical path of the second lens 91 .
  • the frequency doubling crystal 921 is used to double the frequency of the third picosecond laser after the first collimation to form a seventh picosecond laser.
  • the frequency doubling crystal 921 is wrapped with an indium foil with a thickness of 0.05 mm and placed in a clamp 922 to ensure close contact.
  • the clamp 922 material can be made of copper, and this structure can improve the frequency doubling effect.
  • the clamp 922 is connected to the temperature control module 923.
  • the temperature control module 923 may use a semiconductor cooler (Thermo Electric Cooler, TEC).
  • the temperature control module 923 mainly changes the temperature of the clamp 922 to accurately control the temperature of the frequency doubling crystal 921 to ensure high frequency doubling efficiency.
  • the frequency doubling crystal 921 can be a cuboid structure with a square end face and a geometric parameter of 6mm*6mm*16mm.
  • the third lens 93 is disposed on the downstream optical path of the frequency doubling crystal 921 .
  • the third lens 93 is used to collimate the seventh picosecond laser after frequency doubling.
  • the fourth 45° dichroic mirror 94 is disposed on the downstream optical path of the third lens 93 .
  • the fourth 45° dichroic mirror 94 is used to transmit the collimated seventh picosecond laser with frequency doubled, and to reflect the collimated seventh picosecond laser with no frequency doubled toward the laser absorber.
  • the fourth 45° dichroic mirror 94 is used to combine the fundamental frequency light of 1064 nm wavelength (undoubled seventh picosecond laser) and the frequency doubled light of 532 nm wavelength (doubled seventh picosecond laser). )separate. Among them, the 1064nm fundamental frequency light is completely absorbed by the laser absorber 95, thereby ensuring the safety of devices and personnel.
  • the frequency doubling module 9 receives the third picosecond laser.
  • the third picosecond laser is focused onto the frequency doubling crystal 921 through the second lens 91 to double the frequency of the third picosecond laser to form a seventh picosecond laser.
  • the seventh picosecond laser is collimated through the third lens 93 .
  • the fourth 45° dichroic mirror 94 reflects the remaining seventh picosecond laser with a wavelength of 1064 nm during the frequency doubling process into the laser absorber 95 to ensure the output of the seventh picosecond laser with a single wavelength of 532 nm, which corresponds to green light. .
  • the frequency doubling module 9 uses 100W of 1064nm fundamental frequency light, which can achieve a green light output of >50W and a frequency doubling efficiency of >50%.
  • the frequency doubling module 9 in the present disclosure can achieve a green light output of more than 50W based on the fundamental frequency light of more than 100 watts, and can meet the needs of solar cell material cutting, invisible QR code marking, flexible circuit board cutting, and organic light emitting. Precision processing needs in many fields such as diode (OLED) material processing and aerospace composite material drilling.
  • OLED diode
  • the output parameters of the fully polarization-maintaining fiber picosecond seed laser 1 are: average power 20mW, single pulse energy 100nJ, repetition frequency 200kHz, and beam quality M 2 ⁇ 1.1.
  • the picosecond pulse width is 9.8ps (shown in Figure 10).
  • the brightness of the 1064nm picosecond laser output by the high-brightness picosecond laser system of the present disclosure reaches 5.74*10 9 W ⁇ cm -2 ⁇ Sr.
  • Figures 11 and 12 respectively show the wavelength, average power and stability test results of the seventh picosecond laser output through the frequency doubling module 9 in some embodiments of the present disclosure.

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Abstract

一种高亮度皮秒激光系统，包括沿激光传输方向依次设置的全保偏光纤皮秒种子激光器（1）、光纤准直器（2）、空间隔离器（3）、偏振分光棱镜（5）、一级固体行波放大器（6）、二级固体行波放大器（7）和三级固体行波放大器（8），一级固体行波放大器（6）位于偏振分光棱镜（5）的透射光一侧，二级固体行波放大器（7）位于偏振分光棱镜（5）的反射光一侧，光纤准直器（2）通过尾纤与全保偏光纤皮秒种子激光器（1）相连。皮秒激光系统结构简单、性能稳定、易于维护，可实现高亮度1064nm激光输出，通过设置易于集成和拆卸的倍频模块（9），可实现超过50W的绿光输出。

Description

高亮度皮秒激光系统
本公开要求于2022年03月14日提交到国家知识产权局，申请号为：202210244487.2，发明名称为“一种高亮度主振荡功率放大皮秒激光系统”的中国专利申请的优先权，其全部内容通过引用结合在本公开中。
技术领域
本公开属于超快激光技术领域，特别涉及高亮度皮秒激光系统。
背景技术
近年来，高亮度皮秒激光器由于兼具高光谱纯度和高峰值功率的优势，在微加工、精密测距、医学与光谱学等领域得到了重要应用。为了实现高亮度的皮秒激光输出，光纤激光系统可以表现出非常高的增益和低阈值，缺点是高峰值功率下往往会造成光学损伤、产生明显非线性效应等。相比之下，固体激光器具有优势，通常包括端面泵浦和侧面泵浦两种方式，端面泵浦激光系统虽然能够在短的增益介质长度下实现高增益，但是构成增益介质的晶体不能承受过高的功率，影响最终输出激光的功率；而侧面泵浦激光系统面临严重的热致球差效应，光束质量难以控制，影响最终输出激光的亮度。
发明内容
一种高亮度皮秒激光系统，本公开包括沿光路方向依次设置的全保偏光纤皮秒种子激光器、光纤准直器、空间隔离器、偏振分光棱镜、一级固体行波放大器、二级固体行波放大器和三级固体行波放大器；
全保偏光纤皮秒种子激光器，用于射出光谱宽度<0.3nm，线偏振态的皮秒种子激光；
光纤准直器，通过尾纤与全保偏光纤皮秒种子激光器相连，用于准直皮秒种子激光；
空间隔离器，用于隔离后续光路中返回的皮秒激光；
偏振分光棱镜，用于将皮秒种子激光透射至一级固体行波放大器；
一级固体行波放大器，用于对皮秒种子激光的功率第一次放大，形成第一皮秒激光，并将第一皮秒激光返回偏振分光棱镜；
偏振分光棱镜，还用于将第一皮秒激光反射至二级固体行波放大器；
二级固体行波放大器，用于对第一皮秒激光的功率第二次放大，形成第二皮秒激光；
三级固体行波放大器，用于对第二皮秒激光的功率进行第三次放大，形成第三皮秒激光，射向指定区域。
可实施的一些方式中，一级固体行波放大器包括：沿光路方向依次设置的法拉第旋转器、第一半波片、第一45°二向色镜，第一激光晶体和第一0°全反镜，以及第一泵浦光传播方向上依次设置的第一激光二极管和第一透镜组；
法拉第旋转器，用于将皮秒种子激光的偏振态旋转45°，射向第一半波片；
第一半波片，为二分之一波片，用于与法拉第旋转器配合，将皮秒种子激光偏振态调整为水平偏振态，并射向第一45°二向色镜；
第一激光二极管，用于向第一45°二向色镜射出第一泵浦光；
第一透镜组，用于将第一泵浦光准直并聚焦在第一激光晶体；
第一45°二向色镜，用于将皮秒种子激光反射至第一激光晶体，以及将第一泵浦光透射至第一激光晶体；
第一激光晶体，用于对经过的皮秒种子激光功率放大，得到放大后的第四皮秒激光，并将第四皮秒激光射向至第一0°全反镜；
第一0°全反镜，用于将第四皮秒激光返回第一激光晶体；
第一激光晶体，用于对返回的第四皮秒激光继续功率放大，得到第一皮秒激光，并将第一皮秒激光射向第一45°二向色镜；
第一45°二向色镜，还用于将第一皮秒激光，依次沿第一半波片和法拉第旋转器返回偏振分光棱镜，其中，第一皮秒激光经过第一半波片和法拉第旋转器时，第一皮秒激光的水平偏振态转变为竖直偏振态。
可实施的一些方式中，二级固体行波放大器包括沿光路传输方向依次设置的第二激光晶体、第二45°二向色镜、第一透镜和第二半波片，以及第二泵浦光传播方向上依次设置的第二激光二极管和第二透镜组。
第二激光晶体，用于对经过的第一皮秒激光的功率放大，并将功率放大后的第一皮秒激光射向第二45°二向色镜；
第二激光二极管，用于向第二透镜组射出第二泵浦光；
第二透镜组，用于对第二泵浦光准直并聚焦；
第二45°二向色镜，用于反射功率放大后的第一皮秒激光，以及透射第二泵浦光，形成第二皮秒激光射向第一透镜；
第一透镜，用于对第二皮秒激光准直，并射向第二半波片；
第二半波片，用于将第二皮秒激光的竖直偏振态，调整为水平偏振态，并射向三级固体行波放大器。
可实施的一些方式中，三级固体行波放大器包括沿光路传输方向依次设置的第三45°二向色镜、第一56°偏振片、第一侧面泵浦模块、90°旋光器、4f系统、第二侧面泵浦模块、1/4波片、第二0°全反镜，以及调整第一56°偏振片的反射光光路的第二56°偏振片；
第三45°二向色镜，用于将水平偏振态的第二皮秒激光反射至第一56°偏振片；
第一56°偏振片，用于滤除第二皮秒激光中竖直偏振态激光，并射向第一侧面泵浦模块；
第一侧面泵浦模块，用于提供第三泵浦光以及第三激光晶体，第三泵浦光通过第三激光晶体为第二皮秒激光提供能量，使第二皮秒激光功率放大，形成第五皮秒激光，并射向90°旋光器；
90°旋光器和4f系统，用于分别对第一侧面泵浦模块和第二侧面泵浦模块的热致双折射效应补偿；
第二侧面泵浦模块，用于提供第四泵浦光以及第四激光晶体，第四泵浦光通过第四激光晶体为第五皮秒激光提供能量，使第五皮秒激光功率放大，形成第六皮秒激光，并射向1/4波片；
1/4波片，用于调整第六皮秒激光的偏振方向，并射向第二0°全反镜；
第二0°全反镜，用于反射第六皮秒激光，使第六皮秒激光沿光路返回至第二侧面泵浦模块；
第二侧面泵浦模块和第一侧面泵浦模块，还分别用于对第二0°全反镜返回的第六皮秒 激光功率放大，形成第三皮秒激光，射向第一56°偏振片；
第一56°偏振片，还用于反射第三皮秒激光，将第三皮秒激光射向第二56°偏振片；
第二56°偏振片，用于将第三皮秒激光反射至指定区域。
可实施的一些方式中，三级固体行波放大器的光路下游还包括倍频模块，倍频模块包括沿光路输出方向依次设置的第二透镜、倍频晶体、第三透镜、第四45°二向色镜；以及设置在第四45°二向色镜反射光路上的激光吸收器；
第二透镜，用于将第三皮秒激光聚焦至倍频晶体；
倍频晶体，用于对第三皮秒激光倍频，形成第七皮秒激光，并射向第三透镜；
第三透镜，用于对第七皮秒激光准直，并射向第四45°二向色镜；
第四45°二向色镜，用于透射倍频的第七皮秒激光，射向指定区域，以及将未倍频的第七皮秒激光，反射向激光吸收器；
激光吸收器，用于吸收未倍频的第七皮秒激光。
可实施的一些方式中，第一激光晶体和第二激光晶体均为长方体结构，材料均选用键合的Nd:YVO4晶体，第一激光晶体和第二激光晶体的输入和输出激光端面均为4mm*4mm的正方形，长度为35mm。
可实施的一些方式中，倍频晶体采用Ⅰ类相位匹配三硼酸锂晶体，非临界相位匹配角θ＝90°、φ＝0°，倍频晶体为长方体结构，端面为正方形，几何参数为6mm*6mm*16mm。
可实施的一些方式中，还包括：
45°全反镜，设置在空间隔离器的光路下游，用于将准直后的皮秒种子激光反射向偏振分光棱镜。
可实施的一些方式中，全保偏光纤皮秒种子激光器用于产生1064nm波长的皮秒脉冲激光，脉冲宽度<10ps，最大单脉冲能量>100nJ，重复频率调整范围1Hz-20MHz。
可实施的一些方式中，一级固体行波放大器内的填充因子范围为0.7-0.9；二级固体行波放大器内的填充因子为0.85。
附图说明
为了更清楚地说明本公开实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍。
图1为根据本公开一些实施例的本公开示意图；
图2为根据本公开一些实施例的一级固体行波放大器结构示意图；
图3为根据本公开一些实施例的二级固体行波放大器结构示意图；
图4为根据本公开一些实施例的三级固体行波放大器结构示意图；
图5为根据本公开一些实施例的具有倍频模块的本公开示意图；
图6为根据本公开一些实施例的倍频模块结构示意图；
图7为根据本公开一些实施例的本公开输出1064nm激光波长测试结果图；
图8为根据本公开一些实施例的本公开输出1064nm激光输出功率及稳定性测试结果；
图9为根据本公开一些实施例的本公开输出1064nm激光光束质量测试结果图；
图10为根据本公开一些实施例的本公开输出1064nm激光脉冲宽度测试结果图；
图11为根据本公开一些实施例的本公开输出532nm激光波长测试结果图；
图12为根据本公开一些实施例的本公开输出532nm激光输出功率及稳定性测试结果。
图中，1-全保偏光纤皮秒种子激光器；2-光纤准直器；3-空间隔离器；4-45°全反镜；5-偏振分光棱镜；6-一级固体行波放大器；61-法拉第旋转器；62-第一半波片；63-第一45°二向色镜；64-第一激光晶体；65-第一0°全反镜；66-第一透镜组；67-第一激光二极管；7-二级固体行波放大器；71-第二激光晶体；72-第二45°二向色镜；73-第二透镜组；74-第二激光二极管；75-第一透镜；76-第二半波片；8-三级固体行波放大器；801-第三激光晶体；802-第四激光晶体；81-第三45°二向色镜；82-第一56°偏振片；83-第一侧面泵浦模块；84-90°旋光器；85-4f系统；86-第二侧面泵浦模块；87-1/4波片；88-第二0°全反镜；89-第二56°偏振片；9-倍频模块；91-第二透镜；921-倍频晶体；922-夹具；923-温度控制模块；93-第三透镜；94-第四45°二向色镜；95-激光吸收器。
具体实施方式
高亮度皮秒激光器，不仅应用在微加工、精密测距、医学与光谱学等领域，还作为非线性光学变频应用中常用的泵浦光源。皮秒脉冲与物质相互作用的持续时间短，能够避免激光线性吸收、能量转移和扩散等效应的影响，从而实现材料的“冷加工”。
基于半导体泵浦的全固态激光器具有新颖结构的增益介质，可以有效改善热光性能。例如：薄片激光器采用几百微米厚的增益介质进行单面散热，优异的热管理能力可以保证良好的光束质量，同时获得高功率激光输出。但薄片形激光晶体的单通增益较低，多通结构复杂，大大增加了系统的复杂性。另外，板条激光器在技术复杂性上颇具优势，但因其特殊的泵浦结构，需要额外的耦合及整形技术，限制了其进一步的发展。
相比之下，采用光纤皮秒激光器作为种子源，利用行波固体放大器作为放大级，不仅能够获得非常高的增益，同时光束质量也能得到很好控制，是获取高功率皮秒激光的有效方案。为了高功率皮秒激光，一般会使用固体放大器。通常，固体放大器包括两种，一种是基于二极管泵浦的固体增益介质再生放大器，它可以提供很高的增益，但是结构复杂，价格昂贵；另一种是行波放大器，采用多通固体增益介质直接放大低功率的激光种子源，结构简单，易于实现，行波放大器按照泵浦方式分为端泵和侧泵。
端泵的泵浦功率密度高，可实现泵浦光与振荡光良好的模式匹配，可在短的增益介质长度下实现高增益，代表晶体有Nd:YVO4、Nd:GdVO4，缺点是晶体不能承受过高的功率，且需要多级放大器结构，增加了系统的复杂性。侧面泵浦模块的优点是在高功率泵浦时不会轻易炸裂，模块水冷功率可达几千瓦量级，常用晶体包括Nd:YAG、Yb:YAG等，但该类行波放大器所面临的主要问题是增益的热致球差效应，即光束质量难以控制，影响最终输出激光的亮度。
如图1所示，本公开提供了一种高亮度皮秒激光系统，包括沿激光输出方向依次设置的全保偏光纤皮秒种子激光器1、光纤准直器2、空间隔离器3、偏振分光棱镜5(polarization beam splitter，简称PBS)、一级固体行波放大器6、二级固体行波放大器7和三级固体行波放大器8。
其中，全保偏光纤皮秒种子激光器1，用于射出光谱宽度<0.3nm，线偏振态的皮秒种子激光。在一些示例中，全保偏光纤皮秒种子激光器1，具体用于产生1064nm波长的皮秒脉冲激光，光谱宽度<0.3nm，脉冲宽度<10ps，最大单脉冲能量>100nJ，重复频率调整范围1Hz-20MHz。全保偏光纤皮秒种子激光器1具有结构简单、性能稳定、易于维护等优点，能够适合应用于不同的外界环境。
光纤准直器2尾纤与全保偏光纤皮秒种子激光器1的输出端连接，光纤准直器2用于准直皮秒种子激光。通过光纤准直器2的旋转方向和固定位置，实现皮秒脉冲激光水平偏振或者竖直偏振输出，这里采用水平偏振态。在一些示例中，光纤准直器2的工作距离为1m，光纤准直器2输出激光光斑直径设置为D1。
空间隔离器3设置在光纤准直器2的光路下游，用于隔离后续的一级固体行波放大器、二级固体行波放大器和三级固体行波放大器中返回的激光。空间隔离器3可以避免返回的皮秒激光对全保偏光纤皮秒种子激光器的器件造成损伤。在一些示例中，空间隔离器3承受功率为30W。
偏振分光棱镜5设置在空间隔离器3的光路下游，用于透射水平偏振态的皮秒种子激光，以及反射竖直偏振态的皮秒种子激光。在一些示例中，偏振分光棱镜5的消光比>1000:1，针对脉冲宽度为10ps的1064nm激光，镀膜的损伤阈值>1J/cm2。
一级固体行波放大器6设置在偏振分光棱镜5的下游，用于对皮秒种子激光的功率第一次放大，形成第一皮秒激光，并将第一皮秒激光返回偏振分光棱镜5。在一些示例中，一级固体行波放大器6位于偏振分光棱镜5的透射光一侧。
如图2所示，在一些实施例中，一级固体行波放大器6包括沿光路的传输方向依次设置的法拉第旋转器61、第一半波片62、第一45°二向色镜63，第一激光晶体64和第一0°全反镜65，以及第一泵浦光传播方向上依次设置的第一激光二极管67和第一透镜组66。上述各器件置于空间内相互独立，并且几何中心的高度一致，便于调节和提高效率。
法拉第旋转器61设置在偏振分光棱镜的下游光路上，用于将皮秒种子激光的偏振态旋转45°。法拉第旋转器61对应波长1064nm，承受功率>30W。皮秒种子激光通过法拉第旋转器61后，皮秒种子激光的偏振态沿法拉第旋转器61的偏振平面非互易地旋转45°，实现皮秒种子激光的偏振态45°旋转。
第一半波片62为二分之一波片，设置在法拉第旋转器61的下游光路上，用于与法拉第旋转器61配合，将皮秒种子激光偏振态转换为水平偏振态。在一些示例中，第一半波片62对应中心波长1064nm。
其中，法拉第旋转器61、第一半波片62与偏振分光棱镜5能组成一个空间隔离器，该空间隔离器能够隔离后续光路中返回的激光，从而实现对全保偏光纤皮秒种子激光器1的保护。
第一45°二向色镜63设置在第一半波片62的下游光路上，用于将皮秒种子激光反射至第一激光晶体64。在一些示例中，第一45°二向色镜63的镀膜参数为对于888nm泵浦光透过率>98.5％，对于1064nm激光反射率>99％。
第一激光二极管67设置在第一45°二向色镜63的上游光路上，用于向第一45°二向色镜63射出第一泵浦光。在一些示例中，第一激光二极管67的参数为：射出的泵浦光波长为888nm，也可以为878nm或880nm，输出平均功率>100W，光纤芯径400μm，数值孔径NA＝0.22。第一激光二极管67射出的第一泵浦光与通常的808nm波长的泵浦光相比，具有更低的量子亏损，可以大大降低激光晶体热效应，利于实现较好的光束质量。当第一泵浦光射向第一45°二向色镜63的情况下，第一45°二向色镜63还用于将第一泵浦光透射向第一激光晶体64，从而使得第一泵浦光和皮秒种子激光在第一激光晶体64中耦合。
第一透镜组66设置在第一激光二极管67的下游光路上，用于将第一泵浦光准直，并聚焦在第一激光晶体64上。在一些示例中，第一透镜组66由第一镀膜透镜和第二镀膜透镜组 成，其中，第一镀膜透镜和第二镀膜透镜依次设置在第一激光二极管67的下游光路上，且第一镀膜透镜与第一激光二极管67相邻。也就是说，第一镀膜透镜用于对第一激光二极管67射出的第一泵浦光准直；第二镀膜透镜用于将准直的第一泵浦光聚焦到第一激光晶体64上。此时，聚焦在第一激光晶体64上的光斑直径为D2。两片镀膜透镜的镀膜要求为：对第一泵浦光透过率>99.9％。
其中，D1/D2构成填充因子。在D1不变的情况下，可将第一透镜组66中的第一个镀膜透镜的焦距设置为30mm，第二个镀膜透镜的焦距可为45mm。通过焦距为30mm和45mm的透镜组成的第一透镜组66，第一透镜组66可以将第一泵浦光扩束1.5倍，聚焦光斑直径为600μm。第一透镜组66将第一泵浦光聚焦在第一激光晶体64上的光斑直径为D2，D1/D2的填充因子为0.7-0.9。这样，0.7-0.9下的填充因子能够具有较高的第一皮秒激光的提取效率，同时保证较好的光束质量。
第一激光晶体64设置在第一45°二向色镜63的下游光路上，用于对经过的激光功率放大提供增益介质。当混合后的第一泵浦光以及皮秒种子激光经过第一激光晶体64时，即可对皮秒种子激光进行功率放大，从而得到第四皮秒激光，再将第四皮秒激光射向至第一0°全反镜65。在一些示例中，第一激光晶体64为键合的Nd:YVO4晶体。可以为单端键合晶体(Nd:YVO4—YVO4)或双端键合晶体(YVO4—Nd:YVO4—YVO4)。Nd3+离子的掺杂浓度为0.4％。该第一激光晶体64的输入和输出激光端面均为4mm*4mm的正方形，长度为35mm。其中，掺杂Nd3+离子的Nd:YVO4晶体长度33mm，未掺杂Nd3+离子的YVO4晶体长度为2mm。第一激光晶体64与非键合晶体相比，能够大大减小晶体热效应，利于光束质量的控制。第一激光晶体64需要采用水冷散热，水冷温度范围18-25℃。第一激光晶体64在工作过程中，吸收第一泵浦光会产生热透镜效应，其等效为一个热透镜。
第一0°全反镜65设置在第一激光晶体64的下游光路上，用于将第四皮秒激光返回第一激光晶体64。第一激光晶体64能够对第四皮秒激光再次功率放大，从而得到第一皮秒激光。在一些示例中，第一0°全反镜65对于1064nm激光反射率>99.9％。第一0°全反镜65置于第一激光晶体64形成的热透镜焦点处。
其中，第一45°二向色镜63、第一激光晶体64和第一0°全反镜65组成双通放大结构，对经过两次的皮秒种子激光进行两次放大。第一次放大后得到第四皮秒激光，第二次放大后得到第一皮秒激光，从而实现双通放大，提高增益和提取效率。同时，双通放大结构还能够补偿放大级中产生的正球差，防止光束质量的恶化。双通放大后的第一皮秒激光经过第一半波片62和法拉第旋转器61后，变为竖直线偏振态的第一皮秒激光。接下来，由偏振分光棱镜5反射进入二级固体行波放大器7中进行后续的功率放大。
第一45°二向色镜63接收到第一皮秒激光后，将第一皮秒激光反射至第一半波片62。第一皮秒激光依次经过第一半波片62和法拉第旋转器61后，射向偏振分光棱镜5，在此过程中，第一皮秒激光经过第一半波片和法拉第旋转器时，第一皮秒激光的水平偏振态转变为竖直偏振态。
本实施例中，通过一级固体行波放大器6，采用平均功率可达到100W的第一激光二极管67，可以将20mW、100nJ的皮秒激光功率放大到>16W。
如图3所示，在一些实施例中，二级固体行波放大器7位于偏振分光棱镜5的反射光一侧。二级固体行波放大器7包括沿光路传输方向依次设置的第二激光晶体71、第二45°二向色镜72、第一透镜75和第二半波片76，以及第二泵浦光传播方向上依次设置的第二激光二 极管74和第二透镜组73。
其中，第二激光晶体71设置在偏振分光棱镜5的下游，用于对经过的偏振分光棱镜5反射的第一皮秒激光的功率进行功率放大。在一些示例中，第二激光晶体71可选用与第一激光晶体64相同的结构和材料，第二激光二极管74最大输出平均功率>120W的泵浦光。例如，第二激光晶体71均为长方体结构，材料选用键合的Nd:YVO4晶体，Nd3+离子的掺杂浓度为0.4％。该晶体输入和输出激光端面为4mm*4mm的正方形，长度为35mm。其中，掺杂Nd3+离子的Nd:YVO4晶体长度33mm，未掺杂Nd3+离子的YVO4晶体长度为2mm。
第二45°二向色镜72设置在第二激光晶体71的下游光路上，用于反射经过第二激光晶体71的第一皮秒激光。在一些示例中，第二45°二向色镜72镀膜参数为对于第二泵浦光透过率>98.5％，对于1064nm激光反射率>99％。上述各器件置于空间内相互独立，并且几何中心的高度一致，便于调节和提高效率。
第二激光二极管74设置在第二透镜组73的上游光路上，用于向第二透镜组73射出第二泵浦光。在一些示例中，第二激光二极管74可射出波长888nm的泵浦光，还可以射出878nm或880nm的泵浦光，第二激光二极管74最大输出平均功率>120W。
第二透镜组73设置在第二45°二向色镜72的上游光路上，用于将第二激光二极管74射出的第二泵浦光准直，并聚焦在第二激光晶体71上。第二透镜组73由两片镀膜透镜组成。第二透镜组73的作用与第一透镜组66的作用相同，此处不再赘述。
第二45°二向色镜72还用于将第二透镜组73聚焦过来的第二泵浦光透射至第二激光晶体71。另外，由于第二45°二向色镜72还反射了第一皮秒激光，第一皮秒激光和泵浦光在第二激光晶体71处耦合，产生第二皮秒激光。
第一透镜75设置在第二45°二向色镜72的下游光路上。第一透镜75用于对第二皮秒激光准直，并射向第二半波片76。
第二半波片76设置在第一透镜75的下游光路上。第二半波片76用于将第二皮秒激光的偏振态调整为水平偏振态，并射向三级固体行波放大器8。
本实施例中，一级固体行波放大器6输出的第一皮秒激光，经过偏振分光棱镜5进入二级固体行波放大器7的第二激光晶体71时光斑直径为D3。接下来，第二激光晶体71对第二皮秒激光进行功率放大。第二激光二极管74输出的第二泵浦光，经过第二透镜组73准直及聚焦后，聚焦光斑直径大小为D4，二级固体行波放大器7中填充因子(D3/D4)设计为0.85，从而保证光束质量及激光的提取效率。这样，第二45°二向色镜72将第二皮秒激光射向第一透镜75，再经第一透镜75准直后，进入三级固体行波放大器8。通过二级固体行波放大器7，采用平均功率120W的第二激光二极管74，可以将一级固体行波放大器6输出的16W激光功率放大到50W以上。
如图4所示，在一些实施例中，三级固体行波放大器8包括沿光路传输方向依次设置的第三45°二向色镜81、第一56°偏振片82、第一侧面泵浦模块83、90°旋光器84、4f系统85、第二侧面泵浦模块86、1/4波片87和第二0°全反镜88，以及调整第一56°偏振片82的反射光光路的第二56°偏振片89。
其中，第三45°二向色镜81设置在二级固体行波放大器7的下游光路上。第三45°二向色镜81用于将水平偏振态的第二皮秒激光反射至第一56°偏振片82。
第一56°偏振片82设置在第三45°二向色镜81的下游光路上。第一56°偏振片82用于滤除第二皮秒激光中竖直偏振态激光，并将水平偏振态的第二皮秒激光射向第一侧面泵浦 模块83。
第一侧面泵浦模块83设置在第一56°偏振片82的下游光路上。第一侧面泵浦模块83用于提供第三泵浦光以及第三激光晶体801，第三泵浦光通过第三激光晶体801为第二皮秒激光提供能量，使第二皮秒激光功率放大，形成第五皮秒激光，并射向90°旋光器84。
第二侧面泵浦模块86，设置在第一侧面泵浦模块83的下游光路上。第二侧面泵浦模块86用于提供第四泵浦光以及第四激光晶体802，第四泵浦光通过第四激光晶体802为第五皮秒激光提供能量，使第五皮秒激光功率放大，形成第六皮秒激光。
其中，第一侧面泵浦模块83和第二侧面泵浦模块86均由多个巴条阵列组成，波长为808nm。第一侧面泵浦模块83和第二侧面泵浦模块86中分别对应设置第三激光晶体801和第四激光晶体802，其中，第四激光晶体802与第三激光晶体801均为Nd:YAG晶体。第三激光晶体801放置于第一侧面泵浦模块83，第四激光晶体802放置于第二侧面泵浦模块86中并采用水冷散热，水冷温度范围18-22℃。
90°旋光器84和4f系统85(4f系统，是指有两个焦距为f的透镜，相距为2f，物距为f，像距也为f)，依次设置在第一侧面泵浦模块83的下游光路上，且设置在第一侧面泵浦模块83和第二侧面泵浦模块86之间。90°旋光器和4f系统用于对第一侧面泵浦模块83以及第二侧面泵浦模块86中的第三激光晶体801和第四激光晶体802的热致双折射效应补偿，从而改善光束质量。
1/4波片87设置在第二侧面泵浦模块86的下游光路上。1/4波片87用于调整第六皮秒激光的偏振方向。
第二0°全反镜88设置在1/4波片87的下游光路上，且第二0°全反镜88置于第三激光晶体801形成的热透镜的焦点处。第二0°全反镜88用于反射第六皮秒激光，以使第六皮秒激光沿原光路返回。在一些示例中，第二0°全反镜88镀膜参数对于第四泵浦光透过率>98.5％，对于1064nm激光反射率>99％。
第二侧面泵浦模块86和第一侧面泵浦模块83，还分别用于对第二0°全反镜88返回的第六皮秒激光功率放大，形成第三皮秒激光，射向第一56°偏振片82；
第一56°偏振片82，还用于反射第三皮秒激光，将第三皮秒激光射向第二56°偏振片89；
第二56°偏振片82，用于将第三皮秒激光反射至指定区域。
本实施例中，三级固体行波放大器8接收二级固体行波放大器7输出的水平偏振光的第二皮秒激光，依次经过第三45°二向色镜81和第一56°偏振片82后，再依次经过第一侧面泵浦模块83和第二侧面泵浦模块86。第二皮秒激光经过第一侧面泵浦模块83时对第二皮秒激光放大形成第五皮秒激光。第五皮秒激光接下来进入第二侧面泵浦模块86，经过第二侧面泵浦模块86放大后，形成第六皮秒激光。1/4波片87改变第六皮秒激光偏振方向。接下来，经过第一侧面泵浦模块83和第二侧面泵浦模块86进行单次放大的第六皮秒激光再经过第二0°全反镜88全反射。接下来，第六皮秒激光沿着原光路返回，依次经过第二侧面泵浦模块86和第一侧面泵浦模块83中进行二次放大形成第三皮秒激光，实现对皮秒激光的双通放大。在双通放大过程中，设置在第一侧面泵浦模块83和第二侧面泵浦模块86光路之间的90°旋光器和4f系统，泵浦模块的热致双折射效应补偿，保证光束质量。第三皮秒激光经第一侧面泵浦模块83和第二侧面泵浦模块86的双通放大后，由于1/4波片的存在，使得第三皮秒激光的水平偏振态变为竖直偏振态。最后，第三皮秒激光经由第二56°偏振片89输出。通过三 级固体行波放大器8，采用两个平均功率>200W的第一侧面泵浦模块83和第二侧面泵浦模块86，可以将二级固体行波放大器7输出的50W激光功率放大到百瓦以上，同时控制光束质量因子M2<1.3。
在一些实施例中，高亮度皮秒激光系统还包括45°全反镜4。45°全反镜4设置在空间隔离器3的光路下游，用于将准直后的皮秒种子激光反射向偏振分光棱镜5。利用45°全反镜4能够有效减少高亮度皮秒激光系统的整体长度，提高实际应用适用性
综上所述，本公开中一级固体行波放大器、二级固体行波放大器和三级固体行波放大器，均为行波放大器采用直接端面泵浦技术和侧面泵浦技术相结合，仅用三级放大器可将皮秒1064nm输出激光的亮度提升到5.7*109W·cm-2·Sr以上。不仅保持了端面泵浦下高增益、高提取效率的优势，还由于侧泵具有很高的损伤阈值，能够提高最大激光功率。并且，利用第一激光二极管和第二激光二极管替代传统的多级端面泵浦行波放大器，简化激光器结构，易于集成，且提高激光器运行稳定性和延长使用寿命。
另外，在第一激光二极管和第二激光二极管的下游光路上分别对应设置了第一激光晶体和第二激光晶体，实现了球差补偿。利用第一激光晶体和第二激光晶体所带正球差，将第一0°全反镜和第二0°全反镜对应的置于第一激光晶体和第二激光晶体的焦点处，同时调节填充因子，最终改善光束质量。
一般情况下，在以Nd:YVO4晶体固体放大器作为放大级的激光系统中，采用LD双端面泵浦的固体激光放大器与LD侧面泵浦的固体激光放大器两级固体混合放大的方法仅能够实现较小功率的1064nm激光输出，对应光束质量为1.3，亮度通常<1.47*109W·cm-2·Sr。在本公开中，利用一级固体行波放大器、二级固体行波放大器和三级固体行波放大器共三级固体行波放大器结构能够实现高平均功率的1064nm激光输出。也就是说，在以Nd:YVO4晶体固体放大器作为放大级的激光系统仅能够达到本公开的一部分功率，例如，在以Nd:YVO4晶体固体放大器作为放大级的激光系统最大可实现27.65W平均功率的1064nm激光输出，仅为本公开平均功率的25.6％。本公开能够实现103.24W高平均功率的1064nm激光输出，同时光束质量控制在<1.27，激光亮度达到了5.74*109W·cm-2·Sr。
另外，即使LD双端面泵浦的固体激光放大器与LD侧面泵浦的固体激光放大器两级固体混合的结构，继续增加输出功率的情况下，Nd:YVO4晶体会达到增益饱和，输出功率仍然无法达到本公开的功率，甚至继续增加输出功率还会导致较高的泵浦功率未吸收会转化为热，对晶体及镀膜造成损伤，最终激光输出功率会明显低于所实现的27.65W激光输出。也就是说，本公开使用三级固体行波放大器结构侧重于增加皮秒激光亮度。在仅达到本公开部分功率的情况下，需要增加固体行波放大器结构，才能实现本公开所要达到的皮秒激光亮度。
本公开若要达到103.24W高平均功率的1064nm激光输出，需要对全保偏光纤皮秒种子激光器的光谱宽度参数进行限定。也就是说，全保偏光纤皮秒种子激光器的光谱宽度<0.3nm的情况下，才能够实现本公开的如103.24W高平均功率的1064nm激光输出，并且利于提升后端固体放大器工作效率。
如图5和图6所示，在一些实施例中，三级固体行波放大器8的光路下游还包括倍频模块9。倍频模块9包括沿光路输出方向依次设置的第二透镜91、倍频晶体921、第三透镜93、第四45°二向色镜94；以及设置在第四45°二向色镜94反射光路上的激光吸收器95；
本公开其中，第二透镜91设置在三级固体行波放大器8的下游光路上。第二透镜91用于将第三皮秒激光聚焦到倍频晶体921。
倍频晶体921设置在第二透镜91的下游光路上。倍频晶体921用于对第一次准直后的第三皮秒激光倍频，形成第七皮秒激光。在一些示例中，倍频晶体921外包裹厚度0.05mm的铟箔置于夹具922内保证紧密接触。夹具922材料可选用紫铜，该结构能够提高倍频效果。夹具922与温度控制模块923相连。温度控制模块923可以采用半导体制冷器(Thermo Electric Cooler，TEC)。温度控制模块923主要改变夹具922的温度，从而精确控制倍频晶体921的温度，保证较高的倍频效率。
倍频晶体921可采用Ⅰ类相位匹配三硼酸锂晶体(化学式为LiB3O5，简称LBO)，非临界相位匹配角θ＝90°、φ＝0°。倍频晶体921可为长方体结构，端面为正方形，几何参数为6mm*6mm*16mm。
第三透镜93设置在倍频晶体921的下游光路上。第三透镜93用于对倍频后的第七皮秒激光进行准直。
第四45°二向色镜94设置在第三透镜93的下游光路上。第四45°二向色镜94用于透射准直后倍频的第七皮秒激光，以及将准直后未倍频的第七皮秒激光，反射向激光吸收器。在一些示例中，第四45°二向色镜94用于将1064nm波长的基频光(未倍频的第七皮秒激光)和532nm波长的倍频光(倍频的第七皮秒激光)分开。其中，1064nm基频光被激光吸收器95完全吸收，从而保证器件和人员安全。
在本实施例中，倍频模块9接收到第三皮秒激光。第三皮秒激光经过第二透镜91聚焦到倍频晶体921上，将第三皮秒激光倍频，形成第七皮秒激光。第七皮秒激光经由第三透镜93进行准直。第四45°二向色镜94将倍频过程中残留的波长为1064nm的第七皮秒激光反射到激光吸收器95中，保证单一532nm波长的第七皮秒激光输出，532nm波长对应绿光。倍频模块9采用100W的1064nm基频光，可以实现>50W的绿光输出，倍频效率>50％。本公开中倍频模块9能在百瓦以上的基频光的基础上，可实现超过50W的绿光输出，能够满足太阳能电池材料切割、隐形二维码打标、柔性电路板切割、有机发光二极管(OLED)材料加工及航空航天复合材料打孔等多领域的精密加工需求。
如图7至图10，分别展示了经过本公开申请在一些实施例中的输出激光波长、平均功率及稳定性、光束质量和脉冲宽度测试结果。
实验中全保偏光纤皮秒种子激光器1输出参数为：平均功率20mW，单脉冲能量100nJ，重复频率200kHz，光束质量M2<1.1。
结果表明：(1)采用YOKOGAWA(AQ6373B)光谱分析仪测试激光中心波长为1064.21nm(图7所示)。
(2)Thorlabs(S425C-L探头和PM100D表头)测试1064nm平均功率为103.24W，以0.3s/单次为步进连续记录4小时测试功率稳定性为1.74％rms(图8所示)。
(3)采用Duma Optronics(BeamOn WSR UV-NIR)光束质量测试系统测试1064nm激光的光束质量为Mx 2＝1.27，My 2＝1.25(图9所示)。
(4)采用FEMTOCHROME(FR-103XL)自相关测试得到皮秒脉冲宽度为9.8ps(图10所示)。
综上所述，本公开高亮度皮秒激光系统输出的1064nm皮秒激光亮度达到了5.74*109W·cm-2·Sr。
图11和图12分别展示了本公开申请在一些实施例中，经倍频模块9输出第七皮秒激光的波长和平均功率及稳定性测试结果。
结果表明：(1)采用YOKOGAWA(AQ6373B)光谱分析仪测试第七皮秒激光中心波长为532.23nm(图11所示)。
(2)采用Thorlabs(S425C-L探头和PM100D表头)测试532nm激光平均功率为52.04W，以0.3s/单次为步进连续记录4小时测试功率稳定性为1.89％rms(图12所示)。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本公开。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本公开的精神或范围的情况下，在其它实施例中实现。因此，本公开将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (9)

  1. 一种高亮度皮秒激光系统，包括沿光路方向依次设置的全保偏光纤皮秒种子激光器、光纤准直器、空间隔离器、偏振分光棱镜、一级固体行波放大器、二级固体行波放大器和三级固体行波放大器；
    所述全保偏光纤皮秒种子激光器，用于射出光谱宽度<0.3nm，线偏振态的皮秒种子激光；
    所述光纤准直器，通过尾纤与所述全保偏光纤皮秒种子激光器相连，用于准直所述皮秒种子激光；
    所述空间隔离器，用于隔离后续光路中返回的皮秒激光；
    所述偏振分光棱镜，用于将所述皮秒种子激光透射至所述一级固体行波放大器；
    所述一级固体行波放大器，用于对所述皮秒种子激光的功率第一次放大，形成第一皮秒激光，并将所述第一皮秒激光返回所述偏振分光棱镜；
    所述偏振分光棱镜，还用于将所述第一皮秒激光反射至所述二级固体行波放大器；
    所述二级固体行波放大器，用于对所述第一皮秒激光的功率第二次放大，形成第二皮秒激光；
    所述三级固体行波放大器，用于对所述第二皮秒激光的功率进行第三次放大，形成第三皮秒激光，射向指定区域。
  2. 根据权利要求1所述的高亮度皮秒激光系统，其中，所述一级固体行波放大器包括：沿光路方向依次设置的法拉第旋转器、第一半波片、第一45°二向色镜，第一激光晶体和第一0°全反镜，以及第一泵浦光传播方向上依次设置的第一激光二极管和第一透镜组；
    所述法拉第旋转器，用于将所述皮秒种子激光的偏振态旋转45°，射向所述第一半波片；
    所述第一半波片，为二分之一波片，用于与所述法拉第旋转器配合，将所述皮秒种子激光调整为水平偏振态，并射向所述第一45°二向色镜；
    所述第一激光二极管，用于向所述第一45°二向色镜射出第一泵浦光；
    所述第一透镜组，用于将所述第一泵浦光准直并聚焦在所述第一激光晶体；
    所述第一45°二向色镜，用于将所述皮秒种子激光反射至所述第一激光晶体，以及将所述第一泵浦光透射至所述第一激光晶体；
    所述第一激光晶体，用于对经过的所述皮秒种子激光的功率放大，得到放大后的第四皮秒激光，并将所述第四皮秒激光射向至所述第一0°全反镜；
    所述第一0°全反镜，用于将所述第四皮秒激光返回所述第一激光晶体；
    所述第一激光晶体，用于对返回的所述第四皮秒激光继续功率放大，得到所述第一皮秒激光，并将所述第一皮秒激光射向所述第一45°二向色镜；
    所述第一45°二向色镜，还用于将所述第一皮秒激光，依次沿所述第一半波片和所述法拉第旋转器返回所述偏振分光棱镜，其中，所述第一皮秒激光经过所述第一半波片和所述法拉第旋转器时，所述第一皮秒激光的水平偏振态转变为竖直偏振态。
  3. 根据权利要求2所述的高亮度皮秒激光系统，其中，所述二级固体行波放大器包括沿光路传输方向依次设置的第二激光晶体、第二45°二向色镜、第一透镜和第二半波片，以及第二泵浦光传播方向上依次设置的第二激光二极管和第二透镜组；
    所述第二激光晶体，用于对经过的所述第一皮秒激光的功率放大，并将功率放大后的所述第一皮秒激光射向所述第二45°二向色镜；
    所述第二激光二极管，用于向所述第二透镜组射出所述第二泵浦光；
    所述第二透镜组，用于对所述第二泵浦光准直并聚焦；
    所述第二45°二向色镜，用于反射功率放大后的所述第一皮秒激光，以及透射所述第二泵浦光，形成所述第二皮秒激光射向所述第一透镜；
    所述第一透镜，用于对所述第二皮秒激光准直，并射向所述第二半波片；
    所述第二半波片，用于将所述第二皮秒激光的竖直偏振态，调整为水平偏振态，并射向所述三级固体行波放大器。
  4. 根据权利要求1所述的高亮度皮秒激光系统，其中，所述三级固体行波放大器包括沿光路传输方向依次设置的第三45°二向色镜、第一56°偏振片、第一侧面泵浦模块、90°旋光器、4f系统、第二侧面泵浦模块、1/4波片、第二0°全反镜，以及调整所述第一56°偏振片的反射光光路的第二56°偏振片；
    所述第三45°二向色镜，用于将水平偏振态的所述第二皮秒激光反射至所述第一56°偏振片；
    所述第一56°偏振片，用于滤除所述第二皮秒激光中竖直偏振态激光，并射向所述第一侧面泵浦模块；
    所述第一侧面泵浦模块，用于提供第三泵浦光以及第三激光晶体，所述第三泵浦光通过所述第三激光晶体为所述第二皮秒激光提供能量，使所述第二皮秒激光功率放大，形成第五皮秒激光，并射向所述90°旋光器；
    所述90°旋光器和所述4f系统，用于分别对所述第一侧面泵浦模块和所述第二侧面泵浦模块的热致双折射效应补偿；
    所述第二侧面泵浦模块，用于提供第四泵浦光以及第四激光晶体，所述第四泵浦光通过所述第四激光晶体为所述第五皮秒激光提供能量，使所述第五皮秒激光功率放大，形成第六皮秒激光，并射向所述1/4波片；
    所述1/4波片，用于调整所述第六皮秒激光的偏振方向，并射向所述第二0°全反镜；
    所述第二0°全反镜，用于反射所述第六皮秒激光，使所述第六皮秒激光沿光路返回至所述第二侧面泵浦模块；
    所述第二侧面泵浦模块和所述第一侧面泵浦模块，还分别用于对所述第二0°全反镜返回的所述第六皮秒激光功率放大，形成所述第三皮秒激光，射向所述第一56°偏振片；
    所述第一56°偏振片，还用于反射所述第三皮秒激光，将所述第三皮秒激光射向所述第二56°偏振片；
    所述第二56°偏振片，用于将所述第三皮秒激光反射至指定区域。
  5. 根据权利要求1所述的高亮度皮秒激光系统，其中，所述三级固体行波放大器的 光路下游还包括倍频模块，所述倍频模块包括沿光路输出方向依次设置的第二透镜、倍频晶体、第三透镜、第四45°二向色镜；以及设置在所述第四45°二向色镜反射光路上的激光吸收器；
    所述第二透镜，用于将所述第三皮秒激光聚焦至所述倍频晶体；
    所述倍频晶体，用于对所述第三皮秒激光倍频，形成第七皮秒激光，并射向所述第三透镜；
    所述第三透镜，用于对所述第七皮秒激光准直，并射向所述第四45°二向色镜；
    所述第四45°二向色镜，用于透射倍频的所述第七皮秒激光，射向指定区域，以及将未倍频的所述第七皮秒激光，反射向所述激光吸收器；
    所述激光吸收器，用于吸收未倍频的所述第七皮秒激光。
  6. 根据权利要求3所述的高亮度皮秒激光系统，其中，所述第一激光晶体和所述第二激光晶体均为长方体结构，材料均选用键合的Nd:YVO4晶体，所述第一激光晶体和所述第二激光晶体的输入和输出激光端面均为4mm*4mm的正方形，长度为35mm。
  7. 根据权利要求5所述的高亮度皮秒激光系统，其中，所述倍频晶体采用Ⅰ类相位匹配三硼酸锂晶体，非临界相位匹配角θ＝90°、倍频晶体为长方体结构，端面为正方形，几何参数为6mm*6mm*16mm。
  8. 根据权利要求1-7中任一项所述的高亮度皮秒激光系统，其中，还包括：
    45°全反镜，设置在所述空间隔离器的光路下游，用于将准直后的所述皮秒种子激光反射向所述偏振分光棱镜。
  9. 根据权利要求8所述的高亮度皮秒激光系统，其中，所述全保偏光纤皮秒种子激光器用于产生1064nm波长的皮秒脉冲激光，脉冲宽度<10ps，最大单脉冲能量>100nJ，重复频率调整范围1Hz-20MHz。
PCT/CN2023/078203 2022-03-14 2023-02-24 高亮度皮秒激光系统 WO2023174034A1 (zh)

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