A high-contrast petawatt laser device and a control method thereof

Abstract

The application discloses a high-contrast pico-second laser device and a control method thereof. The first cavity mirror of an oscillator is installed on a mirror frame through a first piezoelectric ceramic, and the second cavity mirror is installed on the mirror frame through a second piezoelectric ceramic. For long-time locking of the laser cavity length, the long-time cavity length drift of the laser cavity length will exceed the range of the piezoelectric ceramic. The second piezoelectric ceramic can high-precision synchronize the time of the pump pulse and the seed pulse in the crystal of the parametric amplifier. The stepping motor can solve the long-time drift problem of the pump pulse and the seed pulse. When the expansion and contraction amount of the second piezoelectric ceramic will exceed the limit of the second piezoelectric ceramic, a large delay is introduced through the movement of the stepping motor, so that the voltage on the second piezoelectric ceramic returns to the middle value. The long-time cavity length drift of the regenerative cavity is compensated by using the electric translation stage based on the stepping motor, and the repetition frequency of the regenerative amplifier can be locked to the signal frequency after the frequency division of the oscillator repetition frequency electrical signal for a long time.

Description

Technical Field

[0001] This invention relates to the field of lasers, and more specifically to a high-contrast petawatt laser device and its control method. Background Technology

[0002] With the development of laser technology, the pursuit of higher peak power lasers has always been one of the goals of laser development.

[0003] To obtain high peak power lasers, chirped pulse amplification is currently the mainstream technique. Ti:sapphire crystals, due to their ultra-wide gain bandwidth (tens of fs pulse widths and hundreds of J energies), are the primary gain medium for mesa petawatt lasers.

[0004] With the increase in peak power of laser pulses, new requirements are also placed on laser contrast. For PW(10 15 W) Laser, laser contrast ratio is typically required to be 10. 12 That concludes the discussion. To achieve such contrast, Optical Parametric Chirped Amplification (OPCPA) is one of the mainstream technologies currently used. OPCPA amplification can improve laser contrast.

[0005] The structure of existing high-contrast OPCPA lasers is as follows: Figure 1 As shown, the oscillator outputs a broadband laser, which can be obtained directly from the oscillator or by broadening it using nonlinear effects. The broadband laser consists of two parts: a broadband laser with a center wavelength of λ1 and two narrowband lasers with a center wavelength of λ2. The first narrowband laser with a center wavelength of λ1 serves as a seed for a parametric amplifier, which amplifies the broadband laser to obtain a high-contrast seed source. The second narrowband laser with a center wavelength of λ2 is input to the amplifier to obtain a high-energy laser. This laser can be frequency-doubled as needed and then pumped by a delay unit.

[0006] However, for OPCPA, which utilizes the instantaneous effect of parametric conversion, the timing synchronization requirements for seed and pump are extremely high. For example, if the pump laser is a nanosecond (ns) laser, the timing synchronization of seed and pump needs to be on the order of nanoseconds; if the pump laser is a ps (ps) laser, the timing synchronization of seed and pump needs to be on the order of ps; and if the pump laser is an fs (fs) laser, the timing synchronization of seed and pump needs to be on the order of fs.

[0007] Due to air disturbances, mechanical vibrations, and other factors, the time interval ΔT between seed pulses output by the oscillator is not fixed and exhibits jitter. For OPCPA pumped by ps and fs lasers, this means that if the pump and seed pulses do not originate from the same pulse, there will be time jitter in the parametric amplifier. To solve this problem, current OPCPA primarily employs a passive synchronization method, where the pump and seed pulses originate from the same emitted pulse, such as... Figure 2 As shown, the seed pulses output by the oscillator are numbered 1, 2, 3, 4... in sequence, and the pump pulse and seed pulse acting in the parametric amplifier crystal are both the second pulse.

[0008] However, higher output energy from the OPCPA front end is more beneficial for subsequent amplification to obtain high-contrast laser. To achieve higher OPCPA output, the pump laser needs to have higher energy. This requires stable and high-gain regeneration techniques combined with multi-pass technology, which inevitably increases the pump pulse optical path. In this case, a passive synchronization method is used, where both the pump and seed originate from the same pulse. This places extremely high demands on the delay of the seed light. The most convenient way to solve this synchronization problem is to have the pump and seed originate from different pulses; however, this introduces the problem of jitter due to different laser pulses. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention proposes a high-contrast petawatt laser device and its control method.

[0010] One object of the present invention is to provide a high-contrast petawatt laser device.

[0011] The high-contrast petawatt laser device of the present invention includes: a seed source, a magnifier / stretcher, an amplifier, and a compressor; wherein,

[0012] The seed source includes an oscillator, a regenerative amplifier, a first stretcher, a second stretcher, a first synchronizer, a second synchronizer, a first photodetector, a second photodetector, a reference source, a delay unit, and a parametric amplifier. The oscillator outputs a femtosecond laser with a center wavelength of λ1. The femtosecond laser output from the oscillator is split into two beams, a first laser beam and a second laser beam, with a beam splitting power ratio greater than 1:1. The output characteristics of the first laser beam are the same as those of the oscillator, with a center wavelength of λ1. The first laser beam enters the first stretcher for stretching. A picosecond pulse is obtained as a seed pulse. A second laser beam passes through a filter to obtain a laser with a center wavelength of λ2. The second laser beam is then broadened to a picosecond wavelength by a second stretcher and used as a seed pulse for a regenerative amplifier. After being amplified by the regenerative amplifier, it becomes the pump pulse for a parametric amplifier and is then input to the parametric amplifier after passing through a delay circuit. The pulse width of the first laser beam after being broadened by the first stretcher is τ1, and the pulse width of the second laser beam after being broadened by the second stretcher is τ2, where τ1≤τ2≤2τ1. The fact that the pump pulse of the parametric amplifier is larger than the seed pulse is beneficial for the parametric amplifier to achieve high conversion efficiency.

[0013] The oscillator includes a first cavity mirror, a first gain medium, and an output mirror. The first cavity mirror is mounted on a mirror frame via a first piezoelectric ceramic. Changing the voltage applied to the first piezoelectric ceramic alters its expansion and contraction, thereby changing the oscillator cavity length L1, which is the distance between the first cavity mirror and the output mirror. A portion of the laser output from the oscillator is transmitted to a first photodetector. The first photodetector receives the oscillator repetition frequency, obtains the oscillator repetition frequency electrical signal, and sends it to a first synchronizer. A reference signal from a reference source is also output to the first synchronizer. The function of the first synchronizer is to lock the input repetition frequency to the reference source. The first synchronizer outputs a feedback signal to the first piezoelectric ceramic connected to the first cavity mirror, controlling the expansion and contraction of the first piezoelectric ceramic to control the oscillator cavity length L1, thus changing the oscillator repetition frequency. The first synchronizer achieves oscillator repetition frequency locking.

[0014] The regenerative amplifier includes a second cavity mirror, a third cavity mirror, a second gain medium, a Glan prism, and a Pockels cell. The second cavity mirror is mounted on a frame via a second piezoelectric ceramic. Changing the voltage applied to the second piezoelectric ceramic alters its expansion and contraction, thereby changing the cavity length L2 of the regenerative amplifier, which is the distance between the second and third cavity mirrors. A portion of the laser output from the regenerative amplifier is input to a second photodetector. The second photodetector receives the repetition frequency of the regenerative amplifier, obtains the repetition frequency electrical signal, and outputs it to a second synchronizer. Simultaneously, the oscillator repetition frequency electrical signal obtained by the first photodetector is synchronously transmitted to the second synchronizer. The second synchronizer first divides the oscillator repetition frequency received by the first photodetector to the same repetition frequency as the second photodetector. Furthermore, the second synchronizer locks the regenerative amplifier repetition frequency received by the second photodetector to the frequency obtained by dividing the oscillator repetition frequency received by the first photodetector.

[0015] The laser output from the regenerative amplifier is delayed by a timer and then applied to the parametric amplifier. The time delay provided by the timer is equal to the period of the laser pulse output from the oscillator. The pump pulse output from the regenerative amplifier and the seed pulse output from the oscillator act together on the crystal of the parametric amplifier. At this time, the pump pulse and the seed pulse may not originate from the same pulse. The timer includes first to fourth lenses, an electric translation stage, and a stepper motor. The pump pulse output from the regenerative amplifier is perpendicularly reflected by the first lens into the second lens. The second lens perpendicularly reflects the incident light into the third lens. The third lens perpendicularly reflects the incident light into the fourth lens. The light reflected out by the first lens is antiparallel to the light reflected out by the third lens. The fourth lens perpendicularly reflects the incident light. The second and third lenses are mounted on the electric translation stage, which is connected to the stepper motor, which drives the electric translation stage to move.

[0016] The second synchronizer provides a voltage signal based on the frequency difference between the repetition frequency of the regenerative amplifier received by the second photodetector and the frequency of the oscillator received by the first photodetector after frequency division, and feeds it back to the regenerative amplifier. Simultaneously, the second synchronizer outputs a signal to the stepper motor of the delay unit based on the magnitude of the voltage signal fed back to the regenerative amplifier, controlling the stepper motor to adjust the movement of the electric translation stage, thereby changing the delay time provided by the delay unit. A voltage V is applied to the second piezoelectric ceramic, 0 < V < V0, where V0 is the maximum voltage that can be applied to the second piezoelectric ceramic. When the applied voltage to the second piezoelectric ceramic is V0, the piezoelectric ceramic elongates by l0, where l0 is the elongation of the second piezoelectric ceramic when the maximum voltage is applied. The pump pulse is amplified n times in the regenerative amplifier, where n is a natural number ≥ 2. When the second piezoelectric ceramic... When the voltage on the ceramic is less than the minimum delay voltage V1, V1 = C1 × V0, where C1 is the first coefficient and 0 < C1 < 0.3. At this time, the stepper motor moves by n × l0 / 4, and the direction of the stepper motor movement is to increase the delay time, that is, the second and third lenses move away from the first and fourth lenses. When the voltage on the second piezoelectric ceramic is greater than the maximum delay voltage V2, V2 = C2 × V0, where C2 is the second coefficient and 0.7 < C2 < 1. At this time, the stepper motor moves by n × l0 / 4, and the direction of the stepper motor movement is to decrease the delay time, that is, the second and third lenses move closer to the first and fourth lenses. This allows the repetition frequency of the regenerative amplifier to be locked to the frequency after the oscillator repetition frequency is divided for a long time.

[0017] The femtosecond laser output from the oscillator has a full width at half maximum (FWHM) greater than 50 nm and a spectral density of 1 / e. 2 The wavelength bandwidth is greater than 200nm; the full width at half maximum (FWHM) of the first laser beam output from the oscillator is greater than 50nm; the second laser beam output from the oscillator, after passing through a filter, obtains a laser with a FWHM less than 10nm. The seed of the regenerative amplifier is then processed by the regenerative amplifier to obtain a wavelength greater than 10nm. 6 Gain: High gain, high beam quality, and high stability are achieved using a regenerative amplifier; the seed of the regenerative amplifier is amplified less than 100 times in the regenerative amplifier.

[0018] The synchronizer works by inputting two electrical signals: a reference signal and the repetition frequency information of the locked laser cavity length. The difference in repetition rates between the two signals is compared to obtain a difference signal, which is fed back to the first piezoelectric ceramic. Changing the expansion or contraction of the piezoelectric ceramic alters the laser cavity length, thereby adjusting the output repetition frequency until the laser output frequency matches the reference source signal input to the synchronizer. The reference source signal can be a standard clock signal or a freely operating laser repetition frequency. For the former, the laser cavity length is locked to a fixed value. For the latter, the locked laser cavity length changes with the laser cavity length used as the reference source. For specific repetition frequency locking methods, refer to femtosecond optical frequency comb: principle, operation, and applications, Jun Ye and Steven T. Cundiff, first edition, pp. 38-48.

[0019] For a laser with an oscillator output of 80MHz and a pulse period of 12.5ns, the delay device provides a maximum delay time of 12.5ns.

[0020] Variations in the laser's ambient temperature and vibrations cause changes in the laser cavity length. These changes can be categorized into short-term high-frequency vibrations and long-term cavity length drift. While piezoelectric ceramics offer the advantage of rapid response, they also have the disadvantage of a small range. For long-term locking of the laser cavity length, the long-term cavity length drift will exceed the piezoelectric ceramic's range. Therefore, this invention introduces an electric translation stage based on a stepper motor to compensate for the long-term cavity length drift of the regenerated cavity.

[0021] Another objective of this invention is to provide a control method for a high-contrast petawatt laser device.

[0022] The control method for the high-contrast petawatt laser device of the present invention includes the following steps:

[0023] 1) The oscillator outputs a femtosecond laser with a center wavelength of λ1. The laser output from the oscillator is split into two beams, a first laser and a second laser. The beam splitting power ratio of the first laser and the second laser output from the oscillator is greater than 1:1. The output characteristics of the first laser are the same as those of the oscillator, with a center wavelength of λ1. The first laser enters the first stretcher to obtain a picosecond pulse, which serves as the seed pulse. The second laser output from the oscillator passes through a filter to obtain a laser with a center wavelength of λ2. The second laser is then stretched to a picosecond wavelength by the second stretcher and serves as the seed pulse for the regenerative amplifier. After being amplified by the regenerative amplifier, it serves as the pump pulse for the parametric amplifier and is then input to the parametric amplifier after passing through a delay unit. The pulse width of the first laser after being stretched by the first stretcher is τ1, and the pulse width of the second laser after being stretched by the second stretcher is τ2, where τ1≤τ2≤2τ1. The pump pulse of the parametric amplifier being larger than the seed pulse is beneficial for the parametric amplifier to achieve high conversion efficiency. The seed pulse, after being stretched by the regenerative amplifier, obtains a pulse width greater than 10... 6 Gain, using a regenerative amplifier to obtain high gain, high beam quality and high stability;

[0024] 2) The first cavity mirror of the oscillator is mounted on a mirror frame via a first piezoelectric ceramic. By changing the voltage applied to the first piezoelectric ceramic, the expansion and contraction of the first piezoelectric ceramic is changed, thereby changing the cavity length L1 of the oscillator. The cavity length of the oscillator is the distance between the first cavity mirror and the output mirror. A portion of the laser output from the oscillator is transmitted to the first photodetector. The first photodetector receives the oscillator repetition frequency, obtains the oscillator repetition frequency electrical signal, and sends it to the first synchronizer. The reference signal emitted by the reference source is also output to the first synchronizer. The function of the first synchronizer is to lock the input repetition frequency to the reference source. The first synchronizer outputs a feedback signal to the first piezoelectric ceramic connected to the first cavity mirror, controlling the expansion and contraction of the first piezoelectric ceramic to control the cavity length L1 of the oscillator, thereby realizing the change of the laser repetition frequency. The oscillator repetition frequency is locked through the first synchronizer.

[0025] 3) The second cavity mirror is mounted on the mirror frame via the second piezoelectric ceramic. The expansion and contraction of the second piezoelectric ceramic are changed by altering the voltage applied to it, thereby changing the cavity length L2 of the regenerative amplifier. The cavity length of the regenerative amplifier is the distance between the second and third cavity mirrors. A portion of the laser output from the regenerative amplifier is input to the second photodetector. The second photodetector receives the repetition frequency of the regenerative amplifier, obtains the repetition frequency electrical signal, and outputs it to the second synchronizer. Simultaneously, the oscillator repetition frequency electrical signal obtained by the first photodetector is synchronously transmitted to the second synchronizer. The second synchronizer first divides the oscillator repetition frequency received by the first photodetector to the same repetition frequency as the second photodetector. Furthermore, the second synchronizer locks the regenerative amplifier repetition frequency received by the second photodetector to the frequency after the oscillator repetition frequency received by the first photodetector is divided.

[0026] 4) The laser output from the regenerative amplifier is applied to the parametric amplifier after passing through the delay unit. At this time, the time delay provided by the delay unit is the period of the laser pulse output from the oscillator. The pump pulse output from the regenerative amplifier and the seed pulse output from the oscillator act together on the crystal of the parametric amplifier. At this time, the pump pulse and the seed pulse may not come from the same pulse. The pump pulse output from the regenerative amplifier is perpendicularly reflected by the first lens into the second lens. The second lens perpendicularly reflects the incident light into the third lens. The third lens perpendicularly reflects the incident light into the fourth lens. The light reflected out by the first lens is parallel to the light reflected out by the third lens. The fourth lens perpendicularly reflects the incident light. The second and third lenses of the delay unit are mounted on an electric translation stage. The electric translation stage is connected to a stepper motor and driven to move by the stepper motor.

[0027] 5) The second synchronizer provides a voltage signal based on the frequency difference between the repetition frequency of the regenerative amplifier received by the second photodetector and the frequency of the oscillator received by the first photodetector after frequency division, and feeds it back to the regenerative amplifier. Simultaneously, the second synchronizer outputs a signal to the stepper motor of the delay unit based on the magnitude of the voltage signal fed back to the regenerative amplifier, controlling the stepper motor to adjust the movement of the electric translation stage, thereby changing the delay time provided by the delay unit. A voltage V is applied to the second piezoelectric ceramic, 0 < V < V0, where V0 is the maximum voltage that can be applied to the second piezoelectric ceramic. When the applied voltage to the second piezoelectric ceramic is V0, the piezoelectric ceramic elongates by l0. The pump pulse is amplified n times in the regenerative amplifier, where n is a natural number ≥ 2. When the voltage on the second piezoelectric ceramic is less than the minimum... When the delay voltage is V1, V1 = C1 × V0, where C1 is the first coefficient, 0 < C1 < 0.3. At this time, the stepper motor moves by n × l0 / 4, and the direction of the stepper motor movement is to increase the delay time, that is, the second and third lenses move away from the first and fourth lenses. When the voltage on the second piezoelectric ceramic is greater than the maximum delay voltage V2, V2 = C2 × V0, where C2 is the second coefficient, 0.7 < C2 < 1. At this time, the stepper motor moves by n × l0 / 4, and the direction of the stepper motor movement is to decrease the delay time, that is, the second and third lenses move closer to the first and fourth lenses. This allows the repetition frequency of the regenerative amplifier to be locked to the frequency after the oscillator repetition frequency is divided for a long time.

[0028] Advantages of this invention:

[0029] This invention mounts the first cavity mirror of the oscillator onto a frame via a first piezoelectric ceramic, and the second cavity mirror onto the frame via a second piezoelectric ceramic. Piezoelectric ceramics offer the advantage of fast response but also have the disadvantage of a small range. For long-term locking of the laser cavity length, the long-term cavity length drift will exceed the range of the piezoelectric ceramic. The second piezoelectric ceramic can precisely synchronize the pump pulse and seed pulse timing in the parametric amplifier crystal. A stepper motor can solve the problem of long-term drift of the pump pulse and seed pulse. When the expansion or contraction of the second piezoelectric ceramic exceeds its limit, a large delay is introduced through the movement of the stepper motor, allowing the voltage on the second piezoelectric ceramic to return to the intermediate value. A stepper motor-based electric translation stage is used to compensate for the long-term cavity length drift of the regenerative cavity, enabling the regenerative amplifier repetition frequency to be locked to the signal frequency after frequency division of the oscillator repetition frequency for a long time. Since the laser output from the oscillator and the laser output from the amplifier are strictly synchronized, it is not necessary for the same pulse output from the oscillator to enter the subsequent OPCPA, which reduces the synchronization requirements of the entire system and facilitates system integration. Attached Figure Description

[0030] Figure 1 This is a block diagram of the structure of an OPCPA laser in the prior art;

[0031] Figure 2 A schematic diagram of the pulse timing for OPCPA using a passive synchronization method in the prior art;

[0032] Figure 3 This is a structural block diagram of the seed source of an embodiment of the high-contrast petawatt laser device of the present invention;

[0033] Figure 4 This is a structural block diagram of the oscillator of the seed source in one embodiment of the high-contrast petawatt laser device of the present invention.

[0034] Figure 5 This is a structural block diagram of the regenerative amplifier of the seed source in one embodiment of the high-contrast petawatt laser device of the present invention.

[0035] Figure 6 This is a schematic diagram of the pulse timing of one embodiment of the high-contrast petawatt laser device of the present invention. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0037] like Figure 3 As shown, the high-contrast petawatt laser device in this embodiment includes: a seed source, a magnifier / scaler, an amplifier, and a compressor; wherein,

[0038] The seed source includes an oscillator, a regenerative amplifier, a first stretcher, a second stretcher, a first synchronizer, a second synchronizer, a first photodetector, a second photodetector, a reference source, and a parametric amplifier; among them, the oscillator is capable of outputting femtosecond laser light. The femtosecond laser light output by the oscillator has a center wavelength λ1, a full width at half maximum (FWHM) greater than 50 nm, and a spectral density of 1 / e. 2 The wavelength bandwidth is greater than 200nm. The laser output from the oscillator is split into two beams, the first and second, with a beam splitting power ratio greater than 1:1. The output characteristics of the first laser beam are the same as those of the oscillator: center wavelength λ1, full width at half maximum (FWHM) greater than 50nm. The first laser beam enters the first stretcher to broaden its pulse width to obtain a picosecond pulse, which serves as the seed pulse. The second laser beam passes through a filter to obtain a laser with a center wavelength λ2 and a FWHM less than 10nm. After being broadened to picoseconds by the second stretcher, the second laser beam serves as the seed pulse for the regenerative amplifier. After amplification by the regenerative amplifier, it becomes the pump pulse for the parametric amplifier, which is then input to the parametric amplifier after a delay. The pulse width of the first laser beam after being broadened by the first stretcher is τ1, and the pulse width of the second laser beam after being broadened by the second stretcher is τ2, where τ1≤τ2≤2τ1. The pump pulse of the parametric amplifier being larger than the seed pulse is beneficial for achieving high conversion efficiency in the parametric amplifier. The seed pulse, after being broadened by the regenerative amplifier, obtains a pulse width greater than 10nm. 6 Gain is achieved by utilizing a regenerative amplifier to obtain high gain, high beam quality, and high stability; the seed source is amplified less than 100 times in the regenerative amplifier.

[0039] like Figure 4 As shown, the oscillator includes a first cavity mirror, a first gain medium, and an output mirror. The first cavity mirror is mounted on a mirror frame via a first piezoelectric ceramic. Changing the voltage applied to the first piezoelectric ceramic alters its expansion and contraction, thereby changing the oscillator cavity length L1, which is the distance between the first cavity mirror and the output mirror. A portion of the laser output from the oscillator is received by a first photodetector to obtain the oscillator repetition frequency electrical signal, which is then sent to a first synchronizer. A reference signal from a reference source is also output to the first synchronizer. The first synchronizer locks the input repetition frequency to the reference source. The first synchronizer outputs a feedback signal to the first piezoelectric ceramic connected to the first cavity mirror, controlling the expansion and contraction of the first piezoelectric ceramic to control the oscillator cavity length L1, thus changing the laser repetition frequency. The first synchronizer achieves oscillator repetition frequency locking.

[0040] Variations in the laser's ambient temperature and vibrations cause changes in the laser cavity length. These changes can be categorized into short-term high-frequency vibrations and long-term cavity length drift. While piezoelectric ceramics offer the advantage of rapid response, they also have the disadvantage of a small range. For long-term locking of the laser cavity length, the long-term cavity length drift will exceed the piezoelectric ceramic's range. Therefore, this invention introduces an electric translation stage based on a stepper motor to compensate for the long-term cavity length drift of the regenerated cavity.

[0041] like Figure 5 As shown, the regenerative amplifier includes a second cavity mirror, a third cavity mirror, a second gain medium, a Glan prism, and a Pockels cell. The second cavity mirror is mounted on a frame via a second piezoelectric ceramic. Changing the voltage applied to the second piezoelectric ceramic alters its expansion and contraction, thereby changing the cavity length L2 of the regenerative amplifier, which is the distance between the second and third cavity mirrors. A portion of the laser output from the regenerative amplifier is received by a second photodetector, obtaining the regenerative amplifier repetition frequency electrical signal, which is then output to a second synchronizer. Simultaneously, the oscillator repetition frequency electrical signal received by the first photodetector is synchronously transmitted to the second synchronizer. The second synchronizer first divides the oscillator repetition frequency received by the first photodetector to the same repetition frequency as the second photodetector. Furthermore, the second synchronizer locks the regenerative amplifier repetition frequency received by the second photodetector to the frequency obtained by dividing the oscillator repetition frequency received by the first photodetector.

[0042] The laser output from the regenerative amplifier is then applied to the parametric amplifier after passing through a delay circuit. The delay provided by the delay circuit is equal to the period of the laser pulses output by the oscillator. For example, if the oscillator outputs 80MHz and the pulse period is 12.5ns, then the maximum delay time provided by the delay circuit is 12.5ns. The seed pulses output by the oscillator are sequentially 1, 2, 3, 4… Figure 6 As shown, the second pump pulse output by the regenerative amplifier and the first seed pulse output by the oscillator act together on the parametric amplifier crystal. At this time, the pump pulse and the seed pulse do not come from the same pulse. The delay unit includes first to fourth lenses, an electric translation stage, and a stepper motor. The pump pulse output by the regenerative amplifier is perpendicularly reflected by the first lens into the second lens. The second lens perpendicularly reflects the incident light into the third lens. The third lens perpendicularly reflects the incident light to the fourth lens. The light reflected out by the first lens is parallel to the light reflected out by the third lens. The fourth lens perpendicularly reflects the incident light. The second and third lenses are mounted on the electric translation stage, which is connected to the stepper motor. The stepper motor drives the electric translation stage to move.

[0043] The second synchronizer provides a voltage signal based on the frequency difference between the repetition frequency of the regenerative amplifier received by the second photodetector and the frequency of the oscillator received by the first photodetector after frequency division. This signal is fed back to the regenerative amplifier. The regenerative amplifier, based on the magnitude of the feedback voltage signal, outputs a signal to the stepper motor of the delay unit, controlling the stepper motor to adjust the movement of the electric translation stage, thereby changing the delay time provided by the delay unit. A voltage V is applied to the second piezoelectric ceramic, 0 < V < V0, where V0 is the maximum voltage that can be applied to the second piezoelectric ceramic. When the applied voltage is V0, the piezoelectric ceramic elongates by l0. The pump pulse is amplified n times in the regenerative amplifier, where n is a natural number ≥ 2. When the second piezoelectric ceramic... When the voltage on the piezoelectric ceramic is less than the minimum delay voltage V1, V1 = 0.2 × V0. At this time, the stepper motor moves by n × l0 / 4, and the direction of the stepper motor movement is to increase the delay time, that is, the second and third lenses move away from the first and fourth lenses. When the voltage on the second piezoelectric ceramic is greater than the maximum delay voltage V2, V2 = 0.8 × V0, the stepper motor moves by n × l0 / 4, and the direction of the stepper motor movement is to decrease the delay time, that is, the second and third lenses move closer to the first and fourth lenses. This allows the repetition frequency of the regenerative amplifier to be locked to the frequency after the oscillator repetition frequency is divided for a long time.

[0044] The second piezoelectric ceramic can precisely synchronize the timing of the pump pulse and seed pulse in the parametric amplifier crystal, while the stepper motor can solve the problem of long-term drift of the pump pulse and seed pulse. When the expansion and contraction of the second piezoelectric ceramic exceeds its own limit, a large delay is introduced by the movement of the stepper motor, so that the voltage on the second piezoelectric ceramic returns to the intermediate value.

[0045] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A high-contrast petawatt laser device, characterized in that, The high-contrast picosecond laser device comprises a seed source, an amplification stretcher, an amplifier and a compressor; wherein The seed source comprises an oscillator, a regenerative amplifier, a first stretcher, a second stretcher, a first synchronizer, a second synchronizer, a first photodetector, a second photodetector, a reference source, a time delay device and a parametric amplifier; wherein the oscillator outputs femtosecond laser with a center wavelength λ1; the femtosecond laser output by the oscillator is divided into two beams, which are a first beam and a second beam respectively, and the power ratio of the first beam to the second beam is greater than 1:1; wherein the output characteristics of the first beam are the same as those of the oscillator, the center wavelength λ1, the first beam enters the first stretcher for stretching to obtain picosecond pulses as seed pulses; the second beam passes through a filter to obtain laser with a center wavelength λ2, and after being stretched to picoseconds by the second stretcher, the second beam serves as the seed of the regenerative amplifier, enters the regenerative amplifier after amplification, serves as the pump pulse of the parametric amplifier, and is input to the parametric amplifier through the time delay device; the pulse width of the first beam after being stretched by the first stretcher is τ1, and the pulse width of the second beam after being stretched by the second stretcher is τ2, τ1≤τ2≤2τ1; the width of the pump pulse of the parametric amplifier is greater than that of the seed pulse, which is conducive to obtaining high conversion efficiency of the parametric amplifier; The oscillator comprises a first cavity mirror, a first gain medium and an output mirror; wherein the first cavity mirror of the oscillator is mounted on a mirror frame through a first piezoelectric ceramic, the cavity length L1 of the oscillator is changed by changing the expansion and contraction amount of the first piezoelectric ceramic by changing the voltage applied to the first piezoelectric ceramic, and the cavity length of the oscillator is the distance between the first cavity mirror and the output mirror; a part of the laser output by the oscillator is transmitted to the first photodetector, the first photodetector receives the repetition frequency of the oscillator, obtains an oscillator repetition frequency electrical signal and delivers it to the first synchronizer, and the reference signal emitted by the reference source is also output to the first synchronizer; the function of the first synchronizer is to lock the input repetition frequency to the reference source; the first synchronizer outputs a feedback signal to the first piezoelectric ceramic connected to the first cavity mirror, controls the expansion and contraction amount of the first piezoelectric ceramic, thereby controls the cavity length L1 of the oscillator, thereby realizes the change of the repetition frequency of the oscillator, and realizes the repetition frequency locking of the oscillator through the first synchronizer; The regenerative amplifier comprises a second cavity mirror, a third cavity mirror, a second gain medium, a Gires-Tournois etalon and a Pockels cell; the second cavity mirror is installed on a mirror frame through a second piezoelectric ceramic, the extension and contraction amount of the second piezoelectric ceramic is changed by changing the voltage applied to the second piezoelectric ceramic, thereby changing the cavity length L2 of the regenerative amplifier, the cavity length L2 of the regenerative amplifier is the distance between the second cavity mirror and the third cavity mirror; a part of the output laser of the regenerative amplifier is input to the second photodetector, the second photodetector receives the repetition frequency of the regenerative amplifier, obtains the repetition frequency electrical signal of the regenerative amplifier and outputs to the second synchronizer, at the same time, the repetition frequency electrical signal of the oscillator obtained by the first photodetector is synchronously transmitted to the second synchronizer; the second synchronizer first divides the repetition frequency of the oscillator received by the first photodetector to the same repetition frequency as the second photodetector, and then the second synchronizer locks the repetition frequency of the regenerative amplifier received by the second photodetector to the frequency after the repetition frequency of the oscillator received by the first photodetector is divided; The output laser of the regenerative amplifier acts on the parametric amplifier after passing through the delay device, at this time the time delay provided by the delay device is the period of the output laser pulse of the oscillator; the pump pulse output by the regenerative amplifier and the seed pulse output by the oscillator act on the parametric amplifier crystal at the same time, at this time the pump pulse and the seed pulse can not come from the same pulse; the delay device comprises first to fourth mirrors, a motorized translation stage and a stepper motor, the pump pulse output by the regenerative amplifier vertically reflects through the first mirror and enters the second mirror, the second mirror vertically reflects the incident light into the third mirror, the third mirror vertically reflects the incident light into the fourth mirror, the light reflected by the first mirror is anti-parallel to the light reflected by the third mirror, and the fourth mirror vertically reflects the incident light; the second mirror and the third mirror are installed on the motorized translation stage, the motorized translation stage is connected to the stepper motor, and the motorized translation stage is driven to move by the stepper motor; The second synchronizer provides a voltage signal according to the difference between the frequency of the regenerative amplifier repetition frequency received by the second photodetector and the frequency of the oscillator repetition frequency received by the first photodetector after frequency division, and feeds back to the regenerative amplifier. At the same time, the second synchronizer outputs a signal to the stepper motor of the delay line according to the size of the voltage signal fed back to the regenerative amplifier, controls the stepper motor to adjust the movement of the motorized translation stage, so as to change the delay time provided by the delay line; the voltage applied to the second piezoelectric ceramic is V, 0 l 0, l 0 is the elongation of the second piezoelectric ceramic when the maximum voltage is applied; the pump pulse is amplified n times in the regenerative amplifier, n is a natural number ≥2; when the voltage on the second piezoelectric ceramic is less than the minimum delay voltage V1, V1=C1×V0, C1 is the first coefficient, at this time, the stepper motor is moved, and the moving amount of the stepper motor is n× l 0 / 4, and the moving direction of the stepper motor is to increase the delay time, that is, the direction of the second lens and the third lens moving away from the first lens and the fourth lens; when the voltage on the second piezoelectric ceramic is greater than the maximum delay voltage V2, V2=C2×V0, C2 is the second coefficient, at this time, the stepper motor is moved, and the moving amount of the stepper motor is n× l 0 / 4, and the moving direction of the stepper motor is to decrease the delay time, that is, the direction of the second lens and the third lens moving close to the first lens and the fourth lens, so as to realize that the regenerative amplifier repetition frequency can be locked to the frequency after the oscillator repetition frequency is divided for a long time.

2. The high-contrast petai laser device of claim 1, wherein, The femtosecond laser output by the oscillator has a full width at half maximum greater than 50 nm, and a spectrum 1 / e 2 at a wavelength bandwidth greater than 200 nm.

3. The high-contrast petai laser device of claim 1, wherein, The full width at half maximum of the first beam of laser output by the oscillator is greater than 50 nm.

4. The high-contrast picosecond laser device of claim 1, wherein, The second beam of laser output by the oscillator passes through the optical filter to obtain laser with a full width at half maximum less than 10 nm.

5. The high-contrast picosecond laser device of claim 1, wherein, The seed of the regenerative amplifier is amplified less than 100 times in the regenerative amplifier.

6. A method of controlling a high-contrast petaiaser device as claimed in claim 1, characterized in that The control method comprises the following steps: 1) the oscillator outputs femtosecond laser with central wavelength λ1; the laser output by the oscillator is divided into two beams, which are first laser and second laser respectively; the power ratio of the first laser and the second laser output by the oscillator is greater than 1:1; wherein the output characteristics of the first laser are the same as the output characteristics of the oscillator, with central wavelength λ1, the first laser enters the first stretcher for stretching to obtain picosecond pulse as seed pulse; the second laser output by the oscillator passes through the optical filter to obtain laser with central wavelength λ2, the second laser is stretched to picosecond after passing through the second stretcher and enters the regenerative amplifier as seed, and then is amplified after entering the regenerative amplifier and enters the parametric amplifier as pump pulse after passing through the time delay device; the pulse width of the first laser after stretching by the first stretcher is τ1, and the pulse width of the second laser after stretching by the second stretcher is τ2, τ1≤τ2≤2τ1; the width of the pump pulse of the parametric amplifier is greater than the width of the seed pulse, which is conducive to obtaining high conversion efficiency of the parametric amplifier; the seed pulse obtains gain greater than 10 6 after passing through the regenerative amplifier, high gain, high beam quality and high stability are obtained by using the regenerative amplifier; 2) the first cavity mirror of the oscillator is installed on the mirror frame through the first piezoelectric ceramic, the extension and contraction amount of the first piezoelectric ceramic is changed by changing the voltage applied to the first piezoelectric ceramic, thereby changing the cavity length L1 of the oscillator, the cavity length L1 of the oscillator is the distance between the first cavity mirror and the output mirror; a part of the output laser of the oscillator is transmitted to the first photodetector, the first photodetector receives the repetition frequency of the oscillator, obtains the repetition frequency electrical signal of the oscillator and outputs to the first synchronizer, the reference signal output by the reference source is also output to the first synchronizer; the function of the first synchronizer is to lock the input repetition frequency to the reference source; the first synchronizer outputs a feedback signal to the first piezoelectric ceramic connected to the first cavity mirror, controls the extension and contraction amount of the first piezoelectric ceramic and thereby controls the cavity length L1 of the oscillator, thereby realizing the change of the laser repetition frequency; the repetition frequency of the oscillator is locked through the first synchronizer; 3) the second cavity mirror is installed on the frame through the second piezoelectric ceramic, the extension and contraction amount of the second piezoelectric ceramic is changed by changing the voltage applied to the second piezoelectric ceramic, so as to change the regenerative amplifier cavity length L2, the regenerative amplifier cavity length is the distance between the second cavity mirror and the third cavity mirror; a part of the regenerative amplifier output laser is input to the second photodetector, the second photodetector receives the regenerative amplifier repetition frequency, obtains the regenerative amplifier repetition frequency electrical signal and outputs to the second synchronizer, and at the same time, the oscillator repetition frequency electrical signal obtained by the first photodetector is synchronously transmitted to the second synchronizer; the second synchronizer first divides the oscillator repetition frequency received by the first photodetector to the same repetition frequency as the second photodetector, and then the second synchronizer locks the regenerative amplifier repetition frequency received by the second photodetector to the frequency after the oscillator repetition frequency received by the first photodetector is divided; 4) the regenerative amplifier output laser acts on the parametric amplifier after passing through the delay device, at this time the time delay provided by the delay device is the oscillator output laser pulse period; the pump pulse output by the regenerative amplifier and the seed pulse output by the oscillator act on the parametric amplifier crystal at this time, at this time the pump pulse and the seed pulse can not come from the same pulse; the pump pulse output by the regenerative amplifier is vertically reflected into the second mirror through the first mirror, the second mirror vertically reflects the incident light into the third mirror, the third mirror vertically reflects the incident light into the fourth mirror, the light reflected by the first mirror is opposite parallel to the light reflected by the third mirror, and the fourth mirror vertically reflects the incident light; the second mirror and the third mirror of the delay device are installed on the electric translation stage, and the electric translation stage is connected to the stepping motor, and the electric translation stage is driven to move by the stepping motor; 5) The second synchronizer provides a voltage signal based on the frequency difference between the repetition frequency of the regenerative amplifier received by the second photodetector and the frequency of the oscillator received by the first photodetector after frequency division. This signal is fed back to the regenerative amplifier. Simultaneously, the second synchronizer outputs a signal to the stepper motor of the delay unit based on the magnitude of the voltage signal fed back to the regenerative amplifier. This controls the stepper motor to adjust the movement of the electric translation stage, thereby changing the delay time provided by the delay unit. A voltage V is applied to the second piezoelectric ceramic, where 0 < V < V0, and V0 is the maximum voltage that can be applied to the second piezoelectric ceramic. When the applied voltage to the second piezoelectric ceramic is V0, the piezoelectric ceramic elongates. l 0; The pump pulse is amplified n times in the regenerative amplifier, where n is a natural number ≥ 2; When the voltage on the second piezoelectric ceramic is less than the minimum delay voltage V1, V1 = C1 × V0, where C1 is the first coefficient. At this time, the stepper motor moves by n × l 0 / 4, the stepper motor moves in the direction of increasing the delay time, that is, the second and third lenses move away from the first and fourth lenses; when the voltage on the second piezoelectric ceramic is greater than the maximum delay voltage V2, V2 = C2 × V0, where C2 is the second coefficient, the stepper motor moves by n × l 0 / 4, the stepper motor moves in the direction of reducing the delay time, that is, the second and third lenses move closer to the first and fourth lenses, so that the repetition frequency of the regenerative amplifier can be locked to the frequency after the oscillator repetition frequency is divided for a long time.

7. The control method according to claim 6, characterized by, In step 1), the seed pulse is amplified by a regenerative amplifier to more than 10 6 gain.

8. The control method according to claim 6, characterized by, In step 5), the first coefficient C1 satisfies: 0 9. The control method according to claim 6, characterized by, In step 5), the second coefficient C2 satisfies: 0.7

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