Focusing focus control device of repetition frequency femtosecond laser and control method thereof

Abstract

The invention discloses a pointing stability regulation and control device of a large-aperture laser application terminal and a method thereof, and belongs to the technical field of laser. The beam expanding device is used for moving the first negative lens to compensate the laser divergence angle, and large divergence angle compensation can be provided by moving the negative lens, so that large-range divergence angle compensation can be carried out through the method; when laser energy changes and the position changes of the negative lens, laser wavefront changes are caused, at the moment, the laser wavefront is corrected through the self-adaptive system, and the quality of a laser focusing focal spot is guaranteed; when the change of the divergence angle is small, small-range fine adjustment is carried out by using the control of the divergence angle of the deformable mirror, and the small-range divergence angle or the change of the divergence angle caused by long-term operation is further controlled. The method is used for the consistency of the daily divergence angle and the wavefront of the large-energy laser in daily operation and the long-time divergence angle adjustment and wavefront correction of the large-energy laser in the operation process.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and specifically to a focusing control device and method for a high-repetition-rate femtosecond laser. Background Technology

[0002] Since the introduction of chirped laser pulse amplification (CPA), the peak power of lasers has been steadily increasing. Currently, the peak power of laser pulses can reach several PW (10^6 ppm). 15 (W), laser light intensity can reach 10 22 W / cm 2 Common CPA technology laser systems include... Figure 1 As shown, an oscillator generates an ultrashort pulse (pulse width typically on the order of picoseconds or femtoseconds) as a seed source. This pulse is then time-stretched by a stretcher to obtain a long pulse (pulse width on the order of tens of picoseconds to nanoseconds, the specific length depending on the final energy to be amplified). An amplifier system amplifies the stretched long pulse to obtain a high-energy pulse. This high-energy laser pulse is then compressed to its minimum time scale (back to the order of the seed source pulse width) by a compressor, resulting in a high-peak-power, high-field laser pulse. This high-peak-power, high-field laser pulse is transmitted to the target range at the application end, where it is focused by an off-axis parabolic mirror to achieve high intensity and further interact with matter.

[0003] For high peak power, especially femtosecond lasers with peak power greater than 100 TW, the repetition rate is a crucial parameter, primarily dependent on the pump source's repetition rate. Based on the pump source's repetition rate, femtosecond lasers with repetition rates greater than 100 TW currently fall into two main categories: one is a single-shot laser, emitted every tens of minutes. Due to the low pump source repetition rate, the heat generated by the pump light on the gain crystal is effectively dissipated, resulting in almost no thermal lensing effect on the gain medium. The other type is 1–10 Hz, known as a high-repetition-rate laser. Due to the high pump source repetition rate, a strong thermal lensing effect is formed when the pump light acts on the gain medium. This latter effect alters the laser divergence angle. When different pump energies are used, the thermal lensing effect varies, resulting in different laser divergence angles, which in turn causes the focal point of the laser after focusing by an off-axis parabolic mirror at the target range to shift. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a focusing control device and method for a high-repetition-rate femtosecond laser.

[0005] One object of the present invention is to provide a focusing control device for a high-repetition-rate femtosecond laser.

[0006] The re-frequent femtosecond laser focusing focus control device of the application comprises a CPA laser system, an adaptive optical system, an action system and a controller, wherein An attenuator is arranged after the amplifier group of the CPA laser system, and a beam expansion system is arranged between the attenuator and the compressor; the beam expansion system is composed of a negative lens and a positive lens, the negative lens is placed on a first translation stage, and the negative lens is controlled to move along the laser transmission direction through the first translation stage; the attenuator comprises a first attenuator and a second attenuator, the second attenuator is placed on a second translation stage, and the second attenuator is controlled to move out of or into the optical path through the second translation stage; the controller reads the laser energy output by the compressor; The adaptive optical system comprises a deformable mirror and a wavefront detector; the deformable mirror transmits the laser output by the compressor to a focusing mirror, part of the laser is transmitted to the wavefront detector through a beam splitting device, the wavefront detector detects part of the energy of the laser, and the laser divergence angle is obtained; The action system comprises a focusing mirror and a target body, the focusing mirror focuses the laser on the target body, and the target body is on the focal point; the focusing mirror is placed on a third translation stage, and the distance between the focusing mirror and the target body is adjusted through the third translation stage; The compressor, the wavefront detector, the deformable mirror and the first to third translation stages are respectively connected to the controller.

[0007] The CPA laser system comprises a seed source, a stretcher, an amplifier group, an attenuator, a beam expansion system and a compressor in sequence; wherein the repetition frequency of the amplifier group is 1-10 Hz; in the beam expansion system, the negative lens is in front and the positive lens is at the back along the laser transmission direction, wherein the negative lens is placed on a first translation stage which moves one-dimensionally along the laser transmission direction, the first translation stage drives the negative lens to move along the laser transmission direction, and the laser divergence angle is adjusted by moving the negative lens along the laser transmission direction. The controller reads the laser energy output by the compressor; the laser energy output by the compressor is greater than 5J.

[0008] The second attenuator moves into or out of the optical path, which has no effect on the laser transmission direction. In the attenuator, the first attenuator is placed before the second attenuator.

[0009] The first attenuator comprises a half-wave plate, a first polarizer and a second polarizer; wherein by rotating the first and second polarizers, the first attenuator continuously attenuates the input laser, and the transmittance of the first attenuator is 1%-90%. The first attenuator is fixed in the optical path and cannot be moved.

[0010] The second attenuator comprises: first to fourth mirrors and a light blocking garbage can; the light blocking garbage can is placed behind the first mirror; the first to fourth mirrors are all coated with an anti-reflection film; incident light enters the second attenuator through the first mirror, the first mirror reflects the incident light and changes the direction of the incident light by 90 degrees, and the light transmitted through the first mirror is blocked by the light blocking garbage can; the second mirror reflects the incident light and changes the direction of the incident light by 90 degrees, and the direction of the reflected light is parallel to the direction of the light incident on the first mirror; the third mirror reflects the incident light and changes the direction of the incident light by 90 degrees, and the direction of the reflected light is parallel to the direction of the light incident on the second mirror, and the propagation direction is opposite; the fourth mirror reflects the incident light and changes the direction of the incident light by 90 degrees, and the direction of the reflected light is the same as the direction of the light incident on the first mirror; and the light reflected by the fourth mirror is output light of the attenuator. The second attenuator is arranged on the second translation table, the moving direction of the second translation table is perpendicular to the laser transmission direction, the second attenuator can be moved out of the light path through the second translation table, the position and direction of the exiting light when the second attenuator is moved out of the light path are the same as the position of the output light of the second attenuator when the second attenuator is placed in the light path. The reflectivity of the first to fourth mirrors is less than 0.2%, the first to fourth mirrors are wedge-shaped mirrors; and the overall reflectivity of the second attenuator is less than 10 -6 .

[0011] In the adaptive optical system, the deformable mirror is placed behind the compressor, and the wavefront detector is placed behind the deformable mirror; the deformable mirror transmits the laser output by the compressor to the focusing mirror, part of the laser is transmitted to the wavefront detector through the beam splitting device, and the wavefront detector detects the energy of the full spot part of the laser; the beam splitting device is a beam splitter or a reflective mirror with partial transmission. The wavefront detector measures the laser wavefront information and gives it in the form of Zernike polynomials, wherein the fourth term z4 of the Zernike polynomials represents the laser defocus term and represents the laser divergence angle. The deformable mirror comprises three layers: the first layer is a mirror piece; the second layer below the mirror is a piezoelectric ceramic array, which is used to adjust the surface of the first layer of the mirror piece, so as to compensate for the laser wavefront phase; and the third layer is a whole piece of piezoelectric ceramic, different positions of the piezoelectric ceramic have different voltages, so that the surface of the mirror piece has a certain curvature, and the curvature radius of the bending of the mirror piece is controlled by controlling the voltage on the whole piece of piezoelectric ceramic, so as to adjust the laser divergence angle. The piezoelectric ceramic has a limited expansion and contraction amount, and the ability to adjust the divergence angle is limited.

[0012] The controller is connected to the first translation stage of the beam expander system, which places the negative lens, and controls the movement of the negative lens along the laser transmission direction; the controller is connected to the second translation stage, which places the second attenuator, and controls the second attenuator to move into or out of the optical path; the controller is connected to the compressor, and reads the laser energy output by the compressor; the controller is connected to the third translation stage, which places the focusing lens, and adjusts the distance between the focusing lens and the target by controlling the third translation stage; the controller is connected to the wavefront detector, and records the measurement data of the wavefront detector; the controller is connected to the deformable mirror, and records the voltage of the deformable mirror and provides voltage to the deformable mirror.

[0013] Another objective of this invention is to provide a method for controlling the focusing point of a high-repetition-rate femtosecond laser.

[0014] The focusing point control method for a high-repetition-rate femtosecond laser of the present invention includes the following steps: Step 1: Calibration 1) When the laser operates at low energy, the controller reads the laser energy output by the compressor, and controls the second attenuator to be placed outside the optical path. The wavefront detector measures the divergence angle A1 of the low-energy laser, and reads the position of the first translation stage at this time to obtain the position of the low-energy negative lens as B1. The low-energy laser divergence angle A1 and the position of the low-energy negative lens B1 are recorded in the controller. 2) Based on step 1), the controller changes the voltage V2 of the piezoelectric ceramic plate corresponding to the nth laser divergence angle applied to the entire piezoelectric ceramic plate of the deformable mirror. n The wavefront detector measures the nth laser divergence angle A2 corresponding to the change in voltage. n A2 n =A1±n×c, where c is the single adjustment divergence angle value of the deformable mirror, 0<c<0.2, n=1,2,3……N, where N is the total number of times the voltage of the entire piezoelectric ceramic is changed; the controller records the voltage V2 of the entire piezoelectric ceramic corresponding to the nth laser divergence angle. n ; 3) The laser is driven to a high energy level. The controller reads the laser energy output from the compressor, changes the high-energy laser, and the wavefront detector measures the laser divergence angle A3 at the m-th high energy corresponding to the change in laser energy. m m=1,…,M, where M is the total number of times the laser energy is changed. The controller records the laser divergence angle A3 at the m-th highest energy corresponding to different laser energies. m ; 4) The controller moves the first translation stage, changing the position of the negative lens along the laser transmission direction, so that the laser divergence angle A3 at the m-th high energy is adjusted. m The divergence angle A1 of the low-energy laser is equal to the position of the negative lens B2 recorded by the controller at the m-th high-energy laser. m ; 5) Under different high energy operation, corresponding to different negative lens positions, the adaptive optical system is used to correct the laser wavefront at this time, and the wavefront detector detects the laser wavefront and feeds back to the deformable mirror. The deformable mirror adjusts the surface shape of the mirror lens by using the piezoelectric ceramic array to correct the laser wavefront. Under different high energy, the laser wavefront is corrected respectively, and the controller records the piezoelectric ceramic array voltage V3 under the mth high energy m , m = 1, … M; Second step: focus control 1) Run the laser to low energy, the controller reads the output laser energy of the compressor, and the output laser energy is less than 200mJ. The controller controls the second attenuator to be placed outside the optical path. The controller calls the low energy negative lens position B1 and controls the first translation table to move the negative lens to the low energy negative lens position B1. The laser is focused on the target body through the focusing mirror, and the target body is located at the focal point. The measuring wavefront detector measures the laser divergence angle at this time as the low energy laser divergence angle A1. 2) Increase the laser energy to the required high energy, the controller reads the output laser energy of the compressor, the controller calls the negative lens position B2 corresponding to the mth high energy of the laser energy m , and controls the first translation table to move the negative lens to the negative lens position B2 of the mth high energy m . The controller calls the piezoelectric ceramic array voltage V3 under the mth high energy m and applies it to the piezoelectric ceramic array of the deformable mirror. The wavefront detector measures the laser divergence angle at this time as A4. If A4 = A1, the target body is at the focal point under this high energy. If A4 ≠ A1 and A4 ≤ A1 ± 1.5, calculate |A4-A1| / c, obtain n, and the controller calls the whole piezoelectric ceramic voltage V2 corresponding to the nth laser divergence angle in step 2) of the first step n and applies the voltage to the whole piezoelectric ceramic of the deformable mirror, adjusts the laser divergence angle to the low energy laser divergence angle A1. If A4 ≥ A1 ± 1.5, the laser has a problem and needs to be stopped for maintenance. 3) On the basis of step 2), when the laser divergence angle is the low energy laser divergence angle A1, the laser is put into use, and the wavefront detector measures the real-time laser divergence angle A5. With the increase of the use time of the laser, the real-time laser divergence angle A5 will change. When |A5-A1|=c, the whole piezoelectric ceramic voltage corresponding to the first laser divergence angle is found, the controller calls the whole piezoelectric ceramic voltage corresponding to the first laser divergence angle and applies the voltage to the whole piezoelectric ceramic of the deformable mirror, and controls the laser divergence angle to make A5 = A1. The number of times of operation in this step plus the value of n in step 2) is less than 1.5 / c. When the number of operation steps plus the value of n in step 2) is greater than or equal to 1.5 / c, the laser is stopped for use.

[0015] Wherein, in step 1) of the first step, by starting different numbers of pump sources, high energy or low energy of laser operation is realized, and the laser energy of the laser operation in low energy is less than 200 mJ.

[0016] In step 2) of the first step, the total change of the laser divergence angle characterized by the fourth term z4 of the Zernike polynomial should not exceed 3, that is, n x c < 3, otherwise the correction of the deformable mirror is difficult.

[0017] In step 3) of the first step, by starting different numbers of amplifiers, the laser operation in different laser energies is realized. The high energy can be multiple, such as 1 J, 2 J, 3 J, 4 J, 5 J. When the laser energy is less than the high energy threshold, the controller controls the second attenuator to be out of the light path, and when the laser energy is greater than the high energy threshold, the controller controls the second attenuator to enter the light path; the high energy threshold is 1-3 J.

[0018] Advantages of the present application: The divergence angles of the 1-10 Hz large energy laser are different at different energies, and the divergence angle of the laser changes due to the heat accumulation of the laser crystal and the heat accumulation of the grating in the compressor when the laser is operated at the same energy for a long time. The first negative lens is moved by the beam expander device to compensate for the laser divergence angle. Since the movement of the negative lens position can provide a large divergence angle compensation, a large range of divergence angle compensation can be achieved by this method. When the laser energy changes and the negative lens position changes, the laser wavefront will change. At this time, the adaptive system is used to correct the laser wavefront, which can ensure the quality of the laser focusing focal spot. When the divergence angle changes little, the small range fine adjustment is carried out by using the divergence angle control of the deformable mirror, and the small range divergence angle or the divergence angle change caused by long-term operation is further controlled. The present application is used for the consistency of the divergence angle and the wavefront of the large energy laser in daily operation, and the long-term divergence angle adjustment and wavefront correction of the large energy laser during operation. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a schematic diagram of the laser system of the CPA technology in the prior art; Figure 2 It is a schematic diagram of the focusing focal point control device of the repetitive frequency femtosecond laser of the present application; Figure 3 It is a schematic diagram of the first attenuator of the focusing focal point control device of the repetitive frequency femtosecond laser of the present application; Figure 4 It is a schematic diagram of the second attenuator of the focusing focal point control device of the repetitive frequency femtosecond laser of the present application; Figure 5 It is a schematic diagram of the deformable mirror of the focusing focal point control device of the repetitive frequency femtosecond laser of the present application. DETAILED DESCRIPTION

[0020] The application will be further described below with reference to the drawings and specific embodiments.

[0021] As Figure 2 shown, the repetition frequency femtosecond laser focusing focal point control device of the embodiment comprises a CPA laser system, an adaptive optical system, an action system and a controller; wherein, The CPA laser system comprises a seed source, a stretcher, an amplifier group, an attenuator, a beam expansion system and a compressor in sequence; wherein, the repetition frequency of the amplifier group is 1-10 Hz; the beam expansion system is arranged between the attenuator and the compressor, the beam expansion system is composed of a negative lens and a positive lens, along the laser transmission direction, the negative lens is in front and the positive lens is behind, wherein the negative lens is placed on a first translation stage moving in one dimension along the laser transmission direction, the first translation stage drives the negative lens to move along the laser transmission direction, and the laser divergence angle is adjusted by moving the negative lens along the laser transmission direction; the controller reads the laser energy output by the compressor, and the laser energy output by the compressor is greater than 5J; the attenuator is moved into or out of the optical path, and has no effect on the laser transmission direction; the attenuator comprises a first attenuator and a second attenuator, and the first attenuator is placed before the second attenuator; As Figure 3 shown, the first attenuator comprises a half-wave plate, a first polarizer and a second polarizer; wherein, by rotating the first and second polarizers, the first attenuator continuously attenuates the input laser, and the transmittance of the first attenuator is 1%-90%. The first attenuator is fixed in the optical path and cannot be moved; As Figure 4As shown, the second attenuator comprises: first to fourth mirrors and a light blocking garbage can; wherein the light blocking garbage can is placed behind the first mirror; the first to fourth mirrors are all coated with an antireflection film; incident light enters the second attenuator through the first mirror, the first mirror reflects the incident light and changes the direction of the incident light by 90°, and the light transmitted through the first mirror is blocked by the light blocking garbage can; the second mirror reflects the incident light and changes the direction of the incident light by 90°, and the direction of the light reflected by the second mirror is parallel to the direction of the light incident on the first mirror; the light reflected by the second mirror enters the third mirror; the third mirror reflects the incident light and changes the direction of the incident light by 90°, and the direction of the light reflected by the third mirror is parallel to the direction of the light incident on the second mirror, but the propagation direction is opposite; the light reflected by the third mirror enters the fourth mirror; the fourth mirror reflects the incident light and changes the direction of the incident light by 90°, and the direction of the light reflected by the fourth mirror is the same as the direction of the light incident on the first mirror; the light reflected by the fourth mirror is the output light of the attenuator. The second attenuator is arranged on the second translation stage, the moving direction of the second translation stage is perpendicular to the laser transmission direction, the second attenuator can be moved out of the light path through the second translation stage, the position and direction of the outgoing light when the second attenuator is moved out of the light path are the same as the position of the output light of the second attenuator after the second attenuator is placed in the light path; the reflectivity of the first to fourth mirrors is less than 0.2%, the first to fourth mirrors adopt wedge-shaped mirrors; the overall reflectivity of the second attenuator is less than 10 -6 ; The adaptive optical system comprises a deformable mirror and a wavefront detector; the deformable mirror is placed behind the compressor, and the wavefront detector is placed behind the deformable mirror; the deformable mirror transmits part of the laser output by the compressor to the focusing mirror through a partially transmissive mirror, and the part of the laser is reflected to the wavefront detector through the partially transmissive mirror; the wavefront detector detects the energy of the full spot part of the laser; the wavefront detector measures the laser wavefront information and gives it in the form of Zernik polynomial, wherein the fourth term z4 of the Zernik polynomial represents the laser defocus term and represents the laser divergence angle; Figure 5 As shown, the deformable mirror comprises three layers: the first layer is a mirror piece; the second layer is a piezoelectric ceramic array below the mirror, which is used to adjust the surface shape of the first layer mirror piece, so as to compensate the laser wavefront phase; the third layer is a whole piece of piezoelectric ceramic, and the piezoelectric ceramic at different radius positions applies different voltages, so that the mirror piece surface has a certain curvature, and the curvature radius of the bending of the mirror piece is controlled by controlling the voltage on the piezoelectric ceramic, so as to adjust the laser divergence angle. The piezoelectric ceramic has a limited expansion and contraction amount, and the adjustable divergence angle has a limited ability; The action system comprises a focusing mirror and a target body, the focusing mirror focuses the laser on the target body, and the target body is on the focal point; the focusing mirror is placed on the third translation stage, and the translation stage adjusts the distance between the focusing mirror and the target body; The compressor, the wavefront detector, the deformable mirror and the first to third translation stages are respectively connected to the controller; The controller is connected with the first translation table where the negative lens is placed, and controls the movement of the negative lens along the laser transmission direction; the controller is connected with the second translation table where the second attenuator is placed, and controls the movement of the second attenuator into or out of the light path; the controller is connected with the compressor, and reads the laser energy output by the compressor; the controller is connected with the third translation table where the focusing mirror is placed, and controls the distance between the focusing mirror and the target body; the controller is connected with the wavefront detector, and records the measurement data of the wavefront detector; the controller is connected with the deformable mirror, and records the voltage of the deformable mirror and provides the voltage to the deformable mirror.

[0022] The focus point control method of the repetition frequency femtosecond laser of the embodiment comprises the following steps: First step: calibration 1) By turning on different numbers of pump sources, low-energy laser operation is realized, the controller reads the laser energy output by the compressor, and the laser energy of the low-energy laser operation is less than 200 mJ; the controller controls the second attenuator to be placed outside the light path, the wavefront detector measures the low-energy laser divergence angle A1, and the first translation table position is read to obtain the low-energy negative lens position B1, and the low-energy laser divergence angle A1 and the low-energy negative lens position B1 are recorded in the controller; 2) On the basis of step 1), the controller changes the voltage applied to the whole piezoelectric ceramic of the deformable mirror, and the controller changes the voltage V2 of the whole piezoelectric ceramic corresponding to the nth laser divergence angle applied to the whole piezoelectric ceramic of the deformable mirror n , the wavefront detector measures the nth laser divergence angle A2 n corresponding to the changed voltage n , A2 n =A1±n×0.1, n=1, 2, 3, …, 15, and the total number of times of changing the voltage of the whole piezoelectric ceramic is 15; the controller records the laser divergence angle A2 2n corresponding to the nth time of the whole piezoelectric ceramic voltage V m ; the total change of the laser divergence angle represented by the fourth term z4 of the Zernike polynomial should not exceed 3, i.e. n×c<3, otherwise the deformable mirror is difficult to correct; 3) By turning on different numbers of pump sources, high-energy laser operation is realized, the controller reads the laser energy output by the compressor, and by turning on different numbers of amplifiers, the laser energy of the high-energy laser is changed to 1 J, 2 J, 3 J, 4 J, and 5 J, respectively, the wavefront detector measures the laser divergence angle A3 m; when the laser energy is less than 2J, the controller controls the second attenuator to be outside the light path, and when the laser energy is greater than 2J, the controller controls the second attenuator to be in the light path; 4) The controller controls the first translation stage to change the position of the negative lens along the laser transmission direction under the mth high energy, so that the laser divergence angle A3 under the mth high energy m is equal to the low-energy laser divergence angle A1, and the controller records the position B2 of the negative lens under the mth high energy m ; 5) Under different high energies and corresponding different negative lens positions, the adaptive optical system is used to correct the laser wavefront at this time, and the wavefront detector detects the laser wavefront and feeds back to the deformable mirror, and the deformable mirror adjusts the surface shape of the lens of the deformable mirror by using the piezoelectric ceramic array to correct the laser wavefront; the piezoelectric ceramic array voltage V3 under the mth high energy is recorded by the controller m ; 1) Run the laser to low energy, the controller reads the laser energy output by the compressor, the output laser energy is less than 200mJ, the controller controls the second attenuator to be outside the light path, the controller calls the low-energy negative lens position B1 and controls the first translation stage to move the negative lens to the low-energy negative lens position B1, focuses the laser on the target body through the focusing mirror, and the target body is located at the focal point; the wavefront detector measures the laser divergence angle at this time as the low-energy laser divergence angle A1; 2) Increase the laser energy to the required high energy, the controller reads the laser energy output by the compressor, the controller calls the negative lens position B2 corresponding to the mth high energy of the high-energy laser energy m , and controls the first translation stage to move the negative lens to the negative lens position B2 of the mth high energy m , the controller calls the piezoelectric ceramic array voltage V3 under the mth high energy m and applies it to the piezoelectric ceramic array of the deformable mirror; the wavefront detector measures the laser divergence angle at this time as A4, if A4=A1, the target body is at the focal point under this high energy, if A4≠A1 and A4≤A1±1.5, calculate |A4-A1|×10 to obtain n, the controller calls the whole piezoelectric ceramic voltage V2 corresponding to the nth laser divergence angle in step 2) of the first step n and applies the voltage to the whole piezoelectric ceramic of the deformable mirror, adjusts the laser divergence angle to the low-energy laser divergence angle A1; if A4≥A1±1.5, the laser has a problem at this time, and needs to be stopped for maintenance; 3) Based on step 2), when the laser divergence angle is the low-energy laser divergence angle A1, the laser is put into use, and the wavefront detector measures the real-time laser divergence angle A5; with the increase of the use time of the laser, the real-time laser divergence angle A5 will change, when |A5-A1|=0.1, at this time the first laser divergence angle corresponding to step 2) of the first step is found, the first laser divergence angle corresponding to the whole piezoelectric ceramic voltage is found, the controller calls the first laser divergence angle corresponding to the whole piezoelectric ceramic voltage and applies the voltage to the whole piezoelectric ceramic of the deformable mirror, the laser divergence angle is controlled, and A5=A1; the number of operation steps of this step plus the n value in step 2) is less than 15, when the operation step number plus the n value in step 2) is greater than or equal to 15, the laser is stopped.

[0023] Finally, it should be noted that the purpose of the disclosed embodiments is to help further understand the present application, but those skilled in the art can understand that various replacements and modifications are possible without departing from the spirit and scope of the present application and the appended claims. Therefore, the present application should not be limited to the disclosed content of the embodiments, and the scope of the present application claimed is defined by the scope of the claims.

Claims

1. A focusing focus control device for a high-repetition-rate femtosecond laser, characterized in that, The control device includes: a CPA laser system, an adaptive optics system, an action system, and a controller; wherein... An attenuator is installed after the amplifier group of the CPA laser system, and a beam expander is installed between the attenuator and the compressor. The beam expander consists of a negative lens and a positive lens. The negative lens is placed on a first translation stage, and the negative lens is moved along the laser transmission direction by the first translation stage. The attenuator includes a first attenuator and a second attenuator. The second attenuator is placed on a second translation stage, and the second attenuator is moved out of or into the optical path by the second translation stage. The controller reads the laser energy output by the compressor. The adaptive optics system includes a deformable mirror and a wavefront detector. The deformable mirror transmits the laser output from the compressor to the focusing mirror. Part of the laser is split by a beam splitter and sent to the wavefront detector. The wavefront detector detects part of the laser energy to obtain the laser divergence angle. The system includes a focusing lens and a target. The focusing lens focuses the laser onto the target, which is at the focal point. The focusing lens is placed on a third translation stage, and the distance between the focusing lens and the target is adjusted by the third translation stage. The compressor, wavefront detector, deformable mirror, and first to third translation stages are respectively connected to the controller.

2. The control device according to claim 1, characterized in that, The second attenuator includes: first to fourth reflectors and a light-blocking trash can; wherein, the light-blocking trash can is placed behind the first reflector; the first to fourth reflectors are all coated with anti-reflection films; incident light passes through the first reflector and enters the second attenuator, the first reflector reflects the incident light and changes the direction of the incident light by 90°, and then enters the second reflector, the light transmitted through the first reflector is blocked by the light-blocking trash can; the second reflector reflects the incident light and changes the direction of the incident light by 90°, and then the light is parallel to the direction of the light incident on the first reflector, and the light reflected by the second reflector enters the third reflector; the third reflector reflects the incident light and changes the direction of the incident light by 90°, and then the light is parallel to the direction of the light incident on the second reflector, but the propagation direction is opposite, and the light reflected by the third reflector enters the fourth reflector; the fourth reflector reflects the incident light and changes the direction of the incident light by 90°, and then the light is in the same direction as the light incident on the first reflector, and the light reflected by the fourth reflector is the output light of the attenuator.

3. A control method for a focusing focus control device for a high-repetition-rate femtosecond laser according to claim 1 or 2, characterized in that, The control method includes the following steps: Step 1: Calibration 1) When the laser operates at low energy, the controller reads the laser energy output by the compressor, the wavefront detector measures the divergence angle of the low-energy laser, reads the position of the first translation stage at this time to obtain the position of the low-energy negative lens, and records it in the controller; 2) The controller changes the voltage applied to the entire piezoelectric ceramic of the deformable mirror, and the wavefront detector measures the laser divergence angle corresponding to the change in voltage; the controller records the voltage of the entire piezoelectric ceramic corresponding to each laser divergence angle. 3) The laser is driven to a high energy level. The controller reads the laser energy output by the compressor. The high energy level is changed, and the wavefront detector measures the laser divergence angle corresponding to the change in high energy. The controller records the laser divergence angle at each high energy level. 4) The controller changes the position of the negative lens along the laser transmission direction so that the laser divergence angle at each high energy level is equal to the laser divergence angle at each low energy level. The controller records the position of the negative lens at each high energy level. 5) At different high energies, the negative lens position is used. The wavefront detector detects the laser wavefront and applies the corresponding voltage to the piezoelectric ceramic array to adjust the surface shape of the deformable mirror and correct the laser wavefront. The controller records the piezoelectric ceramic array voltage at each high energy level. Step 2: Focus Control 1) The laser is driven to a low energy level. The controller calls the low-energy negative lens position and controls the first translation stage to place the negative lens in the low-energy negative lens position. The target is located at the focal point. At this time, the laser divergence angle is the low-energy laser divergence angle. 2) Increase the laser energy to the required high energy. The controller calls the corresponding negative lens position under high energy and controls the negative lens to move to the corresponding position. It calls the corresponding piezoelectric ceramic array voltage under high energy and applies it to the piezoelectric ceramic array. Then it calls the whole piezoelectric ceramic voltage corresponding to the laser divergence angle and applies it to the whole piezoelectric ceramic. Adjust the laser divergence angle to the low energy laser divergence angle. 3) When the laser is put into use, the wavefront detector measures the real-time laser divergence angle. When the real-time laser divergence angle changes, the voltage of the entire piezoelectric ceramic corresponding to the laser divergence angle is called and applied to the entire piezoelectric ceramic to control the laser divergence angle to a low-energy laser divergence angle.

4. The control method according to claim 3, characterized in that, In step 1) of the first step, the laser operates with low energy less than 200mJ. The controller controls the second attenuator to be placed outside the optical path. The wavefront detector measures the divergence angle A1 of the low-energy laser and reads the position of the first translation stage at this time to obtain the position of the low-energy negative lens as B1. The low-energy laser divergence angle A1 and the position of the low-energy negative lens B1 are recorded in the controller.

5. The control method according to claim 4, characterized in that, In step 2) of the first step, based on step 1), the controller changes the voltage V2 of the piezoelectric ceramic plate corresponding to the nth laser divergence angle applied to the deformable mirror. n The wavefront detector measures the nth laser divergence angle A2 corresponding to the change in voltage. n A2 n =A1±n×c, where c is the single adjustment divergence angle value of the deformable mirror, 0<c<0.2, n=1,2,3……N, where N is the total number of times the voltage of the entire piezoelectric ceramic is changed; the controller records the voltage V2 of the entire piezoelectric ceramic corresponding to the nth laser divergence angle. n .

6. The control method according to claim 5, characterized in that, In step 3) of the first step, the laser is driven to a high energy level. The controller reads the laser energy output from the compressor, changes the high-energy laser, and the wavefront detector measures the laser divergence angle A3 at the m-th high energy corresponding to the change in laser energy. m m=1,…,M, where M is the total number of times the laser energy is changed. The controller records the laser divergence angle A3 at the m-th highest energy. m .

7. The control method according to claim 6, characterized in that, In step 4) of the first step, the controller moves the first translation stage, changing the position of the negative lens along the laser transmission direction, so that the laser divergence angle A3 at the m-th high energy is changed. m The divergence angle A1 of the low-energy laser is equal to the position of the negative lens B2 recorded by the controller at the m-th high-energy laser. m .

8. The control method according to claim 7, characterized in that, In step 5) of the first step, under different high-energy operating conditions and corresponding to different negative lens positions, the laser wavefront is corrected using an adaptive optics system. The wavefront detector detects the laser wavefront and feeds it back to the deformable mirror. The deformable mirror uses a piezoelectric ceramic array to adjust the surface shape of its lenses to correct the laser wavefront. The laser wavefront is corrected for different high-energy conditions, and the controller records the piezoelectric ceramic array voltage V3 at the m-th high energy level. m .

9. The control method according to claim 8, characterized in that, In step 2) of the second step, the controller calls the position B2 of the m-th high-energy negative lens corresponding to the high-energy laser. m And control the first translation stage to move the negative lens to the position B2 of the m-th high-energy negative lens. m The controller calls the piezoelectric ceramic array voltage V3 at the m-th highest energy. m The laser beam is applied to the piezoelectric ceramic array of the deformable mirror. The wavefront detector measures the laser divergence angle as A4. If A4 = A1, the target is at the focal point at this high energy. If A4 ≠ A1 and A4 ≤ A1 ± 1.5, calculate |A4 - A1| / c to obtain n. The controller then calls the piezoelectric ceramic voltage V2 corresponding to the nth laser divergence angle obtained in step 2) of the first step. n Apply voltage to the entire piezoelectric ceramic of the deformable mirror and adjust the laser divergence angle to the low-energy laser divergence angle A1; if A4≥A1±1.5, the laser has a problem and needs to be shut down for maintenance.

10. The control method according to claim 9, characterized in that, In step 3) of the second step, based on step 2), when the laser divergence angle is obtained as a low-energy laser divergence angle A1, the laser is put into use, and the wavefront detector measures the real-time laser divergence angle A5. As the laser usage time increases, the real-time laser divergence angle A5 will change. When |A5-A1|=c, the controller calls the voltage of the whole piezoelectric ceramic corresponding to the first laser divergence angle and applies the voltage to the whole piezoelectric ceramic of the deformable mirror to control the laser divergence angle so that A5=A1. The number of operations in this step plus the n value in step 2) is less than 1.5 / c. When the number of operation steps plus the n value in step 2) is greater than or equal to 1.5 / c, the laser is stopped.

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