High-quality stable optical parametric multi-stage amplification method and device based on pump energy jitter cancellation

Abstract

The present disclosure relates to a high-quality stable optical parametric multi-stage amplification method and device based on pump energy jitter cancellation, the method comprising: performing first-stage frequency doubling and second-stage frequency doubling on fundamental frequency light to obtain first-stage pump light and second-stage pump light, wherein the energy of the second-stage pump light is greater than that of the first-stage pump light, and the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics; performing first-stage optical parametric amplification on seed light using the first-stage pump light to obtain first-stage signal light after optical parametric amplification; performing second-stage optical parametric amplification on the first-stage signal light using the second-stage pump light to obtain second-stage signal light after optical parametric amplification. Thus, the energy stability point of the second-stage optical parametric amplification can be advanced from the oversaturated region to the unsaturated region, and at the same time, the second-stage signal light satisfies high beam quality and high energy stability, and effectively realizes the conversion of the signal light from the spatiotemporal Gaussian distribution to the spatiotemporal super-Gaussian distribution.

Description

Technical Field

[0001] The present disclosure relates to the field of femtosecond laser technology, and in particular to a high-quality stable optical parametric multi-stage amplification method and device based on pump energy jitter cancellation. Background Art

[0002] Since the first ruby ​​laser was produced in 1960, laser technology has made great progress in more than half a century. Technologies such as Q-switching, mode locking, and chirped pulse amplification (CPA) have made it possible to continuously shorten the pulse width of laser pulses and continuously increase the peak power, continuously promoting the development of ultrashort and ultra-intense laser technology. In addition, pulse outputs shorter than 100fs have been obtained from the oscillator of the mode-locked titanium sapphire crystal. Combined with the previous chirped pulse amplification technology, lasers and laser devices based on this crystal can output laser pulses with peak powers of petawatts PW or even exawatts EW. CPA amplification based on titanium sapphire crystals constitutes the second generation of femtosecond laser technology. However, due to the thermal effect of the laser crystal, high average power and high peak power cannot be achieved at the same time.

[0003] The third generation of femtosecond laser technology based on Optical Parametric Chirped Pulse Amplification (OPCPA) benefits from the inherent characteristics of the second-order nonlinear optical process, and the nonlinear crystal used has only a small amount of absorption in some bands of idler light, so the thermal effect is extremely low, and high peak power and high average power output can be achieved at the same time. Compared with the second generation of CPA technology based on titanium sapphire, OPCPA has many advantages such as high gain, wide bandwidth, high repetition rate, high contrast, and adjustable frequency. In the subsequent stage of applications based on the interaction between ultrashort and ultra-intense laser pulses and plasma, such as the generation of high-order harmonics and attosecond pulses, inverse Compton sources, terahertz THz sources, and tail wave acceleration, it has great potential to replace titanium sapphire lasers.

[0004] However, as a second-order nonlinear optical process, the conversion intensity of optical parametric amplification is directly determined by the intensity of the spatiotemporal overlap of the pump light and signal light involved in the mixing, that is, the pump light energy flows to the signal light faster in strong places and slower in weak places. Therefore, a pump light with a flat-top distribution in both time and space is most suitable as a pump source for an optical parametric chirped pulse amplification system, especially for large systems with output energy of the joule level and peak power of the petawatt level. After amplification of the flat-top distributed pump light, the output signal light will also be a spatiotemporal flat-top distribution before compression.

[0005] Since the seed light of OPCPA is generally Gaussian in time and space distribution and has low energy, the first stage of amplification is generally small signal amplification, and the signal light is still Gaussian in time and space distribution. During the second or third stage amplification process, the signal light completes the transition from Gaussian to super Gaussian. During this transition process, since the light intensity in the center of the signal light is higher, the energy in the nonlinear crystal is saturated first, and energy reflux will occur if the amplification continues. Therefore, generally when the maximum energy point is reached, or when the most stable energy point is reached in the supersaturated region (that is, after the maximum energy point is reached), the center of the time and space distribution of the signal light will be concave, which seriously reduces the quality of the beam.

[0006] For example, a simple simulation can be used to illustrate the above phenomenon, that is, a pump light of 6.7 J, 532 nanometers (nm), half-width diameter of 15 millimeters (mm), half-width pulse width of 1.2 nanoseconds (ns), and 12th-order super-Gaussian distribution in both time and space is used to amplify a signal light of 100 millijoules (mJ), central wavelength of 800nm, half-width diameter of 8mm, half-width pulse width of 0.47ns, and Gaussian distribution in both time and space. A numerical calculation based on the coupled wave equation is performed, which simulates the second-stage amplification of the OPCPA system, and can obtain Figures 1 to 3 The simulation results are shown. Figure 1 The energy of the signal light output by the second-stage parametric amplifier changes with the thickness of the crystal. Figure 1 The three curves in the middle correspond to the case where the pump light energy fluctuates by 5% and does not fluctuate. Signal represents the energy of the signal light, z OPA Represents the crystal thickness of LBO (lithium triborate, LiB3O5) crystal used in optical parametric amplification, 105% E P For the case where the pump light jitters upward by 5%, 95% E P For the case where the pump light jitters downward by 5%, 100% E P For the case where the pump light does not jitter, Figure 1 It can be clearly seen that the signal light has an energy peak (i.e., the maximum energy point), and after the peak is the supersaturated amplification region, where the energy of the signal light and the idler light begins to flow back to the pump light. There is an optimal crystal thickness in this supersaturated region (i.e., the crystal thickness when the three curves intersect, which is also the most stable energy point), which eliminates the energy jitter of the pump light and achieves stable signal light energy output, thus improving the energy stability of the signal light by slightly sacrificing the amplification efficiency.

[0007] Although the pump light has a super-Gaussian distribution, which reduces a series of problems caused by uneven light intensity distribution, due to the spatiotemporal Gaussian distribution characteristics of the signal light, the spatiotemporal distribution of the signal light has a central depression regardless of the energy peak or the most stable energy point. Figure 2 The temporal and spatial distribution of the peak energy of the second-stage parametric amplification signal light is shown. Figure 3 The temporal and spatial distribution of the second-stage parametric amplification signal light energy at the most stable point is shown. Figure 2 and Figure 3 The red lines in the middle are the envelopes at time t=0 and pulse radius r=0, such as Figure 2 and Figure 3 As shown in the figure, at the energy peak, the ratio of the central intensity to the edge intensity of the signal light in the r direction is 67.6%, and the ratio in the t direction is 69.4%; at the most stable energy point, the ratios in the r direction and t direction are 14.5% and 12.5%. This ratio will also be different in OPCPA systems with different parameters. However, the phenomenon of central depression is common at the above two working points. This depression seriously affects the beam quality. If the crystal thickness is selected at such an operating point, it will not only reduce the efficiency of the subsequent parametric amplification, but also affect the subsequent applications based on the interaction between ultrashort and ultra-intense laser pulses and plasma.

[0008] Although the existing technology can select the thickness of the nonlinear crystal used for optical parametric amplification in the unsaturated region (that is, before reaching the maximum energy point) when designing the stage of amplification where the signal light is converted from Gaussian to super-Gaussian in the OPCPA system to obtain higher beam quality, the nonlinear crystal thickness still cannot make the optical parametric amplification reach the most stable energy point. Therefore, how to simultaneously achieve optical parametric amplification with high beam quality and high energy stability is an urgent problem to be solved. Summary of the invention

[0009] In view of this, the present disclosure proposes a high-quality and stable optical parametric multi-stage amplification method and device based on pump energy jitter cancellation, which can achieve optical parametric multi-stage amplification with high beam quality and high energy stability, and effectively realize the conversion of signal light from spatiotemporal Gaussian distribution to spatiotemporal super-Gaussian distribution.

[0010] According to one aspect of the present disclosure, there is provided a method for optical parametric multi-stage amplification, comprising: performing a first-stage frequency doubling and a second-stage frequency doubling on a fundamental frequency light to obtain a first-stage pump light and a second-stage pump light, wherein the energy of the second-stage pump light is greater than that of the first-stage pump light, and the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics; performing a first-stage optical parametric amplification on a seed light using the first-stage pump light to obtain a first-stage signal light after optical parametric amplification; and performing a second-stage optical parametric amplification on the first-stage signal light using the second-stage pump light to obtain a second-stage signal light after optical parametric amplification.

[0011] In a possible implementation, the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics, including: the first-stage pump light has a positive energy jitter characteristic and the second-stage pump light has a negative energy jitter characteristic, or the first-stage pump light has a negative energy jitter characteristic and the second-stage pump light has a positive energy jitter characteristic; the positive energy jitter characteristic includes that the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental frequency light; the negative energy jitter characteristic includes that the energy jitter of the frequency-doubled pump light is negatively correlated with the energy jitter of the fundamental frequency light.

[0012] In one possible implementation, the crystal thickness of the frequency doubling crystal used in the first-stage frequency doubling is in the positive energy jitter region and the crystal thickness of the frequency doubling crystal used in the second-stage frequency doubling is in the negative energy jitter region, or the crystal thickness of the frequency doubling crystal used in the first-stage frequency doubling is in the negative energy jitter region and the crystal thickness of the frequency doubling crystal used in the second-stage frequency doubling is in the positive energy jitter region, so that the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics; wherein the positive energy jitter region includes a thickness region that makes the energy jitter of the frequency-doubled pump light positively correlated with the energy jitter of the fundamental frequency light; and the negative energy jitter region includes a thickness region that makes the energy jitter of the frequency-doubled pump light negatively correlated with the energy jitter of the fundamental frequency light.

[0013] In a possible implementation manner, a root mean square value of energy jitter of the second-stage pump light is smaller than a root mean square value of energy jitter of the first-stage pump light.

[0014] In a possible implementation, the fundamental frequency light is a pulsed laser generated by a solid laser based on a crystal doped with neodymium (Nd) or ytterbium (Yb); the wavelength of the fundamental frequency light includes 1064nm or 1030nm, and the wavelengths of the first-stage pump light and the second-stage pump light include 532nm or 515nm.

[0015] In a possible implementation, the method further includes: extending the pulse width of initial seed light generated by a seed source to obtain the seed light, wherein the pulse width of the seed light is the same as the pulse width of the fundamental frequency light; the seed source includes any one of a supercontinuum generator and a laser oscillator.

[0016] According to another aspect of the present disclosure, there is provided an optical parametric multi-stage amplification device, comprising: a frequency doubling module, used to perform a first-stage frequency doubling and a second-stage frequency doubling on a fundamental frequency light to obtain a first-stage pumping light and a second-stage pumping light, wherein the energy of the second-stage pumping light is greater than that of the first-stage pumping light, and the first-stage pumping light and the second-stage pumping light have opposite energy jitter characteristics; a first-stage optical parametric amplification module, used to perform a first-stage optical parametric amplification on a seed light using the first-stage pumping light to obtain a first-stage signal light after optical parametric amplification; and a second-stage optical parametric amplification module, used to perform a second-stage optical parametric amplification on the first-stage signal light using the second-stage pumping light to obtain a second-stage signal light after optical parametric amplification.

[0017] In a possible implementation, the frequency doubling module includes: a first-stage frequency doubling module, used to perform a first-stage frequency doubling on the fundamental frequency light to obtain a first-stage pump light, and a second-stage frequency doubling module, used to perform a second-stage frequency doubling on the fundamental frequency light to obtain a second-stage pump light; the crystal thickness of the frequency doubling crystal used by the first-stage frequency doubling module is in a positive energy jitter region and the crystal thickness of the frequency doubling crystal used by the second-stage frequency doubling module is in a negative energy jitter region, or the crystal thickness of the frequency doubling crystal used by the first-stage frequency doubling module is in a negative energy jitter region and the crystal thickness of the frequency doubling crystal used by the second-stage frequency doubling module is in a positive energy jitter region, so that the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics; wherein the positive energy jitter region includes a thickness region in which the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental frequency light; and the negative energy jitter region includes a thickness region in which the energy jitter of the frequency-doubled pump light is negatively correlated with the energy jitter of the fundamental frequency light.

[0018] In a possible implementation, the device also includes: a pump source for generating the fundamental frequency light, the pump source including a solid laser based on a crystal doped with neodymium (Nd) or ytterbium (Yb); the wavelength of the fundamental frequency light includes 1064nm or 1030nm, and the wavelengths of the first-stage pump light and the second-stage pump light include 532nm or 515nm.

[0019] In a possible implementation, the device also includes: a seed source, used to generate initial seed light, the seed source includes any one of a supercontinuum generator and a laser oscillator; a pulse width stretcher, used to stretch the pulse width of the initial seed light generated by the seed source to obtain the seed light, the pulse width of the seed light is the same as the pulse width of the fundamental frequency light.

[0020] According to various aspects of the present disclosure, by using a first-stage pump light and a second-stage pump light with opposite energy jitter characteristics and the energy of the second-stage pump light is greater than that of the first-stage pump light, multi-stage optical parametric amplification is performed on the seed light, so that the energy stability point of the second-stage optical parametric amplification can be advanced from the oversaturated region to the unsaturated region, and at the same time, the second-stage signal light satisfies the high beam quality and high energy stability, effectively realizing the conversion of the signal light from the spatiotemporal Gaussian distribution to the spatiotemporal super-Gaussian distribution.

[0021] Further features and aspects of the present disclosure will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.

[0023] Figure 1 A schematic diagram showing a curve of how the energy of the signal light output by the second-stage parametric amplifier changes with the crystal thickness in the related art.

[0024] Figure 2 A schematic diagram showing the spatiotemporal distribution of the energy peak of the signal light of the second-stage parametric amplification in the related art.

[0025] Figure 3 A schematic diagram showing the spatiotemporal distribution of the most stable energy point of the signal light in the second-stage parametric amplification in the related art.

[0026] Figure 4 A flow chart of an optical parametric chirped pulse multi-stage amplification method according to an embodiment of the present disclosure is shown.

[0027] Figure 5 A schematic diagram showing a curve of energy variation of a 532nm pump light obtained by frequency doubling a 10J, 1.2ns, 1064nm fundamental frequency light as a function of the crystal thickness of the frequency doubling crystal according to an embodiment of the present disclosure.

[0028] Figure 6 A schematic diagram showing a curve of the change in percentage of the energy of the 532nm pump light obtained by frequency doubling when the energy of the 10J, 1.2ns, 1064nm fundamental frequency light has 5% positive and negative jitter relative to the energy of the 532nm pump light obtained by frequency doubling when the fundamental frequency light has no jitter as the crystal thickness of the frequency doubling crystal according to an embodiment of the present disclosure is shown.

[0029] Figure 7 A schematic diagram showing a curve of how the energy of the first-order signal light changes with the crystal thickness according to an embodiment of the present disclosure.

[0030] Figure 8A schematic diagram showing a curve of a change in the RMS value of the first-order signal light along with the crystal thickness according to an embodiment of the present disclosure.

[0031] Fig. 9 A schematic diagram showing the spatiotemporal distribution of the first-order signal light according to an embodiment of the present disclosure.

[0032] Fig.10 A schematic diagram showing a curve of how the energy of the second-order signal light changes with the crystal thickness according to an embodiment of the present disclosure.

[0033] Fig.11 A schematic diagram showing a curve of energy variation of the second-stage signal light with respect to the crystal thickness when the second-stage optical parametric amplification is performed without using the second-stage pump light with opposite energy jitter characteristics.

[0034] Fig.12 A schematic diagram showing the spatiotemporal distribution of the most stable energy position of the second-stage signal light when the second-stage optical parametric amplification is performed without using the second-stage pump light with opposite energy jitter characteristics.

[0035] Fig.13 A schematic diagram showing the spatiotemporal distribution of the most stable energy point of the second-stage signal light when the second-stage optical parametric amplification is performed using the second-stage pump light with opposite energy jitter characteristics according to an embodiment of the present disclosure.

[0036] Fig.14 A schematic diagram showing a comparison of the RMS value of the second-stage signal light output by the second-stage optical parametric amplification without using the second-stage pump light with opposite energy jitter characteristics and using the second-stage pump light with opposite energy jitter characteristics according to an embodiment of the present disclosure as a inverse of the crystal thickness.

[0037] Fig.15 A block diagram of an optical parametric multi-stage amplifier according to an embodiment of the present disclosure is shown.

[0038] Fig.16 A block diagram of another optical parametric multi-stage amplifier according to an embodiment of the present disclosure is shown.

[0039] Fig.17 A block diagram of another optical parametric multi-stage amplifier according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0040] Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0041] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0042] The term "and / or" herein is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the term "at least one" herein represents any combination of at least two of any one or more of a plurality of. For example, including at least one of A, B, and C can represent including any one or more elements selected from the set consisting of A, B, and C.

[0043] It should be understood that the terms “include” and “comprising” used in the specification and claims of the present disclosure indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections thereof.

[0044] In addition, in order to better illustrate the present disclosure, numerous specific details are given in the following specific embodiments. It should be understood by those skilled in the art that the present disclosure can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present disclosure.

[0045] As described above, the existing OPCPA system cannot simultaneously achieve high beam quality and high energy stability optical parametric chirped pulse amplification. Therefore, the disclosed embodiment provides a high-quality stable optical parametric multi-stage amplification method and device based on pump energy jitter cancellation. By using the pump light oversaturation frequency doubling method, the signal light can achieve high beam quality and high stability when performing the second-stage optical parametric amplification. This method not only eliminates the signal light energy jitter caused by the pump energy jitter, but also enables the second-stage parametric amplification to work in the unsaturated region, so that the signal light has a super-Gaussian spatiotemporal distribution.

[0046] The following Figures 4 to 17 The high-quality stable optical parametric multi-stage amplification method and device based on pump energy jitter cancellation provided by the embodiments of the present disclosure are introduced in detail.

[0047] Figure 4 FIG. 2 is a flow chart showing a method for optical parametric multi-stage amplification according to an embodiment of the present disclosure. Figure 4 As shown, the method includes: step S11 to step S13.

[0048] In step S11, the fundamental frequency light is subjected to first-order frequency doubling and second-order frequency doubling to obtain first-order pump light and second-order pump light, wherein the energy of the second-order pump light is greater than that of the first-order pump light, and the first-order pump light and the second-order pump light have opposite energy jitter characteristics.

[0049] In practical applications, the fundamental frequency light may be a pulsed laser generated by a solid laser based on a crystal doped with neodymium (Nd) or ytterbium (Yb), whereby the wavelength of the fundamental frequency light includes 1064nm or 1030nm, and then the wavelengths of the first-stage pump light and the second-stage pump light obtained after the first-stage frequency doubling and the second-stage frequency doubling may include 532nm or 515nm. Of course, other pump sources may also be used to output the fundamental frequency light, which is not limited in the embodiments of the present disclosure.

[0050] It can be seen that, like the optical parametric amplification process, the frequency doubling process of the fundamental frequency light also has oversaturated and unsaturated regions, such as Figure 5 The energy curve of a 10J, 1.2ns, 1064nm fundamental frequency light obtained by frequency doubling a 532nm pump light as the thickness of the frequency doubling crystal is shown. Figure 5 The figure shows the case where the fundamental frequency light has a positive and negative jitter of 5% and no jitter, where E 532 represents 532nm pump light, z SHG Represents the crystal thickness of the frequency doubling crystal, RMS 532 Represents the RMS value of 532nm pump light, 95% E 1064 This represents the case where the fundamental frequency light jitters 5% downward, 105%E 1064 This represents the case where the fundamental frequency light jitters 5% upward, 100% E 1064 Represents the situation where the fundamental frequency light does not jitter. Figure 6 The curve of the percentage of the energy of the 532nm pump light obtained by frequency doubling when the energy of the 10J, 1.2ns, 1064nm fundamental frequency light has a 5% positive and negative jitter relative to the energy of the 532nm pump light obtained by frequency doubling when the fundamental frequency light has no jitter varies with the crystal thickness of the frequency doubling crystal. Figure 5 and Figure 6 It can be seen from the figure that at the energy stable point (i.e. Figure 5 The intersection point of the three curves is "A", that is, Figure 6In the area before the intersection of the two curves in the figure, the energy jitter of the 532nm pump light is positively correlated with the jitter of the 1064nm fundamental frequency light, that is, when the energy of the 1064nm fundamental frequency light increases (or decreases) by a few percent, the energy of the 532nm pump light will increase (or decrease) by a certain amount at the same time; in the area after the energy stabilization point, the energy jitter of the 532nm pump light is negatively correlated with the jitter of the 1064nm fundamental frequency light, that is, when the energy of the 1064nm fundamental frequency light increases (or decreases) by a few percent, the energy of the 532nm pump light will decrease (or increase) by a certain amount at the same time.

[0051] Based on this, the 532nm light in the positive energy jitter region can be selected as the first pump light of the first optical parametric amplification, and the 532nm light in the negative energy jitter region can be selected as the second pump light of the second optical parametric amplification. This selection can also be reversed, but it is necessary to maintain that the first pump light and the second pump light used in the first and second optical parametric amplifications have opposite energy jitter characteristics. Wherein, the first pump light and the second pump light have opposite energy jitter characteristics, including: the first pump light has a positive energy jitter characteristic and the second pump light has a negative energy jitter characteristic, or the first pump light has a negative energy jitter characteristic and the second pump light has a positive energy jitter characteristic; the positive energy jitter characteristic includes that the energy jitter of the pump light after frequency doubling is positively correlated with the energy jitter of the fundamental light; the negative energy jitter characteristic includes that the energy jitter of the pump light after frequency doubling is negatively correlated with the energy jitter of the fundamental light.

[0052] In practical applications, any frequency doubling crystal known in the art (i.e., a nonlinear optical crystal used for frequency doubling, such as a BBO crystal (barium borate crystal (β-BaB2O4)), etc.) can be used to achieve the first and second frequency doubling of the fundamental frequency light, and the embodiments of the present disclosure are not limited to this. The embodiments of the present disclosure are not limited to the frequency doubling process of the first and second frequency doubling.

[0053] Wherein, in order to achieve that the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics, the crystal thickness of the frequency doubling crystal used in the first-stage frequency doubling is in the energy positive jitter region and the crystal thickness of the frequency doubling crystal used in the second-stage frequency doubling is in the energy negative jitter region, so that the first-stage pump light has a positive energy jitter characteristic and the second-stage pump light has a negative energy jitter characteristic, or the crystal thickness of the frequency doubling crystal used in the first-stage frequency doubling is in the energy negative jitter region and the crystal thickness of the frequency doubling crystal used in the second-stage frequency doubling is in the energy positive jitter region, so that the first-stage pump light has a negative energy jitter characteristic and the second-stage pump light has a positive energy jitter characteristic;

[0054] The energy positive jitter region includes a thickness region where the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental frequency light. For example, Figure 5The energy positive jitter region shown in the figure is less than 1 mm in crystal thickness, etc. The energy negative jitter region includes a thickness region that makes the energy jitter of the frequency-doubled pump light negatively correlated with the energy jitter of the fundamental frequency light. For example, Figure 5 Crystal thickness greater than 4mm in the medium energy negative jitter region, etc.

[0055] It should be understood that those skilled in the art can design the crystal thickness used for the first-stage frequency doubling and the second-stage frequency doubling according to actual needs. By designing the crystal thickness used for the first-stage frequency doubling and the second-stage frequency doubling, not only can the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics, but the energy of the second-stage pump light can also be made greater than that of the first-stage pump light. For example, the energy of the first-stage pump light can be 500 mJ, and the energy of the second-stage pump light can be 6.7 J. The embodiments of the present disclosure do not limit the energies of the first-stage pump light and the second-stage pump light.

[0056] In practical applications, the crystal thickness, cutting angle, etc. used in the first-stage frequency doubling and the second-stage frequency doubling can be designed so that the root mean square value of the energy jitter of the second-stage pump light is smaller than the root mean square value of the energy jitter of the first-stage pump light. For example, the root mean square value of the energy jitter of the second-stage pump light (i.e., the RMS (Root Mean Square) value of the energy jitter) can be 75% of the root mean square value of the energy jitter of the first-stage pump light. In this way, it is beneficial to generate signal light with better beam quality and more stable energy.

[0057] It should be understood that those skilled in the art can set the crystal thickness, cutting angle and other characteristics used for the first-stage frequency doubling and the second-stage frequency doubling according to actual needs, as long as the energy of the second-stage pump light can be greater than that of the first-stage pump light, the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics and the energy jitter root mean square value of the second-stage pump light is less than the energy jitter root mean square value of the first-stage pump light, and the embodiments of the present disclosure are not limited to this.

[0058] Exemplarily, the first-stage pump light can be a pump light with an energy of 500mJ, a wavelength of 532nm, a half-height full-width spot diameter of 15mm, a half-height full-width pulse width of 1.2ns, and a 12th-order super-Gaussian distribution in time and space; compared with the first-stage pump light, the energy of the second-stage pump light is increased to 6.7J, and the other optical parameters (wavelength, spot diameter and pulse width) are unchanged, and the energy jitter characteristics of the second-stage pump light are opposite to those of the first-stage pump light, and the RMS value of the second-stage pump light is 75% of the second-stage pump light.

[0059] In step S12, the seed light is subjected to a first-stage optical parametric amplification using the first-stage pump light to obtain a first-stage signal light after optical parametric amplification.

[0060] In practical applications, seed light can be understood as light to be subjected to optical parametric amplification. The seed light can be generated by a seed source, and the seed source can include any one of a supercontinuum generator and a laser oscillator.

[0061] Taking into account that the pulse width of the initial seed light generated by the seed source may be different from the above-mentioned fundamental frequency light, thereby affecting the subsequent optical parametric amplification of the seed light using the fundamental frequency light, therefore, in a possible implementation, the method further includes: pulse width widening the initial seed light generated by the seed source to obtain seed light, and the pulse width of the seed light is the same as the pulse width of the fundamental frequency light. Of course, it is also possible not to perform pulse width widening on the initial seed light (that is, directly use the initial seed light generated by the seed source as the seed light to be amplified), as long as the pulse width of the seed light and the fundamental frequency light (or pump light) are in the same order of magnitude. It should be understood that those skilled in the art can use a pulse width stretcher known in the art to achieve pulse width widening of the initial seed light, and this is not limited to the embodiments of the present disclosure.

[0062] In practical applications, nonlinear crystals known in the art (such as BBO crystals) can be used to implement first-stage optical parametric amplification of seed light using first-stage pump light. The embodiments of the present disclosure do not impose any restrictions on the crystal thickness, cutting angle and other characteristics used in the first-stage optical parametric amplification, as well as the optical parametric amplification process, as long as the required first-stage optical parametric amplification function can be achieved.

[0063] Exemplarily, the parameters of the seed light can be: energy 100 microjoules (μJ), central wavelength 800nm, Fourier transform limit 30 femtoseconds (fs), half-height full width spot diameter 8mm, half-height full width pulse width 0.47ns, and Gaussian distribution in both time and space; the first-stage optical parametric amplification of the above seed light can be performed using the first-stage pump light with the above energy 500mJ, wavelength 532nm, half-height full width spot diameter 15mm, half-height full width pulse width 1.2ns, and 12th-order super-Gaussian distribution in time and space. Figure 7 The energy curve of the first-order signal light changes with the crystal thickness. Figure 7 The three curves in the middle correspond to the first-stage pump light energy jittering 5% up and down and no jitter, where E Signal～1 represents the energy of the first-stage signal light, z_1 represents the crystal thickness of the nonlinear crystal used in the first-stage optical parametric amplification, 105% E P For the case where the first-stage pump light jitters upward by 5%, 95% E P For the case where the first-stage pump light jitters downward by 5%, 100% E P For the case where the first-stage pump light does not jitter, and Figure 8 The RMS value of the first-order signal light changes with the thickness of the crystal, where RMS Signal～1Represents the RMS value of the first-stage signal light, assuming that the seed light has no jitter and the first-stage pump light has a jitter of 1%. Fig. 9 The temporal and spatial distribution of the first-order signal light is shown by Figure 7 , Figure 8 and Fig. 9 It can be seen that since the first-stage optical parametric amplifier is in a small signal state (that is, the seed light energy is extremely small, resulting in a large difference between the pump light and the seed light), the first-stage pump light energy is almost not attenuated, and the first-stage signal light distribution is close to a flat top but still unstable. Therefore, the output first-stage signal light energy jitter is relatively large (that is, the RMS value of the first-stage signal light is large). However, it is precisely because of the large energy jitter that the second-stage optical parametric amplifier can achieve stable, high-beam quality output.

[0064] In step S13, the first-order signal light is subjected to second-order optical parametric amplification using the second-order pump light to obtain the second-order signal light after optical parametric amplification.

[0065] It should be understood that the first-stage signal light output by the first-stage optical parametric amplification is used as the seed light for the second-stage optical parametric amplification. In practical applications, a nonlinear crystal known in the art (such as an LBO crystal) can be used to implement the second-stage optical parametric amplification of the first-stage signal light using the second-stage pump light. The embodiments of the present disclosure do not limit the crystal thickness, cutting angle and other characteristics used in the second-stage optical parametric amplification, as well as the optical parametric amplification process, as long as the required second-stage optical parametric amplification function can be achieved.

[0066] For example, the energy of the second-stage pump light can be increased to 6.7 J, and the other optical parameters (wavelength, spot diameter and pulse width) are the same as those of the first-stage pump light. In addition, the energy jitter characteristic of the second-stage pump light is opposite to that of the first-stage pump light, and the RMS value of the second-stage pump light is 75% of that of the first-stage pump light. By using the second-stage pump light to perform the second-stage optical parametric amplification on the first-stage signal light, it can be obtained Fig.10 The energy of the second-order signal light changes with the thickness of the crystal. Fig.10 The three curves in the middle correspond to the first-level signal light energy jittering 10% up and down and no jittering. Signal～2 represents the energy of the second-stage signal light, z_2 represents the crystal thickness of the nonlinear crystal used in the second-stage optical parametric amplification, and 110% E S For the case where the first-level signal light jitters upward by 10%, 90% E S The first-level signal light jitters 10% downward, 100% E S For the case where the first-level signal light does not jitter, Fig.10It can be seen that the three curves have an intersection point "B" in the unsaturated region, and the signal light energy at the intersection point is the most stable. Therefore, the crystal thickness of the nonlinear crystal used in the second-stage optical parametric amplification can be the crystal thickness corresponding to the energy stable point "B" in the unsaturated region, for example, it can be 8mm;

[0067] If the second-stage optical parametric amplifier does not use the second-stage pump light with opposite energy jitter characteristics, that is, the energy jitter characteristics of the second-stage pump light are consistent with the energy jitter characteristics of the first-stage pump light, the output will be as follows: Fig.11 The signal light variation curve shown is Fig.10 and Fig.11 By comparison, it can be seen that when the amplification method with the opposite energy jitter characteristic of the embodiment of the present disclosure is not used, the output signal light changes with the above Figure 1 The trend is basically the same, that is, if the second-stage optical parametric amplifier is to work at the energy stability point, the crystal thickness must be in the oversaturation region, where the center of the signal light spatiotemporal distribution will have a serious depression and the output will be Fig.12 The time-space distribution of the second-level signal light is shown in FIG. The amplification method of the embodiment of the present disclosure can advance the energy stabilization point to the unsaturated region to obtain the following Fig.10 The energy stability point in the unsaturated region of Fig.13 The temporal and spatial distribution of the second-level signal light shown can make the temporal and spatial distribution of the output second-level signal light have no depression, thereby obtaining high-quality second-level signal light.

[0068] Fig.14 A schematic diagram showing a comparison of the RMS value of the second-stage signal light output by the second-stage optical parametric amplification without using the second-stage pump light with opposite energy jitter characteristics and using the second-stage pump light with opposite energy jitter characteristics according to an embodiment of the present disclosure as a function of the crystal thickness, wherein the RMS Signal～2 Represents the RMS value of the second-level signal light, such as Fig.14As shown, when the amplification method with the opposite energy jitter characteristic of the embodiment of the present disclosure is adopted, the lowest value of the RMS estimation is 0.0325%, the crystal thickness is 8mm, and it is in the unsaturated region; while when the amplification method of the embodiment of the present disclosure is not adopted, the lowest value of the RMS estimation is 0.0161%, the crystal thickness is 11.2mm, and it is in the oversaturated region. Although the best RMS obtained based on energy reflux without using the amplification method of the embodiment of the present disclosure is much smaller than the former, in fact, due to the inevitable presence of parametric fluorescence in the parametric amplification process, such an RMS value of less than 0.1% is generally difficult to achieve. Similarly, by comparison, it can be found that if a higher beam quality is to be obtained, the crystal thickness of the second-stage optical parametric amplification should be around 8mm, and if the opposite energy jitter scheme of the embodiment of the present disclosure is not adopted, at this thickness, the RMS value of the signal light is about 2.25%, and the amplification method with the opposite energy jitter characteristic of the embodiment of the present disclosure can almost eliminate the influence of the RMS value of the pump light.

[0069] According to the amplification method of the embodiment of the present disclosure, by using the first-stage pump light and the second-stage pump light with opposite energy jitter characteristics and the energy of the second-stage pump light is greater than the first-stage pump light and the RMS value of the second-stage pump light is less than the RMS value of the first-stage pump light, multi-stage optical parametric amplification is performed on the seed light, which can advance the energy stability point of the second-stage optical parametric amplification from the oversaturated region to the unsaturated region, and at the same time make the second-stage signal light meet the high beam quality and high energy stability, effectively realizing the conversion of the signal light from the spatiotemporal Gaussian distribution to the spatiotemporal super-Gaussian distribution.

[0070] Based on the above optical parametric multi-stage amplification method, the embodiment of the present disclosure also provides an optical parametric multi-stage amplification device, such as Fig.15 As shown, the device comprises:

[0071] A frequency doubling module 121, used for performing a first-stage frequency doubling and a second-stage frequency doubling on the fundamental frequency light to obtain a first-stage pumping light and a second-stage pumping light, wherein the energy of the second-stage pumping light is greater than that of the first-stage pumping light, and the first-stage pumping light and the second-stage pumping light have opposite energy jitter characteristics;

[0072] A first-stage optical parametric amplifier module 122, used for performing a first-stage optical parametric amplification on the seed light using the first-stage pump light to obtain a first-stage signal light after optical parametric amplification;

[0073] The second-stage optical parametric amplification module 123 is used to perform second-stage optical parametric amplification on the first-stage signal light using the second-stage pump light to obtain the second-stage signal light after optical parametric amplification.

[0074] In a possible implementation, the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics, including: the first-stage pump light has a positive energy jitter characteristic and the second-stage pump light has a negative energy jitter characteristic, or the first-stage pump light has a negative energy jitter characteristic and the second-stage pump light has a positive energy jitter characteristic; the positive energy jitter characteristic includes that the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental frequency light; the negative energy jitter characteristic includes that the energy jitter of the frequency-doubled pump light is negatively correlated with the energy jitter of the fundamental frequency light.

[0075] In a possible implementation manner, a root mean square value of energy jitter of the second-stage pump light is smaller than a root mean square value of energy jitter of the first-stage pump light.

[0076] In one possible implementation, Fig.16 As shown, the frequency doubling module 121 includes: a first-stage frequency doubling module 1211, used for performing a first-stage frequency doubling on the fundamental frequency light to obtain a first-stage pumping light, and a second-stage frequency doubling module 1212, used for performing a second-stage frequency doubling on the fundamental frequency light to obtain a second-stage pumping light;

[0077] The crystal thickness of the frequency doubling crystal used by the first-stage frequency doubling module 1211 is in the positive energy jitter region and the crystal thickness of the frequency doubling crystal used by the second-stage frequency doubling module 1212 is in the negative energy jitter region, or the crystal thickness of the frequency doubling crystal used by the first-stage frequency doubling module 1211 is in the negative energy jitter region and the crystal thickness of the frequency doubling crystal used by the second-stage frequency doubling module 1212 is in the positive energy jitter region, so that the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics;

[0078] The positive energy jitter region includes a thickness region where the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental light; the negative energy jitter region includes a thickness region where the energy jitter of the frequency-doubled pump light is negatively correlated with the energy jitter of the fundamental light.

[0079] In one possible implementation, Fig.17 As shown, the device also includes: a pump source 124 for generating the fundamental frequency light, the pump source 124 includes a solid laser based on a crystal doped with neodymium (Nd) or ytterbium (Yb); the wavelength of the fundamental frequency light includes 1064nm or 1030nm, and the wavelengths of the first-stage pump light and the second-stage pump light include 532nm or 515nm.

[0080] In one possible implementation, Fig.17 As shown, the device may also include:

[0081] A seed source 125, used to generate initial seed light, wherein the seed source 125 includes any one of a supercontinuum generator and a laser oscillator;

[0082] The pulse width stretcher 126 is used to stretch the pulse width of the initial seed light generated by the seed source 125 to obtain the seed light, and the pulse width of the seed light is the same as the pulse width of the fundamental frequency light.

[0083] It should be understood that those skilled in the art can design the thickness of the frequency doubling crystal used in the above-mentioned frequency doubling module 121 and the crystal thickness of the nonlinear crystal used in the above-mentioned first-stage optical parametric amplification module 122 and the second-stage optical parametric amplification module 123 according to actual requirements such as the parameters of the seed light to be amplified, and the embodiments of the present disclosure are not limited to this.

[0084] Furthermore, the specific implementation of each module in the device of the embodiment of the present disclosure can refer to the relevant description of each step in the method embodiment of the above embodiment of the present disclosure, and will not be repeated here.

[0085] According to the device of the embodiment of the present disclosure, by adopting the first-stage pump light and the second-stage pump light with opposite energy jitter characteristics and the energy of the second-stage pump light is greater than that of the first-stage pump light, multi-stage optical parametric amplification is performed on the seed light, so that the energy stability point of the second-stage optical parametric amplification can be advanced from the oversaturated region to the unsaturated region, and at the same time, the second-stage signal light satisfies the high beam quality and high energy stability, effectively realizing the conversion of the signal light from Gaussian distribution to super-Gaussian distribution.

[0086] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. An optical parametric multi-stage amplification method, characterized in that: include: Performing a first-stage frequency doubling and a second-stage frequency doubling on the fundamental frequency light to obtain a first-stage pump light and a second-stage pump light, wherein the energy of the second-stage pump light is greater than that of the first-stage pump light, and the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics; Performing first-stage optical parametric amplification on the seed light using the first-stage pump light to obtain first-stage signal light after optical parametric amplification; Performing second-stage optical parametric amplification on the first-stage signal light using the second-stage pump light to obtain second-stage signal light after optical parametric amplification; The first-stage pump light and the second-stage pump light have opposite energy jitter characteristics, including: the first-stage pump light has a positive energy jitter characteristic and the second-stage pump light has a negative energy jitter characteristic, or the first-stage pump light has a negative energy jitter characteristic and the second-stage pump light has a positive energy jitter characteristic; The positive energy jitter characteristic includes that the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental frequency light; the negative energy jitter characteristic includes that the energy jitter of the frequency-doubled pump light is negatively correlated with the energy jitter of the fundamental frequency light.

2. The method according to claim 1, characterized in that The crystal thickness of the frequency doubling crystal used in the first-stage frequency doubling is in the positive energy jitter region and the crystal thickness of the frequency doubling crystal used in the second-stage frequency doubling is in the negative energy jitter region, or the crystal thickness of the frequency doubling crystal used in the first-stage frequency doubling is in the negative energy jitter region and the crystal thickness of the frequency doubling crystal used in the second-stage frequency doubling is in the positive energy jitter region, so that the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics; The positive energy jitter region includes a thickness region where the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental light; the negative energy jitter region includes a thickness region where the energy jitter of the frequency-doubled pump light is negatively correlated with the energy jitter of the fundamental light.

3. The method according to claim 1, characterized in that The root mean square value of energy jitter of the second-stage pump light is smaller than the root mean square value of energy jitter of the first-stage pump light.

4. The method according to claim 1, characterized in that: The fundamental frequency light is a pulsed laser generated by a solid-state laser based on a crystal doped with neodymium (Nd) or ytterbium (Yb); The wavelength of the fundamental frequency light includes 1064 nm or 1030 nm, and the wavelengths of the first-stage pump light and the second-stage pump light include 532 nm or 515 nm.

5. The method according to claim 1, characterized in that The method further comprises: Extending the pulse width of the initial seed light generated by the seed source to obtain the seed light, wherein the pulse width of the seed light is the same as the pulse width of the fundamental frequency light; The seed source includes any one of a supercontinuum generator and a laser oscillator.

6. An optical parametric multi-stage amplifier, characterized in that: include: A frequency doubling module, used for performing first-stage frequency doubling and second-stage frequency doubling on the fundamental frequency light to obtain first-stage pumping light and second-stage pumping light, wherein the energy of the second-stage pumping light is greater than that of the first-stage pumping light, and the first-stage pumping light and the second-stage pumping light have opposite energy jitter characteristics; A first-stage optical parametric amplifier module, used for performing first-stage optical parametric amplification on the seed light using the first-stage pump light to obtain a first-stage signal light after optical parametric amplification; A second-stage optical parametric amplification module, used for performing a second-stage optical parametric amplification on the first-stage signal light using the second-stage pump light to obtain a second-stage signal light after optical parametric amplification; The first-stage pump light and the second-stage pump light have opposite energy jitter characteristics, including: the first-stage pump light has a positive energy jitter characteristic and the second-stage pump light has a negative energy jitter characteristic, or the first-stage pump light has a negative energy jitter characteristic and the second-stage pump light has a positive energy jitter characteristic; The positive energy jitter characteristic includes that the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental frequency light; the negative energy jitter characteristic includes that the energy jitter of the frequency-doubled pump light is negatively correlated with the energy jitter of the fundamental frequency light.

7. The device according to claim 6, characterized in that The frequency doubling module comprises: a first-stage frequency doubling module for performing a first-stage frequency doubling on the fundamental frequency light to obtain a first-stage pumping light, and a second-stage frequency doubling module for performing a second-stage frequency doubling on the fundamental frequency light to obtain a second-stage pumping light; The crystal thickness of the frequency doubling crystal used by the first-stage frequency doubling module is in the positive energy jitter region and the crystal thickness of the frequency doubling crystal used by the second-stage frequency doubling module is in the negative energy jitter region, or the crystal thickness of the frequency doubling crystal used by the first-stage frequency doubling module is in the negative energy jitter region and the crystal thickness of the frequency doubling crystal used by the second-stage frequency doubling module is in the positive energy jitter region, so that the first-stage pump light and the second-stage pump light have opposite energy jitter characteristics; The positive energy jitter region includes a thickness region where the energy jitter of the frequency-doubled pump light is positively correlated with the energy jitter of the fundamental light; the negative energy jitter region includes a thickness region where the energy jitter of the frequency-doubled pump light is negatively correlated with the energy jitter of the fundamental light.

8. The device according to claim 6 or 7, characterized in that The device also includes: A pump source, used to generate the fundamental frequency light, wherein the pump source comprises a solid laser based on a crystal doped with neodymium (Nd) or ytterbium (Yb); The wavelength of the fundamental frequency light includes 1064 nm or 1030 nm, and the wavelengths of the first-stage pump light and the second-stage pump light include 532 nm or 515 nm.

9. The device according to claim 6 or 7, characterized in that The device also includes: A seed source, used to generate initial seed light, wherein the seed source includes any one of a supercontinuum generator and a laser oscillator; The pulse width stretcher is used to stretch the pulse width of the initial seed light generated by the seed source to obtain the seed light, and the pulse width of the seed light is the same as the pulse width of the fundamental frequency light.

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