A Method for Third-Order Dispersion Compensation and Regulation of Short Pulse Lasers Based on a Temperature-Controlled Birefringent Crystal

Abstract

The present invention discloses a method for compensating and regulating the third-order dispersion of short-pulse lasers based on a temperature-controlled birefringent crystal. Through the polarization control of the laser, a specific Jones matrix element of the temperature-controlled birefringent crystal is selected as the spectral modulation function, and an effective method for compensating the third-order dispersion of a short-pulse laser system is constructed. Specifically, through the spectral modulation function, the thickness and temperature control of the birefringent crystal, the lossless transmission of the short-pulse laser spectrum is first ensured. In addition, by adjusting the in-plane rotation angle φ of the crystal, the effective control of the third-order dispersion of the short-pulse laser can be achieved. The present invention is of great significance for compensating and regulating the third-order dispersion of a short-pulse laser system.

Description

Technical Field

[0001] The present invention belongs to the field of dispersion control of short - pulse laser systems. More specifically, it relates to a method for compensating and regulating the third - order dispersion of short - pulse lasers based on a temperature - controlled birefringent crystal, which can achieve the compensation and regulation of the third - order dispersion of lasers in a short - pulse laser system, and further meet the dispersion control requirements for optimizing parameters such as the signal - to - noise ratio of the laser system. Background Technique

[0002] In short - pulse laser systems, in order to simultaneously achieve high - energy and short - pulse - width laser amplification output, chirped - pulse amplification is a frequently used technique, and dispersion regulation is an important technical link. In terms of second - order dispersion regulation, the stretcher broadens the low - energy short - pulse in the time domain, then uses a gain medium or parametric amplification technology to amplify the energy, and finally uses a compressor to perform second - order dispersion compensation on the broadband laser and compress it to the transform - limited pulse to obtain high - energy and short - pulse - width laser pulses. Although the second - order dispersion of the system can be compensated by adjusting the stretcher and compressor, there will still be third - order dispersion that cannot be fully compensated. When broadband laser passes through optical elements such as lenses, beam splitters, polarizers, and gain media, third - order dispersion will be introduced. In addition, for short - pulse fiber laser systems, the third - order dispersion introduced by the fiber is more serious, which will have an adverse impact on the time - domain characteristics of short - pulse laser systems, such as the signal - to - noise ratio and the deterioration of the time - domain pulse characteristics caused by the pulse pedestal. Therefore, it is necessary to effectively control the third - order dispersion. Currently, commonly used methods include programmable acousto - optic modulators (AOPDFs), Gires - Tournois (GT) mirrors, and introducing prisms. However, due to the aperture limitation of AOPDFs, the supported energy is relatively small, and GT mirrors and prisms have disadvantages such as a small dispersion control range and being difficult to adjust. How to find a method that supports high energy, has a large dispersion control range, and is easy to operate is very important for improving the laser performance of ultra - short - pulse laser systems.

[0003] To be applicable to the third - order dispersion compensation of different short - pulse laser systems, taking the domestic Shenguang II high - energy picosecond petawatt laser device as an example, adjusting the compressor can compensate for the second - order dispersion introduced by the stretcher and the transmission medium, but the uncompensated third - order dispersion is about 1.55×10 6 fs 3, although it currently has little impact on the time-domain signal-to-noise ratio characteristics of picosecond petawatt laser devices, with the development of laser devices and the improvement of physical requirements, as well as considering the upgrade of the femtosecond device based on neodymium glass, when the compressed pulse width is in the femtosecond order of magnitude, the third-order dispersion of the system needs to be compensated. In addition, for titanium sapphire lasers or OPCPA amplifiers with a central wavelength of 800 nm, which require compression to a pulse width of 30 fs level, and for high-energy short-pulse fiber laser systems, the third-order dispersion of the system needs to be compensated. Currently, scientific researchers at home and abroad are seeking effective methods for third-order dispersion compensation.

[0004] Therefore, the present invention proposes a method for compensating and regulating the third-order dispersion of short-pulse lasers based on a temperature-controlled birefringent crystal. This method has the advantages of high supported energy, simple structure, strong applicability, and space saving, and can compensate and regulate the third-order dispersion of short-pulse laser systems, which will be of great significance for optimizing laser parameters such as the signal-to-noise ratio of short-pulse laser systems. Summary of the Invention

[0005] The object of the present invention is to address the deficiencies of the prior art and propose a method for compensating and regulating the third-order dispersion of short-pulse lasers based on a temperature-controlled birefringent crystal. This method has the advantages of high supported energy, simple structure, strong applicability, and space saving, and can compensate and regulate the third-order dispersion of short-pulse laser systems. This method will provide a simple and feasible technical approach for the third-order dispersion compensation of short-pulse laser systems.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for compensating and regulating the third-order dispersion of short-pulse lasers based on a temperature-controlled birefringent crystal, the method comprising the following steps:

[0008] Step 1, construct an optical path: place a half-wave plate, a polarizer, and an analyzer in sequence along the output optical axis of the short-pulse laser. Adjust the half-wave plate and control the analyzer to make the transmitted laser energy through the analyzer maximum, and the polarization of the incident laser on the polarizer and the transmitted laser on the analyzer is horizontal polarization;

[0009] Step 2, select a birefringent crystal material, design the thickness d(θ = 90°) and temperature T, design the spectral modulation function of the transmitted laser after the analyzer, corresponding to the m 22 matrix element of the birefringent crystal Jones matrix; design the central wavelength of the temperature T to control the spectral modulation function, and control the spectral modulation function bandwidth through the thickness d, so that the spectral components of the short-pulse laser can completely pass through, and the amplitude of the third-order dispersion introduced by the spectral modulation function can be adjusted through φ;

[0010] Step 3: Insert the birefringent crystal obtained in Step 2 and placed in the temperature control furnace between the polarizer and the analyzer, and make the laser incident normally (θ = 90°). In the transmission optical path of the analyzer, control the angle φ to achieve the dispersion control of the short-pulse laser.

[0011] The spectral modulation function is the Jones matrix of the birefringent crystal, which can be controlled by the polarization of the incident and outgoing lasers; by using the polarization configuration to select the m 22 matrix element, where the parameter

[0012] The half-wave plate (2), the polarizer (3), the birefringent crystal (5) placed in the temperature control furnace (4), and the analyzer (6) are used as a module, which can be directly applied to the laser system with third-order dispersion to be compensated, or transplanted into the laser system after being integrated by light source calibration.

[0013] For the short-pulse laser, the polarization of the laser before entering the birefringent crystal is parallel to the polarization of the laser after exiting the analyzer.

[0014] The birefringent crystal is placed in the temperature control furnace and fixed together on an adjustment frame that can rotate in the plane.

[0015] The dispersion measuring instrument is a spectral phase and dispersion measuring device such as Wizzler and Frog.

[0016] The birefringent crystal is a uniaxial crystal such as quartz, lithium niobate, and calcite with the crystal axis cut in the plane.

[0017] The method for compensating and regulating the third-order dispersion of short-pulse laser based on temperature-controlled birefringent crystal involves the selection of specific structures and parameters including the following aspects:

[0018] 1. Determine the polarization of the laser. Since the birefringence modulation spectral function depends on the Jones matrix of the birefringent crystal, it is necessary to make the polarization of the laser incident on the birefringent crystal and the polarization of the finally output laser parallel to each other, and then select the m in the 11 or m 22 . To achieve the dispersion adjustment function, the present invention selects the m 22 matrix element through the polarization configuration (both incident and outgoing are horizontally polarized), where the parameter

[0019] 2. Determine the type, thickness, and temperature of the birefringent crystal. Since the thickness of the birefringent crystal determines the width of the modulation spectrum and the amplitude of the third-order dispersion amount, it is necessary to first ensure that the spectral bandwidth requirement (Δλ FSR = λ 0 2 / (Δnd)), for convenience of adjustment, θ = 90° is selected in the scheme, and the central wavelength of the spectral modulation function is controlled by temperature, so that the spectral components of the laser can pass through completely in the end.

[0020] 3. Determine the optical axis direction of the birefringent crystal. The crystal axis of the birefringent crystal can be controlled by rotating the adjustment frame to achieve the in-plane rotation angle φ. In the present invention, the third-order dispersion is controlled by the in-plane rotation angle φ, and the additional second-order dispersion introduced during the adjustment process is small. If necessary, pre-compensation can be performed through the laser system expander or compressor. Here, the compensation and regulation functions for achieving the third-order dispersion are mainly described.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: ① For the problem of third-order dispersion compensation and regulation in a short-pulse laser system, the present invention designs a method for compensating the third-order dispersion of a short-pulse laser based on a temperature-controlled birefringent crystal by constructing an optical path and selecting the Jones matrix m of the birefringent crystal through the polarization configuration of the laser 22 as the spectral modulation function; ② By dynamically adjusting the in-plane rotation angle φ of the crystal, the dynamic adjustment of the third-order dispersion amount can be achieved; ③ The present invention can effectively compensate the third-order dispersion in a short-pulse laser system, and has the advantages of high supporting energy, compact structure, and easy adjustment, etc., and can meet the requirements for compensating the third-order dispersion such as improving the signal-to-noise ratio of the laser system. Description of the Drawings

[0022] Figure 1 It is the optical path layout diagram of the method for compensating and regulating the third-order dispersion of a short-pulse laser based on a temperature-controlled birefringent crystal of the present invention.

[0023] Figure 2 Taking the third-order dispersion compensation (bandwidth 3 nm (FWHM), dispersion 1.55×10 6 fs 3 ) of the Shenguang II high-energy petawatt laser system as an example, the theoretical calculation result curve graph, where a is the curve of the third-order dispersion amount and the spectral range varying with the crystal thickness; b is the variation relationship of the third-order dispersion amount with the in-plane rotation angle φ; c is the spectral intensity transmission curve; d is the -1.55×10 6 fs 3 third-order dispersion amount introduced by the compensation. Detailed Embodiment

[0024] The following further elaborates in detail on a method for compensating and regulating the third-order dispersion of a short-pulse laser based on a temperature-controlled birefringent crystal of the present invention in combination with the drawings and specific embodiments, in order to more clearly understand the specific structure and implementation process, but the protection scope of the present invention cannot be limited thereby.

[0025] In this embodiment, the output center wavelength of the Shenguang II high-energy petawatt laser system is 1053 nm, the bandwidth is 3 nm (FWHM), and the third-order dispersion to be compensated is 1.55×10 6 fs 3 .

[0026] The birefringent crystals in this embodiment are lithium niobate, quartz, calcite, uniaxial crystals with crystal axes cut in the plane, and electro-optic crystals with birefringence effects.

[0027] The method for compensating and regulating the third-order dispersion of short-pulse lasers based on temperature-controlled birefringent crystals in this embodiment includes the following steps:

[0028] Step 1, construct the optical path: place a half-wave plate 2, a polarizer 3, and an analyzer 6 along the optical axis of the output of the short-pulse laser 1 in sequence. Adjust the half-wave plate 2 and control the analyzer 6 to make the transmitted laser energy through the analyzer 6 the maximum, and the polarization of the incident laser on the polarizer 3 and the transmitted laser out of the analyzer 6 is horizontal polarization;

[0029] Step 2, select the birefringent crystal material, design the thickness d (θ = 90°) and temperature T, design the spectral modulation function of the transmitted laser after the analyzer (6), corresponding to the m 22 matrix element of the birefringent crystal Jones matrix; design the center wavelength of the temperature T to control the spectral modulation function, and control the spectral modulation function bandwidth through the thickness d, so that all spectral components of the short-pulse laser 1 pass through, and the amplitude of the third-order dispersion introduced by the spectral modulation function can be adjusted through φ;

[0030] Step 3, insert the birefringent crystal 5 obtained in Step 2 placed in the temperature control furnace 4 between the polarizer 3 and the analyzer 6, and make the laser incident normally (θ = 90°). In the transmission optical path of the analyzer 6, use a dispersion measuring instrument 7 for measurement. Turn on the temperature control, and the temperature works at T 1 , so that all spectral components of the short-pulse laser pass through; by controlling the in-plane rotation angle φ, the dispersion amount to be compensated can be obtained.

[0031] The following application example uses a quartz crystal as the birefringent crystal:

[0032] The birefringent quartz crystal is placed on a device with high-precision in-plane rotation adjustment, the angle control accuracy is 0.5°, the processing accuracy of the quartz crystal thickness is ±10 μm, and the above angle control accuracy and processing accuracy can be achieved by existing processes. The analyzer is a thin-film polarizer working at 45°, the working wavelength is 1045 - 1075 nm, the incident angle deviation is 45°, the temperature control range of the temperature control furnace is 25 - 50°, and the temperature control accuracy is 0.1°. The above can meet the design requirements.

[0033] The specific implementation steps are as follows:

[0034] 1. After turning on the laser, along the optical axis direction of Laser 1, first remove the temperature control furnace 4 and the birefringent crystal 5, adjust the half-wave plate 2, control the maximum transmitted energy behind the analyzer 6, and make the polarization of the incident polarizer 3 and the outgoing analyzer 6 laser be horizontal polarization; finally, enter the dispersion measuring instrument 7, measure the second-order and third-order dispersions of the short-pulse laser through the dispersion measuring instrument, and record the data respectively as a reference;

[0035] 2. According to the Jones matrix for birefringent spectral shaping:

[0036]

[0037] Among them,

[0038]

[0039]

[0040]

[0041] d(T) = d 0 [1 + α(T - T 0 )](α = 13.3667×10 -6 at T 0 = 18),

[0042]

[0043] For the purpose of regulating the third-order dispersion introduced by the laser system in this embodiment, through the optical path arrangement and polarization configuration, select the m 22 matrix element. The transmission spectral modulation function is:

[0044] E Out = m 22 E In

[0045]

[0046]

[0047]

[0048] In this embodiment, the thickness of the experimental crystal is 7 mm, θ = 90°, T = 26.7°, which can meet the bandwidth requirement of 3 nm (FWHM) for the laser and -1.55×10 6 fs 3Third-order dispersion amplitude requirements. To more clearly illustrate the dispersion compensation effect, the above formula is used to obtain the following curves: (a) the variation curves of the third-order dispersion and bandwidth with thickness; (b) the variation curve of the third-order dispersion amplitude with the in-plane rotation angle φ; (c) the spectral intensity transmittance curve; and (d) the third-order dispersion compensation curve for a dispersion of -1.55×10 6 fs 3 , as well as the second-order dispersion introduced during this process, as Figure 2 shown. It can be seen from Figure 2 that the present invention can effectively compensate and control the third-order dispersion of a short-pulse laser system.

[0049] Finally, it should be noted that any modifications to the specific embodiments of the present invention or equivalent replacements of some technical features, without departing from the spirit of the technical solution of the present invention, shall fall within the scope of the technical solution claimed in the present invention.

Claims

1. A method for compensating and regulating the third - order dispersion of short - pulse lasers based on a temperature - controlled birefringent crystal, characterized in that, the method comprises the following steps: Step 1, construct an optical path: Place a half - wave plate (2), a polarizer (3), and an analyzer (6) in sequence along the output optical axis of the short - pulse laser (1). Adjust the half - wave plate (2) and control the analyzer (6) to make the energy of the laser transmitted by the analyzer (6) maximum, and the polarization of the laser incident on the polarizer (3) and the laser emerging from the analyzer (6) be horizontally polarized; Step 2, select a birefringent crystal material, design the crystal thickness d and temperature T when the laser is incident normally, and design the spectral modulation function of the laser transmitted after the analyzer (6). Control the central wavelength of the spectral modulation function by adjusting the temperature T, and control the bandwidth of the spectral modulation function by adjusting the thickness d, so that all spectral components of the short - pulse laser (1) pass through, and adjust the amplitude of the third - order dispersion introduced by the spectral modulation function by rotating the in - plane angle φ of the birefringent crystal; Step 3, insert the birefringent crystal (5) placed in the temperature - control furnace (4) obtained in Step 2 between the polarizer (3) and the analyzer (6), and make the laser incident normally. In the transmission optical path of the analyzer (6), measure through a dispersion measuring instrument (7), and realize the dispersion control of the short - pulse laser by controlling the in - plane rotation angle φ of the birefringent crystal; Among them, the spectral modulation function corresponds to the m 22 matrix element of the birefringent crystal Jones matrix and is controlled by the polarization of the incident and outgoing lasers.

2. The method for compensating and regulating the third - order dispersion of short - pulse lasers based on a temperature - controlled birefringent crystal according to claim 1, characterized in that, Selecting the matrix element m of the Jones matrix of the birefringent crystal using the incident / outgoing light polarization configuration 22 , Where \(i = e, o\), that is \(n\) e and \(n\) o are the principal refractive indices of the extraordinary ray and the ordinary ray respectively, \(t\) i , \(s\) i , \(\lambda\) 1i , \(\lambda\) 2i , \(m\) i , \(m\) 1i , \(k\) i are the crystal system coefficients of the refractive indices of the extraordinary ray and the ordinary ray respectively. Among them, \(q\) is the light field transmission coefficient, \(\delta\) e and \(\delta\) o are the phase delay amounts of the extraordinary ray and the ordinary ray respectively, \(\theta\) is the incident angle of the incident laser, \(\lambda\) is the wavelength of the incident laser, \(d\) 0 is the crystal thickness at temperature \(T\) 0 , and \(\alpha\) is the calibration coefficient of the crystal thickness and temperature.

3. The method for compensating and regulating the third - order dispersion of short - pulse lasers based on a temperature - controlled birefringent crystal according to claim 1, characterized in that, The half - wave plate (2), the polarizer (3), the birefringent crystal (5) placed in the temperature - control furnace (4), and the analyzer (6) are used as a module and directly applied to the laser system with third - order dispersion to be compensated, or transplanted into the laser system after being integrated by light - source calibration.

4. The method for compensating and regulating the third - order dispersion of short - pulse lasers based on a temperature - controlled birefringent crystal according to claim 1, characterized in that, For the short - pulse laser (1), the polarization of the laser before entering the birefringent crystal (5) is parallel to the polarization of the laser after emerging from the analyzer (6).

5. The method for compensating and regulating the third - order dispersion of short - pulse lasers based on a temperature - controlled birefringent crystal according to claim 1, characterized in that, The birefringent crystal (5) is placed in the temperature - control furnace (4) and fixed together on an in - plane rotatable adjustment frame.

6. The method for compensating and regulating the third - order dispersion of short - pulse lasers based on a temperature - controlled birefringent crystal according to claim 1, characterized in that, The dispersion measuring instrument (7) is a Wizzler or Frog spectral phase and dispersion measuring device.

7. The method for compensating and regulating the third - order dispersion of short - pulse lasers based on a temperature - controlled birefringent crystal according to claim 1, characterized in that, The birefringent crystal is a uniaxial crystal with its crystal axis cut in the plane.

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