Miniaturized ultra-strong and ultra-short laser dispersion compensation device and method

Abstract

The invention discloses a miniaturized ultra-strong and ultra-short laser dispersion compensation device and method. The miniaturized ultra-strong and ultra-short laser dispersion compensation device comprises a stretcher, a pre-compensation compressor, an amplifier and a compressor. The pulse laser is firstly broadened by the stretcher, partial second-order and third-order dispersion is compensated by the pre-compensation compressor, partial high-order dispersion is increased, then the pulse laser is amplified by the amplifier, and finally the pulse laser is compressed to be close to the Fourier limit pulse width by the compressor. According to the invention, the pulse laser can be broadened to hundreds of picoseconds or even nanoseconds to be amplified under the existing condition and then compressed to be close to the Fourier limit pulse width, and good light beam quality is ensured.

Description

Technical Field

[0001] The present invention belongs to the field of laser technology, and specifically relates to a miniaturized ultra-intense ultra-short laser dispersion compensation device and method. It is applied to a miniaturized dispersion adjustment device and method based on chirped volume Bragg gratings or chirped fiber Bragg gratings, prism grating pairs, amplifiers, and grating pairs in an ultra-intense ultra-short laser system. Background Art

[0002] Ultra-intense ultra-short laser technology can create extreme physical conditions within the laboratory scale, which can greatly promote the development of basic disciplines, frontier interdisciplinary disciplines, and high-tech fields such as the interaction between light and matter. Precise control of the overall dispersion of an ultra-intense ultra-short laser system to eliminate higher-order dispersion, so that the output pulse is as close as possible to the Fourier-transform-limited compressed pulse, and a higher pulse peak power can be obtained at the same energy level, has always been a necessary requirement for ultra-intense ultra-short laser devices. Usually, the dispersion compensation of a laser device can be achieved through the combination of an Offner stretcher and a negative dispersion grating pair. Its disadvantages are that the traditional Offner stretcher occupies a large space, is difficult to install and adjust, and is not suitable for vehicle-mounted platforms because it works in the far field.

[0003] To overcome the above problems, in recent years, chirped volume Bragg gratings (CBGs) and chirped fiber Bragg gratings (CFBGs) have been used because of their small volume, easy installation and adjustment, insensitivity to vibration and suitability for vehicle-mounted platforms, and lower cost. The prism grating pair used as a pre-compressor is flexible in deployment and can perfectly compensate for third-order dispersion, making the dispersion compensation effect of the dispersion compensation device basically the same as that of the "Offner stretcher + negative dispersion grating pair" dispersion compensation scheme. However, the prior art still has problems such as insufficient higher-order dispersion compensation and low system integration, resulting in difficulty in achieving an ideal Fourier-limited pulse width for the output pulse. Summary of the Invention

[0004] In order to overcome the problems of large occupied space and difficult installation and adjustment in the existing amplification process of ultra-intense ultra-short laser pulses, the present invention provides a dispersion compensation device and method. The dispersion compensation device uses the dispersion characteristics of chirped volume Bragg gratings or chirped fiber Bragg gratings, prism grating pairs, and grating pairs to perform dispersion compensation on incident light, and adjusts in combination with the characteristics of the prism grating pair, and finally can obtain a laser output with small dispersion and excellent spot quality. This method has the advantages of high device adaptability, good spot quality, and device miniaturization.

[0005] The present invention is realized through the following technical solutions:

[0006] A miniaturized ultra-intense ultra-short laser dispersion compensation device, characterized in that it includes: a chirped volume Bragg grating or a chirped fiber Bragg grating, a prism grating pair, an amplifier, and a grating pair;

[0007] It is used to overall control the incident pulsed laser to meet the needs of amplification and broadening compression;

[0008] The chirped volume Bragg grating or chirped fiber grating is used to broaden the input pulsed laser to meet the basic requirements of amplification;

[0009] The prism pair is used to receive the compensated pulsed laser and pre-compensate part of the second-order, third-order, and fourth-order chromatic dispersions;

[0010] The amplifier, from the amplification process, is used to amplify the energy of the input pulse and provide a certain amount of chromatic dispersion;

[0011] The grating pair is used for the final adjustment of chromatic dispersion compensation to compress the pulse width of the amplified pulse into a compressed pulse close to the Fourier transform limit;

[0012] The pulsed laser is various linear (mainly Gaussian type) pulsed laser light sources generated by solid-state lasers, fiber lasers, etc.;

[0013] Using the above-mentioned miniaturized ultra-strong ultra-short laser chromatic dispersion compensation device and method, taking only the second to fourth-order chromatic dispersions as an example, its characteristics are that the method includes the following steps:

[0014] Step 1: Use a spectrometer with a suitable wavelength band to measure the spectral curve of the input pulsed laser (5), calculate its corresponding central wavelength and pulse width according to the spectral curve, and fit a similar line type;

[0015] Step 2: Calculate the ratio of the third-order chromatic dispersion to the second-order chromatic dispersion and the range of the ratio of the fourth-order to the third-order chromatic dispersion of the pre-compensation compressor (2) and the compressor (4), combine the chromatic dispersion parameters of the expander (1), and allocate the second-order chromatic dispersion of the pre-compensation compressor (2) and the compressor (4) according to the preset weight Third-order chromatic dispersion Fourth-order chromatic dispersion

[0016] Step 3: According to the required pre-compensation compressor Calculate the incident angle θ of the prism pair in 、the apex angle α of the prism, the light input quantity L in 、the spacing L of the prism pair gap 、the light output quantity L x ,and judge whether the above parameters meet the existing equipment standards through the ray tracing method. If they meet, continue; if not, feedback to the system and repeat Step 2;

[0017] Step 4: Calculate the chromatic dispersion magnitude of the amplifier according to the material characteristics and add it to the chromatic dispersion compensation system;

[0018] Step 5: According to the parameters of the required compressor Calculate the incident angle γ of the grating pair and the grating pair spacing G, and determine whether the above parameters meet the existing equipment standards through the ray tracing method;

[0019] Step 6: Make final adjustments according to the foregoing parameters. If they meet the existing equipment standards, the dispersion compensation process is completed and the corresponding second-order, third-order, and fourth-order dispersions and the corresponding parameters are output. Combine the Fourier spectroscopy theory to calculate the pulse width of the output pulse; if not, feedback to the system to adjust the dispersion value of the stretcher (1), change the dispersion weights of the pre-compensation compressor (2) and the compressor (4), and repeat the above steps.

[0020] Compared with the existing dispersion compensation methods, the advantages of the present invention are as follows:

[0021] 1) The device of the present invention is simple, and the dispersion compensation design of the system can be completed only through brief parameter calculation;

[0022] 2) Devices such as the chirped volume Bragg grating of the present invention are small and can be used for commercial applications;

[0023] 3) The dispersion adjustment method designed by the present invention has a large wavelength adaptation range and can be extended to any common wavelength band;

[0024] 4) The dispersion adjustment method designed by the present invention can theoretically well compensate the second-order, third-order, and fourth-order dispersions of pulsed lasers to obtain output pulses close to the Fourier transform limit. Description of the Drawings

[0025] Figure 1a and Figure 1b is a schematic structural diagram of a miniaturized ultra-strong and ultra-short laser dispersion compensation device of the present invention.

[0026] Figure 2 is a schematic structural diagram of an embodiment of a miniaturized ultra-strong and ultra-short laser dispersion compensation device and method of the present invention. Detailed Embodiment

[0027] The present invention will be further described in detail below with reference to the drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

[0028] The miniaturized ultra-strong and ultra-short laser dispersion compensation device of the present invention mainly includes the following core components (see Figure 1a 、 Figure 1b ):

[0029] Pulse stretcher (1): A chirped volume Bragg grating (CBG) or a chirped fiber Bragg grating (CFBG) is used as a dispersion compensation element to stretch the input femtosecond pulsed laser to picosecond or nanosecond order to reduce the peak power and avoid damage to optical elements caused by nonlinear effects during the amplification process.

[0030] Pre-compensation compressor: A prism-grating pair structure (2-1, 2-2) is used to pre-compensate for partial second-order, third-order, and fourth-order dispersion of the stretched pulse before amplification to optimize the subsequent amplification and compression processes.

[0031] Amplifier (3): A regenerative amplifier or a multi-pass amplifier structure is used to amplify the energy of the pre-compensated pulse and introduce a certain amount of material dispersion (such as titanium sapphire crystal, etc.).

[0032] Compressor: A grating pair structure (4-1, 4-2) is used to finally compensate for the remaining dispersion and compress the amplified pulse to a femtosecond pulse width close to the Fourier transform limit.

[0033] Combined with Figure 2 In the illustrated embodiment, the dispersion compensation method of the present invention includes the following steps:

[0034] Step 1: Measurement of input pulsed laser parameters

[0035] Use a spectrometer to measure the spectral characteristics of the input pulsed laser (5), including the central wavelength (such as 800 nm), spectral bandwidth (such as 11.77 nm), and initial pulse width (such as 80 fs).

[0036] Fit the time-domain line shape (such as Gaussian type) of the pulse according to the measurement data to provide a basis for subsequent dispersion calculation.

[0037] Step 2: Calculation of dispersion compensation parameters

[0038] Calculate the range of second-order, third-order, and fourth-order dispersion ratios of the pre-compensation compressor and the compressor.

[0039] Combined with the dispersion parameters of the pulse stretcher (1), allocate the dispersion compensation ratios of the pre-compensation compressor and the compressor according to the preset weight to ensure overall dispersion balance.

[0040] Step 3: Optimization of prism-grating pair parameters

[0041] According to the required dispersion amount of the pre-compensation compressor 2 Calculate the incident angle θ of the prism-grating pair in , the apex angle α of the prism-grating, the input light quantity L in , the spacing L of the prism-grating pair gap and the output light quantity L x ;

[0042] Use the ray tracing method to verify whether the above parameters meet the existing optical element standards. If they meet the standards, proceed; if not, adjust the dispersion distribution weight and recalculate.

[0043] Step Four: Amplifier Dispersion Compensation

[0044] According to the material properties of the amplifier (3) (such as the dispersion coefficient of the titanium sapphire crystal), calculate the introduced second-order third-order and fourth-order dispersion, and incorporate it into the overall dispersion compensation system.

[0045] Step Five: Grating Pair Parameter Optimization

[0046] According to the required dispersion compensation amount of the compressor calculate the incident angle γ of the grating pair and the grating pair spacing G;

[0047] Verify whether the grating pair parameters are feasible through the ray tracing method. If they do not meet the requirements, return to Step Two to adjust the dispersion distribution scheme; otherwise, proceed to the next step;

[0048] Step Six: Final Adjustment and Output

[0049] Perform final optimization by integrating all parameters to ensure the overall matching of the dispersion compensation system;

[0050] Use the Fourier spectroscopy theory to calculate the pulse width of the output pulse and verify whether it is close to the Fourier limit (such as 100 fs).

[0051] If the result is not ideal, adjust the dispersion value of the stretcher (1) or redistribute the dispersion weights of the pre-compensation compressor and the compressor until the optimal compensation effect is achieved.

[0052] Figure 1a This is the structural schematic diagram of Embodiment 1 of the miniaturized ultra-strong ultra-short laser dispersion compensation device of the present invention, including a reflective chirped volume Bragg grating 1, a prism grating pair 2-1, 2-2, an amplifier 3, a grating pair 4-1, 4-2, an input pulsed laser 5, a polarization beam splitter 6, a λ / 4 wave plate 7, a polarization beam splitter 8, a broadened pulsed laser 9, a roof prism 10, a pulsed laser 11 after passing through the pre-compressor, a pulsed laser 12 after passing through the amplifier, a polarizer 13, a roof prism 14, and an output pulsed laser 15. The input pulsed laser 5 is pulse-broadened by the chirped volume Bragg grating 1, pre-compensated by the pre-compensation dispersion compressor prism grating pair, amplified by the amplifier 3, and finally compensated and output by the grating pair.

[0053] Figure 1bThis is a schematic structural diagram of Embodiment 2 of the miniaturized ultra-strong and ultra-short laser dispersion compensation device of the present invention. The difference is that the chirped volume Bragg grating and the supporting polarization beam splitter and λ / 4 wave plate are replaced by a chirped fiber grating. It includes a chirped fiber Bragg grating 1, prism grating pairs 2-1, 2-2, an amplifier 3, grating pairs 4-1, 4-2, an input pulsed laser 5, a polarization beam splitter 6, a broadened pulsed laser 7, a roof prism 8, a pulsed laser 9 after passing through a pre-compressor, a pulsed laser 10 after passing through the amplifier, a polarizer 11, a roof prism 12, and an output pulsed laser 13. The input pulsed laser 5 is pulse-broadened by the chirped fiber Bragg grating 1, pre-compensated by the prism grating pair of the pre-compensation dispersion compressor, amplified by the amplifier 3, and finally compensated and output by the grating pair.

[0054] The fiber seed light source 5 provides a pulsed laser. The pulsed laser passes through an isolator 6, a λ / 2 wave plate 7, a polarization beam splitter 8, a λ / 4 wave plate 9, and a chirped volume Bragg grating 1 in sequence to broaden the pulse to the corresponding pulse width. After passing through the λ / 4 wave plate 9 and being reflected by the polarization beam splitter 8 to the unidirectional mirror 10, it is pre-compensated by the prism grating pair and the roof prism 11, and then undergoes an energy amplification process through the regenerative amplifier module 3-1 in the amplifier module. The right part is the collimation and reflection part components (including a biconvex lens, a plano-concave lens, and two reflectors) 13 and the coupling component 14. It then undergoes an energy amplification process through the multi-pass amplifier 3-2 in the amplifier module. During this process, the pump sources are four pump sources 12-1 to 12-4 with an energy of 120 mJ, a repetition frequency of 1 kHz, and a pulse width in the ns range. Immediately afterwards, it passes through the collimation and reflection module (including a plano-concave lens, a biconvex lens, a unidirectional mirror, and a reflector) 15, and finally the dispersion is filled by the compressor to compress the pulsed laser to a pulse width close to the Fourier limit. The folding mirror 16 is a supporting device for the compressor and is used to shorten the optical path, as Figure 2 shown. This device can finally obtain a high-efficiency ultra-strong and ultra-short laser with a short pulse width and high peak power.

[0055] In this example, a commercial 1 kHz fiber laser is used as light source 1. The input pulsed laser has a pulse width of 80 fs, a central wavelength of 800 nm, a corresponding bandwidth of 11.77 nm, and an energy of 1 nJ. The stretching factor of chirped volume Bragg grating 1 is 12.5 ps / nm, corresponding to a chirp rate of 2.67 nm / cm, a grating thickness of 50 mm, a diffraction bandwidth of 40 nm, a refractive index modulation of 0.001, and a corresponding diffraction efficiency > 80%. The material of the prism in grating pair 2 is D-ZF93 glass. The scratch density of the grating part is 600 lines / mm, the input angle is -55.3°, the prism apex angle is 33.6°, the light input amount is 15 mm, the light output amount is 30 mm, the grating pair spacing is 77.287 mm, the apex angle spacing of the grating pair is 262.2 mm, and the sizes of the hypotenuses of the grating pair are 45 mm and 90 mm respectively to ensure that the corresponding spectral components can be fully reflected. The dispersion of amplifier 3 is mainly provided by materials such as titanium sapphire crystal, and its size is The scratch density of the grating pair is 1740 lines / mm, the input angle is 59°, the diffraction angle is 26.67°, and the grating spacing is 265.57 mm. After passing through the above components, the pulse width remains basically unchanged, and the pulse energy is amplified by 1.4×10 8 times.

[0056] According to the principle of CPA technology, the pulse is stretched to about 147.13 ps after passing through chirped volume Bragg grating 1, pre-compensated for dispersion and compressed to 97.79 ps after passing through grating pair 2, and compressed to about 100 fs after passing through amplifier 3 and grating pair 4 compressor. The diffraction efficiency of chirped volume Bragg grating 1 during the stretching and compression process is about 75%, the diffraction efficiency of the grating pair is about 40%, and the diffraction efficiency of the grating compressor is about 85%. Finally, a spectrometer is used to measure the spectrum of the collimated light spot. The measurement results show that the spectral components are almost indistinguishable from the incident light. The second-order and third-order dispersions of the compressed output light can be well compensated and the efficiency is high. The remaining fourth-order dispersion can be compensated by reserving part of the second-order dispersion to make up for the broadening effect brought by the fourth-order dispersion.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A miniaturized ultra-strong ultra-short laser dispersion compensation device, characterized in that: Including: A stretcher (1) for temporally stretching the incident pulsed laser (5); A pre-compensation compressor for receiving the stretched pulsed laser (9) and performing pre-compensation for second-order, third-order, and fourth-order chromatic dispersions thereof; An amplifier (3) for amplifying the energy of the pre-compensated pulsed laser; A compressor for performing final chromatic dispersion compensation on the amplified pulsed laser and compressing it to a pulse width near the Fourier limit.

2. A miniaturized ultra-strong and ultra-short laser dispersion compensation device according to claim 1, characterized in that, The pulsed laser (5) is a laser light source with a temporal profile output by a solid-state laser or a fiber laser.

3. A miniaturized ultra-strong and ultra-short laser dispersion compensation device according to claim 1, characterized in that, The stretcher (1) uses a chirped volume Bragg grating or a chirped fiber grating as a chromatic dispersion compensation component.

4. A miniaturized ultra-strong and ultra-short laser dispersion compensation device according to claim 1, characterized in that, The pre-compensation compressor adopts a prism-grating pair structure. Among them, the prism material is a high-dispersion optical glass, and the scratch density of the grating part is 300 lines / mm to 1200 lines / mm; the incident angle of the prism-grating pair is -60° to 60°, and the prism apex angle (α) is 20° to 50°; the spacing of the prism-grating pair is 50 mm to 300 mm.

5. A miniaturized ultra-strong and ultra-short laser dispersion compensation device according to claim 1, characterized in that, The amplifier (3) is a regenerative amplifier or a multi-pass amplifier, and its gain medium is a titanium sapphire crystal, a ytterbium-doped fiber, or an erbium-doped fiber, and the amplified pulse energy is 1 mJ to 1 J.

6. The miniaturized ultra-strong and ultra-short laser dispersion compensation device according to claim 1, characterized in that The compressor adopts a grating pair structure. Among them, the grating scratch density is 1200 lines / mm to 2000 lines / mm; the grating incident angle is 50° to 70°, and the diffraction angle is 20° to 40°; the grating pair spacing is 100 mm to 500 mm.

7. A miniaturized ultra-strong ultra-short laser dispersion compensation method, characterized in that: This method includes the following steps: Step 1, measure the spectral characteristics of the input pulsed laser and fit its central wavelength, bandwidth, and initial pulse width; Step 2: Calculate the third-order dispersion to second-order dispersion ratio and the fourth-order to third-order dispersion ratio range of the pre-compensation compressor and the compressor, and combine the dispersion parameters of the stretcher (1). According to the pre-set weights, allocate the second-order dispersion of the pre-compensation compressor and the compressor Third-order dispersion Fourth-order dispersion Step 3. According to the required pre-compensation compressor calculate the incident angle θ of the prism grating pair in , the apex angle α of the prism grating, the light input quantity L in , the distance L between the prism grating pairs gap , the light output quantity L x , and judge whether it meets the existing equipment standards through the ray tracing method. If it meets, continue; if not, feedback to the system and repeat Step 2; Step 4: Calculate the dispersion of the amplifier and added to the dispersion compensation system; Step 5. According to the parameters of the required compressor calculate the incident angle γ and grating pair spacing G of the grating pair, and determine whether the above parameters meet the existing equipment standards through the ray tracing method; Step 6, adjust the system parameters to make the output pulse close to the Fourier transform limit pulse width.

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