Study On The Pulse Stretching And Compression With Large Dispersive Delay Based On Chirped Volume Bragg Gratings

High-power and high-energy ultrashort laser pulses with duration of tens to hundreds of picoseconds have been widely required in the field of manufacturing industry and scientific research. However, there are many problems in the amplification of picosecond laser pulses. Direct amplification of the picosecond laser pulses will suffer from low efficiency and high cost. Compressing the nanosecond pulse to ~100 ps with the stimulated Brillion scattering(SBS) will induce jitter. Amplification of the laser pulses with duration of tens to hundreds of picoseconds with the conventional chirped pulse amplification(CPA) technology requires large dispersion and enough space.Chirped volume Bragg gratings(CVBGs) have the advantage of high laser-induced damage threshold, large dispersion and simple structure. In order to further understand the pulse stretching and compression and its applications, the bandwidth and dispersion of CVBGs are studied, and a configuration with four uniform CVBGs in symmetrical combination is proposed to obtain large dispersive delay. With the proposed symmetrical configuration, 15 ps laser pulse is stretched to about 1 ns. The main results are as follows:1. With the transfer matrix and fundamental matrix(F matrix) methods, along with the classical coupled wave theory, the bandwidth and dispersion of CVBGs are studied. The results indicate that the pass band and dispersive region of CVBGs show a blue shift as the incident angle increases. The group delay of CVBGs is almost linear with respect to the wavelength, and the maximum group delay is related to the grating thickness. The group delay ripple may be due to the interference between the reflected beams from the incident surface and diffracted beams in gratings, and the ripple can be improved with apodization.2. Pulse stretching and compression with CVBGs is related to the grating thickness, and nanosecond pulse stretching and compression requires a CVBG with thickness of several tens of centimeters. Based on the study of multiple CVBGs in combination, a configuration of four uniform CVBGs in symmetrical combination is proposed in the thesis, which has the advantage of small grating thickness, large dispersive delay, no spatial chirp and “plug-and-play” applications. With the configuration, the 10 ps Gaussian-shape and sech-shape pulses are stretched to 1 ns, and recompressed from 1 ns to 10 ps. These theoretical results are very important for the pulse stretching and compression with large dispersive delay based on CVBGs.3. With a picosecond optical fiber laser with the central wavelength of 1030 nm and duration of 15 ps, the pulse stretching and compression with CVBGs are studied experimentally. Pulse stretching and recompression can be achieved with a single CVBG, and the duration of the recompressed pulse is the same as that of the original pulse. With the configuration of CVBGs in combination, a pulse is stretched from 15 ps to 1 ns, which is consistent with the simulation results. The length of the whole stretcher is about 23 cm.4. The CVBG fabrication is studied with the interference of a plane wave and cylindrical wave and followed by the two-step thermal processing in photo-thermo-refractive glass. The wavelength selection of the CVBG is monitored with a supercontinuum ligh. With the transfer matrix method, the wavelength selection indicates that the groove density of the CVBG is 3650 lp/mm, and the amplitude of the refractive index modulation is 103 ppm.5. The laser-induced damage of CVBGs are studied with a pulse laser, of which the energy is 50 J, the duration is 3 ns and the central wavelength is 1053 nm. With the 1-on-1 test, the zero probability surface laser-induced damage threshold of the grating is 10.3 J/cm2. With the R-on-1 test, the zero probability surface laser-induced damage threshold is 15.2 J/cm2, and the zero probability volume laser-induced damage threshold is 19.1 J/cm2. With an optical microscope, the damages on the sample surface are studied. It shows that higher energy deposition occurs in the back sample surface. With an empirical formula combined with the dispersion curve of the photo-thermo-refractive glass, the nonlinear refractive index is calculated to be 4.7×10-20 m2/W, which lays a good foundation for CVBGs in high-power and high-energy applications.The results achieved in the thesis may be of reference values in improving the CPA technology, and provide a simple and compact solution for picosecond stretching and compression.