Research On Chirped Pulse Spectral Interference And Its Application To The Measurement Of Shock Wave

With the laser technology developing and mature, ultrashort laser pulse interactions with matter have attracted more and more attentions. Actually, the interaction is a very complex process, in which the region of interest tends to occur on a sub-picosecond time scale and requires the testing technique providing a higher time resolution. As a continuous testing technique with spatial and temporal resolution, chirped pulse spectral interferometry (CPSI) takes a power of ultrafast time resolution (femtoseconds for the highest), and therefore provides an important experimental technique for studying the ultrafast laser-matter interactions. Because of high pressure and narrow width, the femtosecond laser-driven shock waves play an important role in the field of studying the dynamic response characteristics and high pressure equation of state at ultra-high strain rates. However, the ultrafast laser-driven shock waves were understood in a very limited way, one important reason is the lack of stable and reliable experimental techniques. Therefore, exploring the diagnostic technique of chirped pulse spectral interferometry and applying it to the ultrafast shock wave research make significance.In this thesis, we firstly study the process of CPSI measuring time-domain perturbations on probe pulse theoretically. And the spectral fringes truncation effects on the time-domain phase perturbation reconstruction have been studied, the results reveal that the data truncation would decrease effective range of the reconstructed phase shift. Moreover, during the reconstruction if frequency-domain phase shift of the probe pulse converts into time-domain by Fourier transform mapping, the data truncation also brings about time resolution decline and signal oscillation which needs to smooth before further derivation. Besides Fourier transform mode, wavelet transform mode is also avaible for extracting the frequency-domain phase shift from spectral fringes when the phase shift conversion between frequency and time domain employs direct mapping. Making a comparison of the both modes, we find that the reconstruction errors in Fourier transform mode are much lower, and for both cases the data truncation does not cause oscillations to the reconstructed time-domain phase shift doing good to the next derivation analysis. However, while a random white noise is added to the spectral fringes, oscillaitons emerge in the reconstruction results, but the wavelet transform mode performs better than Fourier transform mode on noise suppression and therefore it is more suitable for processing low SNR fringe patterns.For the generation of linearly chirped pulses which are used in the CPSI, we build a movable chirped pulse generation module to temporally stretch the femtosecond laser pulse. Furtherly, we propose a linear optical technique called asymmetric spectral interference method for measuring chirp coefficient of the obtained linearly chirped pulse. Studying the measurement principle and applicability theoretically and numerically, we find that the asymmetric spectral interference method is applicable to Gaussian and other waveform chirped pulses, but the measurement errors will be significantly increased while the chirp amount is too small, in addition, if a chirp is intrduced into the reference pulse, the measured chirp coefficient is the result containing the introduced chirp and the chirp under studies. Utilizing the asymmetric spectral interference method, we measured a chirped pulse which was obtained by stretching a femtosecond laser pulse using the chirped pulse generation module, the measurement results show that the pulse frequency-time mapping relationship is approximately linear consistent with stretching properties of the module. Consequently, the asymmetric spectral interference method is experimentally confirmed.Based on a femtosecond laser oscillator, we design and build a static experiment system for simulation of femtosecond laser-driven shock waves and the CPSI diagnosis. During the process, the key experimental techniques are studied and mastered, which provide the technical support for dynamic testing. Utilizing the chirped picosecond laser pulses, we carry out an experiment for studying laser-driven shock waves in aluminum film and the CPSI diagnostic technique. When the shock wave arrive at the aluminum film free surface, the evolution history of free-surface displacement and velocity around the startup moment are acquired by CPSI in a single shot, the test range and time resolution are562.5ps and3.1ps, respectively. Consequently, experimental verification of the CPSI principle is achieved.In order to extend the test range of the CPSI diagnostic technique, we design a scanning spectral interferometer by using a linearly chirped pulse series and a spectrometer-streak camera recording system. The principle and the measurement of time-domain phase shift are studied theoretically and numerically, the results show that scanning spectral interferometer has the same time resolution as CPSI, but much larger test range. And although different sampling intervals of the recording system lead to differences in the spectral interferogram distribution, the measurement accuracy is stable. Aim at improving the weakness of velocity interferometer system for any reflector (VISAR), we design a chirped pulse velocity interferometer based on an imaging spectrometer. By theoretical study of the principle and the characteristics of velocity measurement, we find that the interferometer can achieve picosecond resolution in recording, and reduce the demands for high spectral resolution by producing interference fringes parallel to the direction along the spectral axis. Additionally, the system parameters are easily adjustable when employing a supercontinuum probe pulse and a grating stretcher. Obviously, the application range of velocity interferometer is widened. Consequently, chirped pulse velocity interferometer provides a promising approach for the measurement of laser-driven shock waves.