Application Of Wavelet-transform In Femtosecond Laser Technology

We gave a short review for the progress of femtosecond optical pulses at the beginning of the thesis, and provide a brief introduction to the most widely used three methods for ultrashort optical pulses measurement. In them, spectral phase interferometry for direct electric-field reconstruction plays a crucial role in the loop for feedback compensation of spectral phase. However, in the procedure of filter with conventional Fourier transform technique, different widths of filter result different spectral phases. We introduced wavelet-transform into the spectral phase retrieval of femtosecond optical pulses to remove the uncertainty from conventional technique. Both simulated and experimental spectral shearing interference are applied in the analysis, and the results show that wavelet-transform is an accurate technique and is robust against noises. We took a structured spectrum from chirped pulse amplifier system as an example to demonstrate that this technique is more suitable for structured spectral phase retrieval. To demonstrate how to choose the mother wavelet functions, we examined the effects of spectral phase retrieval using Gabor mother wavelets with different shaping factors, and obtained the optimal range for shaping factors. We also applied wavelet-transform technique into the spectra analysis of terahertz radiations, and discover the time-resolved spectra for terahertz wave. Wavelet-transform technique has been also used as a tool for carrier-envelope phase extraction from f-to-2f beat. Finally, we applied time-frequency analysis method to extract the pulse phases form FROG traces, and obtained reasonably accurate results were from the flat-ridged FROG traces.