Research On The Measurement Of Femtosecond Pulse Based On Auto-Correlation

Since Maiman invented the first laser in 1960, scientists have been exploring methods on achieving an ultrafast pulse with smaller pulse width and higher power. On one hand researches managed to reduce pulse durations from microseconds, nanoseconds, picoseconds, femtosecond to attosecond in experiments while on the other hand, the pulse peak power of order of Petawatt has been achieved. Nowadays, the femtosecond pulse is widely used in cutting-edge researches such as astrophysics, attosecond optics, high harmonic generations and etc. As the pulse width is one of the most important characteristics which reflects the quality of the pulse, the speed and accuracy of the measurements for the pulse width becomes more important for the application of the ultrafast laser pulse. The methods of measuring the pulse width include autocorrelation, frequency-resolved optical gate, spectral phase interferometry for direct electric-field reconstruction. In this research, in accordance with the specific measurement of the pulse width, an auto-correlator was built based on second harmonic intensity autocorrelation principle. The main contents are shown as follows.1. We illustrate the principle of the second harmonic autocorrelation conducting research on the nonlinear crystal parameters, which has a major impact on the measurement of the pulse width. Improving the accuracy of the autocorrelation by optimizing nonlinear crystal parameters.2. Based on the simulation model done in Solidworks and Matlab, we optimized the design of light path to prove the principal of the autocorrelation theory. Building a small-sized table top autocorrelation which is portable and flexible for measuring pulse durations. The user interface is based on Labview software, designing a software to improve the efficiency of measurement. Moreover, studying the influence of the dispersion effect on the measurement of autocorrelation.3. Used under a specific set of experimental conditions of the pulse width of 35 fs and center wavelength at 800 nm. Used this autocorrelation to analyze the laser pulses. We have obtained a pulse width which is consistent with the actual data at hand. Compare and analyze the actual pulse width with the theoretical result, verifying the accuracy of the autocorrelation.4. Re-adjusted the optics to measure the pulse in Optical Parametric Amplification system with center wavelength of 1300 nm, and measured the femtosecond pulse width of 108.1 for the mentioned scheme. In order to make the autocorrelation capable of measuring the pulse width with different wavelengths.