Ultrashort laser pulse characterization by three optical methods: autocorrelation, optical interference, and spectral analysis

Abstract

In this work, we present results on the characterization of ultrashort laser pulses in the range of tens of femtoseconds by three techniques: autocorrelation, spectral analysis and optical interference. Pulses are generated by a Ti-Sapphire (Ti:Sa) laser pumped by a solid state laser. The temporal width of the pulse (FWHM) was measured at different wavelengths from 730 to 820 nm. At the same wavelength, we obtained different values depending on the characterization technique used. We discuss those results and the theoretical models used in each case. For autocorrelation and spectral analysis, we assume an almost-Gaussian pulse to calculate the pulse width. The mathematical model employed allowed us to estimate deviations from this approximation. The experimental results obtained by interferometry allowed us to control the spatial and temporal distance between pulses. The spectral properties of almost-Gaussian functions are considered and applied to characterize to a second-order approximation in the expansion of the coefficients the pulses. Specifically, adding small amounts of odd-order Hermite-Gauss to a Gaussian induces a second-order increase in the time-bandwidth product, while the increase in the time-bandwidth product from adding even-order Hermite-Gaussian is higher-order and hence smaller. We compare the almost-Gaussian functions with femtosecond temporal width pulses data obtained for the Ti:Sa laser.