Acquisition of a Femtosecond Optical Parametric Oscillator Amplifier and Pulse Diagnostics

摘要

This equipment grant was intended to significantly enhance our experimental capabilities in femtosecond time resolved studies of molecular dynamics in condensed media. Two major improvements were the goals. Both have been successfully completed, and have generated results that have already been published. I describe them succinctly. (A) Since electronic recording speeds are limited to the GHz range, time resolved studies on femtosecond time scales invariably involve the use of two or mdre laser pulses, in which time steps are derived as a function of optical delay lines between pump and probe pulses. Quite clearly, to be able to follow the relevant science, the light sources should have the flexibility to tune to system resonances. As such, it is obvious that both pump and probe wavelengths should be tunable. Our femtosecond laser consisted of one tunable leg, one Optical Parametric Oscillator (OPO) pumped by a Ti:Sapphire laser. Under this grant, we developed a second one pumped by the same source, thus creating a two color, independently tunable, yet synchronized femtosecond spectrometer. While our initial intention was to purchase a second OPO, given the unsatisfactory specifications of commercially available units, we designed and constructed our own OPO. The system proved to be quite efficient, enabling us to use intensities as low as 500 microJ/pulse to pump both OPOs. A schematic of our design is presented in Fig. 1. We now boast of a two-color fs spectrometer with 80 fs time resolution (from cross correlation between the two arms) and independent tunability from 480 nm to 2400 nm in each arm. Data obtained with this system, measurements of nonadiabatic dynamics in solids, is already in press.