Dual femtosecond ti: sapphire laser for ultrafast optical sampling two-color pump/probe studies
Luo, Ningyi Daniel
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A pair of self-synchronous Ti: Sapphire lasers have been setup for two-color pump/probe detection in the sub-picosecond time regime. The two 75 femtosecond self-mode-locked Ti:Sapphire lasers, pumped by a cw Argon ion laser, are operated asynchronously at slightly different repetition rates to provide continuously varying dynamic delay times. The two Ti:Sapphire lasers are tunable at 700-890 nm. The shorter wavelength pulses from one laser are used as a pump source, while the longer wavelength pulses are used as a probe. The sum-frequency pulses generated by the cross-correlation of the two laser pulses are used to define the "time-zero" position and trigger the pump/probe process. The experiment is triggered at the difference frequency, and the signal can be averaged many times allowing a weak signal to build up. Dual-time scale is involved with the interpretation of the signal, which allows the experiment to be carried on the real time scale and the signal to be recorded on a much reduced equivalent time scale. Excited state lifetime measurement of laser HITCI has proven that this technology is practically feasible. Several advantages have been seen: (1) independent wavelength tunability of the pump and probe lasers; (2) variable femto- to nano-second pump/probe time delay; (3) fast (^is-ms) data collection time so that the effects of laser phase noise, temperature drift and sample variability are greatly reduced; (4) compact optical layout, without the need for optical delay lines and modulators, and thus, simple optical alignment. This study sheds light on the development of a novel compact high speed optical instmment, which will be useful in time-resolved spectroscopy, optical communication, optical computing, and medical diagnosis. With the addition of a BBO second harmonic generator to one of the two Ti:Sapphire lasers to generate femtosecond tunable UV/blue laser pulses, this dual-laser system can be used to study the critical hydrated electron problem. That was the original motivation of designing and developing this state-of-the-art instmment.