Improved spectral resolution of the femtosecond stimulated Raman spectroscopy achieved by the use of the 2nd-order diffraction method

Prolongation of the picosecond Raman pump laser pulse in the femtosecond stimulated Raman spectroscopy (FSRS) setup is essential for achieving the high spectral resolution of the time-resolved vibrational Raman spectra. In this work, the 2nd-order diffraction has been firstly employed in the double-pass grating filter technique for realizing the FSRS setup with the sub-5 cm−1 spectral resolution. It has been experimentally demonstrated that our new FSRS setup gives rise to a highly-resolved Raman spectrum of the excited trans-stilbene, which is much improved from those reported in the literatures. The spectral resolution of the present FSRS system has been estimated to be the lowest value ever reported to date, giving Δν = 2.5 cm−1.

Laser pulse compression and amplification via Raman backscattering in plasma

A simple theoretical model is proposed for the interaction between two counter-propagating laser pulses (a pump and a seed pulse) in unmagnetized plasma. Pulse compression and amplification are observed via numerical simulation. A one dimensional fluid model for stimulated Raman backscattering is proposed to investigate the pulse compression and pulse amplification mechanisms. To accomplish this, energy is transferred from the long pump pulse to a seed pulse, with a Langmuir plasma wave mediating the transfer. The study focuses on the intensity profile of the pump laser pulse. A Gaussian and a ring intensity profile are, separately, considered for the pump laser pulse.