Development of Femtosecond Stimulated Raman Spectroscopy: Stimulated Raman Gain via Elimination of Cross Phase Modulation

Abstract

We have developed a new femtosecond probe technique by using stimulated Raman spectroscopy. The cross phase modulation in femtosecond time scale associated with off-resonant interaction was shown to be eliminated by integrating the transient gain/loss signal over the time delay between the Raman pump pulse and the continuum pulse. The stimulated Raman gain of neat cyclohexane was obtained to demonstrate the feasibility of the technique. Spectral and temporal widths of stimulated Raman spectra were controlled by using a narrow band pass filter. Femtosecond stimulated Raman spectroscopy was proposed as a highly useful probe in time-resolved vibrational spectroscopy.

Development of a Tunable Femtosecond Stimulated Raman Apparatus and Its Application to β-Carotene

“…Time-resolved femtosecond stimulated Raman spectroscopy (FSRS) is a new ultrafast spectroscopic technique that provides vibrational structural information with high temporal and spectral resolution. , In FSRS experiments, a picosecond near-IR Raman pulse (800 nm, 3 ps, <10 cm -1 bandwidth) creates an energetically well-defined virtual state in the Raman process, and a broadband femtosecond probe pulse (830−930 nm, <20 fs) stimulates the Raman transitions, producing a full vibrational spectrum over a 2000 cm -1 window. − For time-resolved experiments, a femtosecond actinic pulse (460−670 nm, <30 fs) is added to initiate a photochemical reaction. The spectral resolution of FSRS is limited by the bandwidth of the Raman pulse (<10 cm -1 ) or by the molecular vibrational free induction decay, while the time resolution is determined by the cross-correlation of the actinic and Raman probe pulses (typically <50 fs).…”

“…Although these FSRS experiments have been very successful, there are challenges for the routine performance of FSRS in the resonance Raman domain. In most FSRS implementations, the stimulated Raman process is driven around the wavelength of the Ti:Sapphire amplifier (780−820 nm) because it is convenient to generate the Raman pump pulse by spectrally filtering the intense 800 nm fundamental. − It is also feasible to produce picosecond Raman pulses around 400 nm by second-harmonic generation. , However, the use of a Raman pulse at a fixed wavelength in the red or in the near-UV severely limits the types of molecules that can be studied. , In order to extend the scope of FSRS applications, it is necessary to generate a Raman pulse in the visible range that provides better resonance enhancement of the species of interest compared to that of an 800 nm Raman pulse. In addition, tunability is desirable for optimum resonance enhancement and to avoid undesirable nonlinear interference .…”

Mastering Femtosecond Stimulated Raman Spectroscopy: A Practical Guide

“…To achieve these requirements, the most common method of generating a probe pulse is to generate a white light continuum in a medium with a modest nonlinear refractive index and a high damage threshold. These media include sapphire, ,,,,,− CaF 2 , ,,− GdVO 4, yttrium aluminium garnet (YAG), − liquids such as water, ,− noble gases, or photonic crystal fibers. − The choice of material will determine the spectral range of the probe and so must be considered carefully for the given application. For continuum generation in the visible and near-infrared regions of the spectrum, sapphire is a common choice because of its high damage threshold.…”