Behavior of high-order stimulated Raman scattering in a highly transient regime

Abstract

We have investigated the behavior of high-order stimulated Raman scattering in a highly-transient regime. We demonstrate efficient collinear generation of vibrational sidebands in molecular hydrogen and methane using two-color pumping with pulses of duration ϳ 100 fs tuned to a vibrational Raman transition. A Raman spectrum with a large bandwidth was observed, ranging from the IR to the UV. Under some conditions strong pump depletion was observed and up to five anti-Stokes sidebands were observed to have energies exceeding 10% of the transmitted pump pulse energies. A numerical simulation reproduces qualitatively and quantitatively the experimental results and allows us to explain key experimental features. The simulation also confirms that the molecular coherence in the medium is substantially increased by the two-color pumping and allows us to deduce values for the degree of material excitation. The use of this technique looks promising for efficient subfemtosecond pulse generation.

High-Energy, Multicolor Femtosecond Pulses from the Deep Ultraviolet to the Near Infrared Generated in a Hydrogen-Filled Gas Cell and Hollow Fiber

“…When using the vibrational transition of molecular hydrogen with a large Raman shift frequency of 4155 cm −1 [26], it is possible to generate multicolor fs pulses with spectral widths supporting transform-limited pulse durations of about 10 fs. Multicolor generation via the vibrational transition has been investigated both in a hydrogen-filled hollow fiber using two-color fs pump pulses at 800 and 600 nm [12] and in a hydrogen-filled gas cell using shorter two-color NIR pump pulses emitting at 800 and 1200 nm [20]. These investigations have reported multicolor laser emission covering from the DUV to NIR.…”

“…The efficiency of the multicolor generation can be improved by more than one order of magnitude using gaseous media rather than bulk media. In addition, the spectral range from the DUV to the NIR has been covered by employing Raman active gases as the nonlinear media for FWM [9,10,12,14,20,21]. When pumping with short fs pulses with high intensities, self-phase modulation (SPM) and cross-phase modulation (XPM) are simultaneously induced, which results in a broad spectral width for each multicolor emission.…”

“…The generation of multicolor laser emission via FWM has also been investigated in the femtosecond (fs) regime [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Resonant and non-resonant FWM has been investigated in bulk media [11,13,[15][16][17], leading to multicolor laser emission with a pulse energy of about 1 microjoule [17].…”

Wideband pulse propagation: Single-field and multifield approaches to Raman interactions

“…∼ 126THz), as in the transient-regime experiments of Sali et.al. [4,7]. In these experiments, typical pulses might be 70fs and 250fs wide at 800nm (30µJ) and 600nm (120µJ) respectively, and the comb of Raman sidebands generated are narrow and well separated.…”

“…[4,7], where the Raman transition is driven near-resonantly by a pair of intense pump pulses about 100fs long; compared to the transition frequency of about 130THz, the spectra of each pump pulse (and hence the generated sidebands) are relatively narrow. This means that a multi-component model is still not unreasonable, even if numerical considerations might demand that the arrays used to store these spectra overlap in frequency space.…”