User:Uma-raman/Ultrafast Raman Loss Spectroscopy (URLS)

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Ultrafast Raman Loss Spectroscopy (URLS) is a form of Raman spectroscopy that provide vibrational structure information of a molecular system regardless of its nature such as fluorescent or non-fluorescent, weak Raman scatter or low density of scatters. It involves a multi-photon interaction with the molecule to provide the Raman signal that is coherent in nature i.e. have directional properties.

Principle

Ultrafast Raman Loss Spectroscopy (URLS) is an analogue of stimulated Raman scattering (SRS)[[1]] but more sensitive with better signal to noise ratio. Technically, it involves the interaction of two laser sources, viz. a picosecond (ps) Raman pump pulse and a white light (WL) continuum, with a molecule leading to the generation of loss signals on the higher energy (blue) side w.r.t. the wavelength of the Raman pump. This is unlike the gain signal observed on the lower energy (red) side in the case of SRS. Interestingly, these loss signals are found to be at least 1.5 times more intense than the SRS signals. In addition, the very prerequisite of the experimental protocol for signal detection to be on the higher energy side by design eliminates the interference from fluorescence, which appears on the red side. Besides, URLS being a self-phase matched process is experimentally easier.

L.H.S.: Schematic of URLS and SRS spectra.
File:R.H.S.: URLS (blue) and SRS (red) spectra of cyclohexane.

Thus, the rapid data acquisition, natural fluorescence rejection and experimental ease establishes Ultra-fast Raman loss scattering (URLS) as a unique valuable structure determining technique.