Shortening scattering duration by detuning purifies Raman spectra of complex systems

We highlight Resonant Raman scattering as a dynamical process with a finite duration time that results from not only the irreversible homogeneous broadening but also the reversible dephasing caused by the detuning from the resonance, which acts as a camera shutter with a regulated scattering duration. This provides a practical tool of controlling the scattering time. We show that the typical dephasing rates in gas and condensed matter phases are not sufficiently high to make the scattering fast. The detuning from the resonance leads to a strong purification of Raman spectrum from the contamination by higher overtones and soft modes.