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Abstract: Ultrafast lasers have become one of the most powerful tools in coherentnonlinear optical spectroscopy. Short pulses enable direct observation of fastmolecular dynamics, whereas broad spectral bandwidth offers ways of controllingnonlinear optical processes by means of quantum interferences. Special care isusually taken to preserve the coherence of laser pulses as it determines theaccuracy of a spectroscopic measurement. Here we present a new approach tocoherent Raman spectroscopy based on deliberately introduced noise, whichincreases the spectral resolution, robustness and efficiency. We probe laserinduced molecular vibrations using a broadband laser pulse with intentionallyrandomized amplitude and phase. The vibrational resonances result in and areidentified through the appearance of intensity correlations in the noisyspectrum of coherently scattered photons. Spectral resolution is neitherlimited by the pulse bandwidth, nor sensitive to the quality of the temporaland spectral profile of the pulses. This is particularly attractive for theapplications in microscopy, biological imaging and remote sensing, wheredispersion and scattering properties of the medium often undermine theapplicability of ultrafast lasers. The proposed method combines the efficiencyand resolution of a coherent process with the robustness of incoherent light.As we demonstrate here, it can be implemented by simply destroying thecoherence of a laser pulse, and without any elaborate temporal scanning orspectral shaping commonly required by the frequency-resolved spectroscopicmethods with ultrashort pulses.

Autor: X.G. Xu, S.O. Konorov, J.W. Hepburn, V. Milner


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