Multidimensional femtosecond stimulated Raman spectroscopy troubles beyond the four-wave-mixing: present state and outlook towards X-ray regime |
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Miroslav Kloz | |
Department of Physics and Astronomy, Faculty of Sciences, VU University, De Boelelaan 1081, 1081HV Amsterdam, The Netherlands | |
It is exactly half century now since discovery of stimulated Raman scattering (SRS) (1). Despite numerous proof-of-the-principle experiments it is only about a decade since the phenomena got a general analytical use through the special phenomena called femtosecond stimulated Raman scattering (FSRS). When two strongly different pulses are time spatially overlapped in a sample, one spectrally ultra narrow and one ultra short in time, the entire Raman spectra of the sample are imprinted on the broad spectral envelope of the ultra short pulse. While the spectral resolution is determined by the narrow pulse the time gating precision is set by the ultrafast pulse so the time-energy resolution is no longer bound by the time-bandwidth uncertainty principle. This mechanism was recently successfully harnessed in mapping the fastest know bio reactions (2, 3) yet robust FSRS experiment is still under development (4). The supreme time resolution of FSRS opened the door for a fully coherent time domain 2D-Raman experiments (5). After initial optimism 2D Raman signals were discovered to be strongly overwhelmed by parasitic cascading signals (6) and at the moment it is unclear if the problem is fully solvable. Frequency domain 2D Raman experiments were proposed as well and their applicability is currently being evaluated. Many pitfalls encountered during development of FSRS experiments are relevant also for possible X-ray Raman spectroscopies and their solution critically determines perspective of the X-ray stimulated Raman techniques (7) 1. Eckhardt G, et al. (1962) Stimulated Raman Scattering From Organic Liquids. Physical Review Letters 9(11):455-457. |