Vibrational spectroscopy via stimulated Raman induced Kerr lensing

Dekel Raanan,Yaron Silberberg,Julian Lüttig,Dan Oron

doi:10.1063/1.5029809

Dekel Raanan, Yaron Silberberg + Show 2 more

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Journal: APL Photonics	Publication Date: Jul 24, 2018
Citations: 19	License type: cc-by

Affiliation: Weizmann Institute of Science

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We present a new method for the measurement of the stimulated Raman spectrum based on time-dependent spatial modulation of a laser beam as it passes through a Raman active medium. This effect is similar to the instantaneous Kerr lensing and Kerr deflection yet involves resonant vibrations which result in a time-dependent refractive index change. We use sub-nanojoule pulses together with a sensitive pump-probe measurement apparatus to excite and detect the fine (10−5–10−4) temporal and spatial variations in intensity resulting from the Raman-induced Kerr effect. We demonstrate the effect by changing the spatial overlap between the pump and probe at the sample and measuring the time-dependent deformation of the probe beam’s cross section. This method is particularly useful for detection of low-frequency Raman lines, as we demonstrate by measuring the Raman spectrum of neat liquids in a cuvette.

Highlights

Than) the vibrational period of molecules,[15,16] time-domain measurements, known as impulsive stimulated Raman spectroscopy, have gained a lot of interest among researchers in recent years. As some of these techniques do not require spectral filtering of the broadband excitation pulse,[17,18,19] they are attractive for low-frequency Raman spectroscopy and potentially for coherent Raman imaging
The technique we present here is much better suited for microspectroscopy due to the collinear geometry of excitation and the small probed area, requiring much lower light intensity
We investigated two cases: (a) perfect overlap between the pump and probe at the focus, which mainly results in a change in the probe beam size due to pump-induced focusing or defocusing, and (b) imperfect overlap between the pump and probe which mainly results in a displacement of the probe beam

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Introduction

Than) the vibrational period of molecules,[15,16] time-domain measurements, known as impulsive stimulated Raman spectroscopy, have gained a lot of interest among researchers in recent years. As some of these techniques do not require spectral filtering of the broadband excitation pulse,[17,18,19] they are attractive for low-frequency Raman spectroscopy and potentially for coherent Raman imaging.

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