Stimulated Raman spectroscopy using chirped pulses

Abstract

We present a detailed theoretical and experimental characterization of a new methodology for stimulated Raman spectroscopy using two duplicates of a chirped, broadband laser pulse. Because of the linear variation of laser frequency with time (‘chirp’), when the pulses are delayed relative to one another, there exists a narrow bandwidth, instantaneous frequency difference between them, which, when resonant with a Raman‐active vibration in the sample, generates stimulated Raman gain in one pulse and inverse Raman loss in the other. This method has previously been used for coherent Raman imaging and termed ‘spectral focusing’. Here, gain and loss signals are spectrally resolved, and the spectrally integrated signals are used to determine the spectral resolution of the measured Raman spectrum. Material dispersion is used to generate a range of pulse durations, and it is shown that there is only a small change in the magnitude of the signal and the spectral resolution as the pulse is stretched from 800 to 1800 fs in duration. A quantitative theory of the technique is developed, which reproduces both the magnitude and linewidth of the experimental signals when third‐order dispersion and phase‐matching efficiency are included. The theoretical calculations show that both spectral resolution and signal magnitude are severely hampered by the third‐order dispersion in the laser pulse, and hence, a minimal amount of chirp produces the most signal with only a slight loss of spectral resolution. Copyright © 2014 John Wiley & Sons, Ltd.

Polarization dependence of chirp-induced nonlinear Raman scattering spectroscopy of aqueous ions and organic liquids in the THz regime

“…The peak can be assigned to vibrational modes of ZnBr2, ZnBr3and ZnBr4 2complexes [9], which were not resolved by our experiment. In our experiment, an increase of the temporal width of the stretched pulse leads to a higher spectral resolution but reduces the signal-to-noise ratio (see [10]). …”

Perspective: Two-dimensional resonance Raman spectroscopy

“…Future work should explore the possibility of implementing an all-narrowband approach and/or incorporating chirped laser pulses. 80 Singleshot methods, which have proven to be very powerful in 2D photon echo spectroscopy, may also be useful in 2DRR experiments.…”

The Fusion of Microfluidics and Optics for On-Chip Detection and Characterization of Microalgae

“…In a typical Raman spectrum diagram, the abscissa indicates the Raman shift and the ordinate indicates the Raman intensity, which can be used to analyze both components and their content [105]. Although the Spontaneous Raman scattering is very weak, improvements in the hardware and techniques have been made to boost the signal of conventional Raman spectroscopy, such as resonant Raman spectroscopy [106], surface-enhanced Raman spectroscopy [107], confocal Raman spectroscopy [108], coherent anti-Stokes Raman spectroscopy [109] and stimulated Raman spectroscopy [110]; these methods effectively enhance the Raman signal and are widely used in microalgae detection [105].…”