Dispersion‐compensated supercontinuum generation for ultrabroadband multiplex coherent anti‐Stokes Raman scattering spectroscopy

Abstract

We have generated a dispersion-compensated picosecond ultrabroadband supercontinuum light source at the sample position without using any additional compensator such as a prism pair or a grating pair. The dispersion-compensated supercontinuum, which is obtained just by optimizing the length of a photonic crystal fiber, has been used as a Stokes laser source for ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS) spectroscopy. Owing to an optimized temporal overlap between the narrowband pump and the Stokes supercontinuum pulses, a CARS signal has been obtained efficiently with a spectral coverage of more than 2800 cm −1 . Furthermore, a vibrationally resonant CARS signal is observed not only when the pump pulse and the Stokes supercontinuum are temporally overlapped but also when the pump pulse follows the supercontinuum. It can be explained by an impulsive excitation of the vibrational coherence by the supercontinuum and a subsequent probe by a narrowband pump pulse. Using the dispersion-compensated supercontinuum, we can perform not only the frequency-domain multiplex CARS but also the time-domain impulsive CARS measurement by controlling the delay time between the narrowband laser and the supercontinuum. Both these techniques can be applied to microspectroscopy in order to obtain the wide spectral range of vibrational resonances and the suppression of the nonresonant background.

Single-shot detection of bacterial endospores via coherent Raman spectroscopy

“…The same approach was applied by Stauffer et al (27) to CARS on neat solutions of toluene and chloroform as well as rhodamine 6G with an emphasis on prospective monitoring of intramolecular vibrational energy redistribution; another but conceptually similar scheme was also implemented by Hamaguchi et al (28). By delaying a narrowband pump pulse relative to dispersion-compensated supercontinuum (used as a Stokes pulse within a standard broadband CARS scheme), they observed NR background-free CARS signal from impulsively excited vibrational modes of indene.…”

Simple setup for hybrid coherent Raman microspectroscopy

“…This combination of frequency-and time-resolved probing is an example of the so-called hybrid CARS scheme, [1,16,17] introduced under different names since as early as 1980. [18] The pulse timing is used to suppress NR FWM without appreciable reduction of the resonant signal.…”

“…[17,22,23] To the last point, one should note, however, that the present system has two distinct features. First, the broadband laser pulse for impulsive Raman excitation is derived directly from an ultrafast laser source, rather than from continuum generation in a PCF.…”

Nonlinear optical interactions in silicon waveguides

“…This has been so successful that commercial supercontinuum sources, based on photonic crystal fibers, have become widely available. These sources are used for applications such as spectroscopy [22] and optical coherence tomography [23].…”