Abstract
We present a simple hyperspectral Stimulated Raman Scattering (SRS) microscopy method based on spectral focusing of chirped femtosecond pulses, combined with amplitude (AM) and polarization (PM) modulation. This approach permits the imaging of low concentration components with reduced background signals, combined with good hyperspectral resolution and rapid spectral scanning. We demonstrate, using PM-SRS in a Raman loss configuration, the spectrally resolved detection of deuterated dimethyl sulfoxide (DMSO-d6) at concentrations as low as 0.039 % (5.5 mM). In general, background signals due to cross-phase modulation (XPM), two-photon absorption (TPA) and thermal lensing (TL) can reduce the contrast in SRS microscopy. We show that the nonresonant background signal contributing to the SRS signal is, in our case, largely due to XPM. Polarization modulation of the Stokes beam eliminates the nonresonant XPM background, yielding high quality hyperspectral scans at low analyte concentration. The flexibility of our combined AM-PM approach, together with the use of variable modulation frequency and lock-in phase, should allow for optimization of SRS imaging in more complex samples.
Highlights
Coherent Raman scattering (CRS) is a molecule-specific third-order nonlinear optical imaging method wherein contrast is achieved via vibrational Raman resonances [1,2,3,4,5]
We present a scheme based on AM and polarization modulation (PM) of one of the two incident beams (see Fig. 1(d)), permitting multimodal imaging with spectral focusing in a hyperspectral implementation, similar to a previously presented hyperspectral coherent anti-Stokes Raman scattering (CARS) arrangement [6]
Implementations of Stimulated Raman Scattering (SRS) microscopy based on spectral focusing can be integrated with other nonlinear optical imaging modalities such as SHG and TPEF, providing a simple yet powerful approach to label-free hyperspectral multi-modal imaging
Summary
Coherent Raman scattering (CRS) is a molecule-specific third-order nonlinear optical imaging method wherein contrast is achieved via vibrational Raman resonances [1,2,3,4,5] This technique is based on the interaction of laser beams at pump frequency ωp and Stokes frequency ωS with their frequency difference ∆ω = ωp − ωS matching the resonant frequency Ω of a specific molecular vibrational transition of a target molecule within the sample. The prime utility of this method is based on the generated antiStokes beam being in some cases enhanced by orders of magnitude as compared to spontaneous Raman scattering This is because CARS is a stimulated rather than spontaneous process and the magnitude of the CARS signal (ICARS) is proportional to the square of the pump intensity (Ip) and is linear with the Stokes intensity (IS). In samples where cross-phase modulation (XPM) dominates the background, we show that PM largely eliminates this effect, leading to rapid hyperspectral imaging at low analyte concentrations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
