We compare imaging based on coherent and spontaneous Raman scattering (SpRS) under conditions relevant for biological imaging. Using a broadband laser source, we perform spectral domain imaging of polystyrene beads using coherent Stokes Raman scattering and SpRS and find comparable signal levels. Short interaction lengths, low molecule number, and low incident power all reduce the advantages available with coherent Raman methods. We present calculations to support our measurements.

We report spectrally-resolved chemical imaging based on Raman induced Kerr effect spectroscopy (RIKES). When used with circularly-polarized pump excitation, multiplex RIKES offers the potential for spectrally-resolved imaging free of the nonresonant background that plagues coherent anti-Stokes Raman scattering. RIKES does however have a highly sample-dependent birefringent background that limits its sensitivity and can introduce spectral distortions. We demonstrate that in low birefringence samples multiplex RIKES microscopy offers an enhanced signal-to-noise ratio compared to multiplex stimulated Raman scattering (SRS) when implemented in a high polarization-purity, low frequency chopping scheme.

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We present a systematic comparison between coherent and spontaneous Raman scattering under conditions relevant for biological imaging. Using spectral domain imaging, we find that the signal levels for each method are comparable at the low excitation power and low concentrations appropriate for biological samples. For samples of polystyrene beads with a molecular concentration of 10 M, we determine the critical power at which the two methods give equal signal levels to be ∼1.3 mW. The advantages offered by coherent Raman methods are mitigated by the low excitation power, low sample concentrations, and short interaction lengths involved with biological imaging. We present calculations to support our measurements.

We compare imaging using coherent and spontaneous Raman scattering under biological imaging conditions. We perform spectral domain imaging of polystyrene beads and find comparable signal levels for both methods at excitation powers and concentrations most relevant for biological samples. The critical power at which the two methods provide equivalent signal levels is found to be ~1.3 mW in 10 M polystyrene beads and ~7 mW in 13 M 2-propanol. The low sample concentrations and low excitation power necessary for most biological imaging applications reduce the relative advantages offered by coherent Raman methods.