Biomedical imaging – CARS/SRS

Imaging methods based on coherent Raman scattering (CRS) are, nowadays, among the most potent techniques for a rapid visualization of the chemical composition of complex structures with sub-micrometer resolution. In particular, these methods are called Coherent Anti-Stokes Raman Scattering (CARS) and Stimulated Raman Scattering (SRS).

Both involve third-order nonlinear optical processes (3)) where three electromagnetic waves interact with the sample volume to generate a characteristic optical signal. Upon coincidence of the difference frequency of a pair of such waves corresponding to the frequency of a Raman resonance, the signal is greatly enhanced. These techniques are typically employed to image bio-molecules in living or fixed cells or tissues. They offer the great advantage to not require any sort of labeling or staining [1]. Additionally, spectral information is obtained using broadband light sources [2]. The signal-to-noise ratio of these applications benefits greatly from the application of pulsed lasers at high repetition rates.

AFS offers compact, alignment-free sources for hyperspectral coherent Raman spectroscopy fully based on fiber-technology. The extreme tuning speed of our sources enables coverage of all resonances within a few seconds. The outstanding functionality of the systems has been proven in laboratory and clinical environments many times over the last years [3,4].