Wide-field Raman spectroscopic imaging with frequency modulation based spatially encoded light illumination

Raman spectroscopic imaging (RSI) can simultaneously measure the spectra and spatial information of samples. The measured data include two-dimensional spatial images and one-dimensional Raman spectra. Traditionally, RSI can be obtained by point scanning, line scanning, and wide-field illumination schemes. The point scanning scheme provides the best resolution but a lower imaging speed. On the contrary, wide-field illumination can image fast but provides a lower spatial resolution. To integrate the advantages of the two schemes, a complementary scheme for wide-field RSI was proposed, which uses frequency modulation based spatially encoded (FMSE) light as the excitation. In this scheme, all the beams of wide-field illumination are modulated at different frequencies. Thus, each excitation beam has its own modulation frequency, and the excited Raman signal will carry this modulation information. For the detection module, a single point detector was used to collect time series Raman signals carrying the unique modulation information. Using a sparse reconstruction-based demodulation strategy, the Raman image can be recovered effectively. The feasibility of the method was verified with numerical simulations. The reconstruction results showed that it is feasible to conduct Raman spectroscopic imaging with high-resolution and high speed under the illumination of FMSE light and detection of a single-point detector.