Development of a multiplex stimulated Raman microscope for spectral imaging through multi-channel lock-in detection

Abstract

We report the development of a multiplex stimulated Raman microscope for spectral imaging through multi-channel lock-in detection with a single light source. A white pump beam is prepared with a piece of photonic crystal fiber (PCF). The system does not require the synchronization of plural light sources or the scanning of their wavelengths, and thus a jitter-free pair of pump and Stokes beams is obtained, and a high degree of temporal synchronization is attained in the spectra. The multi-channel lock-in detection (extended to 128 channels) enables the observation of pseudo-continuous stimulated Raman spectra, demonstrating the strong ability of qualitative analysis to identify various types of C-H stretching modes such as the symmetric and asymmetric modes of the methylene∕methyl and aromatic groups. Images of a mixed film of polystyrene and polymethylmethacrylate are presented to demonstrate the system's spectral imaging ability. The spatial distribution of these materials is successfully captured through one-time imaging, although the noise of the white light pump beam generated with the PCF limits the system's imaging speed.

Microsecond scale vibrational spectroscopic imaging by multiplex stimulated Raman scattering microscopy

“…The detection sensitivity of our tuned amplifier array is better than the reported lock-in amplifier array 19 and the CMOS camera 18 technologies by nearly two orders of magnitude. For single-color SRS microscopy, the detection sensitivity of 50 μM retinol or 5 mM methanol solution was reported by Freudiger et al with 1 minute integration time 3 .…”

“…With such a scheme the acquisition of a complete Raman spectrum is difficult. Parallel detection of SRS signals has been demonstrated recently by using a CMOS array 18 or a multi-channel lock-in amplifier 19 , both having a moderate detection sensitivity of 10 −4 d I / I modulation depth. Notably, the maximum modulation frequency of current multi-channel lock-in amplifiers is less than 100 kHz 20 .…”

Coherent Raman Scattering Microscopy in Biology and Medicine

“…Rock et al (81) demonstrated recovery of the SRS spectrum after fast signal acquisition from a complementary metal-oxide-semiconductor (CMOS) array with a 20 ms integration time. The recent development of a multichannel lock-in detection scheme has shown promise for multiplex SRS imaging (82). The invention of a compact resonant amplifier array has enabled multiplex SRS imaging with 32 μs pixel dwell time (83).…”

In Situ and In Vivo Molecular Analysis by Coherent Raman Scattering Microscopy

“…For multiplex SRS, a photodiode array (62) or complementary metal-oxide semiconductor array (63) is used to collect dispersed SRS signals. The demodulation can be performed by either subtracting the background from the signal or using demodulators such as a multichannel lock-in amplifier (64) or a tuned amplifier array (31). …”