Raman spectroscopy has been a powerful tool in various fields of science and technology ranging from analytical
chemistry to biomedical imaging. In spite of unique features, Raman spectroscopy has also some limitations. Among
them are weak Raman signal compared to strong fluorescence and relatively complicated setup with expensive and bulky
spectrometer. In order to increase the sensitivity of Raman technique, many clever attempts have been made and some of
them were very successful including CARS, SRS, and so on. However, these still requires expensive and more
complicated setup. In this work, we have attempted to build a real-time compact Raman sensor without spectrometer.
Conventional spectrometer was replaced with a narrow-band optical filter and alternatively modulated two lasers with
slightly different wavelengths. At one laser, Raman signal from a target molecule was transmitted through the optical
filter. At the other laser, this signal was blocked by the optical filter and could not be detected by photon detector. The
alternative modulation of two lasers will modulate the Raman signal from a target molecule at the same modulation
frequency. This modulated weak Raman signal was amplified by a lock-in amplifier. The advantages of this setup
include compactness, low cost, real-time monitoring, and so on. We have tested the sensitivity of this setup and we found
that it doesn’t have enough sensitivity to detect single molecule-level, but it is still good enough to monitor the change of
major chemical composition in the sample.