Raman Spectroscopy Instrumentation and Its Application in Deep Tissue Imaging

Abstract

Raman spectroscopy is based on inelastic scattering, which gives molecular information. Due to its weak nature, for a long-time Raman spectroscopy was limited to only study of molecular interactions, but with the advancement in technology such as highly compact and stable lasers, high quantum efficiency and low noise detectors and so on, Raman spectroscopy today finds itself in wide applications ranging from study on biological cells to space applications. In the first work we aim to develop a 3D Raman imaging system that can give both chemical and morphological information of the concealed object using Universal Multiple Angle Raman spectroscopy (UMARS). Spatial offset Raman spectroscopy (SORS) is a widely used Raman technique and they can obtain Raman signals upto depth of 5 cm. Using UMARS technique we were able to demonstrate that we could obtain Raman signals of deeply buried objects (>5 cm). In the second work, we developed a 3D Raman Monte Carlo model for the UMARS experiments. The model was developed to simulate light propagation inside a chicken tissue with an ellipsoid object containing different chemicals embedded inside it. The 2D Raman intensity map obtained in this simulation was compared to the 2D Raman intensity map obtained by experiments and they were found to be in agreement. In the third work, we developed a low cost (< 4lakhs INR), portable (30×30cm), high throughput (f/3) and minimum optical aberration Raman spectrometer. In the fourth work, we developed a novel spectrometer design. Unlike current diffraction grating based spectrometer, this novel spectrometer utilizes multi diffraction orders. This design can be operated in an optical addition mode, where the different orders (+1 and -1) of the diffraction grating are focused onto the same detector plane such that the same wavelengths of both the order are optically combined to yield better signal to noise ratio. In another mode, this spectrometer records different wavelength range of the diffracted orders onto the detector, thus obtaining a long range spectrum without the need for a complex mechanism for rotating the grating. In the fifth and final work, we developed a low cost charge coupled devices (CCD) data acquisition module for spectroscopy applications. Here a CCD data acquisition system was developed based on field programmable arrays (FPGA).