Design and optimization of a compressive sensing time domain Raman spectrometer (CS-TDRS) for fast probing of thick diffusive media

In recent years, Diffuse Raman Spectroscopy (DRS) is emerging as a new tool for studying biological diffuse media with a high degree of innovation. Thanks to its high specificity to chemical and structural properties of the molecules, it became a unique tool in biomedical diagnosis. Compared to Diffuse Optical Spectroscopy (DOS) based on absorption and scattering techniques, in DRS only one excitation wavelength can generate broadband Raman lines, giving the possibility to retrieve molecular information of diffusive media. The limitation of DRS stays in the Raman signal intensity that can be revealed, this is why it has always been very hard to probe deep tissue throughout Raman scattering. Time domain and frequency domain setups have been tested with successful results making it possible to reach deeper layers of the samples. With this project, we are Introducing a new tool for Time Domain deep Raman probing with the innovative implementation of Compressive Sensing. Thanks to the intrinsic features, sparsity, and incoherence, proper of spectral scenes and detecting structure, it is possible to recover spectral images from fewer measures than common monochromator scanning technique. Due to low number Raman photons scattered from the excited sample, highly costly detection systems such as single photon avalanche diodes (SPAD) with high efficiency in the near infrared region are required. This set up usually takes to an off-budget final system. By the design and set up of a compressive sensing (CS) spectrometer, exploiting the features of a Digital light processor (DLP), it is possible to greatly increase fastness in Raman spectral imaging. CS detection will enable to use single-pixel cameras to retrieve full Raman spectra, drastically decreasing costs. It will be possible to implement innovative diffused optics techniques in the time domain, therefore, having chemical specificity and deep probing in tissues within a very short measuring time. In this thesis are shown the design, the construction and the characterization of the Compressive sensing – Time Domain Raman spectrometer and the results of the first measures on thick diffusive multilayer phantoms.