Static, multimodal-multiplex spectroscopy (MMS) and Coded-excitation Raman spectroscopy
The motivation for this project focused on overcoming challenges in Raman spectroscopy --photon collection efficiency from a weak and inelastic process. Current Raman spectrometers include scanning systems such as the Fourier transform infrared (FTIR) Raman spectrometers and slit-based spectrometers. The downside to scanning systems is cost and scan time for adequate spectrum recovery and slit-based systems are limited in throughput by the width of the slit. We have developed a static, multi-modal multiplex Raman spectrometer. Contrary to current techniques, we combined ideas involving efficient weighing designs such as the Hadamard matrices, used by Golay and applied a static approach. These aperture codes provided an increase in throughput without sacrificing any spectral resolution over slit-based Raman spectroscopy systems.
The image above describes the advantage of using an aperure code over a slit as a function of exposure time. In the aperture coded spectrometer, we replace the input slit with a well-designed aperture code. Each column of the aperture acts as a slit with a unique binary pattern. The Hadamard matrices are mathematically well-defined and invertible codes for independent column code implementation.
The initial goal of the project was to obtain blood alcohol concentrations using Raman spectroscopy as a measurment tool. Raman spectroscopy is a spectroscopic technique with high chemical specificity. Over the past couple of years, we have developed an aperture coded spectrometer whose performance is optimized for extended, incoherent sources. We are currently using these ideas to transition a lab grade instrument into an in vivo biomedical diagnostic tool for characterizing analytes at clinically relevant levels.
The system design of the MMS spectrometer has been through a series of iterations starting from left to right. The current model is the last figure.
Future work includes measuring billirubin concentrations in premature infants diagnosed with jaundice. Detection of other analytes at clinically relevent levels are also of great interest to us.