Design, production and performance analysis of a multi-pass matrix optical system for trace spectroscopy

Önder Aksan, Tuba
The design and fabrication of a multi-pass matrix optical system (MMS) for the atmospheric trace gas measurement system planned to be established is described. The measurement system is a sealed thermal vacuum-capable chamber in which synthetic atmosphere configurations can be obtained by releasing various gases into the system. To increase the sensitivity of spectroscopic measurements, a MMS is designed to extend the optical path inside the chamber. The system, which is a modified Chernin cell design consisting of three objectives and two field mirrors, is adjustable to acquire up to 288 passes along the cavity. The design parameters of the system and the optimum configuration have been determined and simulated utilizing ray tracing technique with OpticStudio. Performance output and optical aberrations have been analyzed. As a result of the analysis, it has been shown that the geometric loss and astigmatism is negligible, off-axis angles are small, and the focal features are preserved. Performance experiments of the MMS were performed using a supercontinuum laser through an optical cuvette placed in open atmosphere environment. Two types of samples are chosen to simulate absorber and scatterrer behaviour. Absorption and scattering spectroscopy in the visible region of crystal violet (CV) and polypropylene (PP) were performed for different passage numbers and different concentrations. As a result of the measurements, the optimum number for the measurement system with a cuvette was determined as 32 with 4x4 matrix arrangement. The detection limit for CV is found to be 2.48 nM and for PP 16.8 μM. The results have been compared to alternative spectroscopy techniques. They show that; the system can be used for detection measurements of molecules and scattering microparticles in many fields ranging from atmospheric studies to environmental science. It offers a reliable, simple, inexpensive, fast and portable solution that can compete with other measurement techniques.


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Citation Formats
T. Önder Aksan, “Design, production and performance analysis of a multi-pass matrix optical system for trace spectroscopy,” M.S. - Master of Science, Middle East Technical University, 2021.