Simulations of the reflection pattern for different types of optical gas chambers to measure the concentration of trace gases using light absorption spectroscopy

The accurate design of an optical gas chamber is critical for enhancing the sensitivity and performance of spectroscopic detection systems. In this work, we present our study on the design of an optical gas chamber that is compatible with broadband and laser-based light sources. The design includes calculations for the physical path length of the gas cell. The optimum path length range calculated by using the radiative transfer equation has been found to be in the range of 300-450 cm. We then simulated the reflection pattern of different chamber geometries to achieve the path length within this range. Various designs were simulated and analyzed to evaluate their effect on beam propagation characteristics, including spot size, divergence, and intensity distribution at the detector plane. Simulation results provide quantitative comparisons of the spot size at the detector, light intensity profiles, and effective absorption path lengths across the gas cells, highlighting the trade-offs between design complexity and detection efficiency. The results and findings demonstrated that the configuration, based on nine concave mirrors (M1 to M9) with a focal length of 250 mm for the first mirror and 500 mm for the other mirrors, is the best design in terms of reflected light intensity. This design has produced the maximum efficiency in retaining the light source's intensity, thereby optimizing gas cell structure in applications such as trace gas detection and environmental monitoring.