Optical MEMS-scale multipass white cell for onchip gas sensing

Spectroscopy-based gas sensing has become a major concern for scientists in different domains due to its diverse applications in environmental monitoring, industrial productions and healthcare applications. For sensing in a confined space, multipass optical gas cells are used to multiply the light-gas interaction length, and thus provide improved sensitivity. In this work, we propose a White-type gas cell for integration with optical MEMS systems such as tunable lasers and FTIR spectrometer. The cell is based on a confocal arrangement of curved micro mirrors. Analytical expression for the total path length is derived in terms of the cell dimensions and the maximum input angle of the light is obtained. The performance of the cell is studied using optical ray tracing for cylindrical and spherical mirrors with aperture size of 250-500 μm and different light excitation conditions. Promising results are obtained with about 2 dB insertion loss and optical path of about 4 mm that could be achieved with a cell volume of about 0.125 mm
³
.