Modeling of performance of mid-infrared gas sensors based on immersion lens diode optopairs

We present model for determination of performance of optical sensor that takes into account fine structure of gas absorption band and specific features of immersion lens LEDs and photodiodes operating in the mid-IR spectral range (3-5 mum). The model incorporates an instrument and transfer functions that enables evaluation of accuracy, sensitivity and limit of detection (LOD) of various optical sensors. The predictions of the model were compared with the experimental values obtained with the CO₂ analyzer based on immersion lens LEDs and photodiodes operating near 4.2 mum spectral band.