Tunable diode laser-based two-line thermometry: a noncontact thermometer for active body temperature measurement

A precise and fast optical thermometer based on a tunable diode laser absorption spectroscopy is developed for breath diagnostics with relevance to noncontact body temperature measurement. As water vapor (H₂O) is the major component in human breath, two optimal absorption lines of H₂O at 1392 nm and 1371 nm are selected for sensitive body temperature measurement by systematically investigating the near-infrared spectral database. The optical thermometer is developed using two distributed feedback diode lasers with the time-division multiplexing technique to achieve real-time measurement. The sensor performance such as accuracy, repeatability, and time response is tested in a custom-designed gas cell with its temperature controlled in the range of 20°C-50°C. By measuring the test air with different water concentrations, the sensor consistently shows a quadratic response to temperature with an R-squared value of 0.9998. Under the readout rate of 1 s, the sensor achieves a measurement precision of 0.16°C, suggesting its potential applications to fast, accurate, and noncontact body temperature measurements.