Ultra-fast and calibration-free temperature sensing in the intrapulse mode

Abstract

A simultaneously time-resolved and calibration-free sensor has been demonstrated to measure temperature at the nanosecond timescale at repetition rates of 1.0 MHz. The sensor benefits from relying on a single laser, is intuitive and straightforward to implement, and can sweep across spectral ranges in excess of 1  cm⁻¹. The sensor can fully resolve rovibrational features of the CO molecule, native to combustion environments, in the mid-infrared range near λ = 4.85  μm at typical combustion temperatures (800–2500 K) and pressures (1–3 atm). All of this is possible through the exploitation of chirp in a quantum cascade laser, operating at a duty cycle of 50%, and by using high bandwidth (500 MHz) photodetection. Here, we showcase uncluttered, spectrally-pure Voigt profile fitting with accompanying peak SNRs of 150, resulting in a typical temperature precision of 0.9% at an effective time-resolution of 1.0 MHz. Our sensor is applicable to other species, and can be integrated into commercial technologies.