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

Abstract

Ultra-fast and calibration-free temperature sensing in the intrapulse mode 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 sweeps 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% (1σ) at an effective time-resolution of 1.0 MHz. Our sensor is applicable to other species, and can be integrated into commercial technologies. KAUST Repository

Intra-pulse laser absorption sensor with cavity enhancement for oxidation experiments in a rapid compression machine

“…The measured on-axis cavity FSR, determined from the cavity fringes and the previously determined tuning range, is consistent with the calculated value of 2964 MHz. For pulse repetition rates between 100 kHz -1.5 MHz, the measured tuning range follows the trends described by Chrystie et al [11], as illustrated in Fig Chemical processes in RCM experiments generally occur on the millisecond time-scale; therefore, a repetition rate of 100 kHz would result in a sufficiently high measurement time resolution (10 μs) while also providing a higher tuning range. Although a 50% duty cycle may seem to be the optimal operating point from Fig.…”

“…Three considerations need to be made: 1) sufficient measurement time resolution for chemical processes in the RCM; 2) spectrally resolved CO absorption line-shapes at high pressures (P ~10 bar); 3) cavity coupling noise suppression via chirp-induced laser line broadening. Chrystie et al [11] had previously shown that for pulsed QCLs, the tuning range decreases with increasing repetition rate, and a maximum tuning range is obtained at 50% duty cycle for a specified repetition rate. A similar characterization of tuning range was performed for the QCL used in this work.…”

CO2 Gas Temperature Sensing near Room Temperature by a Quantum Cascade Laser in Inter Pulse Mode

“…Temperature sensors based on tunable diode-laser absorption measurements have been widely applied in the investigation of plasma [4,5] and combustion processes (see, e.g., Refs. [6][7][8][9][10][11]), whereby the great majority of works focusses on gases at elevated temperatures. Farooq et al, for instance, applied a continuous-wavelength diode laser to measure time-histories of CO 2 gas temperature at typical combustion temperatures (400-1100 K) [6].…”

Intra-pulse H2O absorption diagnostic for temperature sensing in a rapid compression machine

“…Recently in our group, temperature diagnostics based on pulsed mid-infrared QCLs were demonstrated with a high temporal resolution in both shock tube [17,18] and RCM experiments [19]. For the shock tube application, Chrystie et al developed a temperature diagnostic by accessing multiple H 2 O lines with a single QCL [17].…”