Rapid, broadband spectroscopic temperature measurement of using VIPA spectroscopy

Spectroscopic temperature measurements using coherent or incoherent light sources coupled to optical spectrometers have been accomplished by measuring the distribution among the quantized energy levels of a given sample, for example the ro-vibrational intensities of a molecule [1]. Moreover, the dependence of the experimental spectrum on temperature and pressure is also observed via line-shape broadening and line-center shifts. The temperature and pressure of the system can be deduced by comparing the experimental spectrum to a modeled spectrum that includes temperature and pressure dependence. Spectroscopic temperature measurements based on sample absorption have several advantages compared to well-established temperature measurement tools such as thermocouples, thermistors, and blackbody radiation spectral measurements. For example, in an optical setup, light can be passed through a gas sample to measure the temperature in situ and integrated across a remote path of the gas sample, as compared to a point measurement from a device mounted onto the container wall. There has been much research into the development of spectroscopic temperature measurement sensors. Measurements with such systems have been accomplished by rapidly scanning (10 kHz–1 MHz) single-frequency lasers over absorption features in sample gases in harsh environments to measure the linewidth, centroid, and intensity [2–4]. One disadvantage of previous spectroscopic temperature measurements is the trade-off of spectral bandwidth for rapid scanning on timescales of under 1 ms. Specifically, using a single diode laser source, it has been difficult to achieve rapid spectroscopic measurement with spectral bandwidth of more than 15 cm. However, in cases where sample absorption is weak, or where the sample is contained in an Abstract Time-resolved spectroscopic temperature measurements of a sealed carbon dioxide sample cell were realized with an optical frequency comb combined with a twodimensional dispersive spectrometer. A supercontinuum laser source based on an erbium fiber mode-locked laser was employed to generate coherent light around 2000 nm (5000 cm). The laser was passed through a 12-cm-long cell containing CO2, and the transmitted light was analyzed in a virtually imaged phased array-based spectrometer. Broadband spectra spanning more than 100 cm with a spectral resolution of roughly 0.075 cm (2.2 GHz) were acquired with an integration period of 2 ms. The temperature of the CO2 sample was deduced from fitting a modeled spectrum to the line intensities of the experimentally acquired spectrum. Temperature dynamics on the timescale of milliseconds were observed with a temperature resolution of 2.6 K. The spectroscopically deduced temperatures agreed with temperatures of the sample cell measured with a thermistor. Potential applications of this technique include quantitative measurement of carbon dioxide concentration and temperature dynamics in gas-phase chemical reactions (e.g., combustion) and plasma diagnostics.