Abstract
Photothermal spectroscopy (PTS) is a technique used for determining the composition of liquids, solids and gases. In PTS, the sample is illuminated with a radiation source, and the thermal response of the analyte (e.g., refractive index) is analyzed to gain information about its content. Recent advances in this unique method of detecting gaseous samples show that photothermal gas spectroscopy can be an interesting alternative to commonly used absorption techniques. Moreover, if designed properly, sensors using PTS detection technique can not only reach sensitivities comparable with other, more complex techniques, but can significantly simplify the design of the sensor. In this review, recent developments in photothermal spectroscopy of gases will be summarized and discussed.
Highlights
Photothermal spectroscopy (PTS) is a group of spectroscopy techniques commonly used to measure thermal characteristics and optical absorption of samples [1,2,3]
As presented in this review, PT gas detection can be accomplished in numerous dissimilar configurations, encouraging researchers to search for novel, yet unpublished, methods of utilizing the PT effect for precise and selective trace gas analysis
FP interferometric readout of the PT-induced refractive index (RI) modulation has proven to be very sensitive and foremost miniature. With proper design, this configuration is capable of reaching strong absorption lines of molecules located in the mid-infrared wavelength region
Summary
Photothermal spectroscopy (PTS) is a group of spectroscopy techniques commonly used to measure thermal characteristics and optical absorption of samples (solids, liquids or gases) [1,2,3]. Absorption of the molecules causes a reduction of the intensity, which is detected by a photodiode and signal-processed to determine the gas concentration or other properties of the gas (e.g., pressure, temperature, velocity) [9] As this method usually relies on calculating the difference between the input light intensity and the light absorbed by the sample, the performance and accuracy of the sensor is limited especially in the case of small absorption and by reflections and scattering effects usually present in such systems. To PAS, the PTS signal decreases with higher pump laser modulation frequencies [17] This is a direct result of the limited thermal response time of the gas molecules and has been thoroughly explained in Reference [18].
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