Optical Detection Technique Using Quartz-Enhanced Photoacoustic Spectrum

Abstract

A new optical detection approach based on quartz-enhanced photoacoustic spectroscopy (QEPAS) to detect gases is developed. The new method not only employs a modulated laser to excite acoustic wave, as the general QEPAS does, but also adds an extra laser beam without modulation as the detection source to transform the prong vibration into a laser intensity change. Due to the mechanical vibration of the prongs, the intensity of the reflection laser beam is modulated. Thus, the information of the target gas (composition, concentration, etc.) is obtained by demodulating the reflected light. The achieved sensitivity of 1.13 × 10 −6 cm −1 ·W·Hz −1/2 is inter-compared to the sensitivity of the conventional QEPAS. Further developments of the new optical detection approach are also discussed in detail.

Dependence of the Michelson Interferometer-Based Membrane-Less Optical Microphone–Photoacoustic Spectroscopy Gas-Sensing Method on the Fundamental Parameters of a Photoacoustic Gas Cell

“…Similar to our group's previous research [24,27], aluminum, which is a common and frequently used material for manufacturing the PA gas cell [2][3][4][5][6][7][8][9][10][11][12][13][14], is a first choice as a material for the PA gas cell to conduct initial research quite easily and flexibly and later consider other materials. The density of aluminum is 2700 kg/m 3 at 1 atm and 20 • C [28], and the sound velocity in aluminum is 6420 m/s at 1 atm and 20 • C [29].…”

“…In addition to aluminum, four additional common materials have been explored for producing the PA gas cell, which is often utilized as the material for constructing PA gas cells in the PAS research area. These materials include brass, glass, quartz, and stainless steel [2][3][4][5][6][7][8][9][10][11][12][13][14]. Table 6 shows the densities of these materials at 1 atm and 20 • C, while Table 7 indicates their sound velocities under the same conditions.…”

“…This technology allows for the detection of homo-nuclear diatomic gases and results in smaller and more sensitive sensors, as the limit of detection (LOD) of PAS is not fully determined by the length of the light-gas interaction [2]. These properties enable PAS-based gas sensing methods to seamlessly function in harsh environments [4].…”

“…The optical interferometer-based technology is one of the most mainstream PAS-based gas sensing methods [2,5] due to its high sensitivity and simple structure and principle [6]. However, this method is not suitable for some harsh environments [2][3][4][5] because many current mainstream gas sensors based on the technology have movable components, such as diaphragms [7][8][9][10] and cantilever beams [11][12][13][14]. Hence, they are unsuitable for hightemperature and high-pressure applications [1][2][3][4][5].…”

“…However, this method is not suitable for some harsh environments [2][3][4][5] because many current mainstream gas sensors based on the technology have movable components, such as diaphragms [7][8][9][10] and cantilever beams [11][12][13][14]. Hence, they are unsuitable for hightemperature and high-pressure applications [1][2][3][4][5]. Therefore, it is essential to develop optical interferometer-based gas sensing methods based on PAS without any movable components.…”