Photoacoustic spectroscopy

About: Photoacoustic spectroscopy is a research topic. Over the lifetime, 3379 publications have been published within this topic receiving 62892 citations.

Photothermal science and techniques

Abstract: Introduction. History. Overview. Thermal waves. Optical generation of thermal waves - photothermal effect. Instrumentation and detection techniques. Transient thermal phenomena. Photoacoustic spectroscopy and its applications. Thermal wave non-destructive evaluation. Characterization of semiconducting materials. Thermal property measurement. Monitoring and measurement of gases and the atmosphere.

Breath Analysis Using Laser Spectroscopic Techniques: Breath Biomarkers, Spectral Fingerprints, and Detection Limits

Abstract: Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in laser spectroscopic techniques and laser sources have driven breath analysis to new heights, moving from laboratory research to commercial reality. Laser spectroscopic detection techniques not only have high-sensitivity and high-selectivity, as equivalently offered by the MS-based techniques, but also have the advantageous features of near real-time response, low instrument costs, and POC function. Of the approximately 35 established breath biomarkers, such as acetone, ammonia, carbon dioxide, ethane, methane, and nitric oxide, 14 species in exhaled human breath have been analyzed by high-sensitivity laser spectroscopic techniques, namely, tunable diode laser absorption spectroscopy (TDLAS), cavity ringdown spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), cavity enhanced absorption spectroscopy (CEAS), cavity leak-out spectroscopy (CALOS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb cavity-enhanced absorption spectroscopy (OFC-CEAS). Spectral fingerprints of the measured biomarkers span from the UV to the mid-IR spectral regions and the detection limits achieved by the laser techniques range from parts per million to parts per billion levels. Sensors using the laser spectroscopic techniques for a few breath biomarkers, e.g., carbon dioxide, nitric oxide, etc. are commercially available. This review presents an update on the latest developments in laser-based breath analysis.

Noninvasive imaging of hemoglobin concentration and oxygenation in the rat brain using high-resolution photoacoustic tomography

Abstract: Simultaneous transcranial imaging of two functional parameters, the total concentration of hemoglobin and the hemoglobin oxygen saturation, in the rat brain in vivo is realized noninvasively using laser-based photoacoustic tomography (PAT). As in optical diffusion spectroscopy, PAT can assess the optical absorption of endogenous chromophores, e.g., oxygenated and deoxygenated hemoglobins, at multiple optical wavelengths. However, PAT can provide high spatial resolution because its resolution is diffraction-limited by photoacoustic signals rather than by optical diffusion. Laser pulses at two wavelengths are used sequentially to acquire photoacoustic images of the vasculature in the cerebral cortex of a rat brain through the intact skin and skull. The distributions of blood volume and blood oxygenation in the cerebral cortical venous vessels, altered by systemic physiological modulations including hyperoxia, normoxia, and hypoxia, are visualized successfully with satisfactory spatial resolution. This technique, with its prominent sensitivity to endogenous contrast, can potentially contribute to the understanding of the interrelationship between neural, hemodynamic, and metabolic activities in the brain.

In vivo dark-field reflection-mode photoacoustic microscopy.

Abstract: Reflection-mode photoacoustic microscopy with dark-field laser pulse illumination and high-numerical-aperture ultrasonic detection is designed and implemented in noninvasively imaged blood vessels in the skin in vivo. Dark-field optical illumination minimizes the interference caused by strong photoacoustic signals from superficial structures. A high-numerical-aperture acoustic lens provides high lateral resolution, 45–120μm in this system. A broadband ultrasonic detection system provides high axial resolution, estimated to be ∼15μm. The optical illumination and ultrasonic detection are in a coaxial confocal configuration for optimal image quality. The system is capable of imaging optical-absorption contrast as deep as 3mm in biological tissue.

Applications of quartz tuning forks in spectroscopic gas sensing

Abstract: A recently introduced approach to photoacoustic detection of trace gases utilizing a quartz tuning fork (TF) as a resonant acoustic transducer is described in detail. Advantages of the technique called quartz-enhanced photoacoustic spectroscopy (QEPAS) compared to conventional resonant photoacoustic spectroscopy include QEPAS sensor immunity to environmental acoustic noise, a simple absorption detection module design, and its capability to analyze gas samples ∼1mm3 in volume. Noise sources and the TF properties as a function of the sampled gas pressure, temperature and chemical composition are analyzed. Previously published results for QEPAS based chemical gas sensing are summarized. The achieved sensitivity of 5.4×10−9cm−1W∕√Hz is compared to recent published results of photoacoustic gas sensing by other research groups. An experimental study of the long-term stability of a QEPAS-based ammonia sensor is presented. The results of this study indicate that the sensor exhibits very low drift, which allows da...