Photoacoustic Detection Technique Research Articles

Ultra-highly sensitive dual gases detection based on photoacoustic spectroscopy by exploiting a long-wave, high-power, wide-tunable, single-longitudinal-mode solid-state laser.

Photoacoustic spectroscopy (PAS) as a highly sensitive and selective trace gas detection technique has extremely broad application in many fields. However, the laser sources currently used in PAS limit the sensing performance. Compared to diode laser and quantum cascade laser, the solid-state laser has the merits of high optical power, excellent beam quality, and wide tuning range. Here we present a long-wave, high-power, wide-tunable, single-longitudinal-mode solid-state laser used as light source in a PAS sensor for trace gas detection. The self-built solid-state laser had an emission wavelength of ~2 μm with Tm:YAP crystal as the gain material, with an excellent wavelength and optical power stability as well as a high beam quality. The wide wavelength tuning range of 9.44 nm covers the absorption spectra of water and ammonia, with a maximum optical power of ~130 mW, allowing dual gas detection with a single laser source. The solid-state laser was used as light source in three different photoacoustic detection techniques: standard PAS with microphone, and external- and intra-cavity quartz-enhanced photoacoustic spectroscopy (QEPAS), proving that solid-state laser is an attractive excitation source in photoacoustic spectroscopy.

Remote Photoacoustic Sensing Using Single Speckle Analysis by an Ultra-Fast Four Quadrant Photo-Detector.

The need for tissue contact makes photoacoustic imaging not applicable for special medical applications like wound imaging, endoscopy, or laser surgery. An easy, stable, and contact-free sensing technique might thus help to broaden the applications of the medical imaging modality. In this work, it is demonstrated for the first time that remote photoacoustic sensing by speckle analysis can be performed in the MHz sampling range by tracking a single speckle using a four quadrant photo-detector. A single speckle, which is created by self-interference of surface back-reflection, is temporally analyzed using this photo-detector. Phantoms and skin samples are measured in transmission and reflection mode. The potential for miniaturization for endoscopic application is demonstrated by fiber bundle measurements. In addition, sensing parameters are discussed. Photoacoustic sensing in the MHz sampling range by single speckle analysis with the four quadrant detector is successfully demonstrated. Furthermore, the endoscopic applicability is proven, and the sensing parameters are convenient for photoacoustic sensing. It can be concluded that a single speckle contains all the relevant information for remote photoacoustic signal detection. Single speckle sensing is therefore an easy, robust, contact-free photoacoustic detection technique and holds the potential for economical, ultra-fast photoacoustic sensing. The new detection technique might thus help to broaden the field of photoacoustic imaging applications in the future.

A study of the measurement of radiative quantum efficiency using thermal time constants

The thermal time constants were used to analyze the energy transfer mechanism in the laser medium. It can be applied briefly than the photoacoustic detection technique for the radiative quantum efficiency. The time constant was found to be 133 s and 169 s under lasing and nonlasing conditions, respectively, for 4 at.% ceramic Nd:YAG at a pump power of 2.5 W. The radiative quantum efficiency was calculated using the thermal time constants under lasing and nonlasing conditions. A radiative quantum efficiency of 24% was obtained under lasing.

A wavelet-coherence analysis for the identification of muscular co-contraction during waking

The thermal time constants were used to analyze the energy transfer mechanism in the laser medium. It can be applied briefly than the photoacoustic detection technique for the radiative quantum efficiency. The time constant was found to be 133 s and 169 s under lasing and nonlasing conditions, respectively, for 4 at.% ceramic Nd:YAG at a pump power of 2.5 W. The radiative quantum efficiency was calculated using the thermal time constants under lasing and nonlasing conditions. A radiative quantum efficiency of 24% was obtained under lasing.

Body center of mass trajectory and mechanical energy using inertial sensors: a feasible stride?

The thermal time constants were used to analyze the energy transfer mechanism in the laser medium. It can be applied briefly than the photoacoustic detection technique for the radiative quantum efficiency. The time constant was found to be 133 s and 169 s under lasing and nonlasing conditions, respectively, for 4 at.% ceramic Nd:YAG at a pump power of 2.5 W. The radiative quantum efficiency was calculated using the thermal time constants under lasing and nonlasing conditions. A radiative quantum efficiency of 24% was obtained under lasing.

散射光声探测技术及其成像方法

散射光声探测技术及其成像方法

Fiber Bragg grating applied pulsed photoacoustic detection technique for online monitoring concentration of liquid

The need for real-time monitoring of the concentration of raw liquids and wastewater flowing in ducts is one of the significant process controls in chemical plants. A concentration sensor applicable to acidic fluids, however, has not been practically developed because of the maintenance required to sustain performance due to the metal erosion of the electrode from the acidity. To overcome this problem, we propose the fiber Bragg grating applied pulsed photoacoustic (PA) detection technique for online monitoring concentration of liquid. In our technique, optical fiber made of quartz is used for the PA signal generation and detection, for which a 0.6-mm-diameter step index fiber and Bragg grating composed of single mode fiber are used as an object, respectively, so that our metal-free sensor head is not only of small size but is also maintenance-free. The concentration of dye (Rhodamine 6G) dissolved into distilled water was measured to estimate the capability. A Q-switched frequency doubled Nd:YAG laser was used as the PA exiting beam, which is fed to the PA sensor through the fiber. It was experimentally confirmed that the detection linearity was significantly obtained in a concentration range from a few ppm to approximately 200 ppm.

Optical and transport properties of B-doped GaSe semiconductor single crystal

The optical energy band-gap and the nature of the fundamental optical absorption transitions in GaSe:B single crystals have been determined by UV-VIS and photoacoustic spectroscopy. The thermal diffusivity, carrier diffusion coefficient, bulk recombination mean lifetime and surface recombination velocity have been measured using the photoacoustic detection technique.

Laser photoacoustic spectrometer for remote monitoring of atmospheric pollutants

An acoustically resonant CO(2) laser photoacoustic (PA) spectrometer for remote or in situ monitoring of air pollutants has been designed. The salient features of this PA system, along with the optimization tests of various operating parameters that affect the PA signal (buffer-gas pressure, type of buffer gas, laser power, gas concentration, and acoustic modes), are described. The system has been applied for the detection of pollutants emitted from the exhaust of a car located at a remote distance. Also, an alarm system based on the PA detection technique has been built for leak detection of toxic gases at industrial complexes. The minimum detectable concentration of C(2) H(4) and SO(2) with this system is 50 parts in 10(12) by volume and 50 parts in 10(9) by volume, respectively.

Pulsed photoacoustic detection technique applied to the study of multiphoton absorption in molecules

A pulsed laser photoacoustic technique is described. It is optimized for the simultaneous investigations of multiphoton absorption processes as well as rotational relaxation and vibration relaxation studies. The experimental procedure is presented, concerning the calibration of the photoacoustic detector/cell set-up, applying the transmission spectroscopy technique. The obtained relationships, which can be alternatively used for the sensitivity curve S(p, gamma , T) of the apparatus, are analysed. A previously proposed model is confirmed.

An amalgamation between hormone physiology and plant ecology: A review on flooding resistance and ethylene

Both distribution of terrestrial plants and species composition in flood plain communities are strongly influenced by flooding (waterlogging, partial submergence, or submergence). The interaction between a plant's flooding resistance and the seasonal timing, duration, depth, or frequency of flooding often determines plant distribution in flood plains. Flooding may be accompanied by marked physical changes in light, carbon availability, diffusion rate of gases, and density of the environment. Various physiological processes may be affected by these flooding-induced physical changes, including aerobic respiration, photosynthesis, and processes in which light acts as a source of information (e.g., phytochrome photoequilibrium). Certain plant species acclimatize and adapt to these physical changes to relieve the constraints imposed by the flooded environment. Underwater photosynthesis, enhanced shoot elongation, adventitious roots, and aerenchyma formation are typical adaptive responses which are believed to improve the oxygen status of submerged plants. Ethylene and other plant hormones play a central role in the initiation and regulation of most of these adaptive responses, which permit “escape” from anaerobiosis. Mechanisms of direct tolerance of anaerobic conditions, such as a vigorous fermentative respiratory pathway, are of particular importance when the plant is very deeply submerged, or during the night and when the water is sufficiently turbid to exclude light.Studies on the cosmopolitan genus Rumex, distributed in a flooding gradient on river flood plains, have integrated plant hormone physiology with plant ecology. Rumex species showed a high degree of interspecific variation in ethylene production rates, endogenous ethylene concentrations, ethylene sensitivity, and ethylene-mediated growth responses. The field distribution of Rumex species in flooding gradients is explained in terms of a balance between endogenous ethylene concentrations and sensitivity towards this growth regulator (“ethylene economy”). Much data has been gathered using a recently developed laser-driven photoacoustic detection technique capable of detecting six parts of ethylene in 1012 parts air flowing continuously over the plant.

Determination of Residual Unsaturation in Photo-Cured Acrylate Formulations Using Photoacoustic FT-IR Spectroscopy

The advent of Fourier transform infrared spectroscopy has allowed for the use of the photoacoustic detection technique in the infrared region of the electromagnetic spectra. Urban recently described the advantages of photoacoustic Fourier transform infrared spectroscopy (PAS/FT-IR) in the characterization of polymeric coatings and interfaces at various depths at the molecular level. Nonetheless, because of the strong tendency for PAS/FT-IR spectra to be distorted due to saturation of peaks with strong absorbances, PAS/FT-IR has found only limited use as a quantitative procedure. In this report we describe how, with careful selection of a reference peak, one can use the strong peak saturation characteristic of PAS/FT-IR to advantage in the quantification of small amounts of residual unsaturation in a photo-cured acrylate coating.

Picosecond measurements using photoacoustic detection

We report experimental results on picosecond time-resolved photoacoustic measurements of excited-state lifetimes, cross sections, and polarization properties for organic dye molecules in solution, using a new technique in which we detect the total photoacoustic impulse produced by two ultrashort optical pulses with variable time delay between them. The picosecond photoacoustic detection technique reported here appears to be a promising new way to observe weak excited-state cross sections and to perform picosecond lifetime measurements in a large variety of weakly absorbing and/or nonfluorescing atomic and molecular systems.

Photoacoustic study of two-photon absorption in hexagonal ZnS

Photoacoustic detection technique is employed to investigate two-photon absorption (TPA) effects in ZnS over a wide frequency range with polarized 5 nsec dye laser pulses. By analyzing the dispersion and polarization dependence of TPA, we find that near the band gap, the TPA in ZnS occurs via allowed-forbidden type one-step, two-photon transitions.

High-resolution measurement of HCl overtone vibration-rotation bands by intracavity dye laser techniques

High-resolution measurements of HCl (5-0) and (7-0) overtone vibration-rotation bands have been made with an ultrasensitive intracavity dye laser quenching technique. The spectra of HCl (5-0), (6-0), and (7-0) overtone bands and intensities of the (5-0) and (6-0) bands obtained by an intracavity dye laser photoacoustic detection technique are also reported. A brief comparison of dye laser quenching and photoacoustic detection techniques is also reported.