Infrared Optoacoustic Spectroscopy and Detection

Claspy, P. C.

doi:10.1016/b978-0-12-544150-6.50011-8

Cited by 10 publications

(10 citation statements)

References 20 publications

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“…The use of a quartz tuning fork as a detector has also been introduced, which has shown high sensitivity and immunity from the problem of the window signal (13-15). As described in numerous reviews of photoacoustic trace gas detection and resonators over the years (16)(17)(18)(19)(20)(21)(22)(23)(24)(25), all of these different approaches have achieved varying degrees of success-the overall result being that the photoacoustic effect now stands as one of the premier methods of trace gas detection, possessing a simplicity of construction that makes it sufficiently robust to be used in the field, a reasonable degree of selectivity, remarkably high sensitivity, and an unprecedented linear response range.…”

Section: Significancementioning

confidence: 99%

Photoacoustic trace detection of gases at the parts-per-quadrillion level with a moving optical grating

Bai

Chen

Zhao

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The amplitude of the photoacoustic effect for an optical source moving at the sound speed in a one-dimensional geometry increases linearly in time without bound in the linear acoustic regime. Here, use of this principle is described for trace detection of gases, using two frequency-shifted beams from a CO 2 laser directed at an angle to each other to give optical fringes that move at the sound speed in a cavity with a longitudinal resonance. The photoacoustic signal is detected with a high-Q, piezoelectric crystal with a resonance on the order of 443 kHz. The photoacoustic cell has a design analogous to a hemispherical laser resonator and can be adjusted to have a longitudinal resonance to match that of the detector crystal. The grating frequency, the length of the resonator, and the crystal must all have matched frequencies; thus, three resonances are used to advantage to produce sensitivity that extends to the parts-per-quadrillion level. (1) is that in a one-dimensional geometry, an optical beam moving in an absorbing medium at the sound speed generates a traveling compressive wave whose amplitude, in the linear acoustics limit, increases in direct proportion to the irradiation timewithout bound. Here, we report the application of this principle for trace detection of gases in a scheme where a pair of frequency-shifted laser beams produced by two acousto-optic modulators operating at slightly different frequencies are combined in space to produce a moving optical grating tuned to an absorption of an infrared active gas. The angle between the two beams is adjusted so that the fringe spacing of the grating Λ along with the frequency difference in the two beams Ω obeys the rule ΩΛ = 2πc; that is, the grating is tuned so that it moves at the sound speed with each antinode in the optical beam pattern moving synchronously with its photoacoustically generated compressive wave. It is shown here that, when a moving grating is produced in a cavity with two parallel reflecting surfaces resembling a laser resonator, two resonance conditions exist for generation of the photoacoustic effect-the first one when the grating motional speed matches the sound speed and the second one when twice the length of the cavity is an integral number of wavelengths of the sound wave. In addition, the method makes use of a resonant piezoelectric crystal as one of the reflecting surfaces of the detection cell so that the effects of three matched resonances are used to advantage to produce high sensitivity.The theory of operation of the detector is based on solution of the wave equation for pressure for a moving optical grating in a resonator. The wave equation for the photoacoustic effect in an inviscid fluid when heat conduction effects can be ignored (1, 5) is given bywhere c is the sound speed, t is the time, β is the coefficient of thermal expansion, CP is the specific heat capacity, and H is the optical energy deposited per unit volume and time. Consider a pair of phase-coherent, frequency-shifted optical beams directed at an angle to...

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Section: Significancementioning

confidence: 99%

Photoacoustic trace detection of gases at the parts-per-quadrillion level with a moving optical grating

Bai

Chen

Zhao

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…[2][3][4][5][6][7][8][9][10][11][12] The low-power PA technique has been predominantly utilized in the field of spectroscopy, [11][12][13][14][15][16][17][18] with substantial applications in trace gas detection. 5,[19][20][21][22][23] It exhibited significantly higher sensitivity than most other techniques, [24][25][26][27] with concentration sensitivity in the parts per billion. [3][4][5]25,27 PA spectroscopy is a powerful analytical tool for examining the optical absorption properties of solids as it directly measures the energy absorbed by the material on exposure to light.…”

Section: Introductionmentioning

confidence: 99%

“…[31][32][33] Several types of PA cells have been proposed by various investigators. 4,19,31,[34][35][36][37] PA cells made of a kilohertz microphone and piezoelectric transducers (PZT) have been widely studied. 31,34,37,38 Gas-microphone PA cells were generally used to study powder and samples with large surface to volume ratio, whereas PZT PA cells were used for liquid and bulk solids.…”

Section: Introductionmentioning

confidence: 99%

“…The PA cell was designed to fit into existing optical microscopes for multimodal imaging. As the PA spectroscopy technique can be used to study samples in any state such as solid, liquid, and gas, 19,33,34 numerous applications exist, such as coagulation tests to study clotting disorders like thrombophilia and hemophilia, blood pattern analysis (BPA) in forensics, 67 and monitoring the penetration of drugs into membrane acceptor systems. 68 …”

Section: Introductionmentioning

confidence: 99%

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Low-power noncontact photoacoustic microscope for bioimaging applications

2017

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Abstract. An inexpensive noncontact photoacoustic (PA) imaging system using a low-power continuous wave laser and a kilohertz-range microphone has been developed. The system operates in both optical and PA imaging modes and is designed to be compatible with conventional optical microscopes. Aqueous coupling fluids are not required for the detection of the PA signals; air is used as the coupling medium. The main component of the PA system is a custom designed PA imaging sensor that consists of an air-filled sample chamber and a resonator chamber that isolates a standard kilohertz frequency microphone from the input laser. A sample to be examined is placed on the glass substrate inside the chamber. A laser focused to a small spot by a 40× objective onto the substrate enables generation of PA signals from the sample. Raster scanning the laser over the sample with micrometer-sized steps enables high-resolution PA images to be generated. A lateral resolution of 1.37 μm was achieved in this proof of concept study, which can be further improved using a higher numerical aperture objective. The application of the system was investigated on a red blood cell, with a noiseequivalent detection sensitivity of 43,887 hemoglobin molecules (72.88 × 10 −21 mol or 72.88 zeptomol). The minimum pressure detectable limit of the system was 19.1 μPa. This inexpensive, compact noncontact PA sensor is easily integrated with existing commercial optical microscopes, enabling optical and PA imaging of the same sample. Applications include forensic measurements, blood coagulation tests, and monitoring the penetration of drugs into human membrane.

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“…It was discovered more than a century ago ͑Bell, 1880, 1881͒ and has been an important research tool in spectroscopy and trace gas detection ͑see Kreuzer, 1977;Rosencwaig, 1980;Kreuzer and Patel, 1971;Claspy, 1977;Dewey, 1974;Dewey et al, 1973;Goldan and Goto, 1974͒ The photoacoustic effect can be described in terms of energy transfer. A photon will be absorbed by a molecule when its wavelength matches a resonance peak in the molecule's absorption spectra.…”

Section: Introductionmentioning

confidence: 99%

Parametric dependencies for photoacoustic leak localization

Yönak

Dowling

2002

The Journal of the Acoustical Society of America

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Unintended gas or liquid leaks from manufactured components or manufacturing systems may be detrimental to consumers, manufacturers, and the environment. Thus, leak testing is important for quality, safety, and environmental reasons. This paper describes parametric dependencies for photoacoustic leak localization. The technique is based on the interaction of 10.6-micrometer radiation from a carbon dioxide (CO2) laser and a photoactive tracer gas, sulfur hexafluoride (SF6). For the current investigations, acoustic signals are generated by scanning a laser beam at high speed through gas plumes formed above calibrated leaks. These signals are remotely measured with a four-microphone linear array and analyzed using Bartlett and minimum-variance-distortionless (MVD) matched-field processing (MFP) techniques to determine leak location. This paper extends prior work in photoacoustic leak testing through (i) use of more signal frequencies; (ii) parametric study of four different laser scan rates; and (iii) examination of mismatch between the actual acoustic environment and the propagation model used in the MFP; and (iv) presentation of leak localization results on a curved surface. For a 12-watt CO2 laser exciting the small SF6 gas plume produced by a one-cm3-per-day leak with microphones placed 0.41 m from the leak location, root-mean-square localization uncertainties as small as +/-0.5 mm on a line scan of 0.46 m can be achieved when the largest possible number of signal frequencies fall in a measurement bandwidth of approximately 70 kHz.

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Infrared Optoacoustic Spectroscopy and Detection

Cited by 10 publications

References 20 publications

Photoacoustic trace detection of gases at the parts-per-quadrillion level with a moving optical grating

Photoacoustic trace detection of gases at the parts-per-quadrillion level with a moving optical grating

Low-power noncontact photoacoustic microscope for bioimaging applications

Parametric dependencies for photoacoustic leak localization

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