Resonant photoacoustic spectroscopy

Hess, Peter

doi:10.1007/3-540-12065-3_1

Cited by 57 publications

(21 citation statements)

References 62 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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“…Subsequently, many experimental and theoretical works have been reported in the literature, proving the applicability of the method not only in spectroscopy, but also in various fields of physics, chemistry, biology, medicine, and engineering. The potential of laser photoacoustic spectroscopy has been discussed in several review articles (Patel & Tam, 1981;West, 1983;Hess, 1983;Tam, 1986;Sigrist, 1986Sigrist, , 2003Meyer & Sigrist, 1990;Harren & Reuss, 1997;Harren et al, 2000;Miklos et al, 2001;Schmid, 2006) and books (Pao, 1977;Rosencwaig, 1980;Zharov & Letokhov, 1986;Hess, 1989;Mandelis, 1992Mandelis, , 1994Gusev & Karabutov, 1993;Sigrist, 1994;Mandelis & Hess, 1997).…”

Section: Historical Remarksmentioning

confidence: 99%

Laser photoacoustic analysis of complex gas mixtures

Городничев¹,

Белов²,

Федотов³

et al. 2015

HoBMSTU.SIE

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“…Furthermore, the photon energy is too small to induce chemical reactions. For 1 atm pressure, the vibrational-translational non-radiative decay time is typically around 10 -6 -10 -9 s, whereas the radiative lifetime is between 10 -1 and 10 -3 s (Hess, 1983). Thus, in practice, the absorbed energy is completely released as heat, appearing as translational (kinetic) energy of the gas molecules.…”

Section: Photoacoustic Effect In Gasesmentioning

confidence: 99%