Showing papers on "Photoacoustic spectroscopy published in 1986"
IBM1
TL;DR: In this article, the theory and applications of photo-acoustic (also called optoacoustic) methods belonging to the more general area of photothermal measurement techniques are reviewed, covering excitation of gaseous or condensed samples with modulated continuous light beams or pulsed light beams.
Abstract: This paper reviews the theory and applications of photoacoustic (also called optoacoustic) methods belonging to the more general area of photothermal measurement techniques. The theory covers excitation of gaseous or condensed samples with modulated continuous light beams or pulsed light beams. The applications of photoacoustic methods include spectroscopy, monitoring deexcitation processes, probing physical properties of materials, and generating mechanical motions. Several other related photothermal methods, as well as particle-acoustics and wave-acoustics methods are also described. This review complements an earlier and narrower review [Rev. Mod. Phys. 53, 517 (1981)] that is mainly concerned with sensitive detection by pulsed photoacoustic spectroscopy in condensed matter.
1,183 citations
TL;DR: In this article, the effects of photoacoustic spectroscopy (PAS) in gaseous media are reviewed and a simple experimental method for the determination of Beyer's nonlinearity parameter B/A is presented.
Abstract: The laser generation of sound in liquids and gases is reviewed. The sound‐generating mechanisms of laser interaction with matter are discussed with emphasis on the thermoelastic process. The studies on strongly absorbing liquids include detailed theoretical considerations of the thermoelastic sound generation with pulsed lasers. Acoustic waveforms for H2O and D2O are calculated analytically on the basis of a model laser‐pulse shape. Both free and rigid boundaries on the surface of the liquid are considered. Good agreement between theory and experiments with respect to waveforms and amplitudes is obtained. The experiments are performed with a hybrid CO2 laser and piezoelectric or optical detection of the acoustic transients. In view of a present controversy, special emphasis is put on the temperature dependence of the acoustic amplitudes in H2O, D2O, and in aqueous MgSO4 solutions. Good agreement is found between experimental data and a new, pure thermal model which takes heat conduction into account. The distortion of the acoustic waveform during the propagation through the liquid is treated in terms of sound absorption, diffraction, and nonlinear acoustics. A simple experimental method for the determination of Beyer’s nonlinearity parameter B/A is presented. In the last section some characteristics of photoacoustic spectroscopy (PAS) in gaseous media are reviewed. This method has been demonstrated to be highly sensitive. The measurement of absorption coefficients as low as 10− 8 cm− 1 is possible. PA studies on H2O vapor are discussed with new results on line and continuum absorption in the 9–11‐μm wavelength range. Finally, the impact of PAS on trace gas analysis is demonstrated. With PAS the detection of gas concentrations in the ppb range is feasible. The operational characteristics of a stationary CO laser and a mobile CO2 laser‐PAS system are presented, including first results on continuous i n s i t u air pollution monitoring.
365 citations
TL;DR: In this article, a simple method is demonstrated for obtaining the thermal diffusivity of solids, by measuring the phase lag between a front and rear illumination, at a single chopping frequency.
Abstract: A simple method is demonstrated for obtaining the thermal diffusivity of solids, by measuring the phase lag between a front and rear illumination, at a single chopping frequency. The method is tested using some semiconductor and glass samples.
126 citations
TL;DR: In this paper, a conceptual basis for the technique of time delay photothermal wave spectroscopy is presented and the signal generation and appropriate system functions in the time delay and frequency domains are introduced and discussed from the point of view of correlation and spectral analysis and processing.
Abstract: A conceptual basis for the technique of time delay photothermal wave spectroscopy is presented. The signal generation and appropriate system functions in the time delay and frequency domains are introduced and discussed from the point of view of correlation and spectral analysis and processing.
65 citations
TL;DR: Threshold fluences for ablative formation of gaseous products for each excimer laser line were calculated from the photoacoustic spectrum and the measured threshold for the KrF laser.
Abstract: Photoacoustic spectra of normal artery wall and of atherosclerotic plaque are reported. Threshold fluences for ablative formation of gaseous products for each excimer laser line were calculated from the photoacoustic spectrum and the measured threshold for the KrF laser.
58 citations
TL;DR: In this article, it was shown that PVF2 films over PET change the thermal diffusion length such that the sample PVF 2 on PET becomes optically transparent and thermally thick.
Abstract: Photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR) is used to study films of poly(vinylidine fluoride) (PVF2) and poly(ethylene terephthalate) (PET). It is shown that PVF2 films over PET change the thermal diffusion length such that the sample PVF2-on-PET becomes optically transparent and thermally thick. By changing the mirror velocity of the Michelson interferometer it is possible to obtain spectra at various sample depths. The intensity of the carbonyl band of the lower PET film changes as a function of the mirror velocity. The log-log plot of these quantities gives a slope of −3/2, which agrees with theoretical predictions for thermally thick and optically transparent samples.
48 citations
TL;DR: In this article, the theory of the photoacoustic signal was developed for acoustic resonances in a cylindrical resonator, and measurements were performed to determine the signal strength in the pressure range between 1 and 760 Torr for CH4 and C2H6.
Abstract: The theory of the photoacoustic signal is developed for acoustic resonances in a cylindrical resonator. Measurements were performed to determine the signal strength in the pressure range between 1 and 760 Torr for CH4 and C2H6. For CH4 the optical power absorbed in the cavity is nearly constant but vibrational relaxation varies the signal in the investigated pressure region. C2H6 shows a strong pressure dependence of the optical power absorbed, however, V–R,T relaxation is so fast that in this case no relaxational variation of the signal is observed in the range of ν/p values studied. As expected, the strength of the acoustic signal is proportional to optical power deposition in this case. For CH4, the influence of V–V and V–R,T exchange processes on the photoacoustic signal is studied in detail. The ratio of heat generated by fast V–V processes to heat generated by slow V–R,T transfer is determined. Using the relaxation time 5.2 ns bar obtained by laser‐induced fluorescence experiments for double quantum V–V exchange between the stretching levels ν1,ν3 and the bending levels ν2,ν4 a value of 33 ns bar is derived for single quantum V–V exchange between these manifolds.
47 citations
TL;DR: In this paper, the first frequency modulated (FM) time delay photothermal deflection (mirage effect) spectrometer with a ns rise time spectrally flat beam position detector unit was demonstrated.
Abstract: FM time delay laser excitation has been implemented in a photothermal deflection spectrometric apparatus with fast rise‐time optics. The performance of the system was studied in both frequency and time delay domains. The spectrometer was further used in the study of thin quartz layers on an opaque substrate. In this work we have demonstrated the operation of the first frequency modulated (FM) time delay photothermal deflection (mirage effect) spectrometer with a ns rise time spectrally flat beam position detector unit. It was established by use of a blackbody reference that the spectrometer is responsive to impulsive heat sources in the sample with no measureable instrumental distortion of the frequency or time delay domain responses. The sensitivity of the device was tested successfully in the measurement of thermal parameters of thin quartz layers on absorbing backings. It was further shown that our spectrometer is sensitive to thin SiO2 layers on Si wafers. The data were largely consistent with Green’s...
45 citations
TL;DR: The use of pyroelectric sensors for the detection of radia- tion-induced thermal wave phenomena is reviewed and this new detection scheme is compared with more established photoacoustic and photo- thermal techniques.
Abstract: The use of pyroelectric sensors for the detection of radia- tion-induced thermal wave phenomena is reviewed. This new detection scheme is compared with more established photoacoustic and photo- thermal techniques. Examples emphasizing the versatility and the unique properties of this new detection scheme as well as its inherent limitations are discussed.
37 citations
TL;DR: In this article, the authors report on in vivo measurements on human skin treated with sunscreens, and the transfer properties of the open-ended detector are discussed theoretically and experimentally.
Abstract: Photoacoustic spectroscopy offers the opportunity of detecting the diffusion of light-absorbing drugs into the skin. We report on in vivo measurements on human skin treated with sunscreens. The experimental setup is described, and the transfer properties of the open-ended detector are discussed theoretically and experimentally.
36 citations
TL;DR: In this article, Fourier transform infra-red (FTi.r.) photoacoustic spectroscopy in combination with deuterium exchange was used to determine the accessibility of the NH groups of Kevlar 49 fibres.
TL;DR: In this paper, the generation of americium pseudocolloids in groundwaters rich and poor in humic substances is investigated, where the size fractionation is realized by ultrafiltration as well as by ultracentrifugation, and the colloid composition is characterized by analysis of the dissolved organic carbon, neutron activation analysis and inductively coupled plasma atom emission spectrometry.
Abstract: The generation of americium colloids in groundwaters rich and poor in humic substances is investigated. The size fractionation is realized by ultrafiltration as well as by ultracentrifugation, and the colloid composition is characterized by analysis of the dissolved organic carbon, neutron activation analysis and inductively coupled plasma atom emission spectrometry. The process responsible for the generation of americium pseudocolloids in two selected groundwaters is demonstrated with the help of laser-induced photoacoustic spectroscopy which provides high speciation sensitivity.
TL;DR: In this article, the authors used Fourier transform infrared photoacoustic spectroscopy for quantitative surface analysis of silica treated with trifunctional coupling agents such as γ-Methacryloxypropyltriethoxysilane (γ-MPS), γγ-Glycidoxypropyltrimethoxyselane (GPS), and γα-Aminopropyltri-ethoxisilane(γ-APS), and obtained the calibration curves for several characteristic bands of the coupling agents.
Abstract: Fourier transform infrared photoacoustic spectroscopy has been used for quantitative surface analysis of silica treated with trifunctional coupling agents such as γ-Methacryloxypropyltriethoxysilane (γ-MPS), γ-Glycidoxypropyltrimethoxysilane (γ-GPS), and γ-Aminopropyltri-ethoxysilane (γ-APS). The calibration curves are obtained for several characteristic bands of the coupling agents. Using a highly polarizable gas in the photoacoustic cell and comparing the spectra with a nonpolarizable coupling gas, it is possible to evaluate orientation of the coupling agents on the silica surface. The type of orientation is a function of the extent of surface coverage. At low surface coverage, coupling agents tend to take a perpendicular orientation with respect to the surface, and increasing surface coverage leads to parallel orientation. Increasing the coupling agent concentration also causes orientational changes of the species which form chemical bonds with the silica surface (hydroxyl, water, and carbonyl groups).
TL;DR: In this article, the usefulness of optothermal spectroscopy for quantitative analysis is discussed and it is shown theoretically and experimentally that optothermal Spectroscopy is comparable to ordinary transmission spectroscopic for the determination of optical absorption coefficients.
Abstract: The usefulness of optothermal spectroscopy for quantitative analysis is discussed. It is shown theoretically and experimentally that optothermal spectroscopy is comparable to ordinary transmission spectroscopy for the determination of optical absorption coefficients.
TL;DR: The combined spectroscopic approach is shown to raise the level of confidence regarding data interpretation through consistency arguments between the PAS and PCS results, an insight not easily obtained solely through conventional PC or optical-absorption measurements.
Abstract: Microphone gas-coupled photoacoustic spectroscopy (PAS) and photocurrent spectroscopy (PCS) have been applied simultaneously to high-resistivity, (0001)-oriented, single crystals of pure n-type CdS in order to obtain detailed information about the importance of the nonradiative capture or recombination channels at defect states below the band-gap energy of these materials. The primary spectral responses of well-characterized samples at open circuit and in the presence of perturbing transverse ac or dc electric fields, as well as secondary PA and PC spectra were found to be largely consistent with a substantial enhancement of the nonradiative recombination quantum efficiency at sub-band-gap wavelengths, concomitant with free-carrier trapping at defect centers (presumably sulphur vacancies) responsible for the observed red quenching of the photoconductivity. Our combined spectroscopic approach, besides the new direct information it yields concerning intrinsic band-to-band transition contributions to the PA and PC spectra as well as band-gap defect structure information, is also shown to raise the level of confidence regarding data interpretation through consistency arguments between the PAS and PCS results, an insight not easily obtained solely through conventional PC or optical-absorption measurements.
TL;DR: The effect of neutron irradiation on the photoacoustic spectra of Er2O3 and NdO3 in powder form has been studied in this article, which shows a quenching effect on the signal which regains its intensity after a lapse of some time.
Abstract: The effect of neutron irradiation on the photoacoustic spectra of Er2O3 and Nd2O3 in powder form has been studied The irradiation shows a quenching effect on the photoacoustic signal which regains its intensity after a lapse of some time It is believed that the irradiation changes the oxidation state of the rare-earth ions from M3+ to M2+ The half-life of the recovery process Er2+ to Er3+ in the case of irradiated Er2O3 is found to be 46 h
TL;DR: In this article, the phase and amplitude information in the photoacoustic signal were used to calculate the absolute absorption spectrum from the photo-acoustic data, under certain conditions, easily fulfilled in typical experiments, for asbestos fibers (chrysotile).
Abstract: Strong absorption bands of photoacoustic Fourier-transform spectra are often truncated relative to weaker bands owing to signal saturation. To correct this problem, we propose processing both the phase and the amplitude information in the photoacoustic signal. Under certain conditions, easily fulfilled in typical experiments, we are able to calculate the absolute absorption spectrum from the photoacoustic data. Experimental results are given for asbestos fibers (chrysotile).
TL;DR: In this article, a multidisciplinary approach is demonstrated to elucidate coal weathering at a molecular level using Fourier Transform Infrared Photoacoustic Spectroscopy (FT-IR/PAS).
Abstract: A multidisciplinary approach is demonstrated to elucidate coal weathering at a molecular level. Fourier Transform Infrared Photoacoustic Spectroscopy (FT-IR/PAS) provides a technique for a compositional depth profile of coal by simply varying the modulation frequency (mirror velocity) of the light impinging upon the solid surface. In order that the potential of this technique in this field could be evaluated, large-sized coal samples were examined. The PA difference spectra obtained from the spectra taken at different modulation frequencies (i.e., different depths), on a sample aged in air, demonstrate the appearance of negative features in the CH infrared absorption which are indicative of a coal alteration. Therefore, different coal layers can be distinguished by FT-IR/PAS. The application of the same technique to the study of a coal sample heated in air at 200°C allows the detection of different oxidation mechanisms operating inside and outside the coal. Although quantitative results are difficult to obtain, the technique can be successfully proposed for a qualitative description of coal weathering.
TL;DR: In this article, photoacoustic spectroscopy is used for the detection of sorbed water in two polymers used for their dielectric properties in electric cables: ethylene-propylene rubber and cross-linked polyethylene.
Abstract: Photoacoustic spectroscopy is used for the detection of sorbed water in two polymers used for their dielectric properties in electric cables: ethylene–propylene rubber and cross-linked polyethylene. The wavelength range is between 2 and 4 μm, where the OH-bond valence vibrations are observable. As the technique used distinguishes between surface and bulk absorption of the infrared beam, correlations have been made with relative humidity, and water content as measured by another technique, and with other studies of water-sorption processes in polymers.
TL;DR: In this article, the compositional dependence of the bandgap EO, derived from these measurements, is presented and contrasted with the GeSe and Si-S systems, qualitatively explained with a model which accounts for differing numbers of homopolar and heteropolar bonds as the composition is varied.
Abstract: The optical properties near the fundamental absorption edge has been studied for a series of SixSe1−x glasses using photoacoustic spectroscopy. The compositional dependence of the bandgap EO, derived from these measurements, is presented and contrasted with the GeSe and the SiS systems. This data is qualitatively explained with a model which accounts for differing numbers of homopolar and heteropolar and heteropolar bonds as the composition is varied. Additional support for this interpretation is found in the compositional behavior of the glass transitions of these alloys.
TL;DR: In this paper, a photoacoustic method for distinguishing the surface nonradiative recombinations from the bulk ones in GaAs is presented, based on the noncontact photo-acoustic spectroscopy with a Michelson interferometry.
Abstract: A new photoacoustic method for distinguishing the surface nonradiative recombinations from the bulk ones in GaAs is presented. The method is based on the noncontact photoacoustic spectroscopy with a Michelson interferometry. It is shown that the surface contributions in a Cr‐doped GaAs are relatively large even with the below‐gap excitations. The bulk property is shown to be observed with the simultaneous continuous light irradiation with the photon energy above the energy gap.
TL;DR: In this article, a one-dimensional theoretical model is presented in which the cross-correlation photoacoustic response to pseudo-random-binary-sequence (PRBS) optical excitation is evaluated for systems of variable optical absorption coefficients.
Abstract: Cross-correlation photoacoustic spectroscopy (CPAS) of condensed matter carries spectroscopic information related to the optical absorption coefficient of solids in both signal magnitude and time delay channels. A one-dimensional theoretical model is presented in which the cross-correlation photoacoustic response to pseudo-random-binary-sequence (PRBS) optical excitation is evaluated for systems of variable optical absorption coefficients. The model is further compared to CPAS data from powders of Ho2O3 in the visible spectral range.
TL;DR: The cattle retina and retinal pigment epithelium are examined by means of photoacoustic spectroscopy under conditions where structural integrity is maintained, giving a 3-D image of the posterior ocular tissues.
Abstract: The cattle retina and retinal pigment epithelium are examined by means of photoacoustic spectroscopy under conditions where structural integrity is maintained. Depth-related information is obtained about the chromophore distribution within the samples by analysis of the frequency dependence of the spectra giving a 3-D image of the posterior ocular tissues.
TL;DR: In this paper, the spectral properties of the terrestrial atmosphere in the infrared 8 to 14 μm spectral window performed with laser photoacoustic spectroscopy on the basis of results from previous airborne measurements on spectral emission are summarized.
Abstract: This paper summarizes experiments on the spectral properties of the terrestrial atmosphere in the infrared 8 to 14 μm spectral window performed with laser photoacoustic spectroscopy on the basis of results from previous airborne measurements on spectral emission. Following a description of the experimental arrangement, novel results on supersaturated water vapor, continuum and line absorption are presented and discussed in relation to actual models of the atmosphere. Besides the measurement of the absorption by supersaturated water vapor in a diffusion chamber, the experimental determination of the water-pressure dependence of the continuum absorption at −10°C and the identification of four weak and narrow absorption lines in the 8 to 14 μm window as pure high-J rotational transitions of the H2O molecule are of interest.
TL;DR: Fourier transform infrared photoacoustic spectroscopy has been applied to determine the structure and orientation of pyridine and γ-Metacryloxypropyltriethoxysilane (γ-MPS) on the alumina surface as mentioned in this paper.
Abstract: Fourier transform infrared photoacoustic spectroscopy has been applied to determine the structure and orientation of pyridine and γ-Metacryloxypropyltriethoxysilane (γ-MPS) on γ-Al2O3 surface. Adsorption of pyridine on activated γ-Al2O3 leads to formation of a pyridinium ion (pyN+-H) and pyridine N-oxide. The orientation of pyridinium ion on the alumina surface is random, whereas the pyridine N-oxide is parallel with respect to the surface. The adsorption of oligomers of γ-MPS gives parallel layers on the alumina surface. At low γ-MPS surface coverage, the carbonyl groups interact with the surface hydroxyl groups. Increasing surface coverage leads to an excess of the free C=O species.
TL;DR: In this article, a digital model based on discretization of time and space coupled with a finite-difference approximation of the governing heat-diffusion equations is proposed to gain an understanding of the way in which sample properties affect the impulse response.
Abstract: Impulse-response photoacoustic spectroscopy provides information on the depth distribution of chromophores in solid samples. To gain an understanding of the way in which sample properties affect the impulse response, a digital model has been generated. This model is based on discretization of time and space coupled with a finite-difference approximation of the governing heat-diffusion equations. The simulations are compared with experimental results.
TL;DR: In this article, photoacoustic spectroscopy (p.a.s.) was used to determine the concentration of copper and iron in two-component samples, respectively, and referring to the calibration graphs.
TL;DR: In this paper, the signal-magnitude and time-delay channels of cross-correlation photoacoustic spectroscopy (CPAS) were investigated and the experimental results were found to be in general agreement with a one-dimensional theoretical model of the CPAS-signal generation.
Abstract: The spectroscopic information related to the optical-absorption coefficients of solids and liquids, which is contained in the signal-magnitude and time-delay channels of cross-correlation photoacoustic spectroscopy (CPAS), has been investigated. Powders of holmium oxide and aqueous solutions of black India ink of variable concentrations were used as solid and liquid samples, respectively. The experimental results were found to be in general agreement with a one-dimensional theoretical model of the CPAS-signal generation.
TL;DR: The extent of the decrease in chlorophyll a fluorescenece caused by the addition of continuous 710 nm light superimposed on modulated (20 Hz) 550 nm light was used to determine the distribution of this absorbed light between photosystems I (α) and II (β).
Abstract: Usisng intact leaves, the extent of the decrease in chlorophyll a fluorescenece caused by the addition of continuous 710 nm light superimposed on modulated (20 Hz) 550 nm light was used to determine the distribution of this absorbed light between photosystems I (α) and II (β). The Fo and Fm levels, which defined the total variable fluorescenece, were taken as equal to those obtained with excess 710 nm light and with saturating blue-green light, respectively.An analogous procedure was used with a photoacoustic detector, saturating white light defining a base line for oxygen yield, the levels with an without 710 nm light being used to define β and α respectively.The two methods gave similar values for the distribution of light between the two photosystems for the experimental conditions used, β averaging 0.55 for a range of Triticum genotypes and Brachypodium sylvaticum grown in high or low light.
TL;DR: Sensibilites relatives des mesures effectuees avec du tetrachlorure de carbone, de l'eau, of l'acetone, du methanol, and du dioxyde of carbone as discussed by the authors.
Abstract: Sensibilites relatives des mesures effectuees avec du tetrachlorure de carbone, de l'eau, de l'acetone, du methanol et du dioxyde de carbone