Combined optical and acoustical method for determination of thickness and porosity of transparent organic layers below the ultra-thin film limit Rev. Sci. Instrum. 82, 103111 (2011) Spatial anisotropy of the acousto-optical efficiency in lithium niobate crystals J. Appl. Phys. 108, 103118 (2010) Observation of the forbidden doublet optical phonon in Raman spectra of strained Si for stress analysis Appl. Phys. Lett. 97, 041915 (2010) High-resolution laser lithography system based on two-dimensional acousto-optic deflection Rev. Sci. Instrum. 80, 085105 (2009) Additional information on J. Appl. Phys.When chopped light impinges on a solid in an enclosed cell, an acoustic signal is produced within the cell. This effect is the basis of a new spectroscopic technique for the study of solid and semisolid matter. A quantitative derivation is presented for the acoustic signal in a photoacoustic cell in terms of the optical. thermal, and geometric parameters of the system. The theory predicts the dependence of the signal on the absorption coefficient of the solid, thereby giving a theoretical foundation for the technique of photoacoustic spectroscopy. In particular, the theory accounts for the experimental observation that with this technique optical absorption spectra can be obtained for materials that are optically opaque.

not available. 2:30 AA2. Chemical aspects of optoacoustic spectroscopy. M.B. Robin Molecular spectroscopists have studied the absorption of optical radiation for over 100 years, but only in the last five years have experiments come forth on the subsequent relaxation of the molecular excitation to produce heat. By detecting this heat as an acoustic pulse using sensitive microphones and bolometers, the eventual fate of absorbed photons can be followed, both energetically and kinetically. Several examples of the unique information derived from this acoustic method of molecular spectroscopy will be presented. Abstract not available. 3:30 AA4. Photoacoustic spectroscopy of solids.There are a great many substances, both organic and inorganic, that, because of their physical state, cannot be readily studied by conventional absorption or reflection techniques. In photoacoustic spectroscopy, light absorbed by the sample is converted into a measurable acoustic signal, and spectra closely corresponding to optical absorption spectra, can be obtained on any type of solid or semisolid material, whether it be crystalline, powder, smear, gel, etc. The physical processes underlying the photoacoustic effect in solids, and a mathematical analysis of the production of the photoacoustic signal will be presented. The methodology of photoacoustic spectroscopy will also be described. Various applications of this technique in the fields of physics, chemistry, biology, and medicine will be discussed. These applications will be treated under three main headings: bulk studies, surface studies, and de-excitation studies.

We show that thermal wave detection and analysis can be performed, in a noncontact and highly sensitive manner, through the dependence of sample optical reflectance on temperature. Applications to the study of microelectronic materials are illustrated by an example of measuring the thickness of thin metal films.

A new technique has been developed that employs highly focused laser beams for both generating and detecting thermal waves in the megahertz frequency regime. This technique includes a comprehensive 3-D depth-profiling theoretical model; it has been used to measure the thickness of both transparent and opaque thin films with high spatial resolution. Thickness sensitivities of +2% over the 500-25,000-A range have been obtained for Al and SiO 2 films on Si substrates.

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