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.

Applications of photoacoustic sensing techniques

This review describes recent instrumentation developments of the thermal lens techniques. It will begin with a brief discussion of the theory of the techniques. Its main focus is, however, on the detail description of various instruments. Specifically, the discussion will begin with the description of single beam instruments which were initially developed following by dual beam instruments. Elaboration will be focused on some of the most sophisticated instruments which were developed recently. These include differential thermal lens instruments, multiwavelength and spectral tunable instruments, circular dichroism spectropolarimeters, rotoreflecting instruments, and miniaturized thermal lens instruments. Selection of lasers, focusing, modulation, sample position, sample cells, data acquisition, noise reduction, and applications of acousto‐optic tunable filters will also be discussed. The future of the techniques in terms of instrumentation will be finally forecasted.

Analytical thermal lens instrumentation

This review considers the technique of thermal lens spectrometry and its applications to chemical measurements in solid, liquid and gaseous phases. Practical applications, theoretical treatments and instrumental developments are considered in terms of their analytical use and potential.

Thermal lens spectrometry. A review

The authors present experimental data for a high-power CO/sub 2/ laser which confirm the validity of a simple analysis for the beam divergence and beam quality of the output beam from a large-bore multimode stable-cavity laser oscillator. The multimode beam parameters can be accurately predicted from a simple theory using only the geometrical parameters of the stable resonator. The data also suggest that a laser of this type with a uniform gain profile across the tube bore oscillates preferentially in the highest order modes allowed by the laser cavity rather than, for example, equipartitioning the output power among all the allowed cavity modes. >

Output beam propagation and beam quality from a multimode stable-cavity laser

The Wigner distribution function (WDF) is used to study the propagation of partially coherent beams through optical systems. The width and divergence of multimode beams are defined in terms of moments of the WDF. It is shown that these and other parameters of partially coherent beams of arbitrary form may be calculated using geometrical ray traces. Generalized transformation laws of these beam parameters by an ABCD optical system are obtained. These laws are tested experimentally for multimode beams and thin lenses. The applications of the ray tracing method can be extended to a non-ABCD system with mild aberrations.

Generalized beam parameters and transformation laws for partially coherent light

A novel method for measuring refractive index of gases and liquids is presented based on moire deflectometry. We demonstrate this technique by measuring the refractive index of diluted sucrose solutions and of air at atmospheric pressure.

Refractive-index measurements by moire deflectometry

A method based on moire deflectometry for direct determination of the number of transverse modes of radiation of a light beam is presented. An expression for the number of transverse modes of a light beam, as a function of the beam divergence, is derived. We demonstrate the method for a Cu-vapor laser-beam analysis.

Direct determination of the number of transverse modes of a light beam.

In this paper we suggest a new optical technique, moire deflectometry, for V-T relaxation rate studies in gases. By using this technique we map the thermal lens induced by absorption of an infrared laser radiation. We have shown that the thermal lens is significantly broader compared to the pump beam profile. We also show that measurement far from the beam axis provides a better bound to the relaxation time than an on-axis measurement.

Ziv Karny

Papers

Refractive-index measurements by moire deflectometry

Direct determination of the number of transverse modes of a light beam.

Spatial analysis of the CO 2 laser-induced thermal lens in SF 6 by moire deflectometry