Page 394 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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Encyclopedia of Physical Science and Technology EN012C-562 July 26, 2001 15:30

Photoacoustic Spectroscopy

Konka Veeranjaneyulu
Roger M. Leblanc
University of Miami

I. Introduction
II. Photoacoustic Effect and Signal Generation
III. Advantages
IV. Instrumentation
V. Applications

GLOSSARY Thermal diffusivity The thermal diffusivity is given by
κ
α = where κ is the thermal conductivity, ρ is the
ρc
Background light Nonmodulated white light used to sat- density, and c is the thermal capacity.
urate the photochemistry of the photosystems.
Depth-profile Depth specific characterization of a sam-
ple based on the frequency dependence of the thermal THE PHOTOACOUSTIC effect is based on the conver-
sample. sion of absorbed light energy into heat by means of radi-
Modulation frequency The amplitude of the measuring ationless deexcitation processes. On irradiation of a solid
light beam chopped at required frequency to generate or liquid sample by intensity modulated light, a heat wave
the photoacoustic signal at the same frequency. of the same frequency is generated in the sample. The
Optical absorption length Penetration depth of the inci- heat wave is transferred by diffusion to the surface of the
dent light flux. sample, where oscillatory thermal effects are generated in
Phase angle Phase angle shift of photoacoustic signal the coupled gas. These can be detected as an acoustic sig-
relative to the modulation frequency. nal. This technique is known as gas-coupled photoacoustic
Thermal deactivation Relaxation pathway of an opti- spectroscopy.
cally excited molecule, wherein the excitation energy
is converted into heat.
Thermal diffusion length The thermal diffusion length
I. INTRODUCTION
α
(µ s ) is defined by µ s = where α is the thermal
π f
diffusivity of the sample and f is frequency. Electromagnetic radiation, including the frequency range
that is visible to the human eye, is a convenient and
This work is dedicated to Professor Danuta Fra¸ckowiak, Institute of
effective probe to study a wide range of biophysi-
Physics, Poznan University of Technology, Piotrowo 3, 60-965 Poznan,
Poland, on the occasion of her 75th birthday. cal and biochemical processes of biological systems.

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