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The observation and quantative measurement of optical heterodyne detection at 337 μm using a HCN laser and an epitaxial n-type GaAs photoconductor are reported. The measured NEP amounted 1.4 × 10−14 W Hz−1.

The use of the photoacoustic effect for new applications in agricultural biology is the subject of this chapter. Section 8.1 deals with the photoacoustic detection of ethylene that is produced by specific plant species during senescence and inundation. It was jointly written by the groups of Molecular and Laser Physics (F. Harren, J. Reuss, F. Bijnen) and Experimental Botany (L. Voesenek, C. Blom) from the Catholic University, Nijmegen, and E. Woltering, associated with the Sprenger Institute in Wageningen.

The natural aerobic spoilage of meat and that of meat inoculated with pure cultures is a complex process caused by microbial growth associated with the onset of various energy metabolisms. Chemical changes characterizing the end phase of bacterial activity at each of the distinct stages of their growth lead to the production of a well-defined sequence of volatiles [1]. In microbiology, determination of the microbial count number (number of bacteria per unit surface of meat) by elaborate plate counting techniques has become the common way to follow the growth and establish spoilage criteria. In principle predictions of the shelf-life of various meat products can be made if the relationship between the microbial count and the concentration of a specific volatile as the indicator of product deterioration can be found.