Efeito fotoacustico a baixas temperaturas
AUTOR(ES)
Alba Rosa Lopez Parada
DATA DE PUBLICAÇÃO
1985
RESUMO
Photoacoustic Effect has being used to study optical and thermal properties of many types of materials. as solids, semisolids, liquids and gases. For low temperatures the experimental chamber needs to have special design. The photoacoustic cell is used in combination with a cryostat. To allow the sample temperature variation. The cell is constructed according to Helmholtz resonator model. It consist of two chambers connected together by a narrow tube. One chamber is the sample chamber, in thermal contact with a cold finger and the other is the microphone chamber kept at room temperature. The cell caracterizatuion has been made using a carbon sample. We have done scanning of the modulation frequency of the exciting light, sample temperature variation, and pressure variation of the gas inside the cell for different kinds of gases. In this work we discuss the Photoacoustic Effect Theory in solids and the characteristics of the cell we have projected and constructed to study optical and thermal properties of some materials. We have done some preliminar measurements on: depth profiling in GaAs sample with double structure to allow a precise depth reference; light absorption by a GaAlAs sample; phase transition in LiNH4SO4 (LAS) sample in the temperature range 140 K to 330 K as examples of projects to be developed in the near future
