THERMAL WAVE IMAGING USING HARMONIC DETECTION OF THE PHOTOACOUSTIC SIGNAL

Abstract We describe a thermal wave imaging system based on gas-microphone detection of the harmonic component of the photoacoustic (PA) signal. In this system the sample is excited by a laser beam modulated at a frequency ƒ and the detection of the associated thermal wave field is carried out at a frequency 2ƒ. The technique demonstrates lateral resolution comparable to conventional thermal wave systems based on detection of the fundamental component of the PA signal, but provides for better contrast in depth-profiling applications.