Signal processing and image reconstruction in microscopic acoustical holography

Acoustical imaging employs acoustical energy to produce information. It can provide different information from that obtained with other types of imaging. The techniques of digital signal processing and image reconstruction greatly enhance the potential of modern acoustical imaging. Digital acoustical holography represents one of the important examples. In this paper, we describe the application of digital acoustical holography in microscopic imaging. The image signal is acquired from a scanning laser acoustic microscope (SLAM). We show how to model the imaging process as a two-dimensional linear system. The signal processing for extracting the desired acoustic wavefield information and the process of image reconstruction are discussed. The design of two-dimensional digital filters to accomplish the task is briefly addressed. Finally, we present the first high-quality high-resolution microscopic subsurface images reconstructed with digital acoustical holography.