Detection of the defocused transfer function of a confocal reflection acoustic microscope (SAM) by imaging of a step and a sphere

The main advantage of the SAM is given by the fact, that the image contrasts are constructed by the ultrasonic waves and their reaction with the elastic discontinuities of the specimen. Some pat of the image structure is depending on the material distributions and their elastic parameters; another will be modified by the imaging conditions of the instrument. Image interpretation is closely related to these two classes of image contrast. Whereas the first kind of contrasts - especially known by the V(z)-function - mostly is used for microcharacterization of thin films and solids, the second kind of contrasts is deduced from the wave optical considerations, applied on the confocal acoustic reflection microscope and can be treated like amplitude contrast and phase transfer functions. These are useful for the description of structures, to reveal their real shape or distribution on the surface or inside the bulk specimen especially for reconstruction processes by inverse filtering in the Fourier domain of the image structure signals. It is shown, how the optical transfer function of the instrument can be found and is separated into the modulation transfer function (MTF) and the phase transfer function. The classical method is to analyze the images of scratches and material steps. Another way is to detect the MTF by imaging a sphere and scanning it at several focus positions.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.