Metrological application of laser scattering

Laser light scattering as a rapid, non-destructive technique finds many industrial applications like on-line surface imperfection measurement. In addition, its statistical-averaging ability makes it accurate and repeatable, and useful for the calibration of the standard reference materials for metrology, such as, for example, surface roughness, particle size, and electron microscope magnification. In many metrological applications of light scattering, the metrological accuracy of the instrument is more crucial than the corresponding theory associating the scattering with the metrological factors to quantify. A precision goniometric scatterometer/diffractometer, therefore, has been developed. As a light source, the collimated HeNe and argon ion lasers are used, with which the wavelengths of 632.8, 514.5, and 488.0 nm, are available. The goniometer has 6 degrees of freedom. The precision of scattering polar angle is enhanced by choosing a long rotating arm placed on the stepmotor-controlled rotary table whose angle is read by the angle encoder. The receiver has a wide dynamic range without intensity attenuation and receiver aperture change, which is made by cascading three kinds of detectors: photodiode, photo-multiplier in direct current mode, and photo-multiplier in pulse counting mode.