The Applications of the Heterodyne Interferoemetry

Optical interferometry is widely used in many precision measurements such as displacement[1, 2], vibration[3, 4], surface roughness[5, 6], and optical properties[7-14] of the object. For example, holographic interferomter [1-3] can be used to measure the surface topography of the rigid object. The emulsion side of the photographic plate faces the object and is illuminated by a plane wave at normal incidence. Therefore, the reflection type hologram is recorded the interference signals between the incident wave and scattered wave from the object within the emulsion layer. Then the hologram is reconstructed with laser light and the information of object surface can be obtained. The Speckle interferometry [2-4] can be used to measure the motion of the rough surface. To compare the two exposure specklegrams, then the phase difference related to the surface movement can be obtained. Abbe refractometer [7, 8] is an easy method to determine the refractive index of the material based on the total internal reflection (TIR). That means the refractive index of the testing sample will be limit by the hemisphere prism installed in the refractometer. The ellipsometer [9-12] is widely used to measure the thickness and refractive index of film or bulk materials. Typically, the optical components of ellipsometer included polarizer, compensator, sample, and analyzer. Hence, there were many different types of ellipsometer for refractive index and thickness measurement of the sample. Most popular type is rotating polarizer and analyzer ellipsometer which can be divided into rotating polarizer type and rotating analyzer type. Both of them are analysis of the ellipsometric angles (, ) which determined directly from the adjustable angular settings of the optical components. The accuracy of the ellipsometric measurement are typically within the range 0.01 and 0.05 in (, ) [13, 14].