<title>Heterodyne interferometry using two wavelengths for dimensional measurements</title>

Abstract

Optical methods become useful tools for dimensional measurements. Different techniques have been developed in the last few years. In addition to the well known time of flight and phase measuring principles other methods such as focussing and interferometric techniques are implemented. Today, laser interferometry is probably one of the most commonly used interferometric methods in metrology. A stabilized He-Ne laser is freque9tly used as light source with an absolute stability of better than 10 . The accuracy for length measurements is limited by the atmospheric conditions (humidity, temperature, pressure) rather than by the laser stability.