Question

On what factor the accuracy of laser interferometer mainly depends ?

Answer 1

Answer:

Explanation:

The stability of laser interferometer systems depends on the stability of the wavelength which, in turn, is dependent on the laser frequency and the fluctuations of the refractive index of the medium (typically air or vacuum), or how well the wavelength variations can be calibrated inline using an (absolute) refractometer. The stability of an optical encoder mainly depends on the stability of the scale material (e.g. invar, glass, steel, zerodur) or how well the thermal expansion can be predicted using information from temperature sensors. Interferometers are traceable to SI standards by comparing the laser frequency with a reference laser, where scales are traceable to the SI standard by comparing the scale lines with a laser interferometer-based comparator which is ideally positioned in vacuum (Kunzman et al., 1993; Maeda, 2001; Holzapfel, 2008). Linearity has two aspects: coarse errors and interpolation errors. Laser interferometers do not have coarse errors, while for scales the coarse errors must be calibrated. The differences can be reduced by application of calibrated scales and inline error correction. Interpolation errors of laser interferometers are comparable and typically in the range of 1–20 nm. For high-end encoders and interferometers, these periodic deviations can be reduced to sub-nanometer level by inline calibration. The measuring range is easily scalable to several meters for interferometers whereas for encoder systems the range is limited to the size at which the scales can be manufactured and mounted to a base with sufficient stability. In most machines with stapled linear actuators, it is easier to integrate a scale than an interferometer.