عنوان

Nano-Metrology Based on the Laser Interferometers.

9533070617

9789533070612

b610659

Nano-Metrology Based on the Laser Interferometers.

[Book]

Saeed Olyaee

INTECH Open Access Publisher

2010

The optical interferometry is the most frequent technique which has been widely used in metrology systems with subnanometer resolution. In this chapter, first we have discussed an overview of principals of interferometry, interfere phenomenon in the laser interferometers and their applications. A comparison of homodyne interferometers, advantages and disadvantages with heterodyne interferometers was also investigated. The optical setup and electronic sections of two- and three-longitudinal-mode heterodyne interferometers was then described. A frequency-path model of the nano-displacement measurement system based on the laser heterodyne interferometers was presented. This model is described by the AC reference, AC interference, DC interference and optical power components of the multi-mode, multi-path interferometer. The main parameters affecting the displacement measurement accuracy were discussed in the fourth section. The most important errors are related to imperfect alignment of the optical setup and nonideal polarized modes. The periodic nonlinearity is the principal limitation of the laser interferometers involving polarized light. Therefore, we have analyzed and modelled the periodic nonlinearity resulting from ellipticity and nonorthogonality of the polarised modes, deviation angle and unequal transmissionreflection coefficients of the PBS and a rotation angle of polarizer with two main approaches; plane wave and matrix method based on the Jones calculus. Then by using two polarizers oriented under +45º and -45º, a half-wave plate, and another avalanche photodiode, the periodic nonlinearity has been considerably decreased. In addition it was shown that the first-order nonlinearity can be effectively reduced compared to the second-order nonlinearity.

Open Access Collection.

Saeed Olyaee

Saeed Olyaee

Samaneh Hamedi

[Book]

Y