��l=1.22f ��D(2)where �� is the wavelength of the light source, f is the focal length of the detector��s lens system, and D the diameter of the objective lens�� aperture.The reasoning behind this phenomenon is diffraction, and the Rayleigh criterion defines the smallest shift selleck chem that can be detected in a triangulation system, which, in turn, defines the maximum depth resolution of the system, simply by inserting Equation 1 into Equation 2. This criterion may slightly underestimate the resolution in some specific cases, but real inspection systems are usually far from reaching it.So a discouraging deadlock exists, as the improvement of depth resolution can only be obtained by increasing the triangulation angle or decreasing the working distance, which both might be an issue in a real system.

This physical limitation can be improved using interferometric techniques, as will be discussed in the next section.2.?Beyond the Rayleigh Limit with Conoscopic HolographyInterferometric techniques make Inhibitors,Modulators,Libraries use of the interference pattern generated when two coherent sources arrive at the detection plane with a small optical path difference; this difference generates in a detector an image composed of dark and white fringes, Inhibitors,Modulators,Libraries from which the distance information can be extracted.Usually this is done by splitting the laser light and making it travel through different paths, with one set as the reference and the other being reflected by the inspected object. In this way, it is possible to recover shape information from an object by making both beams interfere.

These setups have problems when applied in on-line inspection systems, as they normally need very careful setups to avoid misalignments and are quite sensitive to environmental conditions such as vibrations or air turbulence. This lack of robustness mainly derives from the fact that both wavefronts Inhibitors,Modulators,Libraries travel through different paths. Fortunately there are some techniques that do not have this limitation, the so-called common-path interferometric techniques. Conoscopic Holography is one of them.2.1. Conoscopic HolographyConoscopic Holography is an incoherent-light interferometric technique, based on the double refraction property of uniaxial crystals which was developed by Sirat and Psaltis in 1985 [2]. The basic system is shown in Figure 3.Figure 3.Conoscopic Holography working principle (courtesy of SPIE).

When a polarized monochromatic light ray Inhibitors,Modulators,Libraries crosses an uniaxial crystal, it is divided into two orthogonal polarizations, (ordinary and extraordinary rays) which travel at different speeds through the crystal. The speed of the ordinary Cilengitide ray is constant; however, the speed of the extraordinary ray depends on the angle of selleck Sunitinib incidence. In order to make both rays interfere in the detector plane, two circular polarizers are placed before and after the crystal.