The edge of the optic is marked with an arrow indicating the thickest part of the optic. The arrow points toward the front surface of the optic, which should face the incident beam. For a horizontally propagating beam the mark should be positioned on top so that the wedge is perpendicular to the plane of incidence.

When the collimation tester is aligned at a 45º angle of incidence with respect to the incident beam, an interference pattern is formed. By adjusting the input beam condition and observing the fringe pattern, the collimation of the beam can be accurately obtained.

When a horizontal beam is collimated, fringes will be horizontally oriented. If a beam is diverging or converging, fringe orientation will be tilted slightly.

UV Grade Fused Silica is synthetic amorphous silicon dioxide of extremely high purity providing maximum transmission from 195 to 2100 nm. This non-crystalline, colorless silica glass combines a very low thermal expansion coefficient with good optical qualities, and excellent transmittance in the ultraviolet region. Transmission and homogeneity exceed those of crystalline quartz without the problems of orientation and temperature instability inherent in the crystalline form. It will not fluoresce under UV light and is resistant to radiation. For high-energy applications, the extreme purity of fused silica eliminates microscopic defect sites that could lead to laser damage.