Wedged substrates can separate the reflected beams from the front and back surfaces by having an angled wedge on the second surface. They can be used as a reference test plate for interferometers and as beam samplers, enabling to “Pick Off” a portion of the beam for detectors. Wedged substrates are not coated on both sides. Keep in mind there is a 3.5 to 4% reflection of the bare glass surfaces. If the wedged substrate is inserted in the optical path of the laser beam, the transmitted beam is inclined slightly, causing the refraction. It is also available beam sampler (BS4) coated with anti-reflection coating on the back. Other coating options are available so please contact us for more information.