Broadband beam samplers split off, or sample, 1-10% of a beam's energy via Fresnel reflection from a single uncoated surface. This enables beam monitoring with minimal transmitted power loss. The optic's back surface is slightly wedged and AR coated to prevent ghosting.
In a beam sampler, percentage of reflected light is determined by the Fresnel reflection from a single surface. At the nominal 45° AIO the beam sampler reflects approximately 10% and 1% for s- and p- polarizations, respectively. Reflectance from a single uncoated surface in both S- and P- polarizations is shown.
N-BK7 is an excellent lens material for most visible and near infrared applications. It is the most common borosilicate crown optical glass, and it provides great performance at a good value. Its high homogeneity, low bubble and inclusion content, and straightforward manufacturability make it a good choice for transmissive optics.
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.
Three broadband antireflection coatings are offered for 45° angle of incidence beams. NC.1 covers the 440-700 nm spectral range. NC.2 covers the 600-1000 nm spectral range. NC.3 covers the 1110-1550 nm spectral range.
A common application for beam samplers is picking off a portion of a beam in order to track changes in beam power vs time using a detector. This information may be used as part of a feedback loop to regulate power, or could simply be used to log power in order to normalize experimental results at a later time. For measuring beam power, the beam sampler should be oriented such that the laser is p-polarized. This choice will maximize transmitted power and attenuate power incident on the detector.