Conventional beam splitters were discussed in the last Photonics News issue; in this issue, we will look at somewhat rarer components: diffractive optical elements (DOEs) and cubes.
Beam splitter cubes are used in power separation without beam displacement. The classic beam splitter cube is produced for a certain wavelength and direction of polarization. The heart of the cube is the hypotenuse, to which the appropriate dielectric coating is applied. The surfaces of beam entry and exit on the cube are AR coated, which means that four layers in total are applied to the cube. This explains the relatively high cost of cubes.
Polarizing beam splitter cubes. These components are always used when the laser power can be split via polarization. Cemented cubes are used for lasers with low energy and power densities; they are also available with broadband coatings. Optically-contacted versions are available for high-power applications: Damage thresholds above 10 J/cm² (10 ns, 10 Hz, 1064 nm) are quite resilient. In combination with L/2 retardation plates, polarization beam splitting cubes can even be used in power regulation.
Diffractive beam splitters are used for precise power separation in high-power lasers: in fact, it is even possible to separate the power into several identical beams (beam matrix). They are commonly used in laser material processing to make holes at precisely defined intervals, for example. With just one compact element, it is even possible to achieve two-dimensional beam matrices of 9x9 spots.
