Prisms and transmissive beamsplitters are common optical elements used to split laser beams into two separate beams. These devices are common at visible and the IR wavelengths. For very high laser powers in the IR (1 to 10.6 µm), most prisms and beamsplitters are not useful because they suffer from thermal lensing. This occurs especially in CO2 lasers at CW power levels > 500 W. For these high powers, it is possible to split the beam using a metal rooftop prism.
Rooftop beamsplitters, made from copper, are direct water cooled. This allows use at laser powers in excess of 6 kW. A 90° rooftop mirror is used to physically split the beam into two working beams. These two beams will travel 180° from each other. With some simple mirrors, the beams are used in welding and heat treating applications.
The rooftop mirror is made from a single substrate with two precision-aligned mirrors. Each mirror surface is flycut to achieve figure and finish. The angle between each mirror’s face is controlled to within 10 arc seconds (if required).