Output couplers (partial reflectors)
PR | 193 nm - 8000 nm
Partially reflective mirrors (partial reflectors or output couplers, sometimes also called beamsplitters) are laser components used in stable optical resonators (for unstable resonators please check variable reflection mirrors). Output coupler is very similar to laser line or broad band mirror, however it reflects (and transmits) desired portion of light.
3photon output couplers are coated using electron beam evaporation (EBE), ion assisted deposition (IAD) or ion beam sputtering (IBS) technologies.
Output couplers manufactured by 3photon can be either single band (e.g. 193 nm, 248 nm, 308 nm, 1064 nm, 808 nm, 1030 nm, 2300 nm, etc.) or broad band (500-550 nm, 700-850 nm, 1000-1100 nm).
Infrared broadband output couplers are also available in 3000-8000 nm (3-8 μm) range.
In pulsed solid-state lasers and continuous wave (CW) lasers
Most common glasses (various grades of Fused Silica, Schott N-BK7 and their equivalents) have good transmission values from ultraviolet (UV) throughout to infrared (IR). However, lasers can emit longer, or shorter wavelengths and these common materials must be substituted with other materials which could be supplied by 3photon, such as Magnesium Fluoride (MgF2), Calcium Fluoride (CaF2), Zinc Selenide (ZnSe), Germanium (Ge) or others.
In Excimer lasers
Output coupler’s substrate and applied coating material must be fluorine and chlorine resistant due to exposure to laser gas.
Radius of curvature (ROC)
Stability highly depends on the shape of Output coupler (Partial reflection mirror). Depending on the design of optical cavity (concentric, confocal or other), cavity length and diameter, the Output coupler (Partial reflection mirror) can either be flat or curved (convex or concave curvature).
In order to eliminate interference caused by multiple reflections inside the Output coupler (Partial reflection mirror) 3photon suggest using wedged substrate. Even small wedge will decrease interference.
The dielectric partial reflection mirror coating is applied on the side facing the laser cavity (front side). To lower the losses of transmitted beam the outer side (back side) usually is coated with anti-reflective (AR) coating optimized for same wavelengths.
Reflection and Transmission
Depending on laser medium and cavity structure the reflection values may vary. Laser output couplers are described by reflection and transmittance values (R/T), which determine what portion of light is transmitted through and what portion is reflected to the cavity. 3photon can produce various ratios of R/T: 10/90; 20/80; 30/70; 40/60; 50/50; 60/40; 70/30; 80/20; 90/10; 95/5 and other custom reflection vs. transmittance rations.
Angle of incidence
Dielectric output coupler (Partial reflection mirror) coating can also be designed to work on different angles if necessary. Usually the 3photon standard output coupler has normal incidence angle (0°), however experienced 3photon engineers can design output couplers to work in your desired angle 22.5°, 45°, 56° or broad angle diapason 0-22°; 0-45°.
Sometimes two high reflection mirrors can be used in front and back of the laser cavity, the most popular alternatives are:
A. Drill small hole in the center of one mirror. This way small portion of the light passes through. 3photon can drill the hole according to your requirements.
B. Rotating mirrors system calibrated to allow required portion of light to pass through.