Output couplers (partial reflectors)
PR | 193 nm - 8000 nm
Partially reflective mirrors, also known as partial reflectors, output couplers, or sometimes beamsplitters, are essential laser components for stable optical resonators. (For unstable resonators, see variable reflection mirrors.) Output couplers function similarly to laser lines or broadband mirrors but are designed to reflect and transmit specific portions of light.
3photon output couplers are coated using advanced technologies such as electron beam evaporation (EBE), ion-assisted deposition (IAD), and ion beam sputtering (IBS).
They are available as single-band (e.g., 193 nm, 248 nm, 308 nm, 1064 nm, 808 nm, 1030 nm, 2300 nm, etc.) or broadband (500–550 nm, 700–850 nm, 1000–1100 nm) designs.
Infrared broadband output couplers are also offered in the 3000–8000 nm (3–8 μm) range.
- Substrates
- Alternatives
Material
For pulsed solid-state and continuous wave (CW) lasers, common glasses (e.g., Fused Silica, Schott N-BK7, and their equivalents) offer excellent transmission from ultraviolet (UV) to infrared (IR).
However, for lasers emitting outside this range, alternative materials like Magnesium Fluoride (MgF₂), Calcium Fluoride (CaF₂), Zinc Selenide (ZnSe), and Germanium (Ge) are available from 3photon.
In Excimer lasers
For Excimer lasers, substrates and coatings must be resistant to fluorine and chlorine due to exposure to laser gases
Radius of Curvature (ROC)
Stability largely depends on the shape of the output coupler (partial reflection mirror). Depending on the optical cavity design (concentric, confocal, etc.), cavity length, and diameter, the output coupler can be flat or curved (convex or concave).
o reduce interference from multiple reflections within the output coupler, 3photon recommends using a wedged substrate. Even a slight wedge can significantly reduce interference.
The dielectric partial reflection mirror coating is applied to the front side (facing the laser cavity). To minimize transmitted beam losses, the back side is typically coated with an anti-reflective (AR) coating optimized for the same wavelengths.
Reflection and Transmission
Reflection values depend on the laser medium and cavity structure. Laser output couplers are characterized by reflection and transmission (R/T) ratios, indicating the portion of light transmitted and reflected. 3photon offers R/T ratios such as 10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20, 90/10, 95/5, and custom configurations.
Angle of Incidence
Dielectric output coupler coatings can be customized to function at various angles of incidence if needed. The standard 3photon output coupler is designed for normal incidence (0°), but their engineers can design couplers for specific angles, such as 22.5°, 45°, 56°, or broader ranges (0–22°, 0–45°).
Alternatives to output couplers include using two high-reflection mirrors at the front and back of the laser cavity:
A. Drilling a small hole in the centre of one mirror to allow a portion of the light to pass. 3photon can customize hole sizes based on your requirements.
B. Using a rotating mirror system calibrated to pass a specified portion of light.
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