Air-gap polarizers tolerate 10X more power than cemented designs
A scientist at Lumus Optical has developed a new coating-design technique (patent pending) for a polarizing cubic beamsplitter.
A scientist at Lumus Optical (Rehovot, Israel) has developed a new coating-design technique (patent pending) for a polarizing cubic beamsplitter. Using a Fabry-Perot configuration with two identical coated mirrors separated by an air space, the polarizer was modeled to ensure that the angle of incidence in the coating is below the total internal reflection (TIR) angle to achieve high extinction ratio (>100:1) and high laser damage threshold (LDT) for a 1065 nm YAG laser.
Based upon modeling parameters, two fused-silica prisms with identical coatings were designed to be optimized at an incident angle of 40.5°. With a high reflection for s-polarization and a low reflection for p-polarization for each separate mirror, and modeling the air space as a thin layer, the overall design resulted in a wide-spectrum polarizer. To achieve high LDT, hafnium oxide (HfO2) and silicon dioxide (SiO2) were chosen as the coating materials. Experimenting with 6 and 15 alternating high- and low-index layers transmitted >99.5% of the p-polarization and <0.5% of the s-polarization. Optimization with OptiLayer software (www.optilayer.com) resulted in single- and double-wavelength designs (for 1065 and 1540 nm) with high-extinction performance that survived laser power levels of >500 MW/cm2 compared to cemented polarizers that could only withstand power levels of <50 MW/cm2. Reference: M. Gilo, Optical Interference Coatings (OIC) conference paper 2482171, Tucson, AZ (Jun. 2016).