Variable reflection mirrors
R = 15% - 40% | 266 - 2500 nm
Variable reflection mirrors (VRM) also known as radial gradient reflection mirrors (RGRM), graded reflection mirrors (GRM) or (super) Gaussian mirrors are unique optical components, designed for specific wavelength with variable reflection value depending on distance from the center of mirror on the mirror ‘s surface. Usually this coating has highest reflection at its center. These mirrors can be produced only by few optical thin film coating companies worldwide.
The simplest method to produce variable reflection mirror is to deposit single high reflection index layer using specifically designed mask. VRM (GRM) usually are produced either by fixed mask method (employing shadowing effect) or by rotating mask method
- Advantages and disadvantages
- To improve beam profile (shape) and produce high quality laser beam in non-stable (unstable) resonators with high pulse energies and low divergence;
- 3photon variable reflection mirrors are mostly used in Nd:YAG (Nd:Y3Al5O12) laser systems as cavity optics (Gaussian output coupler);
- In order to achieve higher pumping efficiency variable reflection mirrors (VRM) are used in frequency doubling systems
Advantages and disadvantages using VRM in resonators
- Very good extraction efficiency;
- Near-perfect values of M2;
- Lower divergence;
- Smaller uniformity of field in comparison to other resonator types;
- Repetition frequency and input energy can be adjusted in very narrow ranges.
- Variable Reflectivity Profile is only working for the single specific wavelength;
- Extremely stable for high power applications;
- Reduces risk of optical damage in high energy laser systems.