Durable and Cost-Effective Neutral Density Filters Utilizing Multiple Reflections in Glass Slide Stacks

We propose an application of a stack of glass slides as a broadband neutral density filter with high (> 100 W/cm
²
) damage threshold. The influence of multiple reflections on the filter transmittance is analyzed with transfer matrix method. The numerical study proves that the filter spectrum is determined by material dispersion and degree of wavelength averaging occurring due to light incoherence and limited measurement resolution. Varying the angle of light incidence can be used to extend the possible optical density range of the filters. The numerical results are verified by spectral measurements with setups containing coherent and incoherent light sources. The applicability of the filters is proven in a concentrated sun simulator.