Majority of interference filters are designed to be used at normal angle of incidence (AOI). The primary effect of an increase in the incident angle on an interference coating is a shift in spectral performance toward shorter wavelengths. In other

The Choi-Jamiołkowski isomorphism is an isomorphism between linear maps from Hilbert space \({\cal H}\) to Hilbert space \({\cal K}\) and operators living in the tensor product space \({\cal H}\otimes{\cal K}\). This isomorphism provides a simple way of studying linear maps

Approximation of the error function, $${\rm erf}(z) = \frac{2}{\sqrt{\pi}}\int_{-\infty}^{z}\!{\rm d}x\,{\rm e}^{-x^2},$$ using elementary functions could be useful, particularly for PDC and spatial walk-off simulations… Wikipedia, Sergei Winitzki’s paper