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It is possible to do diffractive optics really cheap - either with photography (with a non-digital camera) or a widely available DTP polygraphic technique. …

Are there any materials, which give total internal reflection for perpendicular incidence? Here, by this phenomena I mean: no absorption (including for evanescent propagation inside), finite evanes …

The vacuum state is the thermal state for $T=0K$. How to compare if a state is close enough to the vacuum state? By counting photons (for vacuum it is zero). The occupation for photons is given by Bos …

A naive explanation says that a beam after its focal point is inverted, not only in the sense of its spatial distribution but also in the sense of the direction of the electrical field vector (minus s …

The operation you mentioned $$\Delta \hat{a} = \hat{A}-\langle \hat{A}\rangle \hat{I}$$ is just shifting of the annihilation operator. Typically people even drop the identity and write $$\hat{a}_{new} …

1. Of course wall sometimes absorbs the photon (light do not evade it in any way). To have interference, you need to have no information (in terms of excitation, creation of photographic grain of what …

Air is everywhere, not only in slit, but also in the optical path before and after the slit. However, interaction with transparent media (e.g. air, water, glass) can be easily included: by use of ref …

Consider a problem in classical electrodynamics, when a monochromatic beam experiences total internal refraction when traveling from a medium with $n>1$ to a medium with refractive index $1$ - see sch …

It is not an complete answer, but (hopefully) it may help: $$\text{tr} \left( A B \right) = \pi \int W_A(r) W_B(r) dr = \pi \int P_A(r) Q_B(r) dr,$$ where $A$ and $B$ are self-adjoint operators, $r=(p …

It's a non-trivial problem, which also involves how you define a photon in a medium - as a interacting particle and treating excitation of medium separately, or as a "dressed particle", including the …