An electro-optical switch includes an optical assembly arranged to transmit laser-radiation. The optical assembly comprises an active optical crystal. On one of two opposite surfaces of the crystal is an optical window formed from a material having a refractive index lower than the material of the crystal. Heat deposited, as a result of transmission of the laser-radiation, at the surface of the crystal in contact with the widow is transferred to the window, thereby reducing the potential for optical damage to the crystal surface. The window is sufficiently thick that it has an odd integer multiple of quarter-wavelengths optical thickness at a wavelength about equal to a wavelength of the laser-radiation, thereby behaving as an antireflection device for the crystal at that wavelength. In one embodiment of the optical assembly, the active optical crystal is a cadmium telluride crystal and the window is formed from cesium bromide.