Electromagnetic radiation reflected normally causing interference to itself Is it possible to have a body reflect almost perfectly any radiation falling  normally with the insident ray so that the reflected ray interferes with the incident and hopefully reduce or cancel it out ?
 A: High-quality optical lenses are often coated to reduce reflections. A thin film of a transparent material with a different index of refraction is coated onto the lens, with a thickness of a quarter of the wavelength of the light of interest. Incoming light passes through the coating and bounces off the other side, returning to the top surface half a wavelength out of phase. This partially cancels the reflection from the top surface. The result is that more light gets through the lens, giving a brighter image with better contrast, and less is reflected away or bounced around inside the instrument.
It only works perfectly at one specific wavelength. For optical equipment designed to work with the full range of visible light, such as binoculars, this is usually in the green part of the spectrum, where the eye is most sensitive and in the centre of the visible range, to give the best overall performance. This is why such lenses often appear to have a bluish tinge - light is preferentially reflected at the ends of the spectrum.
Conversely, dielectric mirrors can be made with transparent coatings with a thickness designed to reinforce the reflection. For specific, narrow wavelengths they can reflect 99.999% of the light.
A: "Interference" is the linear superposition of waves, i.e. it is really the absence of interaction of the wave with itself. As a result the energy in waves can not disappear and waves can not actually "cancel" out. They form minima and maxima that can be located in fixed positions in space ("standing waves") instead. We can therefor find "dark" regions  with a diminished amplitude, but they are always near "bright" regions (often called interference stripes, rings etc.) where the amplitude is increased.
If we want to reduce the total energy of a wave, then we need an absorber material that removes energy from the wave. One can, however, increase the efficiency of imperfect absorbers by placing them in the regions of maximal intensity or, alternatively, one can reduce the absorption of such materials by using them in standing wave minima.
