Recording Wavelengths Research Articles

Recursive design for an efficient HOE with different recording and readout wavelengths

The design of a holographic optical element for focusing a collimated off-axis beam to an on-axis point is described. It is designed according to a novel recursive technique in which the recording is done at a wavelength which differs from the readout. In this recursive technique the final holographic optical element is recorded by using other holograms to provide the aspheric recording wavefronts necessary for reducing the aberrations and maximizing the diffraction efficiency. The design is illustrated with an example where an f/3.0 focusing element is recorded at 514.5 nm and read out at 1064 nm. A spot size of 15microm and a diffraction efficiency of ~60% were measured.

Image Distortions in Display Holograms

AbstractThe fidelity of reconstruction of 3-dimensional images by reflection and transmission holograms is investigated, concentrating on the measurement and theoretical modelling of large-scale geometric distortions in holograms illuminated by white or monochromatic light. Variable parameters include: recording and replay wavelengths; object position at recording; emulsion thickness and refractive index; replay light-source angle and distance; presence of a glass substrate, its thickness and refractive index. Holograms were recorded on Agfa 8E56HD photographic plates, and measurements made of image-point directions as a function of position on the hologram, revealing considerable image distortions even for modest changes in parameter values between recording and replay. The results are accurately modelled by the theory, which gives numerical values for point-by-point image positions, without any resort to paraxial approximations.

The Purification of Water by Ultraviolet Radiation

Little is known regarding the exact nature of radiant energy. It is quite certain, however, that radiant energy is propagated by wave motion. The fact that the waves are transmitted through a vacuum calls for a carrier. Scientists have for years regarded the ether as the medium by and through which these radiations are propagated. If a time should come when the hypothesis of an ether must be discarded, the change will not materially affect the properties and applications of ultraviolet energy. The human eye is capable of receiving and recording wave lengths of radiant energy that vary from 390 m/x to 770 m/*. The former figure2 is the value given for the wave length of visible violet light; the latter is for the wave length of the visible red. The wave length values for the other spectrum colors lie within these limits. Wave lengths of radiant energy that are shorter than 390 m/* are invisible. Ultraviolet radiation, with its arbitrary subdivisions, (near, intermediate and extreme) occupies this short wave length region of the spectral range of radiant energy. Since the velocity of radiant energy in space is approximately 3 X 1010 cm/sec, the frequencies may be calculated by dividing the velocity by the wave length. When, for example, the wave length is 400 m/i (the frontier of visible radiation) the frequency has the value 75 X 1013 per second. It follows that the frequencies of radiations in the ultraviolet are much higher, since the wave lengths in this region are shorter than 400 m/x. It may be said, then, that ultraviolet radiation is characterized by (1) invisibility, (2) short wave length, and (3) high frequencies. They are quite easily absorbed by matter. Relatively few substances allow the radiation to pass through them. Clear fused quartz,