Практикум по переводу с английского языка на русский. Базарова Б.Б - 71 стр.

                                    3.3.     ТЕКСТЫ ДЛЯ ПЕРЕВОДА
                                                  TEXT 1
                                       The principles of holography
     Holography is a photographic technique, where the picture (hologram) becomes three-
dimensional. Well-defined laser light is needed to create the hologram. Laser light is monochromatic,
coherent, parallel, and intensive. Every single part of the hologram acts like a lens or an eye and
registers the whole motive from its particular viewing angle. This gives a 3-D effect when we look at
the hologram. The hologram consists of a glass plate or film covered with a photographic emulsion of
extremely high resolution (3000-5000 lines/mm) and high sensitivity. If the hologram is exposed twice
(double exposure) and something has happened to the surface of the object in the meantime, black
interference fringes can appear on the hologram. These fringes are caused by differences in amplitude
and phase of the laser light on the different exposure occasions. They can be looked upon as a mapping
of the alterations in the surface. Every fringe represents a change equivalent to half the wavelength of
the light. If a He-Ne laser is used, this means that deformations or movements of 0.3 μ.m can be
measured. Successive measurements can be made to subdivide and follow large-scale movements.
     The holographic set-up contains a laser, a spatial filter, a plate holder, and sometimes a reference
mirror. If measurements are made on human beings, a powerful pulsed laser is needed; otherwise, an
inexpensive continuous-wave laser is sufficient. Ready-to-use equipment for industrial purposes is
now available on the market, which makes the technique much simpler and reduces the measurement
time. This time can vary between one and 15 minutes. Today, the time-consuming part is the
evaluation of the hologram, which generally demands a specialist. The evaluation can be both
qualitative or quantitative and comparative, which means that it can vary from a rapid glance by eye to
heavy computer work.
     The phenomenon known as “speckle pattern” is obtained when spatially coherent light waves
from, for instance, a laser are reflected from a surface. The speckle technique can be used for
measurement purposes in such a case.




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