INTERFEROMETRIC
MEASUREMENT OF ANGLE
With
laser interferometer it is possible to measure length to accuracy of 1 part in
106 on a routine basis. With the help of two retro reflectors placed at a fixed
distance and a length measuring laser interferometer the change in angle can be
measured to an accuracy of 0.1 second. The device uses sine Principle. The line
joining the poles the retro-reflectors makes the hypotenuse of the right
triangle. The change in the path difference of the reflected beam represents
the side of the triangle opposite to the angle being measured. Such laser
interferometer can be used to measure an angle up to ± 10 degrees with a
resolution of 0. 1 second. The principle of operation is shown in fig.
Fig
4.11 Interferometric Angle Measurement
Laser Equipment for
Alignment Testing
This testing is particularly suitable in aircraft
production, shipbuilding etc. Where a number of components, spaced long
distance apart, have to be checked to a predetermine straight line. Other uses
of laser equipment are testing of flatness of machined surfaces, checking
square ness with the help of optical square etc. These consist of laser tube
will produces a cylindrical beam of laser about 10mm diameter and an auto
reflector with a high degree of accuracy. Laser tube consists of helium-neon
plasma tube in a heat aluminum cylindrical housing. The laser beam comes out of
the housing from its centre and parallel to t stability is the order of 0.2”detectorofhead
arcand per read out unit. Number of photocell are arranged to compare laser
beam in each half horizontally and vertically. This is housed on a shard which
has two adjustments to translate the
detector in its two orthogonal measuring directions perpendicular to the laser
beam. The devices detect the alignment of flat surfaces perpendicular to a
reference line of sight.
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