Laser interferometry or ESPI, also known as computer-aided speckle pattern interferometry (CASPI), television holography, and video holography, is the electronic processing of speckle patterns produced by a laser interferometer consisting of two laser beams (using a beam splitter) generated from the same laser source.

1. Laser interferometery
By
Naresh.B

2.  Introduction:
interferometer uses ac laser as light
source and thus used to measure large distance,the
laser beam wavelength is exact and pure for highly
accurate measurements.
Principle:
1.Optical technique
2.Digital electronics

3. construction
1.Two frequency Zeeman laser
2.Beam splitter
3.Fixed internal cube corners
4.External cube corners
5.Photo detector
6.Amplifiers
7.Pulse converter

4. Description
 Two Frequency laser: Two frequency laser one is
polarized vertically and the other is polarized
horizontally.
 Beam spliter: splites beam
 Cube coners: 2 cube corners required one is
placed externally and the other is placed
internally,both are used to reflect laser beam.
 Photo detector: receives signal from splitter and
change into electrical signals.

5.  Amplifiers: it is used to separate frequency
difference
 Pulse converter: It is used to extract information
as pulse signal.
 Laser interferometery has the following
Advantages.
 High repeatability
 High accuracy
 Long range optical path
 Easy intallations
 Wear and tear

6. Schematic arrangement of laser
interferometer:

7. working
 The above shown is the schematic diagram of laser
interferometer.
 Two frequency Zeeman laser generates light of two
slightlydifferent frequencies with opposite circular
polarisation.
 These beams get split up by beam splitter B One part
travels towards B and from there to external cube
corner here the displacement is to the easued.
 The interferometer uses cube corner reflectors which
reflect light parallel to its angle of incidence.
 Beam splitter B2 optically seperates the frequency J
which alone is sent to the movable cube corner
reflector.

8.  The second frequency from B2 is sent to a fixed reflector
which then rejoins f1 at the beam splitter B2 to produce
alternate light and dark interference flicker at about 2
Mega cycles per second.
 Now if the movable reflector moves, then the returning
beam frequency Doppler-shifted slightly up Thus the
light beams moving towards photo detector P2 have
frequencies f2 and (f1 ± Δf1) and P2 changes these
frequencies int signal from beam splitter B2 and changes
the reference beam frequencies f1 and f2 into electrical
signal.
 An AC amplifier A separates frequency. Difference signal
f2 –f1 and A2 separates frequency difference signal.
 The pulse converter extracts i. one cycle per half
wavelength of motion. The up-down pulses are counted
electronically and displayed in analog or digital form.

9. Use of laser in interferometery
 The laser in interferometery is used to find
accurate measurements of length.
 The accuracy of laser measurement is in order of
0.1µm in 100m
 In modified laser design, a single frequency is
selected from coherent beam and used for
interferometric measurement.
 Time consumption is Less

10. Measure other things apart from
distance
 Straightness Measurement
 Combined straightness and displacement
measurement
 Straightness measurement via autocollimation
 Flatness via autocollimation

11. thank you