Laser interferometry utilizes an AC laser for precise distance measurements through the interference of beams of slightly different frequencies. The system includes components like beam splitters, cube corner reflectors, and photo detectors to achieve high accuracy, with measurement errors as small as 0.1μm over 100m. Advantages include high repeatability, ease of installation, and the ability to measure various parameters such as straightness and flatness.

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