Laser interferometry

LASER INTERFEROMETR

YBY

Kaviyarasan.S

LASER LASER (light amplification by Stimulated emission of Radiation) It is the powerful ,Monochromatic light

source The advantage of laser is production of

coherent light which is very intense at small point

PRINCIPLE OF LASER Stimulated emission Population inversion Incident photon is equal to the emission

photon EG : when xenon flash tube excites the

atom of ruby rod ,it produce photon, where incident photon of flash tube is equal to emitted photon of ruby rod.

photon is packs of charge.

PRINCIPLE OF INTERFEROMETRY Interferometry :

It is used to understand nature of light

It is a family of techniques in which waves, usually electromagnetic, are superimposed in order to extract information about the waves

INTERFEROMETRY Interferometry means the complete

study about the frequency signals of light.

In other words , interferometry is investigation of wave signals of light.

The highest point of the wave is called crest ,lowest point of the wave is called trough.

The distance between two crest or trough is called wavelength(l).

The maximum disturbance of wave is called amplitude(A),either it may be in crest or trough.

Light is allowed to interfere where it produce dark band of waves corresponding to the frequency of light.

Only monochromatic lights are used to investigate waves of light.

Monochromatic lights are used in measuring flatness and determining length of slip gauges.

USE OF LASER IN INTERFEROMETRY The laser in interferometry is used to

find accurate measurements of length. The accuracy of laser measurement is in

order of 0.1mm in 100m. In modified laser design ,a single

frequency is selected from coherent beam and used for interferometric measurement.

Time consumption is less.

PARTS OF LASER INTERFEROMETRY parts involved in interferometry ;

I. Two frequency laser source

II. Optical element

III. Laser head measurement receiver

IV. Measurement display

TWO FREQUENCY LASER SOURCE The two frequency laser source

becomes HE-NE type that generates stable coherent light beam of two frequency.

Laser is oscillated at two frequency by placing the laser in cylindrial permanent magnet.

In two frequency one is polarised horizontally and other is polarised vertically.

Two frequency waves allowed to pass through quarter and half wave plate that seperates two frequency in two perpendicular direction.

So we get two frequency of laser.

OPTICAL ELEMENT various optical element are ,1. Beam splitter2. Beam bender3. Retro reflector

BEAM SPLITTER:

It is used to split laser into separate beams along different axes

The output intensity can be adjusted by the reflectivity of beam.

BEAM BENDERS It is used to deflect the light beam

around corners of object from laser to each axis

RETRO REFLECTOR This type of reflectors are found in cube

corners prism that reflect parallel light rays of incident ray.

Laser head measurement receiver: It is used to detect part of

returning beam as f1-f2 ie, difference between frequency.

Measurement display: The measurement display

has a microcomputer to compute and display results.

TYPES OF AC INTERFEROMETERSTANDARD INTERFEROMETER: The displacement is

between cube corner and ,it is least expensive used where ever it is possible

SINGLE BEAM INTERFEROMETER: Here the out going and

returning beam are super imposed on eachother having parallel light rays.

DIFFERENCE BETWEEN

LASER INTERFEROMETER 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.

CONSTRUCTION1. Two frequency zeeman laser2. Beam splitter3. Fixed internal cube corners4. External cube corners5. Photo detector6. Amplifiers7. Pulse converter

DESCRIPTION Two frequency laser: Two frequency

laser one is polarised vertically and other is polarised horizontally.

Beam splitter: splits beam Cube corners: 2 cube corners are

required one is placed externally and other is placed internally, both are used to reflect laser beam.

Photo detectors: receives signal from splitter and change into electrical signals.

Amplifiers: it is used to separate frequency difference

Pulse converter: It is used to extract information as pulse signal

Working: