Presented By:Presented By:

Abdul Jabbar Abdul Jabbar (PhD Student)(PhD Student)

Department of PhysicsDepartment of Physics

International Islamic University IslamabadInternational Islamic University Islamabad

A Presentation onA Presentation on

Michelson InterferometerMichelson Interferometer

OutlinesOutlines

InterferometersInterferometers Basic ConceptsBasic Concepts Michelson InterferometerMichelson Interferometer Configuration Configuration Michelson-Morley ExperimentMichelson-Morley Experiment Applications of Michelson InterferometerApplications of Michelson Interferometer

InterferometersInterferometers For the investigation of the various line profiles, For the investigation of the various line profiles,

interferometers are preferentially used because, with interferometers are preferentially used because, with respect to spectral resolving power, they are superior respect to spectral resolving power, they are superior even to large spectrometers.even to large spectrometers.

In laser spectroscopy the different types of In laser spectroscopy the different types of interferometers not only serve to measure emission or interferometers not only serve to measure emission or absorption but also essential device for:absorption but also essential device for:

(i) narrowing the spectral width of lasers (ii) (i) narrowing the spectral width of lasers (ii) monitoring the laser linewidth (iii) to precisely monitoring the laser linewidth (iii) to precisely measure wavelength, distance, index of refraction, measure wavelength, distance, index of refraction, and temporal coherence of optical beams.and temporal coherence of optical beams.

Basic ConceptsBasic Concepts The basic principle all interferometers may be The basic principle all interferometers may be

summarized as:summarized as: The incident lightwave with intensityThe incident lightwave with intensity I I00 is divided is divided

into two or more partial beams, which pass different into two or more partial beams, which pass different optical path lengths before they are again optical path lengths before they are again superimposed at the exit of the interferometer.superimposed at the exit of the interferometer.

Since all partial beams come from the same sourceSince all partial beams come from the same source , , they are coherent.they are coherent.

The maximum transmitted intensity is obtained when The maximum transmitted intensity is obtained when

all partial waves interfere constructivelyall partial waves interfere constructively..

Michelson InterferometerMichelson Interferometer

The The Michelson interferometerMichelson interferometer is the most is the most common configuration for optical common configuration for optical interferometry and was invented by Albert interferometry and was invented by Albert Abraham Michelson.Abraham Michelson.

Michelson wanted to measure the speed of the Michelson wanted to measure the speed of the earth moves through the ether (the medium in earth moves through the ether (the medium in which light travels).which light travels).

By measuring the interference between light By measuring the interference between light paths at right angles, one could find the paths at right angles, one could find the direction & speed of the ether.direction & speed of the ether.

Michelson became the first American to win Michelson became the first American to win the Nobel Prize in physics in 1907.the Nobel Prize in physics in 1907.

He continued pioneering optical He continued pioneering optical measurements: measurements: The speed of lightThe speed of light The size of starsThe size of stars Using a particular wavelength of light as a Using a particular wavelength of light as a

distance standarddistance standard

ConfigurationConfiguration It consists of two highly polished mirrors MIt consists of two highly polished mirrors M11 & M & M22 A A

source S emits monochromatic light that hits the source S emits monochromatic light that hits the surface M at point C. M is partially reflective, so one surface M at point C. M is partially reflective, so one beam is transmitted through to point B while one is beam is transmitted through to point B while one is reflected in the direction of A.reflected in the direction of A.

Configuration Cont..Configuration Cont..

Both beams recombine at point C to produce an Both beams recombine at point C to produce an interference pattern (assuming proper alignment) interference pattern (assuming proper alignment) visible to the observer at point E.visible to the observer at point E.

There are two paths from the (light) source to the There are two paths from the (light) source to the detector.detector.

One reflects off the semi-transparent mirror, goes to One reflects off the semi-transparent mirror, goes to the top mirror and then reflects back, goes through the top mirror and then reflects back, goes through the semi-transparent mirror, to the detector.the semi-transparent mirror, to the detector.

The other first goes through the semi-transparent The other first goes through the semi-transparent mirror, to the mirror on the right, reflects back to the mirror, to the mirror on the right, reflects back to the semi-transparent mirror, then reflects from the semi-semi-transparent mirror, then reflects from the semi-transparent mirror into the detector.transparent mirror into the detector.

Configuration Cont..Configuration Cont..

The principle is when a parallel beam of light coming The principle is when a parallel beam of light coming from a monochromatic extended light source is incident from a monochromatic extended light source is incident on a half silvered glass plate, it is divided into two beams on a half silvered glass plate, it is divided into two beams of equal intensities by partial reflection and transmission.of equal intensities by partial reflection and transmission.

If these two paths differ by a whole number (including 0) If these two paths differ by a whole number (including 0) of wavelengths, there is constructive interference and a of wavelengths, there is constructive interference and a strong signal at the detector.strong signal at the detector.

If they differ by a whole number and a half wavelengths If they differ by a whole number and a half wavelengths (e.g., 0.5, 1.5, 2.5 ...) there is destructive interference and (e.g., 0.5, 1.5, 2.5 ...) there is destructive interference and a weak signal.a weak signal.

Interference PatternInterference Pattern The Michelson interferometer produces interference The Michelson interferometer produces interference

fringes by splitting a beam of monochromatic light so fringes by splitting a beam of monochromatic light so that one beam strikes a fixed mirror and the other a that one beam strikes a fixed mirror and the other a movable mirror. When the reflected beams are movable mirror. When the reflected beams are brought back together, an interference pattern results.brought back together, an interference pattern results.

Michelson Morley Exp..Michelson Morley Exp..

Michelson, along with Edward Morley, used Michelson, along with Edward Morley, used this interferometer for the famous Michelson-this interferometer for the famous Michelson-Morley experiment (1887) in which this Morley experiment (1887) in which this interferometer was used to show the constancy interferometer was used to show the constancy of the speed of light across multiple inertial of the speed of light across multiple inertial frames, which removed the conceptual need for frames, which removed the conceptual need for a luminiferous ether to provide a rest frame for a luminiferous ether to provide a rest frame for light.light.

ApplicationsApplications The most well known application of the The most well known application of the

Michelson Interferometer is the Michelson-Michelson Interferometer is the Michelson-Morley experiment that provided evidence for Morley experiment that provided evidence for special relativity.special relativity.

The Michelson Interferometer has been used The Michelson Interferometer has been used for the detection of gravitational waves, as a for the detection of gravitational waves, as a tunable narrow band filter, and as the core of tunable narrow band filter, and as the core of Fourier transform spectroscopy.Fourier transform spectroscopy.

There are also some interesting applications as There are also some interesting applications as a "nulling" instrument that is used for a "nulling" instrument that is used for detecting planets around nearby stars.detecting planets around nearby stars.

For most purposes, however, the geometry of For most purposes, however, the geometry of the Mach-Zehnder interferometer is more the Mach-Zehnder interferometer is more useful.useful.

A further application is to produce a delay line A further application is to produce a delay line interferometer that converts phase modulation interferometer that converts phase modulation into amplitude modulation in DWDM into amplitude modulation in DWDM networks.networks.

Einstein Tribute to MichelsonEinstein Tribute to Michelson

"My honored Dr. Michelson, it was you who "My honored Dr. Michelson, it was you who led the physicists into new paths, and through led the physicists into new paths, and through your marvelous experimental work paved the your marvelous experimental work paved the way for the development of the theory of way for the development of the theory of relativity.“ – Albert Einstein, 1931.relativity.“ – Albert Einstein, 1931.

THANKSTHANKS