Laser Interferometer for Gravitational Wave observation

Gravitational waves have very low frequency so it is very difficult to detect them by using any ordinary detectors and systems. For detection of gravitational waves a laser Interferometric system prepare i.e. known as LIGO. It contains combination of Michelson interferometer and Fabry perot interferometer, which provide long path for travel laser beams between mirrors. High speed detectors used for detection of changes occurs in ripples due to effect of gravitational waves during propagation between mirrors.

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Wavelength measurement of light by Interferometer

As we know two coherent light source interference produce interference fringes which can shows various measurement factors change. The wavelength of light depends on the change in phase of signals or number of fringes with respect to change in distance between two sources. When half of wavelength distance is change than a fringe is pass or 2π phase change occur. So during change in distance we can calculate change in phase which is used for wavelength measurement. wavelength of light λ=(2Δd)/N where Δd is change in distance and N is change in number of fringes. Fringes detected by michleson interferometer by CCD.

Principle of Michleson Interferometer

The Michleson Interferometer is a two interferometer, when two coherent light beams interface with each other than maxima (bright fringe) occur where maxima of one beam superimpose with maxima of other beam and minima (dark fringe) occur where maxima of one beam superimpose with minima of other beam. For good quality of fringes we need coherent source so we use a beam splitter for split a beam into two parts. Beam travel at 90 degree with each other. Now use two mirrors for reflect back beams to beam splitter and superimpose with each other. A good quality michleson interferometer can be used for measurement operations like:- Wavelength of light Refractive index of glass slits Refractive index of air or gas Now the same principle used for detection of change in gravitational waves as discus in various posts.

Phase detection from fringes

Interferometery fringes contains signal inform of amplitude or phase. The amplitude contains large amount of noise i.e. very difficult to remove. So it is better to use phase value of detected signal. There are many techniques of phase detection like Fourier transform Fringe skeletonization Phase-stepping Temporal heterodyning Spatial heterodyning (carrier frequency) Phase locking Phase-shifting The phase stepping method provide continuous phase detection of live fringes.

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