LIGO and gravitational wave detector

Monika Sachan

LIGO and gravitational wave detectors are both used to detect gravitational waves. LIGO is a large-scale observatory in the USA that detects the cosmic gravitational wave and a change in distance between 1/10,000th width of a proton. Scientists are building the prototype tabletop detector to capture gravitational waves at higher frequencies than LIGO and axions dark matter particles collide with each other that frequency is also measured.


Ligo stands for Laser Interferometer Gravitational-Wave Observatory in the USA. It is a large-scale observatory to detect the cosmic gravitational wave, a change in distance between its 1/10,000th width of a proton, and also to develop gravitational-wave observations like astronomical units. Two observatories are in the USA and detect by the laser interferometer.

This announced the first observation of gravitational waves in September 2015 and it detects the singles of two black holes with masses of 29 and 36 solar masses merging at a distance of 1.3 billion light-years. In the last fraction of a second of the merger, it released greater than 50 times the power of all the stars in the seeing universe combined and single increased the frequency from 35 Hz to 250 Hz to the period of 0.2 seconds.

Working of LIGO:

This concept was built upon early work by many scientists to test a component of Albert Einstein’s theory of general relativity gravitational waves.

Structure of LIGO
[credit: LIGO observatory]

LIGO’s interferometers look like arms 4km long. In an interferometer, the larger the arm, the smaller the measurements, it can observe. Then mirrors are inserted near the beam splitter to make easy multiple reflections of the laser and increase the distance traveled by the beams. By the Fabry Perot cavity, in entering the instrument with the beam splitter, the laser in each arm bounces between two mirrors about 300 times before being merged with the beam from the other arm and the power of the cavity is 100kW. It has two functions:

1. It builds up the laser light within the interferometer, which increases LIGO’s sensitivity. 

2. It increases the distance traveled by each laser from 4km to 1200km thereby solving our length problem.

When a gravitational wave passes in this device, the space-time within the local area is changed. It depends on the source of the wave and polarization, it results in an effective change in length between the beams will affect the light currently in the cavity to become slightly out of stage with the incoming light. The cavity will periodically get very slightly out of coherence and the beams, which are tuned to damage the interference at the detector, will have a very slight periodically varying detuning and it is a measurable signal.

After an equivalent of approximately 280 trips down the 4 km length to the far mirrors and back again, the two separate beams leave the arms and recombine at the beam splitter. The beams coming back from two arms are kept out of phase so that when the arms are both incoherent and interfering, their light waves subtract, and no light should reach the photodiode. When a gravitational wave passes through the interferometer, the distances along the arms of the interferometer are shortened and lengthened, causing the beams to become slightly less out of phase. This leads to the beams coming in phase, creating a resonance; hence, some light arrives at the photodiode, indicating a sign. The light that doesn’t contain a sign is returned to the interferometer employing a power recycling mirror, thus increasing the facility of the sunshine within the arms. In actual operation, noise sources can cause movement within the optics which produces similar effects to real gravitational wave signals; an excellent deal of the art and complexity in the instrument is found ways to scale back these spurious motions of the mirrors. Observers compare signals from both sites to scale back the consequences of noise.

LIGO is the largest and most aspiring project funded by the NSF. As of December 2019, LIGO has made 3 runs and made 50 detections of gravitational waves. 

INDIGO, is a will be plan collaborative project between the LIGO Laboratory and the Indian Initiative in Gravitational-wave Observations (IndIGO) to create a device of the gravitational-wave detector in India. The Advanced LIGO detectors to be installed, commissioned, and operated by an Indian scientist.

Gravitational wave detector:

Physicists are building a prototype tabletop detector to capture the gravitational waves at higher frequencies than LIGO and axions a dark matter particle collides with each other that frequency is also measured.

If axions, dark matter particles are actually real then researchers think that they would form clouds around black holes in huge numbers, producing enough gravitational waves to be detected from Earth.
[Credit: Asimina Arvanitaki/Stanford University]

Searching for the new atom particle see the above image shows that extends the accelerator of high energy. This small-scale experiment increases the knowledge of particles. In July 2019, a group of researchers explained the slew of an experimental hunt for introduced the new type of physics in the virtual meeting of the APS Division of Atomic, Molecular & Optical Physics (DAMOP). During all the sessions, Andrew Geraci described a prototype tabletop gravitational-wave detector that he and his team have started building of Northwestern University in Illinois. The device uses the function of levitating the nanoparticle to detect gravitational waves at high frequencies far off the range of giant laser interferometers likes LIGO. The enlarged frequency range might spot the axions of dark matter particles as well as other unknown sources of gravitational waves in the universe.

“Every time we have looked at the Universe using a new range of high frequency of the electromagnetic spectrum, we learned something new, we still don’t know till we look!” says Nancy Aggarwal, a postdoc at Northwestern and also a member of the team and observing in a new high-frequency range of gravitational-wave.

The team of designers that detects nanoparticles is levitated within optical cavities at bright spots of standing waves created by lasers. When a gravitational wave passes through, it changes the length of the cavities and pushes the levitated particles to new locations. The experiment requires the ability to sense little force that up to 21 newtons, which is shown by the Andrew and his team. and advantage of the levitated particle method are that it would be sensitive to higher frequencies of gravitational waves than LIGO because it is limited by the thermal noise of the particles’ motions and gets better at higher frequencies.

The prototype levitated particle system, which is a size of 1m, could detect signals with high frequencies as 300 kHz and low as 10 kHz. If experiments go well, then the team hopes to build a 10-m version that Geraci says would be competitive with LIGO’s sensitivity is also the 10 kHz range.

The team might be looked for gravitational waves that would be emitted if axions dark matter particles that collide with each other. If axions that dark matter particles actually real then researchers think that they would form clouds around black holes in huge numbers, producing enough gravitational waves that are to be detected from Earth. The researchers don’t know about the mass of axions particles. 

“That would be the kind of smoking-gun signature you’d hope to find if that process was there and the axions existed,” Geraci says. but still, this takes time because the device is in the testing process and this is only one type of example and there would be more in new physics.


  1. Ryan James Marshman, Anupam Mazumdar, Gavin Morley, Peter F Barker, Steven Hoekstra, Sougato Bose. Mesoscopic Interference for Metric and Curvature (MIMAC) & Gravitational Wave Detection. New Journal of Physics, 2020; DOI: 10.1088/1367-2630/ab9f6c


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