Interferometric sensor for “GW-like” signal

Context: Interferometric gravitational wave detectors are basically Michelson interferometers able to measure the difference of the arms lengths with a precision of about 10-18m (@100Hz). When a gravitational wave passes, it will stretch and squeeze the space with opposite effect in the two directions [Fig. 1]. These changes in the arms lengths create an interference pattern in the output of the interferometer, that can be read through a photodiode. Analyzing the output of the interferometer and all the main sources of noise is possible to trace back to the gravitational wave signal.

Effect of a gravitational wave (propagating in the direction perpendicular to the plane of the paper) on the arms of a Michelson interferometer.

Project:

In this project the student will build a small Michelson interferometer. The end mirrors will be attached to piezoelectric actuators, that will give control on their movements. The piezo can be used to send a signal to the mirrors and modify their position. The student will study the output of the interferometer and will analyze how it changes when different signals are sent to the mirrors.

In the first part of the project the student will build and characterize the interferometer, analyzing the noises sources that affect the output. Then the mirrors will be moved, sending different kinds of signal to the piezo attached to the mirrors: starting with simple sinusoidal oscillations and ending with a “gravitational wave-like” signal (chirp signal).

Mentor: Dr. Daniela Pascucci

Number of students: 1

“Gravitational” Waves on a Ripple Tank

Overview: Gravitational waves are ripples in the curvature of spacetime predicted in Einstein’s general theory of relativity, first detected in 2015 from the merger of a binary of black holes. Ripples on the surface of water are on the other hand caused by the Newtonian gravitational field of the earth, and are also known as “gravity” waves. They can be produced on a tank of water, such as a wave tank or a ripple tank. This projects brings the two together, and uses gravity waves to simulate gravitational waves. Some of the key features of gravitational waves are common to all of wave physics, and can already be observed in the surface wave simulation experiment.

The ripple tank used to simulate surface waves on water.
The observed “chirp” signal is a characteristic pattern of increasing amplitude and frequency.

Project description: In previous year’s project we set up a ripple tank to produce “wakes” on the surface of water using a motor [Fig 1, left panel]. These wakes resemble gravitational waves emitted from an inspiralling compact binary. The amplitude of the ripples fall off as one over square root of the distance from the source – this is the idea behind how gravitational-wave sources act as standard distance indicators or “standard sirens.” We investigated what kinds of waves (frequencies, amplitudes) can be produced and detected with our setup. We could also crudely measure the fall-off of the amplitude with distance using a laser sensor.

We will follow up on the previous year’s project and try to investigate (i) how to better measure the amplitude of the ripples / wakes, (ii) whether fluids other than water can give us a access to a wider range of frequencies, and (iii) how closely we can produce a “chirp” gravitational-wave pattern [Fig 1, right panel]. The student will compare and contrast the simulation with real gravitational waves. We will eventually move towards having a setup which we can use for public demonstration.

Mentor: Prof. Archisman Ghosh

Number of students: 1