Acoustic interferometer to mimic LIGO experiment

Published: 6 December 2016| Version 1 | DOI: 10.17632/svvjnx5n4r.1
Contributor:
Edoardo Paluan

Description

The aim of the project is to create an optical interferometer which can detect the acoustic analogue of a supernova explosion. The fingerprint of an acoustic wave propagating from a diapason will be measured. A Michelson Morley interferometer1 will be used, whereby analysis of the interference pattern will allow for the calculation of the frequency of the diapason.

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Steps to reproduce

In a Michelson interferometer, light from a monochromatic source (S) is divided by a beam splitter (BS), oriented at an angle of 45° to the beam, producing two beams of equal intensity. The transmitted beam (T) travels to mirror M2 where it is reflected back to BS. 50% of the returning beam is then deflected by 90° at the beam splitter and is made to strike the detector (D). The reflected beam travels to mirror M1, where it is reflected. Again, 50% of the beam passes straight through the BS and reaches the detector. The Laser is a He-Ne laser, having a polarized wavelength of 633nm (red). The wave is coherent and monochromatic; since the beam is coherent, light from other sources will not interfere with the interference pattern. Mirrors provide a way for the beam to change its direction of travel, if M1 and M2 are misaligned, the recombination of the beams occurs at a different location in the BS, resulting in the formation of two signals on D which do not form an interference pattern. When working with laser light, a cube beamsplitter (CB) possesses the best combination of optical performance and power handling ,CBs avoid displacing the beam by being perpendicular to the incident beam. To achieve the best possible performance, CBs should be operated with collimated light as convergent or divergent beams will contribute unwanted spherical aberrations to the setup. A piezoelectric was connected to a signal generator and attached to M2. This acted as a test for the apparatus and allowed the mirror to oscillate at various frequencies. The distance travelled by M2 due to excitation of the piezoelectric was a secondary investigation inherent in the project. The detector used allowed the intensity of light hitting it to be recorded. When two or more waves interact with one another an interference pattern is produced. This pattern is a result of the phase difference between the waves. When the waves are in phase constructive interference occurs and the resulting amplitude of the two superimposed waves is a maximum, on a screen, this is seen as a light fringe. When the waves are π out of phase, destructive interference occurs and the resulting amplitude is 0, on a screen this is seen as a dark fringe.