### PHYS101 LO9 Shaan Aroeste

1. S H A A N A R O E S T E P H Y S 1 0 1 – L M 2 Michelson Interferometers
2. Michelson Interferometer The following is an explanation of how and why a Michelson interferometer works. This learning object assumes a previous understanding of the basics of light waves.
3. Michelson Interferometer A Michelson interferometer is used to observe interference. It does this through a setup involving a light source, a light detector, a beam splitter, and mirrors. By splitting the beam of light and introducing differences in path length for the resulting beams, interference can be induced.
4. Michelson Interferometer The following slides will explain this concept in greater detail. Legend Light wave (original) Light wave (split) Light wave (recombined) Mirror Light source Beam splitter Light detector
5. Michelson Interferometer First, the Michelson interferometer emits a beam of light of a fixed wavelength from the source. This beam travels through the beam splitter, resulting in 2 waves (still same wavelength) being sent to different mirrors.
6. Michelson Interferometer The mirrors each reflect their respective beam back toward the splitter. In this case, the distance between each mirror from the splitter is the same.
7. Michelson Interferometer When the beams reach the splitter, they are both in the same spot and aimed in the same direction. Because they occupy the same space, interference must occur. In this case, it is constructive because the mirrors are the same distance away, thus the number of wavelengths is the same. Note the resulting amplitude is now 2A. This should result in a bright light being observed on the detector.
8. Michelson Interferometer Now let’s modify the experimental settings by moving the right mirror to the right by λ/4 (one quarter of the beam’s wavelength)
9. Michelson Interferometer Just as before, a light of a fixed wavelength is emitted, is split into two, and each beam travels to its respective mirror. This time, however, the right beam’s mirror is slightly further away, a length of λ/4.
10. Michelson Interferometer Because the right mirror has been shifted, a phase difference has been introduced between the waves corresponding to the two mirrors. Because the distance moved is λ/4, and that distance is travelled twice (oncoming and reflected beam) the phase is now λ/2 or π.
11. Michelson Interferometer Once these 2 waves combine at the same spot as before, their phase difference results in complete destructive interference. As a result, it is expected that no light will be observed at the detector.
12. Michelson Interferometer I hope this helped to elucidate the functionality and underlying theory of this ingenious device. Thank you for reading.