1. Online Guidance
In the 19th century, most physicists had accepted the idea of a luminiferous ether – a medium through which light propagates – and it had been assumed to exist in both corpuscular, and wave theories of light, for different reasons.
If Earth was, indeed, moving through this ether, it should be possible to detect this motion by interferometry of light where one path lies parallel to the “ether wind” – similar to “wind” one might feel from an automobile window – and the other perpendicular, and of the same length. In 1887 Michelson and Morley undertook their famous interferometer experiment to determine some of the properties of this ether. Michelson expected the perpendicular path to take less time, and thus lead to a shift in the fringe pattern; however, the experiment yielded no such shift.
This experiment is one of the first to find evidence against the existence of the luminiferous ether, although this was not the interpretation at the time, and finds itself among the modern tests of Einstein’s Special Theory of Relativity. Today, this experimental setup is easily reproduced and often utilizes LASERs instead of white light as used by Michelson and Morley.
Objective
In this experiment you will become familiarized with the concept of interferometry and how light can be used to perform very precise and subtle measurements. You will learn how to construct a Michelson interferometer using the equipment at your disposal, as well as the physics behind the central phenomenon of this demonstration.
Description
The working principle of the Michelson interferometer lies in the ability of light to interfere with itself.
This interferometer is a simple setup in which coherent light from a LASER is split by a beamsplitter into two perpendicular beams of equal amplitudes. These beams are then reflected by mirrors positioned at predetermined distances from the beamsplitter. After reflection, the beams are allowed to recombine and interfere with each other. This interference is passed through a convergent lens in order to magnify the pattern and is then projected onto a screen where the interference pattern becomes apparent. This interference pattern is characteristic of the difference in optical path taken by the two beams. For example, if the distances between the beamsplitter and the mirrors were not exactly equal, or one beam were passed through a dense (n>1) optical medium, while the other was not.
By cleverly coupling this optical path difference to a different physical quantity, a Michelson interferometer is capable of performing high precision measurements, compared to wavelength (not limited to visible light), of a variety of interesting phenomena.
2. Examples of Use
The Michelson interferometer is most famously used in the detection of gravitational waves as predicted by Einstein’s General Theory of Relativity. These waves warp the fabric of spacetime, making ever-so-slight differences in optical path length by physically changing the way distance is calculated across each arm of the interferometer. When researchers measure an optical path length difference, they know it originated from gravitational waves passing through the observatory and the earth as a whole. Most notably, such setups are utilized in the LIGO facilities in Louisiana and Washington, as well as the VIRGO facility in Italy.
In general, the Michelson interferometer has become a staple apparatus and today it is widely used for a variety of measurements, both in research and industry, such as wavelength and distance, surface profiling, refractive index, and much more.
3. K-Optics Kit
The K-Optics Michelson Interferometer kit is uniquely low-cost in the landscape of Michelson interferometer kits, allowing demonstrations to incorporate first-hand experience for the student. Additionally, the kit is highly modular – a quick-change mechanism allows replacement of optical elements quickly and efficiently. Each element is placed on-axis, requiring minimal adjustment from the user. The kit employs a wide variety of K-Optics parts, each designed carefully and purposefully to seamlessly integrate into the K-Optics ecosystem.
4. Animation
The following animation describes the setup assembly for Michelson's Experiment (on Optic Table (2x1))
5. List of Elements
The K-Optics Michelson Interferometer Experiment comes in two variants. The following is a representative list of materials in the Michelson Interferometer Experiment (2x1):
6. Safety Guidelines
Do NOT direct the LASER beam toward any person, pets, or other animal eyes nor any other body part.
Do NOT place yourself in a position where your eyes approach the axis of the LASER beam (even with eye protection). Keep beam paths below or above eye level while sitting or standing (as appropriate).
Do NOT place or remove elements while the LASER is operating! To avoid unexpected reflections, turn the LASER off before making changes to the setup.
Do NOT leave an operating LASER unattended.
When working with a Class II LASER (such as this), it is crucial to prioritize safety to prevent any potential risks to eyes and skin. These LASERs emit visible light at low power levels, which may not cause immediate harm but still pose a risk if proper precautions are not taken. Avoid directing the laser beam towards reflective surfaces that could scatter the light, as well eyes and skin of humans or animals. Remember that even though Class 2 LASERs are considered relatively safe, responsible handling and adherence to safety guidelines are paramount to prevent any accidents or injuries.