Lecture 24 : Michelson Interferometer and Its Applications - I
IIT Roorkee July 2018・2 minutes read
The Michelson interferometer, invented by Albert Abraham Michelson, is an essential optical tool for measuring properties like wavelength and coherence, with significant applications in experiments such as LIGO's detection of gravitational waves. Its setup involves a beam splitter that creates two coherent light beams reflecting off mirrors, allowing for the formation of interference patterns that reveal critical information about light’s spectral properties.
Insights
- The Michelson interferometer, invented by Albert Abraham Michelson in 1887, is a crucial optical tool that has been pivotal in both historical and modern physics, notably in the Michelson-Morley experiment which disproved the existence of ether and in LIGO's first detection of gravitational waves in 2016, showcasing its versatility in measuring various physical properties like wavelength and distance.
- Coherence is essential for the functioning of the interferometer, as it requires light waves to have the same frequency and a constant phase difference; the concept of coherence length is vital, as it determines the maximum distance over which light waves can maintain this relationship, with lasers being favored for their long coherence lengths that enable clear interference patterns to be observed.
Get key ideas from YouTube videos. It’s free
Recent questions
What is an interferometer used for?
An interferometer is an optical device used to measure various physical properties of light, such as wavelength, distance, and index of refraction. It operates on the principle of interference, where two or more light beams are combined to produce a pattern that can reveal information about the light's characteristics. Interferometers are essential in many scientific experiments, including those that explore the fundamental properties of light and its behavior in different mediums. They are particularly valuable in precision measurements and have applications in fields like metrology, astronomy, and even gravitational wave detection.
How does coherence affect light waves?
Coherence is a fundamental property of light waves that describes the correlation between their phases. For two light waves to be coherent, they must have the same frequency and maintain a constant phase difference over time. This means that coherent waves can produce stable and predictable interference patterns, which are crucial for experiments that rely on wave interference, such as those conducted with interferometers. In contrast, incoherent waves lack a consistent phase relationship, leading to random interference patterns that are less useful for precise measurements. Understanding coherence is essential for applications in optics and wave physics.
What is the coherence length in optics?
Coherence length is the maximum distance over which a light wave maintains its coherence, meaning it can produce stable interference patterns. This length is critical in experiments involving wave interference, as strong interference fringes can only be observed when the path difference between interfering waves is less than the coherence length. In practical terms, this is why lasers, which typically have long coherence lengths, are preferred in interferometric experiments. The coherence length determines how far apart the light beams can travel before they lose their ability to interfere constructively or destructively, impacting the quality and visibility of the resulting interference patterns.
Who invented the Michelson interferometer?
The Michelson interferometer was invented by Albert Abraham Michelson in 1887. This device has become one of the most important tools in optical physics, allowing for precise measurements of light's spectral properties. Michelson's work with the interferometer not only advanced the field of optics but also played a significant role in historical experiments, such as the Michelson-Morley experiment, which sought to detect the presence of ether. The invention of the Michelson interferometer marked a pivotal moment in the study of light and has had lasting implications in both theoretical and experimental physics.
What are interference fringes in optics?
Interference fringes are patterns of light and dark bands that result from the constructive and destructive interference of light waves. When two coherent light beams overlap, they can interfere with each other, leading to regions of increased intensity (bright fringes) where the waves reinforce each other and regions of decreased intensity (dark fringes) where they cancel each other out. The formation of these fringes is a key aspect of experiments using interferometers, as they provide visual evidence of the interference effects. The spacing and visibility of the fringes can be influenced by factors such as the wavelength of light, the path length difference between the beams, and the coherence length of the light source.
Related videos
Eduphile
interference in thin films
LearnoHub - Class 11, 12
Wave Optics Class 12 Physics | Chapter 10 | CBSE JEE NEET | One Shot
Learn Chemistry Online
B.Sc. III Year | Photochemistry | Measurement of quantum yield | क्वांटम लब्धि का मापन
Digital University APSIT
Interference due to wedge shaped film by Shiv Kore
Looking Glass Universe
I did the double slit experiment at home
Summary
00:00
Understanding the Michelson Interferometer's Functionality
- The Michelson interferometer is a widely used optical tool for measuring physical properties such as wavelength, distance, index of refraction, and temporal coherence of optical beams, which are essential in various experiments, including Young's double slit experiment.
- Coherence is a critical concept in wave interference, defined by two light waves having the same frequency and a constant phase difference; coherent waves maintain a phase difference of 0, while incoherent waves lack any phase relationship.
- The coherence length is the maximum distance over which a wave maintains its coherence, and strong interference fringes can only be observed when the path difference between interfering waves is less than this coherence length, which is why lasers are preferred in interferometric experiments due to their long coherence lengths.
- The Michelson interferometer, invented by Albert Abraham Michelson in 1887, is known for its precise analysis of light's spectral properties and is historically significant for the Michelson-Morley experiment, which nullified the existence of ether.
- In 2016, the Michelson interferometer was instrumental in LIGO's first direct detection of gravitational waves, highlighting its importance in modern physics.
- The setup of the Michelson interferometer includes a light source, a diffuser, a beam splitter (a semi-silvered glass plate), two mirrors (M1 and M2), and a detector where interference fringes are observed; the beam splitter divides the light into two coherent beams.
- The beam splitter creates a virtual image of the light source and the mirrors, allowing the two beams to reflect off M1 and M2 and then recombine at the beam splitter before reaching the detector, where interference patterns are formed.
- The distance from the beam splitter to mirrors M1 and M2 is denoted as d1 and d2, respectively; adjusting the position of mirror M1 using a micrometer screw changes d1, affecting the optical path length difference (delta d = |d1 - d2|) and consequently the interference pattern.
- The optical path length difference leads to the formation of interference fringes, which can be circular due to the air film between mirror M2 and the virtual image of mirror M1, resulting in Haidinger fringes when viewed on a screen.
- The phase difference between the two beams can be calculated from the optical path difference, with an additional phase shift of π introduced by the beam splitter, which reflects part of the light while allowing the rest to transmit, affecting the overall interference pattern observed.
18:28
Interference Patterns in Mirror Experiments
- The beam splitter reflects part of the light to mirror M2, where it undergoes internal reflection before returning to the detector, while another part of the light is transmitted to mirror M1, reflecting back to the detector. The blue arrow represents the path to mirror M2, and the red arrow represents the path to mirror M1, with the internal reflection of the blue ray and external reflection of the red ray resulting in a phase shift of π radians, which is crucial for determining conditions of constructive and destructive interference.
- As the separation between the mirrors (denoted as delta d) decreases, the angle theta m must also decrease to maintain the equality in the interference equation, leading to a shrinking of the concentric circular fringes towards the center. This behavior is similar to the Newton's ring experiment, where reducing delta d results in the disappearance of fringes at the center of the pattern, ultimately leading to a completely dark field of view when delta d reaches 0.
- When delta d is increased after reaching 0, new circular fringes begin to appear from the center of the field of view. Initially, as delta d is reduced, the fringes shrink and disappear, resulting in uniform darkness when the mirrors overlap. Upon increasing delta d in the opposite direction, the number of fringes increases, repopulating the field of view with new fringes emerging from the center. Further discussion on the Michelson interferometer is planned for the next class.
