common-path interferometers (original) (raw)
Author: the photonics expert (RP)
Definition: interferometers where the sensitivity to mechanical noise is reduced by largely using a common optical path for the interfering light beams
photonic devices- interferometers
- etalons
- common-path interferometers
- Fabry–Perot interferometers
- Fizeau interferometers
- Gires–Tournois interferometers
- Mach–Zehnder interferometers
- Michelson interferometers
- Twyman–Green interferometers
- white light interferometers
- (more topics)
Related: interferometersFourier transform spectroscopy
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Contents
What are Common-path Interferometers?
In many types of interferometers — for example, Michelson interferometers — the two light beams which finally interfere with each other travel on substantially different geometric paths. As a result, the interference signal becomes highly sensitive to any misalignment, also due to mechanical noise, for example in the form of vibrations or shocks. That problem is largely suppressed in common-path interferometers, which are made such that the interfering beams travel along essentially the same paths.
Common-path interferometer setups are obviously attractive because they usually do not require special measures to suppress mechanical noise influences, and the alignment is much less critical. They often work with rather simple and compact optical setups. They can be used in very different application areas, such as gyroscopes, Fourier transform spectroscopy, wavefront sensing, femtosecond time-resolved interferometry and pulse characterization.
The following sections give some examples of common-path interferometers. However, there are many more variants of them; see the bibliography for further examples.
Example: Sagnac Interferometer
Figure 1: A Sagnac interferometer, realized with bulk optical elements.
In a Sagnac interferometer, the interfering beams travel along a ring, but in opposite directions. Figure 1 shows a realization based on bulk optics; versions based on optical fibers are in fact more common. In any case, there is a path length difference generated by rotations around an axis perpendicular to the loop plane; Sagnac interferometers can therefore be used for gyroscopes. On the other hand, changes in the mirror positions can affect the path length, but not the path length difference for the counterpropagating beams.
Point Diffraction Interferometers
Point diffraction interferometers are used for high-precision wavefront sensing and optical testing. In such systems, the optical field under investigation is focused onto a small pinhole fabricated in an otherwise opaque or weakly transmissive plate. The pinhole acts as a spatial filter: It transmits only the low-spatial-frequency components of the beam, effectively producing a clean reference wavefront. The surrounding regions of the plate are designed to have a small but finite transparency (typically on the order of 0.1%), allowing a portion of the unfiltered light to pass through.
The light transmitted through the pinhole therefore represents a nearly perfect spherical reference wave, while the light transmitted through the other regions carries the aberrations of the test beam. When these two components overlap and interfere beyond the pinhole plane, they generate an interference pattern (or interferogram) that encodes information about the wavefront distortions present in the original beam. By analyzing this pattern — often using digital image processing techniques — one can reconstruct the wavefront shape with high accuracy.
The technique is widely applied in optical system testing, high-resolution microscopy, and adaptive optics for characterizing aberrations in lenses, mirrors, and laser beams.
Interferometers Based on Different Polarizations
There are common-path interferometers where the two interfering beams travel along the same path and in the same direction, but have different polarization states. Interference then occurs at a polarizer.
The path length difference can be created based on birefringence, and it can be varied e.g. by inserting a wedge made from a birefringent material to some extent into the beam. This operation principle can be used, for example, for realizing a Fourier transform spectrometer [7] even for light with relatively short wavelengths.
Another application of similar interferometers is the sensitive detection of changes in birefringence.
Frequently Asked Questions
This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).
What is a common-path interferometer?
A common-path interferometer is an optical instrument where the two light beams that will interfere with each other travel along essentially the same geometric path. This design makes the interferometer very robust against environmental disturbances.
What is the primary advantage of a common-path design over, e.g., a Michelson interferometer?
The primary advantage is its low sensitivity to mechanical noise, such as vibrations and shocks. Since the interfering beams share a common path, these disturbances affect both beams almost identically, keeping their path length difference stable.
What is a Sagnac interferometer?
A Sagnac interferometer is a common-path interferometer where two beams travel in opposite directions around a closed loop path. It is sensitive to rotation about an axis perpendicular to the loop plane and is therefore widely used for gyroscopes.
How can different polarizations be used in a common-path interferometer?
In some designs, two beams with different polarization states travel along the same physical path. A path length difference is created between them using a birefringent optical element, and interference is observed after passing them through a polarizer.
Bibliography
| [1] | J. Dyson, “Very stable common-path interferometers and applications”, J. Opt. Soc. Am. 53 (6), 690 (1963); doi:10.1364/JOSA.53.000690 |
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| [2] | T. W. Liepmann and F. A. Hopf, “Common path interferometer based on second harmonic generation”, Appl. Opt. 24 (10), 1485 (1985); doi:10.1364/AO.24.001485 |
| [3] | C. S. Anderson, “Fringe visibility, irradiance, and accuracy in common path interferometers for visualization of phase disturbances”, Appl. Opt. 34 (32), 7474 (1995); doi:10.1364/AO.34.007474 |
| [4] | M. Nikoonahad, S. Lee and H. Wang, “Picosecond photoacoustics using common-path interferometry”, Appl. Phys. Lett. 76 (4), 514 (2000); doi:10.1063/1.125805 |
| [5] | V. Tsatourian et al., “Common-path self-referencing interferometer for carrier–envelope offset frequency stabilization with enhanced noise immunity”, Opt. Lett. 35 (8), 1209 (2010); doi:10.1364/OL.35.001209 |
| [6] | J. Chandezon et al., “In-line femtosecond common-path interferometer in reflection mode”, Opt. Express 23 (21), 27011 (2015); doi:10.1364/OE.23.027011 |
| [7] | A. Oriana et al., “Scanning Fourier transform spectrometer in the visible range based on birefringent wedges”, J. Opt. Soc. Am. A 33 (7), 1415 (2016); doi:10.1364/JOSAA.33.001415 |
(Suggest additional literature!)
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