Interferometers are devices for analyzing slight differences in spectroperformance by enabling examination of the interference fringe generated by the superimposition of two divided optical paths.
Integrated components for interferometer designed for a specific purpose or application are placed at any position on an optical vibration isolator and used for various light measurements.
Brief overviews of interferometers will be given first. See the detailed description page for information on specific types of interferometers.

General characteristics of interferometers

Allow direct observation of interference fringes.
Allow measurement of subtle changes.
Allow non-contact measurement.
Allow real-time measurement.

Example of Mach-Zehnder interferometer configuration (3D diagram)

An interference fringe is generated on the screen by superimposing two divided optical paths, L1 and L2.

A sample is then placed into optical path L1, and light is allowed to pass through the sample.

This changes the number or the motion of the interference fringes, on the basis of which changes the optical properties of the sample can be determined.

Interferometer types and characteristics

Type	Key features	Applications
Mach-Zehnder Interferometer	Larger interferometer enables a larger work area and a wider optical path.	Visualization of fluids, determination of strain in transparent objects, pressure measurements, etc.
Michelson Interferometer	Wider applications	Measurements of wavelength, wavelength ratio, refractive index, dispersion, precise length, surface roughness, coating thickness, and other parameters.
Twyman-Green interferometer	Allows measurement of wave front aberrations of transmission samples.	Measurement of wave front aberrations of lenses and prisms
Fizeau Interferometer	Enables measurement of the precision of spherical or flat surfaces for each wavelength of light.	Measurement of flatness, parallelism, and others parameters
Schlieren Device	Converts a slight change in refractive index into a contrast of light and shade	Visualization of fluid, measurement of strain in transparent objects, and other applications

Major components can be integrated to enable easier construction of typical interferometers. See the following table for the number of the components needed.

For example, the components for a Mach-Zehnder interferometer can be used to construct a Michelson interferometer or Fizeau interferometer.

See the detailed description page for detailed information on respective components.

	Laser	Special filter	Collimator lens	Mirror	Half mirror	Concave mirror	Screen	CCD holder	Collimation checker	Target	Vibration Isolation Systems	Easy-setup darkroom
Michelson Interferometer	1	1	1	2	1	0	(1)	1	(1)	(1)	(1)	(1)
Mach-Zehnder Interferometer	1	1	1	2	2	0	(1)	1	(1)	(1)	(1)	(1)
Fizeau Interferometer	1	1	1	1	2	0	(1)	1	(1)	(1)	(1)	(1)
Schlieren Device	1	1	1	0	0	2	(1)	1	(1)	1	(1)	(1)

Interference fringe

Although light has some of the properties of wave phenomena, these waves cannot be observed directly visually. If a light beam is divided into two beams by a beam splitter and the two divided beams superimposed, an interference pattern results, a phenomenon characteristic of wave behavior which can be visually observed. This phenomenon results from the superimposing of the peaks and valleys of light waves, making the superimposed light brighter in some areas and darker in other areas. Since the differences in travelling distance of the two lights (optical path differences) are integer multiples of the wavelength of the original light?i.e., in phase?the wave phases are reinforced. When light is projected onto a screen, it appears as a fringe pattern. This clearly visible fringe is called an interference fringe. Interferometers are based on this phenomenon.

When laser beams are irradiated from two directions (angle between two light rays: θ), interference causes superimposition of the wave fronts, partly strengthening and partly weakening the beam. The standing wave thus formed in this manner produces the interference fringe consisting of bright and dark spots on screen.

The interference fringe is expressed by the equation: sin (θ/2) = λ/(2P), where λ is the wavelength of light and P is the wavelength of the standing wave above. When θ becomes smaller, P becomes larger.

Practical applications of interference patterns

Light interference patterns are used to evaluate the accuracy of precise spherical or flat surfaces.

In the figure to the left, interference fringes are seen from above the sample when using a Newton ring observation device.

Flatness = λ/2 x Number of fringes (4) = 2λ
Flatness = λ/2 x b/a = λ/2 x 1/5 = λ/10

Key features of Sigma Koki products

Applications of interferometer

Visualization of fluids: Interferometers allow real-time measurement, enabling visualizing of changes in the flow of fluids, including gas and liquids.

Measurement of strain in transparent objects: Internal strain can be determined if the object is a light-transmitting object.

Wavelength measurement: Michelson interferometers enable measurement of the wavelength of light. They also allow measurement of other basic optical characteristics, including refractive index, surface roughness, coating thickness, and dispersion.

Wave front aberration: When light is transmitted through a lens, prism, or similar component, phase shifts emerge between incident and output wave fronts.

Measurement of flatness and parallelism: The flatness and parallelism of precision parallel plates need to be evaluated. These measurements can be made easily with a Fizeau interferometer.

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