N-Slit interferometer
Encyclopedia
The N-slit interferometer is an extension of the double-slit interferometer
also known as Young's double-slit interferometer. One of the first known uses of N-slit arrays in optics was illustrated by Newton
. In the first part of last century, Michelson
described various cases of N-slit diffraction.
Feynman
described thought experiment
s, of two-slit quantum interference, of electrons using Dirac's notation. This approach was extended to N-slit interferometers using narrow-linewidth laser illumination, that is, illumination by indistinguishable photons, by researchers working on the measurement of complex interference patterns. These interferograms are accurately reproduced, or predicted, by the N-slit interferometric equation
for either even (N = 2, 4, 6,…), or odd (N = 3, 5, 7,…), numbers of slits.
, use prismatic beam expansion
to illuminate a transmission grating, or N-slit array, and a photoelectric detector array (such as a CCD
or CMOS
) at the interference plane to register the interferometric signal. The expanded laser beam illumination in the N-slit interferometer can also take the shape, via the introduction of a convex lens prior to the prismatic expander, of a beam extremely elongated in the propagation plane and extremely thin in the orthogonal plane. This use of one-dimensional (or line) illumination eliminates the need of point-by-point scanning in microscopy and microdensitometry. Thus, these instruments can be used as straight forward N-slit interferometers or as interferometric microscopes (see section on microscopy).
. Recent experimental developments include intra-interferometric path lengths of 35 meters and 527 meters.
These large, and very large, N-slit interferometers are also being used to study the effect of intra interferometric clear air turbulence and the effect of microscopic disturbances on propagating interferometric signals. This work has yielded the first observation of diffraction patterns superimposed over propagating interferograms.
These diffraction patterns (as shown in the first photograph) are generated by inserting a spider web
fiber (or spider silk
thread) on to the propagation path of the N-slit interferogram. The position of the spider web fiber is perpendicular to the plane of propagation.
Note: N-slit interferometers include three-slit interferometers (or triple-slit interferometers), four-slit interferometers, etc.
.
The multiple-prism expanded laser beam is also described as an extremely elongated laser beam
. The elongated dimension of the beam (25-50 mm) is in the plane of propagation while the very thin dimension (~25 μm) of the beam is in the orthogonal plane. This was demonstrated, for imaging and microscopy applications, in 1993. Alternative descriptions of this type of extremely elongated illumination might include the terms line illumination, linear illumination, thin light sheet illumination, and plane illumination.
N-slit interferometers are also of interest to researchers working in atom optics, Fourier imaging, and
quantum computing.
Double-slit experiment
The double-slit experiment, sometimes called Young's experiment, is a demonstration that matter and energy can display characteristics of both waves and particles...
also known as Young's double-slit interferometer. One of the first known uses of N-slit arrays in optics was illustrated by Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
. In the first part of last century, Michelson
Albert Abraham Michelson
Albert Abraham Michelson was an American physicist known for his work on the measurement of the speed of light and especially for the Michelson-Morley experiment. In 1907 he received the Nobel Prize in Physics...
described various cases of N-slit diffraction.
Feynman
Richard Feynman
Richard Phillips Feynman was an American physicist known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics and the physics of the superfluidity of supercooled liquid helium, as well as in particle physics...
described thought experiment
Thought experiment
A thought experiment or Gedankenexperiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences...
s, of two-slit quantum interference, of electrons using Dirac's notation. This approach was extended to N-slit interferometers using narrow-linewidth laser illumination, that is, illumination by indistinguishable photons, by researchers working on the measurement of complex interference patterns. These interferograms are accurately reproduced, or predicted, by the N-slit interferometric equation
N-slit interferometric equation
Quantum mechanics was first applied to optics, and interference in particular, by Paul Dirac. Feynman, in his lectures, uses Dirac’s notation to describe thought experiments on double-slit interference of electrons...
for either even (N = 2, 4, 6,…), or odd (N = 3, 5, 7,…), numbers of slits.
N-slit laser interferometer
The N-slit laser interferometers, introduced by DuarteF. J. Duarte
F. J. Duarte is a laser physicist and author/editor of several well-known books on tunable lasers. He introduced the generalized multiple-prism dispersion theory and has discovered various multiple-prism grating oscillator laser configurations...
, use prismatic beam expansion
Beam expander
Beam expanders are used in laser physics either as intracavity or extracavity elements. They can be telescopic in nature or prismatic. Generally prismatic beam expanders use several prisms and are known as multiple-prism beam expanders....
to illuminate a transmission grating, or N-slit array, and a photoelectric detector array (such as a CCD
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
or CMOS
Active pixel sensor
An active-pixel sensor is an image sensor consisting of an integrated circuit containing an array of pixel sensors, each pixel containing a photodetector and an active amplifier. There are many types of active pixel sensors including the CMOS APS used most commonly in cell phone cameras, web...
) at the interference plane to register the interferometric signal. The expanded laser beam illumination in the N-slit interferometer can also take the shape, via the introduction of a convex lens prior to the prismatic expander, of a beam extremely elongated in the propagation plane and extremely thin in the orthogonal plane. This use of one-dimensional (or line) illumination eliminates the need of point-by-point scanning in microscopy and microdensitometry. Thus, these instruments can be used as straight forward N-slit interferometers or as interferometric microscopes (see section on microscopy).
Secure optical communications
These interferometers, originally introduced for applications in imaging, are also useful in optical metrology and have been proposed for secure optical communications in free spaceFree-space optical communication
Free-space optical communication is an optical communication technology that uses light propagating in free space to transmit data for telecommunications or computer networking."Free space" means air, outer space, vacuum, or something similar...
. Recent experimental developments include intra-interferometric path lengths of 35 meters and 527 meters.
These diffraction patterns (as shown in the first photograph) are generated by inserting a spider web
Spider web
A spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....
fiber (or spider silk
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...
thread) on to the propagation path of the N-slit interferogram. The position of the spider web fiber is perpendicular to the plane of propagation.
Note: N-slit interferometers include three-slit interferometers (or triple-slit interferometers), four-slit interferometers, etc.
Expanded beam interferometric microscopy
As previously mentioned the original application of the N-slit laser interferometer was interferometric imaging. In particular, the one dimensionally expanded laser beam (with a cross section 25-50 mm wide by ~25 μm high) was used to illuminate imaging surfaces (such as silver-halide films) to measure the microscopic density of the illuminated surface. Hence the use of the description interferometric microdensitometer. Resolution down to the nano regime can be provided via the use of interinterferometric calculationsN-slit interferometric equation
Quantum mechanics was first applied to optics, and interference in particular, by Paul Dirac. Feynman, in his lectures, uses Dirac’s notation to describe thought experiments on double-slit interference of electrons...
.
The multiple-prism expanded laser beam is also described as an extremely elongated laser beam
Beam expander
Beam expanders are used in laser physics either as intracavity or extracavity elements. They can be telescopic in nature or prismatic. Generally prismatic beam expanders use several prisms and are known as multiple-prism beam expanders....
. The elongated dimension of the beam (25-50 mm) is in the plane of propagation while the very thin dimension (~25 μm) of the beam is in the orthogonal plane. This was demonstrated, for imaging and microscopy applications, in 1993. Alternative descriptions of this type of extremely elongated illumination might include the terms line illumination, linear illumination, thin light sheet illumination, and plane illumination.
N-slit interferometers are also of interest to researchers working in atom optics, Fourier imaging, and
quantum computing.
See also
- Beam expanderBeam expanderBeam expanders are used in laser physics either as intracavity or extracavity elements. They can be telescopic in nature or prismatic. Generally prismatic beam expanders use several prisms and are known as multiple-prism beam expanders....
- Double-slit experimentDouble-slit experimentThe double-slit experiment, sometimes called Young's experiment, is a demonstration that matter and energy can display characteristics of both waves and particles...
- MicroscopyMicroscopyMicroscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...
- N-slit interferometric equationN-slit interferometric equationQuantum mechanics was first applied to optics, and interference in particular, by Paul Dirac. Feynman, in his lectures, uses Dirac’s notation to describe thought experiments on double-slit interference of electrons...