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Topic: Coherence length

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	Definition: coherence length (Site not responding. Last check: 2007-10-08)
		coherence length: The propagation distance from a coherent source to a point where an electromagnetic wave maintains a specified degree of coherence.
		Note 2: In optical communications, the coherence length, L, is given approximately by L =
		Note 3: Coherence length is usually applied to the optical regime.
	www.its.bldrdoc.gov /fs-1037/dir-008/_1055.htm (101 words)

	[No title]
		Coherence is a measure of the correlation that exists between the phases of the wave measured at different points.
		The coherence of a wave depends on the characteristics of its source.
		It is perfectly coherent in space and time, its coherence length and coherence time are both infinite.
	electron9.phys.utk.edu /optics421/modules/m5/Coherence.htm (994 words)

	Coherence length - Wikipedia, the free encyclopedia
		In physics, coherence length is the propagation distance from a coherent source to a point where an electromagnetic wave maintains a specified degree of coherence.
		In long-distance transmission systems, the coherence length may be reduced by propagation factors such as dispersion, scattering, and diffraction.
		The coherence length is the optical path length difference of a self interfering laserbeam which corresponds to a 50% fringe visibility, where the fringe visibility is defined as V = (I
	en.wikipedia.org /wiki/Coherence_length (250 words)

	SCI.CRYONICS : Brain scanning: Brian's idea
		For nontechnical people, I explain what is the coherence length for both, a classical and a quantum wave: In the classical case, coherence is defined only for a wave by looking at another wave.
		This is coherence length as it applies to waves on a water pond for example.
		The space blurring of the photon is simply its coherence length or put in another way, the length of the wave packet associated to the photon.
	www.cryonet.org /cgi-bin/dsp.cgi?msg=3363 (779 words)

	Module 1-8
		For example, the longitudinal coherence length is determined by the range of frequencies present in the beam.
		Longitudinal coherence length is important whenever a laser beam is split and recombined to form an interference pattern.
		In most applications that involve interferometry, the longitudinal coherence length of the laser light must be known; and in many cases steps must be taken to extend the coherence length.
	www.cccc.edu /instruction/slympany/ELN/236/Mod8/Mod8.htm (3952 words)

	ASAP '97 The Determination of Signal Coherence Length William M. Carey (Site not responding. Last check: 2007-10-08)
		The signal gain is related to the horizontal coherence length through relationships from the statistical theory of antennas.
		Signal gain measurements in the transverse direction are proffered as a practical measure of coherence length for both broad-band and narrow-band signals.
		The measurement of broad-band and narrow-band coherence functions are discussed with emphasis on the role of partly-coherent noise backgrounds, multipath interference effects, and averaging constraints.
	www.ll.mit.edu /asap/asap_97/abstract/2.html (164 words)

	What is the coherence length? What is the coherence time?
		Coherence length is the space over which a wave is 'nicely' sinusoidal.
		Coherence time is related to the classical uncertainty principle and is thus a little more complex.
		The coherence time is approximately equal to 1/delta v, where delta v, is the bandwidth of the source.
	www.physlink.com /Education/AskExperts/ae372.cfm (210 words)

	Quantum optics with gamma radiation
		The coherence is created by the connection of the two states of the doublet with a single fourth quantum state with some resonant or quasi-resonant radiation (called the driving field).
		Coherence and interference effects in the interaction of light with matter led to very interesting and somewhat unexpected results in the field of quantum optics, such as gain without inversion, electromagnetically induced transparency, changes in index of refraction etc. [4].
		The concepts of coherence and interference were applied to nuclear resonant scattering of synchrotron radiation and a new nuclear interferometer was designed in which one observes the interference between two nuclear resonant scattering amplitudes, one from a reference sample and one from a sample under investigation.
	www.europhysicsnews.com /full/23/article5/article5.html (3997 words)

	LightVision's - Practical Holography by Christopher Outwater & Eric Van Hamersveld
		It is related to the length of the laser tube and the purity of the phase of light emitted and the wavelength itself.
		The coherence length also places an upper limit on the size, especially depth, of the object which can be holographed be setting definite bounds to the path difference of the reference and object beams.
		This is the approximate length of an average 5 milliwatt, HeNe laser.
	www.lightvision.com /howto/chap6.htm (746 words)

	Intro to OCT - Slide 2 (Site not responding. Last check: 2007-10-08)
		The coherence length of a light source is the distance over which the phase of the light wave remains predictable.
		If the light source were coherent, then upon motion of the reference arm, the detector would produce an interference pattern even for large path length differences between the sample and reference arms (plot on bottom left).
		For a short coherence length source, however, motion of the reference arm produces an interference pattern at the detector only when the path lengths of the interferometer arms are matched to within the coherence length of the source (plot bottom right).
	www.fitzpatrick.duke.edu /biophotonics/research/OCT/slide_2.htm (249 words)

	coherence
		Temporal coherence is determined by the coherence length L
		Coherence width is the distance along the wavefront (perpendicular to the direction of propagation), within which the amplitude and phase of the wave can be considered well defined and therefore predictable.
		Coherence of a source can be improved by various physical arrangements and optical components (increasing the distance from the source, focusing and passing light through a small pinhole aperture, etc.).
	www.acs.ryerson.ca /~kantorek/ELE884/coherence.htm (582 words)

	ENME 489F (Site not responding. Last check: 2007-10-08)
		Use it to demonstrate the concepts of coherent interference, calculate coherence length, and visibility.
		The light in the upper and lower arms of the interferometer are recombined by a second 2x2 coupler to produce coherent interference.
		is the coherence length of the source, and BW is the bandwidth of the intensity field at one half of its original intensity (as shown in Figure 2).
	www.enme.umd.edu /class/ENME489F_Laboratory1.htm (548 words)

	Module 1-8
		For example, the longitudinal coherence length is determined by the range of frequencies present in the beam.
		Longitudinal coherence length is important whenever a laser beam is split and recombined to form an interference pattern.
		In most applications that involve interferometry, the longitudinal coherence length of the laser light must be known; and in many cases steps must be taken to extend the coherence length.
	cord.org /cm/leot/course01_mod08/mod01-08frame.htm (3794 words)

	Characteristic Lengths in Superconductors
		Arising in the theoretical and experimental investigations of superconductivity are two characteristic lengths, the London penetration depth and the coherence length.
		It is related to the Fermi velocity for the material and the energy gap associated with the condensation to the superconducting state.
		One of the characteristic lengths for the description of superconductors is called the coherence length.
	hyperphysics.phy-astr.gsu.edu /hbase/solids/chrlen.html (433 words)

	Abstract Title Page
		Coherence is a measure of the temporal or spatial phase relationship between wavetrains.
		Coherence length is a measure of the maximum optical path difference that can exist between two waves that will still interfere with each other.
		Coherence time is the time delay that may exist between to waves that will still interfere with each other.
	www.liteachers.org /wankel/optics.html (2247 words)

	Hecht
		Coherence is the degree to which electromagnetic radiation maintains a near-constant phase relationship, both temporally and spatially.
		It then stands to reason that laser coherence length is essentially the space or distance over which we can predict the phase of a wave or beam.
		In the case of measuring length we find that our coherence length is proportional to the distance we can accurately measure using interference.
	www.u.arizona.edu /~invisibo/report.html (481 words)

	COMMENTS ON SPACIAL AND TEMPORAL COHERENCE (Site not responding. Last check: 2007-10-08)
		The spatial coherence length is determined by the cavity and cavity reflectivity in a laser.
		The coherence length is the maximum distance at which two points in the field can be interfered with contrast.
		The temporal coherence length determines the maximum depth of the object in a reflection hologram, and the spatial coherence length determines the lateral size.
	www.cat.ernet.in /others/lasinfo/coher.html (219 words)

	Course # 10: Module 4: Michelson Interferometers
		The character of the fringes is directly related to the different optical path lengths traveled by the two beams and, therefore, is related to whatever causes a difference in the optical path lengths.
		Coherence can be defined as the degree of stability of phase of a wave (light wave in our case) both in space and in time.
		Thus, a highly coherent source that gives off light with no phase change will produce a long wave train and will be characterized by a long coherence length.
	cord.org /cm/leot/course10_Mod04/Module10-4.htm (3767 words)

	Laser Focus World - Coherence gating works in full color
		Coherence gating is based on a simple principle: holograms can only be formed within the coherence length of the laser beam used.
		In a conventional holographic setup in which the available coherence length is short, the reference beam and object beam paths are carefully measured.
		Each reflection increases the length of that beam path, lessening the likelihood that it will be sufficiently matched with the reference to interfere properly to form a hologram.
	www.laserfocusworld.com /articles/article_display.html?id=147422 (713 words)

	Introduction
		spatial coherence is due a non-uniformity of the amplitude.
		coherence time Δt is the duration for which a single wave exists.
		This final equation of intensity, [9], shows that when two coherent waves of light are superimposed (they are allowed to interfere with each other), then the total intensity depends on the phase difference between them at the time the intensity is measured.
	www.u.arizona.edu /~nmeraz/report.htm (1008 words)

	Quantum structures of trapped ions (Site not responding. Last check: 2007-10-08)
		The coherence length determines the length scale over which quantum interferences should be visible.
		We are, at present, analysing the mathematical properties of the coherence length and investigating means by which it might be measured.
		Our coherence length, which derived from our work on ion interferometry and hot Schroedinger cat states, seems to have applications beyond the field of trapped ions and atoms.
	www.ucc.ie /ucc/depts/physics/opto/quantumoptics.htm (411 words)

	[No title]
		It is related to the length of the laser tube and the purity of the phase of light emitted and the wavelength itself.
		The coherence length also places an upper limit on the size, especially depth, of the object which can be holographed be setting definite bounds to the path difference of the reference and object beams.
		The coherence length is vitally affected by the type of laser used.
	www.holo.com /holo/book/book6&7.html (5265 words)

	UC San Diego physicists observe new property of matter
		Coherence means that such waves are all 'in sync.' The spontaneous coherence of the matter waves is the reason behind some of the most exciting phenomena in nature such as superconductivity and lasing."
		A famous example of spontaneous coherence of matter waves is the Bose-Einstein condensate, which is a state predicted by Einstein some 80 years ago.
		"This is evidenced by the behavior of the coherence length we were able to extract from the light pattern (as shown in the figure) emitted by excitons as they recombine.
	www.eurekalert.org /pub_releases/2006-11/uoc--usd110106.php (845 words)

	Laser projection display system - Patent 6577429
		The display apparatus claimed in claim 2, wherein phase delays introduced by the de-speckling modulator are on the same order as the coherence length of the laser light source, the beam shaping comprises a pair of fly's eye lenslet arrays and the de-speckling modulator is located between the fly's eye lenslet arrays.
		The second lenslet array 178b is separated from the first lenslet array 178a by approximately the focal length of the lenslets on the first lenslet array 178a, such that each lenslet in the first lenslet array 178a focuses light into the corresponding lenslet in the second lenslet array 178b.
		The focal lengths of the lenslet arrays and condenser lens 185 are typically chosen to provide sufficient working distance near the linear spatial light modulator 200 that the opto-mechanics can be designed with relative ease.
	www.freepatentsonline.com /6577429.html (11917 words)

	Neutrino 'Coherence Length'?
		The coherence length is the optical path length difference of a self interfering laserbeam which corresponds to a 50% fringe visibility, where the fringe visibility is defined as V = (Imax - Imin)/(Imax + Imin) and I is the fringe intensity.
		Note that optical coherence is used in stellar interferometery as well as lasers - the key idea is that photons will have visible interference fringes as long as the difference in path lengths is not too great.
		The coherence length is a measure of the maximum path length difference at which fringes will still occur.
	www.physicsforums.com /showthread.php?p=983381 (260 words)

	Equipment - HoloWiki - A Holography FAQ
		The coherence length is measured by a Michelson Interferometer, and given by the maximal path length difference where reasonable fringe contrast occurs.
		When you find the focal length (which is from the focal point of the lens to the center of the collimator, write it down directly on the back or side of the collimator for future reference thus needing to do this procedure once for that mirror.
		Plano-convex lenses have a positive focal length defined by f=R/(n-1) where R is the radius of curvature and n is the index of refraction of the glass used.
	www.holographyforum.org /HoloWiki/index.php/Equipment (7411 words)

	Ophthalmic Hyperguide. Section: Cataract and IOLs
		The ideal axial length measurement technique should be one that can be carried out in an upright position, without corneal contact or compression, and with a level of accuracy high enough for outcomes consistently within 0.25 diopter of the target refraction.
		By employing a partially coherent light source rather than ultrasound, the IOLMaster appears to have fulfilled all of the most important objectives for measuring the axial length of the human eye with a level of accuracy unimaginable just a few years ago.
		Because OCB measures from the corneal vertex to the retinal pigment epithelium, and A-scan ultrasound measures from the corneal vertex to the vitreoretinal interface, some method of calibration is necessary to avoid a measurement error of 0.20 mm, or the approximate thickness of the retina at the center of the macula.
	ophthalmic.hyperguides.com /tutorials/cataract/iol_master/tutorial.asp (2704 words)

	III
		Coherence is the ability of light to interfere with a delayed or displaced version of itself.
		Interference with a displaced version produces a measure of transverse coherence and yields a measure of the coherence area and the transverse coherence length l
		Transverse coherence is measured by examining the maximum separation distance two pinholes can be placed in a beam and still demonstrate interference.
	www.seas.upenn.edu /~tcom503/book/sec_iii.html (878 words)

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