Characteristics comparison of backward and forward pumped spectrum pre-sliced multi-wavelength fibre sources
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It is shown that both single exposure and double exposure two-wavelength holography provide a good method of using visible light to obtain an interferogram identical to what would be obtained if a longer nonvisible wavelength were used. Both techniques provide for the real-time adjustment of defocus and tilt in the final interferogram. When both hologram exposures are made simultaneously, the sensitivity to air turbulence is essentially the same as if the longer nonvisible wavelength were used. Results are shown for testing both lenses and mirrors at equivalent wavelengths at 6.45 micro, 9.47 micro, 14.20 micro, 20.22 micro, and 28.50 micro obtained by using an argon laser for the visible light source.
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The classical Huygens–Fresnel theory of diffraction breaks down for aperture dimensions less than four to five wavelengths. Keller's Geometrical Theory of Diffraction, on the other hand, is known to fit the exact solution very well for slit-widths as small as two wavelengths. A comparative study of the correlation of the Keller and Kirchhoff theory with measurements of the far-field pattern behind slit-widths 1.092 μ, 1.21 μ, and 2.67 μ, ruled in an aluminum film of thickness 120 nm, has been undertaken. The theory is evaluated for thin slits and for thick round-ended slits of wavelength dimensions, and also for dielectric and conducting edges. The latter are compared with edge-diffraction measurements. The results lead to the conclusion that, at optical frequencies, the inability to fabricate edges of precisely describable size and shape have the effect of extending the relative usefulness of Kirchhoff theory to apertures of wavelength dimensions.
Aperture (computer memory)
Ptychography
Fresnel number
Kirchhoff's diffraction formula
Fresnel equations
Huygens–Fresnel principle
Fresnel zone
Geometrical optics
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The complex correlation coefficient of two fully developed speckle fields of different wavelengths is evaluated for two different geometries, and its meaning is discussed in connection with two-wavelength-measurement techniques applied to rough surfaces (e.g., two-wavelength rough-surface interferometry, two-wavelength holography, electronic speckle pattern interferometry). It is shown that in both geometries the correlation coefficient is high enough to permit meaningful measurements to be performed if the surface under test is slightly defocused, provided that the tilt of the surface normal to the optical axis of the measurement arrangement is small enough.
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Holographic interferometry
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Achromatic lens
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An autofocusing method for two-wavelength digital holographic microscopy (TWDHM) based on the wavelength dependence of the diffraction process is proposed. Red and green lights are employed for the illumination of the TWDHM, and the generated holograms are recorded simultaneously by a color CCD camera. Due to the wavelength dependency of the diffraction process, the farther the reconstruction plane is from the image plane, the larger the difference is between the red and green light distributions. Thus, the image plane can be determined by finding the minimum of the variation between the red and green lights on their amplitude distributions. The feasibility of the proposed method is demonstrated by simulation and experiment.
Digital Holographic Microscopy
Digital holography
Diffraction efficiency
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Kinoforms (diffractive optical elements) were designed to produce different fan-out (i.e., spot) patterns when illuminated with green (543-nm wavelength) and red (633-nm) light. Three design examples are presented, each using one of three different techniques for this wavelength discrimination. If the fan-out pattern is to be produced in the near field (Fresnel region) of the kinoform, focusing–defocusing distinguishes between the two colors. For a far-field pattern the color distinction can be obtained either by active suppression of unwanted spots, which also decreases the diffraction efficiency, or, preferably, by an increase in the maximum phase modulation of the kinoform (to more than 2π rad). All three examples were designed with a method based on the full scalar wave equation and optimal-rotation-angle optimization. The designed kinoforms were manufactured and performed, at least qualitatively, as predicted by the design.
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Diffraction efficiency
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We show that all the structural properties of periodic dielectric multilayers can be accurately determined by a combined measurement of the transmission as a function of the wavelength and of the reflection as a function of the angle of incidence when the wavelength of the incident light is fixed. This method is applied to determine the structural properties of two commercial dielectric mirrors, and the results obtained are compared with a measurement of the same structural parameters by use of another technique based on the more standard optical guiding method.
Reflection
Reflection coefficient
Fresnel equations
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Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text N. S. Kapany, J. J. Burke, and K. Frame, "Diffraction by Apertures of Wavelength Dimensions," Appl. Opt. 5, 1082-1082 (1966) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article
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We demonstrate that, under suitable conditions, subwavelength feature variations of an object can affect the corresponding far-field diffraction pattern in a measurable way. We present an experiment in which width variations of less than 1/100 of the wavelength are measured with a slit whose width is 100 times the wavelength. Integral and differential intensity measurements in the far field are fully consistent with standard diffraction theory even in the subwavelength variation regime. In particular, slit modulations of 6 nm with a wavelength of 670 nm are shown to follow theoretical calculations within the experimental sensitivity of ~10(-5) .
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Ptychography
Intensity
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