Search results for "Fresnel"
showing 10 items of 100 documents
Focal switch: a new effect in low-Fresnel-number systems
2010
It is shown for the first time we believe, that when a spherical wave illuminates a certain type of diffracting screen, in addition to the expected focal-shift effect, depending on the value of the Fresnel number of the focusing system, a focal switch effect can appear, i.e., an increase in the height of the lateral lobe of the axial-intensity distribution over that of the central lobe.
Temporal effects in ultrashort pulsed beams focused by planar diffracting elements
2006
The pulse envelope of an ultrashort pulsed beam is evaluated on the focal points of a Fresnel zone plate. The description of the field dynamics is given in terms of a diffraction-induced pulse train. Within these terms we follow an analytical procedure to characterize the temporal broadening observed at the principal focus, which is significant if the number of Fresnel zones exceeds the number of cycles in the pulse. For Gaussian-type envelopes, the focal field may be accurately expressed in a simple closed form. This expression has a flat-top shape at the principal focus and other odd-order foci, and a two-peak envelope in the case of a low-integer even-order focus. Finally, extremely high…
Focal-shift formula in apodized nontelecentric focusing systems
2007
A single analytical formulation for evaluating the focal shift in any apodized nontelecentric focusing setup is reported. The formulation is also useful in the case of imaged paraxial beams. We show explicitly that the magnitude of the focal shift is determined by only one parameter that depends on the effective width of the pupil filter and its axial position. To illustrate our approach we examine different focusing setups.
Parallel phase-shifting digital holography based on the fractional Talbot effect
2010
A method for recording on-axis single-shot digital holograms based on the self-imaging phenomenon is reported. A simple binary two-dimensional periodic amplitude is used to codify the reference beam in a Mach-Zehnder interferometer, generating a periodic three-step phase distribution with uniform irradiance over the sensor plane by fractional Talbot effect. An image sensor records only one shot of the interference between the light field scattered by the object and the codified parallel reference beam. Images of the object are digitally reconstructed from the digital hologram through the numerical evaluation of the Fresnel diffraction integral. This scheme provides an efficient way to perfo…
Theory of quantum fluctuations of optical dissipative structures - Application to the study of squeezing and intensity fluctuations of DOPO cavity so…
2007
We present a general theory of quantum fluctuations of dissipative structures in nonlinear optical cavities with transverse translation invariance. Perfect squeezing of the transverse momentum, detectable under homodyning, occurs irrespectively of the system parameters.
Nonlinear dynamics of a semilinear photorefractive oscillator
2001
The experimental study of the dynamics of an empty coherent semilinear photorefractive oscillator is reported. It is shown that starting from a certain coupling strength the oscillation occurs with two frequencies shifted symmetrically with respect to the frequency of the pump wave. The threshold of bifurcation in oscillation spectrum depends on pump intensity ratio.
Scattering on Riemannian Symmetric Spaces and Huygens Principle
2018
International audience; The famous paper by L. D. Faddeev and B. S. Pavlov (1972) on automorphic wave equation explored a highly romantic link between Scattering Theory (in the sense of Lax and Phillips) and Riemann hypothesis. An attempt to generalize this approach to general semisimple Lie groups leads to an interesting evolution system with multidimensional time explored by the author in 1976. In the present paper, we compare this system with a simpler one defined for zero curvature symmetric spaces and show that the Huygens principle for this system in the curved space holds if and only if it holds in the zero curvature limit.
Diffractive m-bonacci lenses.
2017
[EN] Fibonacci zone plates are proving to be promising candidates in image forming devices. In this letter we show that the set of Fibonacci zone plates are a particular member of a new family of diffractive lenses which can be designed on the basis of a given m-bonacci sequence. These lenses produce twin axial foci whose separation depends on the m-golden mean. Therefore, with this generalization, bifocal systems can be freely designed under the requirement at particular focal planes. Experimental results support our proposal. (C) 2017 Optical Society of America
Three-dimensional field distribution in the focal region of low-Fresnel-number axicons.
2006
Three-dimensional intensity and phase distributions generated by microaxicons are evaluated in the low-Fresnel-number regime. Apertured and nonapertured conical wavefronts may generate transverse patterns with notable deviations from the expected nondiffracting Bessel beam. First-order analytical expressions are proposed for the evaluation of the wave field produced by axicons of different Fresnel number in the focal region.
Analytical formula for calculating the focal shift in apodized systems
1998
We report a quite simple analytical formula for the evaluation of the focal shift in apodized systems, with or without rotational invariance. Specifically it is shown that the magnitude of the focal shift is determined by the product of the Fresnel number of the focusing geometry and the standard deviation of a mapped version of the azimuthal average of the pupil transmittance. To illustrate our approach, several examples are examined.