Search results for "Fresnel"
showing 10 items of 100 documents
Single-zone-plate achromatic fresnel-transform setup: Pattern tunability
1997
Abstract White-light point-source illumination results in the chromatic blurring of the optical field diffracted by an aperture. In this paper, broadband dispersion compensation for a continuous set of Fresnel diffraction patterns associated with an arbitrary input transparency is carried out, in a sequential way, by means of a single on-axis blazed zone plate. The input is illuminated with a white-light converging spherical wavefront and the diffractive lens is inserted at the virtual source plane. We recognize that the position of the input along the optical axis permits to achieve a different achromatic Fresnel diffraction pattern with low residual chromatic aberrations. The theory deriv…
Totally incoherent optical processing operations with achromatic diffraction-based setups
2000
We report on a novel family of totally incoherent, chromatic-dispersion compensated hybrid (refractive-diffractive) lens setups for implementing, in the Fraunhofer or in the Fresnel diffraction region, different achromatic diffraction-based processing operations.
Three-dimensional behavior of apodized nontelecentric focusing systems.
2002
The scalar field in the focal volume of nontelecentric apodized focusing systems cannot be accurately described by the Debye integral representation. By use of the Fresnel–Kirchhoff diffraction formula it is found that, if the aperture stop is axially displaced, the focal-volume structure is tuned. We analyze the influence of the apodizing function and find that, whereas axially superresolving pupil filters are highly sensitive to the focal-volume reshaping effect, axially apodizing filters are more inclined to the focal-shift effect.
High-contrast white-light Lau fringes
2004
We present a new optical assembly with which to achieve Lau fringes with totally incoherent illumination. Gratinglike codification of the spatially incoherent source combined with an achromatic Fresnel diffraction setup allows us to achieve Lau fringe-pattern visibility of almost 100% with broadband light. The white-light character to our proposed setup is in stark contrast to previous monochromatic implementations. Potential implications of this fact are identified.
Multiplexing THz Vortex Beams With a Single Diffractive 3-D Printed Lens
2019
[EN] We present a novel method for experimentally generating multiplexed THz vortex beams by using a single three-dimensional printed element that combines a set of radially distributed spiral phase plates, and a binary focusing Fresnel lens. With this element, we have experimentally demonstrated that THz multiplexing can be tailored to fit within a small space on an optical bench. Results are presented beside numerical simulations, demonstrating the robust nature of the experimental method.
Effective Fresnel-number concept for evaluating the relative focal shift in focused beams
1998
We report on an analytical formulation, based on the concept of effective Fresnel number, to evaluate in a simple way the relative focal shift of rotationally nonsymmetric scalar fields that have geometrical focus and moderate Fresnel number. To illustrate our approach, certain previously known results and also some new focusing setups are analytically examined.
Geometrical Transformations In The Fraunhofer Plane
1987
A virtual display of the Fraunhofer diffraction pattern is generated solely by illuminating the object with a point source. If this pattern is imaged with an anamorphic system, several linear geometrical transformations can be achieved. Furthermore, a nonsymmetrical Fourier transformer with a variable degree of anamorphic magnification on the Fraunhofer pattern can be implemented.
Analysis of Fresnel Zone Plates Focusing Dependence on Operating Frequency
2017
[EN] The focusing properties of Fresnel Zone Plates (FZPs) against frequency are analyzed in this work. It is shown that the FZP focal length depends almost linearly on the operating frequency. Focal depth and focal distortion are also considered, establishing a limit on the frequency span at which the operating frequency can be shifted. An underwater FZP ultrasound focusing system is demonstrated, and experimental results agree with the theoretical analysis and simulations.
Pinhole Zone Plate Lens for Ultrasound Focusing
2017
[EN] The focusing capabilities of a pinhole zone plate lens are presented and compared with those of a conventional Fresnel zone plate lens. The focusing properties are examined both experimentally and numerically. The results confirm that a pinhole zone plate lens can be an alternative to a Fresnel lens. A smooth filtering effect is created in pinhole zone plate lenses, giving rise to a reduction of the side lobes around the principal focus associated with the conventional Fresnel zone plate lens. The manufacturing technique of the pinhole zone plate lens allows the designing and constructing of lenses for different focal lengths quickly and economically and without the need to drill new p…
Twin axial vortices generated by Fibonacci lenses.
2013
Optical vortex beams, generated by Diffractive Optical Elements (DOEs), are capable of creating optical traps and other multifunctional micromanipulators for very specific tasks in the microscopic scale. Using the Fibonacci sequence, we have discovered a new family of DOEs that inherently behave as bifocal vortex lenses, and where the ratio of the two focal distances approaches the golden mean. The disctintive optical properties of these Fibonacci vortex lenses are experimentally demonstrated. We believe that the versatility and potential scalability of these lenses may allow for new applications in micro and nanophotonics.