Radon-Wigner display: a compact optical implementation with a single varifocal lens

A new optical implementation of the Radon-Wigner display for one-dimensional objects is presented, making use of the fractional Fourier transform approach. The proposed setup makes use of only two conventional refractive elements: a cylindrical lens and a varifocal lens. Although the exact magnifications cannot be achieved simultaneously for all the fractional transforms, an optimum design can be obtained through balancing the conflicting magnification requirements. Experimental results are obtained with a commercially available progressive addition lens. For comparison, computer simulations are also provided.     

The analytical description and experiments of the optical bottle generated by an axicon and a lens

Based on the interferential theory, we deduce a new type of analytic expression suitable for describing the evolutions of the optical bottle beam generated from the axicon-lens optical system illuminated by the Gaussian beam for the first time. The theory does not use much approximation in the process of mathematical analysis and can better illustrate the optical bottle beam evolutions at any positions. With the derived expression, the three-dimensional (3D) longitudinal and transverse intensity profiles of the optical bottle beam are simulated numerically. The numerical calculations have been confirmed by the experimental results.     

Force mapping of an optical trap using an acousto-optical deflector in a time-sharing regime

We suggest and study experimentally a time-sharing protocol for acousto-optical deflectors (AODs) that permits one to map the radial optical trapping force of optical tweezers without using a controllable flux control or an additional beam. Variations of the trapping potential due to modifications of the optical system are easily detected in terms of the force map. The protocol can be used in optical tweezers that already include an AOD without adding new elements in the existing optical system.     

Plasma-deformation mechanism of nanocluster array formation on CdTe crystal surface under the action of a single laser pulse

A plasma-deformation mechanism is proposed which can explain the phenomenon of nanocluster array formation on a CdTe crystal surface under the action of a single nanosecond pulse of a ruby laser. The nonmonotonic dependence of the lateral size of nanoclusters on the laser radiation intensity predicted by the proposed model agrees with experiment.     

Thermal characteristics of optical pulse transit time delay and fiber strain in a single-mode optical fiber cable

Thermal characteristics of optical pulse transit time delay and fiber strain in a single-mode optical fiber cable are investigated theoretically and experimentally. Measurements of the transit time delay shift are made by a spatial interference technique using a 1.5-in long fiber, six-fiber unit, and cable. Experimental results for a jacketed fiber whose fiber axis is well centered in nylon coating are in good agreement with those predicted from the theory. A jacketed fiber whose fiber axis is positioned eccentrically from the jacket center exhibits a small change in fiber strain at low temperature due to fiber buckling compared with that for the well-centered jacketed fiber. The loss increase for the off-centered jacketed fiber is explained by the buckling model. Furthermore, thermal characteristics of the unit-type cable examined here are found to coincide with those for the constituent six-fiber unit.     

Alteration of imaging properties of an optical pickup's objective lens by a nonrotationally symmetric coating

One can control the aberrations of an optical readout system by varying the width of a strip of antireflection coatings deposited upon plastic objective lenses. It is found that one can control the magnitude of the third-order astigmatism of the system by changing the coating width. This process has the advantage that it does not significantly cause other kinds of aberration such as coma and spherical aberrations to deteriorate. When these nonrotational symmetrically (NRS) coated lenses are used for off-axis operations such as tracking movements in optical drives, the change in the magnitude of the astigmatism (DAS) that is generated can be made smaller than those of symmetrically coated or noncoated lenses. As much as a 73% decrease in DAS was observed experimentally with a NRS-coated lens. Including the birefringence of the plastic material in the analysis yields a low and constant level of astigmatism generated by shifting of the objective lens.     

Fraunhofer diffraction of laser beams with amplitude modulations and phase fluctuations by a lens with a central obscure aperture

Abstract

By using the statistical-optics model and generalized Huygens-Fresnel diffraction integral, Fraunhofer diffraction of high-power laser beams with amplitude modulations (AMs) and phase fluctuations (PFs) focused by a lens with a central obscure aperture has been studied. Detailed numerical calculation results have been given, showing the dependence of the intensity distribution at the geometrical focal position and the power (energy) focus-ability of high-power laser beams not only on the obscure ratio, but also on the truncation parameter, AMs and PFs of beams.     

Spectral changes and spectral switches of partially coherent beams focused by an aperture lens

Starting from the propagation law of partially coherent polychromatic light in the space-frequency domain, detailed numerical results and physical analysis are given to elucidate spectral changes and spectral switches at the geometrical focal plane of Gaussian Schell-model beams focused by an aperture lens. It is found that, in contrast to the aperture-induced spectral anomalies of spatially fully coherent polychromatic light, for partially coherent polychromatic light aperture diffraction plays an important role in spectral switching, but the truncation parameter, spectral correlation, and bandwidth all affect its spectral behavior.     

Influence of air annealing temperature and time on the optical properties of Yb:YAG single crystal grown by HDS method

8 at.% Yb:YAG plate single crystal with the dimension of 170 mm × 150 mm × 30 mm was grown in vacuum by Horizontal Directional Solidification method. Aimed at blue-green color centers, annealing treatments of 15 mm × 15 mm × 1 mm samples from 900 °C to 1400 °C for 5 h and at 900 °C from 5 h to 40 h in air were conducted. The absorption spectra, emission spectra, fluorescence lifetime and X-ray photoelectron spectroscopy of samples under different annealing conditions were measured at room temperature, respectively. Annealing at above 1000 °C for 5 h or at 900 °C for 40 h made the blue-green color centers disappear and the samples turned to transparent. Absorption coefficients decreased in the 300 nm–800 nm wavelength range, emission intensities increased and emission bands broadened around 486 nm and 1029 nm with increasing temperature up to 1200 °C, then varied inversely. These values decreased or increased monotonically with increasing annealing time at 900 °C. The maximal increases of fluorescence lifetime were 62.3% and 64.7%, respectively. The calculated emission cross section of 1200 °C for 5 h was up to 4.4 × 10⁻²⁰ cm². In X-ray photoelectron spectroscopy, the concentrations of oxygen vacancies reduced from 1.28% down to absence by annealing. These experiments show that color centers are detrimental to the optical properties of HDS-Yb:YAG laser crystal and optimal annealing treatments should be conducted.     

Modeling of a mode conversion ultrasonic motor in the regime of slip

A simple mechanical model of a mode conversion ultrasonic motor is suggested. It is revealed that the vibrational motion of the beam's tip is transformed into a unidirectional rotation of a rotor, owing to the dependence of the magnitude of the frictional force on the direction of slip. The model developed enables one to investigate the behavior of the motor in transient, periodic and steady-state modes of operation and to study the influence of the motor's parameters on the maximum torque, velocity of revolution, efficiency etc.     

Apodizing of an achromatic lens by a gray-glass negative lens element

The apodizing performance of a plano-concave lens made of gray glass was analyzed numerically. It was found that apodizing performance depends solely on the edge transmittance of the lens (a zero center thickness is assumed here) for any reasonable ratio of radius of curvature of the concave surface and the lens radius. If a modest increase in the size of the central diffraction peak and light losses introduced by such a lens can be accepted, it is possible to reduce energy diffracted into diffraction rings approximately tenfold.     

Theory of the undulator superradiance of an electron beam pulse in the group synchronism regime

The properties of the superradiance of a short electron beam pulse moving in an undulator field and exciting a waveguide mode field under group synchronism conditions are analyzed. This regime is shown to be characterized by the maximum growth rate of superradiance instability. The development of such instability results in bunching of the particles and the coherent emission of a short electromagnetic pulse by the beam pulse. Pis’ma Zh. Tekh. Fiz. 25, 8–16 (April 26, 1999)     

Fatigue strength of a single crystal in the gigacycle regime

The objective of this work is to investigate the fatigue behavior of a single crystal nickel-based superalloy in the gigacycle regime. Testing from 10⁶ to 10⁹ cycles at 593 °C was performed using an ultrasonic fatigue system operating at 20 kHz. Multiple tests were performed at stresses near the fatigue limit to determine the variability in fatigue life in this regime. Endurance limit results were compared to similar data generated on conventional servohydraulic test systems to determine if there are any frequency effects. Scanning electron microscopy was then used to determine the initiation sites and the failure mechanisms. Initial results indicate little or no frequency effect on the fatigue strength or failure mechanisms of PWA 1484 at 593 °C.     

New approach for the design of an optical square pulse generator

What is believed to be a new approach for the design and analysis of a reconfigurable optical square pulse generator using the concept of temporal optical integration and the digital signal processing method is presented. The reconfigurable square pulse generator is synthesized using compact active semiconductor-based waveguide technology, and it consists simply of the cascade of a tunable microring resonator (or a tunable all-pole filter) and a tunable asymmetrical Mach-Zehnder interferometer (or a tunable all-zero filter). The reconfigurable generator can convert an input picosecond pulse (i.e., soliton or Gaussian pulse) into an optical square pulse. The pulse width of the generated square pulse can be adjusted by controlling the time delay of a variable delay element in the tunable all-zero filter. The reconfigurable generator can convert an input picosecond pulse train into return-to-zero (RZ) and non-return-to-zero (NRZ) signals with square pulse shapes. The repetition rates of the generated RZ and NRZ signals can be varied by adjusting the bit period of the input picosecond pulse train, the input pulse width, and the time delay of the variable delay element. The effect of the deviation of the parameter values on the generator performance is also studied.     

Spectral evolution of an optical pattern generated by spatial modulation instability in a reorientational Kerr nonlinear medium

An experimental investigation is reported on the role of molecular reorientational nonlinearity in the spectral evolution of multifilamentation patterns induced by spatial modulation instability (MI) in a nonlinear Kerr medium. The influence of molecular reorientational Kerr nonlinear response on the spatial MI is analyzed theoretically by the standard stability analysis. The spatial MI gain spectra obtained by experimental measurements were found to agree with the theoretical derivation. In addition, by changing the launch average power, we also analyze the spatial spectral behavior of the optical pattern in such media. It is shown that, for higher launch average power, there will be secondary spatial stripes, manifesting as the original spatial modulation frequency doubling in the spatial frequency domain, which originated from the molecular reorientational Kerr nonlinearity response.     

Avalanche semiconductor detector for single optical photons with a time resolution of 60 ps

Single optical photons can be detected by semiconductor diodes, that can operate in the triggered avalance mode. Physical properties and structural requirements of such single photon avalance diodes (SPADs) are analyzed. A simple silicon device which has interesting performances (60 ps resolution in single-photon timing, and low dark count rate (less than 10³ pps at room temperature)) is described. Possible applications are discussed and experimental results are reported (measurements of fast fluorescent decays, and optical time-domain reflectometry in optical fibers with 1 cm resolution). Relations between the device performance and physical phenomena are considered. Criteria are derived for designing and implementing SPAD devices with improved performances. Possible new structures are presented and evaluated.