Showing papers on "Physical optics published in 2000"

Phase‐Sensitive X‐Ray Imaging

Abstract: The basic principles of x‐ray image formation and interpretation in radiography have remained essentially unchanged since Rontgen first discovered x rays over a hundred years ago. The conventional approach relies on x‐ray absorption as the sole source of contrast and draws exclusively on ray or geometrical optics to describe and interpret image formation. This approach ignores another, potentially more useful source of contrast—phase information. Phase‐sensitive techniques, which can be understood using wave optics rather than ray optics, offer ways to augment or complement standard absorption contrast by incorporating phase information.

Propagation-induced polarization changes in partially coherent optical beams

Abstract: Propagation of a partially coherent optical beam inside a linear, nondispersive, dielectric medium is studied, taking into account the vector nature of the electromagnetic field. Propagation-induced polarization changes are studied by using the Gaussian-Schell model for the cross-spectral-density tensor. The degree of polarization changes with propagation and also becomes nonuniform across the beam cross section. The extent of these changes depends on the coherence radius associated with the cross-correlation function. For optical beams with symmetric spectra, the bandwidth of the source spectra is found to play a relatively minor role.

Optical phase space, Wigner representation, and invariant quality parameters.

Abstract: Wigner’s quasi probability and related functional and operator methods of quantum mechanics have recently played an important role in optics. We present an account of some of these developments. The symmetry structures underlying the ray and wave approaches to paraxial optics are explored in some detail, and the manner in which the Wigner phase-space representation captures the merits of both approaches is brought out. A fairly self-contained analysis of the second or intensity moments of general astigmatic partially coherent beams and of their behavior under transmission through astigmatic first-order optical systems is presented. Geometric representations of the intensity moments that render the quality parameters or polynomial invariants manifest are discussed, and the role of the optical uncertainty principle in assigning unbeatable physical bounds for these invariants is stressed. Measurement of the ten intensity moments of an astigmatic partially coherent beam is considered.

Reconstruction and assessment of the least-squares and slope discrepancy components of the phase.

Abstract: The concept of slope discrepancy developed in the mid-1980’s to assess measurement noise in a wave-front sensor system is shown to have additional contributions that are due to fitting error and branch points. This understanding is facilitated by the development of a new formulation that employs Fourier techniques to decompose the measured gradient field (i.e., wave-front sensor measurements) into two components, one that is expressed as the gradient of a scalar potential and the other that is expressed as the curl of a vector potential. A key feature of the theory presented here is the fact that both components of the phase (one corresponding to each component of the gradient field) are easily reconstructable from the measured gradients. In addition, the scalar and vector potentials are both easily expressible in terms of the measured gradient field. The work concludes with a wave optics simulation example that illustrates the ease with which both components of the phase can be obtained. The results obtained illustrate that branch point effects are not significant until the Rytov number is greater than 0.2. In addition, the branch point contribution to the phase not only is reconstructed from the gradient data but is used to illustrate the significant performance improvement that results when this contribution is included in the correction applied by an adaptive optics system.

Measurement Theory and General Relativity

Abstract: The theory of measurement is employed to elucidate the physical basis of general relativity. For measurements involving phenomena with intrinsic length or time scales, such scales must in general be negligible compared to the (translational and rotational) scales characteristic of the motion of the observer. Thus general relativity is a consistent theory of coincidences so long as these involve classical point particles and electromagnetic rays (geometric optics). Wave optics is discussed and the limitations of the standard theory in this regime are pointed out. A nonlocal theory of accelerated observers is briefly described that is consistent with observation and excludes the possibility of existence of a fundamental scalar field in nature.

Experimental validation of surface scattering and emission models

Abstract: Multifrequency polarimetric scattering and emissivity measurements have been carried out on three experimental dielectric models, characterized by random surfaces with different statistics. The results of the measurements have been compared with simulations obtained through physical models based on the classical approximations of physical optics (PO), geometrical optics (GO), small perturbation (SP), and integral equation model (IEM). The comparison of experimental data with theory has shown that, even when the parameters of the observed surface are well determined and known, some discrepancy may exist between models and measurements. Except for a few cases, this discrepancy is quite small and may be insignificant for many practical applications. The IEM has been proven to have a wider range of applicability with respect to other tested approximations.

Focusing of electromagnetic waves by paraboloid mirrors. I. Theory

Abstract: We derive a solution to the problem of a plane electromagnetic wave focused by a parabolic mirror. The solution is obtained from the Stratton-Chu integral by solving a boundary-value problem. Our solution can be considered self-consistent. We also derive the far-field, i.e., Debye, approximation of our formulas. The solution shows that when the paraboloid is infinite, its focusing properties exhibit a dispersive behavior; that is, the structure of the field distribution in the vicinity of the focus strongly depends on the wavelength of the illumination. We show that for an infinite paraboloid the confinement of the focused energy worsens, with the energy distribution spreading in the focal plane. 2000 Optical Society of America [S0740-3232(00)01309-0] OCIS codes: 260.0260, 260.2110, 050.1960, 260.5430.

Experimental challenges in fullerene interferometry

Abstract: We discuss the experimental challenges in coherent matter wave optics with fullerenes. In particular, the properties of our matter wave source and the features of our efficient, molecule-selective detector with high spatial resolution are presented. Their development was crucial for the successful recording of the molecular quantum interference patterns of individual molecules.

Phasing the primary mirror segments of the Keck telescopes: a comparison of different techniques

Abstract: We have developed and tested extensively three different methods for phasing the primary mirror segments of the Keck telescopes. Two of these, referred to as the broadband and narrowband algorithms respectively, are physical optics generalizations of the Shack-Hartmann technique. The third, Phase Discontinuity Sensing, is a physical optics generalization of curvature sensing. We evaluate and compare experimental results with these techniques with regard to capture range (as large as 30 micrometers ), run-to-run variation (as small as 6 nm), execution time (as short as twenty minutes), systematic errors, ease of implementation, and other factors, in the context of the Keck telescopes and also of future very large ground-based telescopes.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Insertion Devices for Synchrotron Radiation and Free Electron Laser

Abstract: An introduction to the theory of charged particle transport generalities on synchrotron radiation generalities on free electron lasers optical systems in the geometrical and wave optics framework Wigner distribution and synchrotron radiation sources synchrotron radistion sources, insertion devices and beam current limitations constructing and measuring insertion devices free electron lasers as insertion devices synchrotron radiation beam lines - X-ray optics.

Comparative analysis of absorbance calculations for integrated optical waveguide configurations by use of the ray optics model and the electromagnetic wave theory.

Abstract: Focusing on the use of planar waveguides as platforms for highly sensitive attenuated total reflection spectroscopy of organic thin films, we extend the ray optics model to provide absorbance expressions for the case of dichroic layers immobilized on the waveguide surface. Straightforward expressions are derived for the limiting case of weakly absorbing, anisotropically oriented molecules in the waveguide–cladding region. The second major focus is on the accuracy of the ray optics model. This model assumes that the introduction of absorbing species, either in the bulk cladding or as an adlayer on the waveguide surface, only causes a small perturbation to the original waveguide-mode profile. We investigate the accuracy of this assumption and the conditions under which it is valid. A comparison to an exact calculation by use of the electromagnetic wave theory is implemented, and the discrepancy of the ray optics model is determined for various waveguide configurations. We find that in typical situations in which waveguide-absorbance measurements are used to study organic thin films (kl/nl ≤ 10-1, h/λ ≈ 10-2) the discrepancy between the ray optics and the exact calculations is only a few percent (2–3%).

Diffraction from a truncated grounded dielectric slab: a comparative full-wave/physical-optics analysis

Abstract: The problem of diffraction at the edge of a semi-infinite grounded dielectric slab excited by a line source is investigated. This canonical problem may be used as a reference solution in the high-frequency regime for patch antennas radiating from a finite grounded slab. Both physical optics (PO) and integral equation (IE) approaches are used and compared. The PO formulation is cast in a convenient asymptotic form that neatly describes the diffraction processes associated with the various wave species. The IE, solved by the method of moments, is formulated by enforcing the continuity of the electric field on an infinite aperture orthogonal to the slab. This allows a drastic reduction of unknowns, provided that appropriate entire domain basis functions are used that are shaped to match the asymptotic behavior of the aperture field. Comparison between the PO and IE solutions is presented to determine the range of validity of PO.

Shaped double-shell dielectric lenses for wireless millimeter wave communications

Abstract: The main drawbacks of homogeneous dielectric lenses are the internal reflections at the lens surface, and eventually the size (typically 10-20 /spl lambda/ diameter, 5-10 /spl lambda/ depth), despite the millimeter wavelengths. This paper shows that these drawbacks can be alleviated in a shaped double-shell dielectric lens antenna. An example of a double-material lens is discussed in terms of the radiation patterns, internal reflection losses, and frequency behaviour. Geometric optics (GO) formulation is used at the first design step, and physical optics (PO) is used to obtain the actual radiation pattern. The synthesis method has been generalised for the case where two refracting interfaces are considered. An important target for millimetre wave wireless applications is the shaped elevation pattern that ideally compensates for the free-space loss in each observation direction within a cell. This corresponds to a sec/sup 2//spl theta/ radiation pattern, and it is adopted as the target pattern in the example included. Appropriate design further allows for some control of the cell spillover.

Mode structure and ray dynamics of a parabolic dome microcavity

Abstract: We consider the wave and ray dynamics of an electromagnetic field in a parabolic dome microcavity. The structure of the fundamental s wave involves a main lobe in which the electromagnetic field is confined around the focal point in an effective volume of the order of a cubic wavelength, while modes with finite angular momentum have a structure that avoids the focal area and have correspondingly larger effective volumes. The ray dynamics indicate that the fundamental s wave is robust with respect to small geometrical deformations of the cavity, while the higher order modes are unstable, giving rise to optical chaos. We discuss the incidence of these results on the modification of the spontaneous emission dynamics of an emitter placed in such a parabolic dome microcavity.

Optical Traps as Force Transducers: The Effects of Focusing the Trapping Beam through a Dielectric Interface

Abstract: The use of optical forces generated by a focused laser beam for manipulating single polymer chains and colloidal particles has begun to receive increasing attention in polymer and colloid science and in biophysics. Devices based on such optical traps are increasingly used for probing the elasticity of single polymer chains and for studying the structure and mechanical behavior of biopolymers and their relation to biological activity. Colloidal forces and viscoelastic behavior of the suspending fluids can also be examined through the use of optical traps as force transducers and from the dynamics of optically bound probe particles. Such applications require a precise understanding of the trap potential and its dependence on the distance between the trap center and the glass/liquid interfaces that exist in experimental arrangements. This paper addresses some of the issues relevant to the above class of applications of optical traps using wave optics calculations. It is shown that the use of simple geometric...

Phase-space interferences as the source of negative values of the Wigner distribution function

Abstract: It is shown that the negative values of the Wigner distribution function in classical optics are a consequence of the phase-space interference among the Gaussian beams into which an arbitrary light distribution (or a superposition of light distributions) can be decomposed. These elementary Gaussian beams partition the phase space in wave optics in adjacent, interacting, finite-area cells, in contrast to geometrical optics, where the phase space is continuous and a light beam can be decomposed into a number of perfectly localized, non-interacting rays.

Experimental study of the surface waves on a dielectric cylinder via terahertz impulse radar ranging

Abstract: Employing an ultrafast optoelectronic terahertz impulse radar range with subpicosecond resolution, we have characterized the electric-field time-domain response from an impulsively excited dielectric cylinder The bandwidth of the measurement extends from 200 GHz to 14 THz and late time response is observed at times exceeding that to traverse 40 target radii at c A physical optics (PO) model is employed to identify the different mechanisms of scattering for the temporally isolated signals Through analysis of the first and second surface-wave signals it is determined that the surface wave has a propagation velocity of 091c and an effective index of refraction of n=110+0073i The first measurement of the coupling efficiency of this surface wave through the cylinder via an interior chord at the critical angle is performed along with the determination of the /spl pi//2 phase shift associated with the single axis caustic of this interior chord in the PO model

Polarizer–analyzer optics

Abstract: The principles behind the design and operation of polarization‐based optics for nuclear resonant scattering of synchrotron radiation are discussed. With perfect single crystals and collimated X‐rays emitted from undulator‐based third‐generation synchrotron radiation sources, polarization‐selective optics with a sensitivity of parts per billion can be obtained. A general approach to optical activity is introduced, and the polarization dependence of the index of refraction is calculated for nuclear forward scattering for a medium with unidirectional symmetry. Some recent experimental results are reviewed and future applications are discussed.

Optical kicked system exhibiting localization in the spatial frequency domain

Abstract: An optical kicked system with free-space light propagation along a sequence of equally spaced thin phase gratings is presented and investigated. We show, to our knowledge for the first time in optics, the occurrence of the localization effect in the spatial frequency domain, which suppresses the spreading of diffraction orders formed by the repeated modulation by the gratings of the propagating wave. Resonances and antiresonances of the optical system are described and are shown to be related to the Talbot effect. The system is similar in some aspects to the quantum kicked rotor, which is the standard system in the theoretical studies of the suppression of classical (corresponding to Newtonian mechanics) chaos by interference effects. Our experimental verification was done in a specific regime, where the grating spacing was near odd multiples of half the Talbot length. It is shown that this corresponds to the vicinity of antiresonance in the kicked system. The crucial alignment of the gratings in-phase positioning in the experiment was based on a diffraction elimination property at antiresonance. In the present study we obtain new theoretical and experimental results concerning the localization behavior in the vicinity of antiresonance. The behavior in this regime is related to that of electronic motion in incommensurate potentials, a subject that was extensively studied in condensed matter physics.

Simple formulas for the calculation of the average physical optics RCS of a cylinder and a flat plate over a symmetric window around broadside

Abstract: Closed-form formulas for the arithmetic-average radar cross section (RCS) of a perfectly conducting cylinder and of a perfectly conducting rectangular plate are derived The derivations proceed under the assumption that the conditions governing the use of the physical optics approximation are satisfied Examination of the behavior of these formulas reveals simple approximations of very reasonable accuracy The approximations allow quick and easy evaluation of dynamically collected RCS data in which the scattering phenomenology can be modeled by either a cylinder or a rectangular plate

Wave-optics applications in charged-particle-beam transport

Abstract: An overview of electron wave-optics applications to charged-particle-beam transport is presented in the context of the thermal wave model (TWM). The quantization of the electron optics is presented both in the configuration space and in the phase space. The former provides a description in terms of the Schrodinger-like equation for a complex function whose squared modulus is proportional to the transverse density profile. The latter provides a phase-space description in terms of a von Neumann-type equation for a sort of Wigner function. The main results concerning the Gaussian electron optics, including the theory of coherent states for charged-particlle beams and the beam transport through optical devices with multipole aberrations, such as sextupoles and octupoles, are reviewed within the above wave-like framework. In particular, some investigations concerning luminosity estimates in linear colliders as well as comparisons between the TWM results and the standard tracking simulations, recently discussed in the literature, are summarized. Finally, a fresh tomographic technique to study the beam transport in both the classical-like and quantum-like domains in terms of a marginal distribution, fully similar to the one used in quantum optics, is reviewed. In particular, a comparison between the beam Wigner function and the beam marginal distribution is presented.

Recent Trends in the Analysis of Quasioptical Systems

Abstract: The recent trend in microwave instruments is the use of multiple millimeter and submillimeter wavelength bands. These systems are typically analyzed by using physical optics, Gaussian beams or ray tracing techniques. Physical optics offers high accuracy at the expense of computation time. This trade-off becomes particularly apparent in the analysis of multiple reflector antennas, such as beam waveguide antennas, where physical optics is used to compute the current on each reflector from the current on the previous reflector. At the other end of the spectrum is ray tracing approaches that ignore diffraction effects entirely. These methods are fast but sacrifice the ability to predict some effects accurately. An intermediate approach is to use an appropriate set of expansion functions to model the field between the reflectors. If the set is chosen wisely only a few coefficients need to be determined from each reflector current. The field is then computed at the next reflector through the use of the expansion functions and their coefficients rather than by using the previous reflector current. For a beam waveguide system with no enclosing tubes an excellent set of expansion functions is the Gaussian beam mode set. In many cases a preliminary design which includes the effects on diffraction may be obtained by considering only the fundamental mode and a thin lens model for the reflectors. Higher-order modes are included to model the effects of the curved reflector, which include asymmetric distortion of the beam, cross polarization, and beam truncation. This paper describes a computer code implementing higher-order Gaussian beam scattering by multiple reflector systems. There are four essential steps in the algorithm. (1) Compute the current on the first reflector using physical optics using either a feed model or by an incident set of Gaussian beam modes. (2) Find the direction of propagation for the reflected Gaussian beam-set using ray tracing. (3) Determine the waist size and location for the output beam set by examining the amplitude and phase distribution of the current on the reflector. (4) Compute the amplitudes of the individual modes in the output mode set. These steps are then repeated for each addition reflector in the chain. In each of these cases the previous Gaussian beam set provides the input field for the current calculation. Details of the four steps discussed above will be discussed. Examples will compare results from the Gaussian beam approach to pure physical optics, illustrating both its merits and limitations. Hybrid approaches capable of eliminating some of the limitations will also be discussed.

Electromagnetic scattering by nonplanar junctions of resistive sheets

Abstract: Approximate uniform asymptotic expressions are provided to determine the field scattered by a penetrable wedge illuminated at normal incidence. The wedge is formed by two resistive sheets or two thin dielectric slabs definable as resistive sheets having identical geometric and electromagnetic characteristics. The solution is limited to wedge angles and source positions where internal reflections cannot occur. It is obtained by using a geometrical optics (GO) approximation for the field internal to the slabs and by performing a uniform asymptotic evaluation of the physical optics (PO) radiation integral in the hypothesis that a resistive sheet condition is valid. Samples of numerical results so obtained are presented and compared with other methods to demonstrate the effectiveness of the proposed technique.

PO near-field expression of a penetrable planar structure in terms of a line integral

Abstract: An exact line integral representation of the physical optics (PO) field scattered in the near zone by a penetrable planar structure illuminated by a plane wave is discussed.

Radiation patterns of sources placed near the truncation of a semi-infinite dielectric structure: the demonstration case of a magnetic line current

Abstract: Numerical methods are presented to estimate the radiation pattern of a magnetic line current placed near the truncation of a dielectric structure. The problem is solved using the integral equation technique, expansion wave concept, and physical optics approximation. The comparison between different methods permits to understand better the possibilities of each of the methods.

Exact geometrical optics solution for an isorefractive wedge structure

Abstract: A structure consisting of four right-angle wedges with a common edge, made of four different materials isorefractive to one another is considered. If a certain relation is satisfied among the four intrinsic impedances of the materials, then an incident plane wave generates reflected and transmitted plane waves that constitute the exact solution to the boundary-value problem. This geometrical-optics exact solution is valid for arbitrary polarization and arbitrary direction of incidence of the primary wave.

Symmetry approach to reveal hidden coherent structures in quantum optics. General outlook and examples

Abstract: A general invariant-algebraic approach to reveal hidden coherent structures (closed complexes and configurations of states) is developed in quantum-optical models due to symmetry of their HamiltonianH. This approach is based on using the mathematical concept of dual algebraic pairs, incorporating action of both invariance groups and dynamic-symmetry algebras. Its general features are demonstrated on some recent examples: (i)G-invariant biphotons and related invariant treatment of unpolarized light and (ii) quasispin clusters and optical atoms in nonlinear models of quantum optics. The first example leads to a positive solution (within the framework of composite field theory) of the old problem put in polarization optics by Fresnel—the existence of elementary waves of unpolarized light. The second example yields a new mathematical technique for analyzing a wide class of nonlinear problems in quantum optics and laser physics that, in turn, enables one to reveal new coherent effects and phenomena in the process of time evolution of the models under study.

Phase matching in nonlinear χ (2) photonic crystals: errata

Abstract: In Ref. 1: 1. On p. 1204, second column, last paragraph, the formula for k 2 should be k 2 ෇ 2pn 2 ͞l 2. 2. On p. 1205, f irst column, first paragraph, the formula for d should be d ෇ ͑4p͞Dk 2 ͒ ͓͑p 2 1 q 2 1 pq͒͞3͔ 1͞2 , Dk 2 ෇ jk 2 2 2k 1 j .