Polarization Aberration Effects Propagated in Optical Systems

Abstract

The propagation and imaging of polarized light through optical systems described by a polarization aberration expansion is treated by combining a scalar operator calculus with the Jones calculus. The martrix-operator framework provides a means for handling diffraction and propagation in optical systems containing polarization aberrations. An expansion for the polarization aberration function of an optical system, similar to the expansion of the wavefront aberration function into defocus, tilt, piston, and higher-order terms, is analysed. These polarization aberration terms introduce phase changes in the diffraction image proportional to the first and second derivatives of the non-polarization aberrated image structure.     

Simulation of an active underwater imaging through a wavy sea surface

A numerical simulation for underwater imaging through a wavy sea surface has been done. We have used a common approach to model the sea surface elevation and its slopes as an important source of image disturbance. The simulation algorithm is based on a combination of ray tracing and optical propagation, which has taken to different approaches for downwelling and upwelling beams. The nature of randomly focusing and defocusing property of surface waves causes a fluctuated irradiance distribution as an illuminating source of immersed object, while it gives rise to a great disturbance on the image through a coordinate change of image pixels. We have also used a modulation transfer function based on Well’s small angle approximations to consider the underwater optical properties effect on the transferring of the image. As expected, the absorption effect reduces the light intensity and scattering decreases image contrast by blurring the image.     

Correction of optical phase aberrations using binary-amplitude modulation

We show that phase aberrations in an imaging system can be mitigated using binary-amplitude masks that reduce destructive interference in the image spatial frequency domain. Appropriately designed masks increase the magnitude of the optical transfer function and prevent nulls. This offers a low-cost, transmission-mode alternative to phase correction as used in active and adaptive optics, without a restriction on the waveband of operation.     

A Proposal to Classify Methods Employed to Detect Thin Phase Structures Under Coherent Illumination

Since the phase contrast function can be identified in a unique manner in terms of its even and odd components, these can be used to compare and classify the methods employed for detecting thin phase structures. It is shown that under coherent illumination, the methods may be conveniently classified into symmetric and antisymmetric bandpass filters. Simple diagrams are used to analyse the filtering effects that these filters have over the spatial filtering content of the image irradiance. Furthermore, this treatment can be used when designing new methods or when selecting a method for detection of thin phase structures. Several examples are analysed and two new Schlieren techniques are suggested.     

High-definition imaging system based on spatial light modulators with light-scattering mode

We have developed a prototype high-definition imaging system using polymer-dispersed liquid-crystal (PDLC) light valves, which can modulate unpolarized light with high spatial resolution and exhibit a high optical efficiency, based on the light-scattering effect. We fabricated high-definition light valves with a fine polymer-matrix structure in a PDLC film by controlling the curing conditions used during the photopolymerization-induced phase separation and formation process. This device has excellent characteristics, such as a high resolution, with 50 lp/mm for a limiting resolution and greater than 20 lp/mm at the 50% modulation transfer function point, and a reflectivity of greater than 60%. An optically addressable full-color projection display was designed, consisting of three PDLC light valves, a schlieren optical system based on shift-decentralization optics with a xenon lamp illumination and input-image sources with 1.5 million pixels, including electrical image compensation of the gamma characteristics. We succeeded in displaying pictures on a 110-inch screen with a resolution of 810 TV lines and a luminous flux of 1900-2100 American National Standards Institute lumens.     

Ultrathin Planar Cavity Metasurfaces

An ultrathin planar cavity metasurface is proposed based on ultrathin film interference and its practicability for light manipulation in visible region is experimentally demonstrated. Phase of reflected light is modulated by finely adjusting the thickness of amorphous silicon (a‐Si) by a few nanometers on an aluminum (Al) substrate via nontrivial phase shifts at the interfaces and interference of multireflections generated from the planar cavity. A phase shift of π, the basic requirement for two‐level phase metasurface systems, can be accomplished with an 8 nm thick difference. For proof of concept, gradient metasurfaces for beam deflection, Fresnel zone plate metalens for light focusing, and metaholograms for image reconstruction are presented, demonstrating polarization‐independent and broadband characteristics. This novel mechanism for phase modulation with ultrathin planar cavity provides diverse routes to construct advanced flat optical devices with versatile applications.     

Irradiance inversion theory to retrieve volume scattering function of seawater

An attempt to retrieve the volume scattering function (VSF) of source-free and no-inelastic-scattering ocean water is made from the upwelling irradiance Eu and downwelling irradiance Ed. It will be shown, from the radiative transfer equation, that the VSF of seawater can be calculated by the planar irradiances when the scattering phase function of the suspended particles in the backward direction and the molecular VSF are known. On the derivation of the hydrosol VSF, several optical properties such as the absorption coefficient a; the scattering coefficients of hydrosol, b, b(f), b(b) and those of the suspended particles, b(p), b(fp), b(bp); the beam attenuation coefficient c; the average cosines mu, mu(d), and mu(u); and the backscattering shape factor for the downwelling light stream, r(du), will also be obtained. On the derivation of those optical parameters, classical knowledge related to interrelationships between inherent optical properties and apparent optical properties and obtained with Monte Carlo numerical simulations is analytically verified. The present theory can be applied to surface waters and any wavelengths, except for waters and wavelengths with an extremely low b(b)/a ratio.     

Nondestructive measurement of an optical fiber refractive-index profile by a transmitted-light differential interference contact microscope

A novel transmitted-light differential interference contrast (DIC) system is used for nondestructive measurement of the refractive-index profile (RIP) of an optical fiber. By means of this system the phase of a measured light beam can be modulated with an analyzer, and the phase distribution of a fiber is obtained by calculation of the various interference patterns. The measurement theory and structure and some typical applications of this system are demonstrated. The results of measuring RIPs in graded-index fiber are presented. Both the experimental results and theoretical analysis show that the system takes the advantage of high index resolution and of sufficient measurement accuracy for measuring the refractive index of the optical fiber. The system has strong ability to overcome environmental disturbance because of its common-path design. Moreover, one can use the system to measure the RIP along the fiber axis and acquire an image of the three-dimensional RIP of the fiber.     

Modeling of a slit-scan-type aerial image measurement sensor used for optical lithography

Theoretical modeling of a slit-scan-type aerial image measurement sensor used for optical lithography is presented. Slit transmission properties are fully represented by the slit transfer function in terms of incident and scattering angles of light, which is then incorporated into the scheme of a partially coherent imaging formula to obtain an expression for image profiles measured by slit scanning. As an exemplary case, we analyze the influence of a 100 nm width slit used in an ArF lithography system. To understand the mechanism of image profile changes by slit transmission, we focus on frequency transfer characteristics of sinusoidal patterns.     

Solar spectral irradiometer for validation of remotely sensed hyperspectral data

A new solar spectral irradiometer that operates in the visible and near-infrared spectral ranges has been developed. This instrument takes advantage of a new concept optical head that collects the light that impinges on a hemispheric surface, thus improving the instrument angular response with respect to traditional devices. The technical characteristics of the instrument are investigated and detailed, and its radiometric calibration, performed by means of a Langley-like method, is discussed. A new simplified theoretical model that accounts for the diffuse irradiance observed in an optically thin plane-parallel atmosphere has been developed to improve the fit of the irradiance diurnal evolution. An alternative polynomial parametric representation of monochromatic diffuse irradiance evolution has been attempted, but satisfactory results were not obtained from the fitting of experimental data. The new instrument could be useful to carry out remote-sensing validation campaigns.     

Fast, automatically darkening welding filter offering an improved level of safety

A mode of operation is introduced for the standard 90° twisted nematic (TN) liquid-crystal cell when placed together with an interference filter and positioned between crossed polarizers such that a small stimulating voltage of between ±2.0 and ±13.0 V is required in order to attain the light state. Further incrementation of the driving electronics reverts the system back to a darker phase. Such cells offer advantages over those of the standard 90° TN device operating in the normally white mode, in that the unit maintains the fast response time from the light to the dark state associated with the employment of TN cells placed between crossed polarizers. In addition, a low transmittance state is achieved when the unit is in the inactivated phase; this is an effect usually correlated with the normally black mode of operation. These cells are therefore ideal candidates for incorporation into fast, automatically darkening, welding filters that are designed to change rapidly from the light to the dark protective state, while offering an improved level of safety by not holding in a potentially hazardous light state should the controlling electronics malfunction. The requirement for this phenomenon to be observed is that the cell displays a low optical transmittance over the green wavelengths of the visible spectrum when in the inactivated phase and placed between crossed polarizers. The presence of an interference filter that possesses a peak transmittance over the central part of the visible spectrum is also necessary. It is shown that there are only two possible cell types that satisfy this criteria, and the optical properties of such cells are analyzed in some detail.     

Real Time,in situ Observation of the Photocatalytic Destruction of Saccharomyces cerevisiae Cells by Palladium-modified Nitrogen-doped Titanium Oxide Thin Film

Palladium-modified nitrogen-doped titanium oxide(TiON/PdO) thin film was synthesized by the ion-beamassisted deposition technique,which enabled a heavy nitrogen doping and the subsequent light absorption extension to ~700 nm for a better usage of the solar spectrum.Based on TiON/PdO thin film and a phase contrast microscope,a micro-reaction chamber was developed,which allowed the simultaneous optical excitation of the photocatalytic thin film and the phase contrast image observation of cells in it.The real time,in situ observation of the photocatalytic destruction of Saccharomyces cerevisiae(S.cerevisiae),an essential eukaryotic unicellular model of living cells,was conducted with this new observation technique,which demonstrated clearly that the photocatalytic destruction effect was much stronger than the photodamage effect caused by the visible light irradiation alone in the disinfection process.     

SNAPSHOTS

The late twentieth century development in digital imaging technologies has led to claims that we are in the midst of both a transformation of representation and a reconfiguration of vision. This essay considers the ways in which photography's structural reliance on light has shaped our understanding of representation, and the ways in which that understanding might be extended and reshaped through the digital imaging technologies of ultrasound, MRI and CT. Operating through a sonic and haptic mediation of the body, these imaging technologies cannot be contained within the realm of light, vision and visible reality. As such, they bring into play an alternative reading of the ways in which reality may be imaged — an alternative which calls upon touch as much as sight in determining the referentiality and indexicality of an image and its relationship to the real. The indexicality of photography is premised on light's “magical transfer” of the real into representation. Harboured within this understanding of the photograph's relation to the referent is a desire for a material, haptic contact with that reality. Is light the only possible agent of the “magical transfer” between reality and representation? Or can indexicality and referentiality be refounded within a tactile relation, based not on light's transcendent illumination, but on the physical contact between the world and its image?     

Modified channeled spectrum for fast measurement of thin films

A simple and effective technique for the simultaneous measurement of the refractive index and the thickness of thin films is proposed. The method is based on the spectral dependence of the visibility of interference fringes that result from thin-film interference when the film is illuminated with a white light. The film is on the special substrate, and an optical contact is provided between them. The measurement consists of finding the local change of the fringes' visibility in the observed channeled spectrum expressed as the seaming change of the fringes' periodicity. The method can be applied for real time optical inspection during the manufacturing of thin polymer films.     

Extended depth of field through wave-front coding

We designed an optical-digital system that delivers near-diffraction-limited imaging performance with a large depth of field. This system is the standard incoherent optical system modified by a phase mask with digital processing of the resulting intermediate image. The phase mask alters or codes the received incoherent wave front in such a way that the point-spread function and the optical transfer function do not change appreciably as a function of misfocus. Focus-independent digital filtering of the intermediate image is used to produce a combined optical-digital system that has a nearly diffraction limited point-spread function. This high-resolution extended depth of field is obtained through the expense of an increased dynamic range of the incoherent system. We use both the ambiguity function and the stationary-phase method to design these phase masks.     

Coherent use of opposing lenses for axial resolution increase. II. Power and limitation of nonlinear image restoration

We analyze the ability of nonlinear image restoration to remove interference artifacts in microscopes that enlarge the axial optical bandwidth through coherent counterpropagating waves. We calculate the images of an elaborate test object as produced by confocal, standing-wave, incoherent illumination interference image interference, and 4Pi confocal microscopes, and we subsequently investigate the extent to which the initial object can be restored by the information allowed by their optical transfer function. We find that nonlinear restoration is successful only if the transfer function is sufficiently contiguous and has amplitudes well above the noise level, as is mostly the case in a two-photon excitation 4Pi confocal microscope.     

Optical systems under broad-band illumination: Analysis based on a wigner distribution function approach

Abstract

The irradiance produced by an optical imaging system suffering from aberrations under broad-band illumination is analysed in the phase-space domain of the Wigner distribution function associated with a modified one-dimensional pupil aperture. To this end, a coordinate transformation is employed in such a way that the varying irradiance along different paths in the image space can be derived from different slices of the Wigner distribution function, which involve both the defocus distance and the dispersion properties of the optical system. The method is illustrated by comparing the axial irradiance distribution for different primary aberrations. Also, the irradiance along parabolic paths is obtained in order to analyse the coma effect.     

On the relationship between radiance and irradiance: determining the illumination from images of a convex Lambertian object

We present a theoretical analysis of the relationship between incoming radiance and irradiance. Specifically, we address the question of whether it is possible to compute the incident radiance from knowledge of the irradiance at all surface orientations. This is a fundamental question in computer vision and inverse radiative transfer. We show that the irradiance can be viewed as a simple convolution of the incident illumination, i.e., radiance and a clamped cosine transfer function. Estimating the radiance can then be seen as a deconvolution operation. We derive a simple closed-form formula for the irradiance in terms of spherical harmonic coefficients of the incident illumination and demonstrate that the odd-order modes of the lighting with order greater than 1 are completely annihilated. Therefore these components cannot be estimated from the irradiance, contradicting a theorem that is due to Preisendorfer. A practical realization of the radiance-from-irradiance problem is the estimation of the lighting from images of a homogeneous convex curved Lambertian surface of known geometry under distant illumination, since a Lambertian object reflects light equally in all directions proportional to the irradiance. We briefly discuss practical and physical considerations and describe a simple experimental test to verify our theoretical results.     

Evaluation of optical properties of decorative coatings by spectroscopic ellipsometry

Some of the hard coatings (e.g. TiN, TiCN, TiCN, TiAlCN) occur in different colours. Using goniospectroscopy in the visible wavelength range colours are deduced by measuring the spectral reflectance factor R_λ. This factor depends on both the samples and the white reference as well as on the geometry of illumination and measurement. It is very difficult or even impossible to distinguish colours according to their origin and to relate them to bulk material composition, thin film coatings and interference layers by means of goniospectroscopy as unpolarized light is used. By using polarized light in spectroscopic ellipsometry these difficulties could be overcome as there is no reference to white and the geometric influences of illumination and measurement are negligible, but on the contrary the visual impression is not correctly described. From the measurement of the relative amplitude ratio tan Ψ and the relative phase shift cos Δ it is possible to calculate either the parallel and normal components R_p and R_s of the reflectivity R or the complex refractive index N = n + ik as well as the dielectric function = ₁ + i₂ which are strongly related to the electronic structure of the material used. It is shown that in this way it is possible to describe optical properties more physically, to separate interference effects and to detect changes in stoichiometry.     

Imaging through Nonlinear Metalens Using Second Harmonic Generation

The abrupt phase change of light at metasurfaces provides high flexibility in wave manipulation without the need for accumulation of propagating phase through dispersive materials. In the linear optical regime, one important application field of metasurfaces is imaging by planar metalenses, which enables device miniaturization and aberration correction compared to conventional optical microlens systems. With the incorporation of nonlinear responses into passive metasurfaces, optical functionalities of metalenses are anticipated to be further enriched, leading to completely new application areas. Here, imaging with nonlinear metalenses that combine the function of an ultrathin planar lens with simultaneous frequency conversion is demonstrated. With such nonlinear metalenses, imaging of objects with near infrared light while the image appears in the second harmonic signal of visible frequency range is experimentally demonstrated. Furthermore, the functionality of these nonlinear metalenses can be modified by switching the handedness of the circularly polarized fundamental wave, leading to either real or virtual nonlinear image formation. Nonlinear metalenses not only enable infrared light imaging through a visible detector but also have the ability to modulate nonlinear optical responses through an ultrathin metasurface device while the fundamental wave remains unaffected, which offers the capability of nonlinear information processing with novel optoelectronic devices.