Polarization properties of retroreflecting right-angle prisms

The cumulative retardance Delta(t) introduced between the p and the s orthogonal linear polarizations after two successive total internal reflections (TIRs) inside a right-angle prism at complementary angles phi and 90 degrees - phi is calculated as a function of phi and prism refractive index n. Quarter-wave retardation (QWR) is obtained on retroreflection with minimum angular sensitivity when n=(sqr rt 2+1)(1/2)=1.55377 and phi =45 degrees. A QWR prism made of N-BAK4 Schott glass (n=1.55377 at lambda=1303.5 nm) has good spectral response (<5 degrees retardance error) over the 0.5-2 microm visible and near-IR spectral range. A ZnS-coated right-angle Si prism achieves QWR with an error of < +/- 2.5 degrees in the 9-11 microm (CO(2) laser) IR spectral range. This device functions as a linear-to-circular polarization transformer and can be tuned to exact QWR at any desired wavelength (within a given range) by tilting the prism by a small angle around phi =45 degrees. A PbTe right-angle prism introduces near-half-wave retardation (near-HWR) with a < or =2% error over a broad (4< or =lambda< or =12.5 microm) IR spectral range. This device also has a wide field of view and its interesting polarization properties are discussed. A compact (aspect ratio of 2), in-line, HWR is described that uses a chevron dual Fresnel rhomb with four TIRs at the same angle phi =45 degrees. Finally, a useful algorithm is presented that transforms a three-term Sellmeier dispersion relation of a transparent optical material to an equivalent cubic equation that can be solved for the wavelengths at which the refractive index assumes any desired value.     

Achromatic angle-insensitive infrared quarter-wave retarder based on total internal reflection at the Si-SiO2 interface

An achromatic infrared (lambda = 1.2-4 microm), Si-prism quarter-wave retarder (QWR) is described that uses total internal reflection at a buried Si-SiO2 interface at an angle of incidence phi near 33 degrees, where deltaDelta/deltaphi = 0. The retardance delta deviates from 90 degrees by < +/- 2 degrees within a field of view of +/- 10 degrees (in air) over the entire bandwidth. Because the SiO2 layer at the base of the prism is optically thick, this QWR is unaffected by environmental contamination.     

Embedded centrosymmetric multilayer stacks as complete-transmission quarter-wave and half-wave retarders under conditions of frustrated total internal reflection

A centrosymmetric multilayer stack of two transparent materials, which is embedded in a high-index prism, can function as a complete-transmission quarter-wave or half-wave retarder (QWR or HWR) under conditions of frustrated total internal reflection. The multilayer consists of a high-index center layer sandwiched between two identical low-index films with high-index-low-index bilayers repeated on both sides of the central trilayer, maintaining the symmetry of the entire stack and constituting a QWR (Delta(t)=90 degrees or 270 degrees ) or HWR (Delta(t)=180 degrees ) in transmission. A QWR design at wavelength lambda=1.55 microm is presented that employs an 11-layer stack of Si and SiO(2) thin films, which is embedded in a GaP cube prism. The intensity transmittances for the p and s polarizations remain >99% and Delta(t) deviates from 90 degrees by <+/-3 degrees over a 100 nm spectral bandwidth (1.5< or =lambda< or =1.6 microm), and by < or =+/-7 degrees over an internal field view of +/-1 degrees (incidence angle 44 degrees < or = phi(0)< or =46 degrees inside the prism). An HWR design at lambda=1.55 microm employs seven layers of Si and SiO(2) thin films embedded in a Si cube, has an average transmittance >93%, and Delta(t) that differs from 180 degrees by <+/-0.3 degrees over a 100 nm bandwidth (1.5< or =lambda< or =1.6 microm) and by <+/-17 degrees over an internal field view of +/-1 degree . The sensitivity of these devices to film-thickness errors is also considered.     

Wide-angle, high-extinction-ratio, infrared polarizing beam splitters using frustrated total internal reflection by an embedded centrosymmetric multilayer

A centrosymmetric multilayer stack of two transparent thin-film materials, which is embedded in a high-index prism, is designed to function as an efficient polarizer or polarizing beam splitter (PBS) under conditions of frustrated total internal reflection over an extended range of incidence angles. The S(LH)(k)LHL(HL)(k)S multilayer structure consists of a high-index center layer H sandwiched between two identical low-index films L and high-index-low-index bilayers repeated (k times) on both sides of the central trilayer maintaining the symmetry of the entire stack. For a given set of refractive indices, all possible solutions for the thicknesses of the layers that suppress the reflection of p-polarized light at a specified angle, and the associated reflectance of the system for the orthogonal s polarization, are determined. The angular and spectral sensitivities of polarizing multilayer stacks employing 3, 7, 11, 15, and 19 layers of BaF(2) and PbTe thin films embedded in a ZnS prism, operating at lambda=10.6 microm, are presented. The 15- and 19-layer stack designs achieve extinction ratios (ER) >30 dB in both reflection and transmission over a 46 degrees -56 degrees field of view inside the prism. Spectral analysis reveals additional discrete polarizing wavelengths other than the design wavelength (lambda=10.6 microm). The 11-, 15-, and 19-layer designs function as effective s-reflection polarizers (|R(s)|(2)>99%) over a 2-3 microm bandwidth. The effect of decreasing the refractive index contrast between the H and L layers on the resulting ER is also considered.     

Wavelength, temperature, and voltage dependent calibration of a nematic liquid crystal multispectral polarization generating device

Rapid calibration of liquid crystal variable retarder (LCVR) devices is critical for successful clinical implementation of a LC-based Mueller matrix imaging system being developed for noninvasisve skin cancer detection. For multispectral implementation of such a system, the effect of wavelength (lambda), temperature (T), and voltage (V) on the retardance (delta) required to generate each desired polarization state needs to be clearly understood. Calibration involves quantifying this interdependence such that for a given set of system input variables (lambda,T), the appropriate voltage is applied across a LC cell to generate a particular retardance. This paper presents findings that elucidate the dependence of voltage, for a set retardance, on the aforementioned variables for a nematic LC cell: approximately 253 mV/100 nm lambda-dependence and approximately 10 mV/ degrees CT-dependence. Additionally, an empirically derived model is presented that enables initial voltage calibration of retardance for any desired input wavelength within the calibration range of 460-905 nm.     

Infrared broadband 50%-50% beam splitters for s-polarized light

Prisms and slabs made of high-refractive-index materials such as ZnSe, Ge, and Si can be designed as broadband, 50%-50%, beam splitters (BSs) for obliquely incident s- polarized light in the near- and mid-IR. The beam-splitting face of the prism or slab is uncoated, while the exit face is antireflection coated. The split beams travel in orthogonal directions when light is incident at the Brewster angle. A novel design is also described that uses Brewster-angle reflection at the SiO2-Si interface to achieve a 50%-50%s-polarization BS over the 1.2-3.5 microm spectral range. Such s-polarization BSs are particularly suited for interferometry and holography.     

Mid-infrared diffused planar waveguides made of silver halide chloro-bromide

We have developed waveguides for the mid-IR spectrum using silver halide crystals. Diffused planar waveguides constructed from silver chlorobromide (AgClBr) with different diffusion thicknesses were designed and characterized. The waveguides were based on our changing the refractive index of the guiding layer by a diffusion of Br- ions into crystalline AgCl substrates. The waveguides were analyzed and investigated with a 10.6-microm CO2 laser, and the optically measured thicknesses of the waveguides were found to vary between 65 and 600 microm. The propagation losses were in the range of 4-16 dB/cm, and the maximal entrance angle was 62 degrees. The output beam distribution was measured and was in good correlation with a numerical analysis simulation based on a ray-tracing model, by use of the eikonal equation.     

Design and performance of a stable linear retarder

The National Institute of Standards and Technology (NIST) has developed a nominally quarter-wave linear retarder for wavelengths near 1.3 mum that is stable within +/-0.1 degrees retardance over a range of wavelength, input angle, temperature, and environmental variations. The device consists of two concatenated Fresnel rhombs made from a low stress-optic-coefficient glass that minimizes the residual birefringence from machining and packaging. Device machining, assembly, and antireflection coating tolerances are discussed, and the theoretical performance is compared with measurements. Humidity can modify retardance of the total-internal-reflection surfaces; we discuss packaging that mitigates this effect and provides an estimated 10-year lifetime for the device. Several measurement methods were intercompared to ensure that the device retardance can be measured with an uncertainty less than 0.1 degrees . Similar retarders will be certified by NIST and made available as Standard Reference Materials.     

Polarizing properties of embedded symmetric trilayer stacks under conditions of frustrated total internal reflection

An all-transparent symmetric trilayer structure, which consists of a high-index center layer coated on both sides by a low-index film and embedded in a high-index prism, can function as an efficient polarizer or polarizing beam splitter under conditions of frustrated total internal reflection over a wide range of incidence angles. For a given set of refractive indices, all possible solutions for the thicknesses of the layers that suppress the reflection of either the p or s polarization at a specified angle, as well as the reflectance of the system for the orthogonal polarization, are determined. A 633 nm design that uses a MgF2-ZnS-MgF2 trilayer embedded in a ZnS prism achieves an extinction ratio (ER) > 40 dB from 50 degrees to 80 degrees in reflection and an ER > 20 dB from 58 degrees to 80 degrees in transmission. IR polarizers that use CaF2-Ge-CaF2 trilayers embedded in a ZnS prism are also considered.     

Near-field microscopy by elastic light scattering from a tip

We describe ultraresolution microscopy far beyond the classical Abbe diffraction limit of one half wavelength (lambda/2), and also beyond the practical limit (ca. lambda/10) of aperture-based scanning near-field optical microscopy (SNOM). The 'apertureless' SNOM discussed here uses light scattering from a sharp tip (hence scattering-type or s-SNOM) and has no lambda-related resolution limit. Rather, its resolution is approximately equal to the radius a of the probing tip (for commercial tips, a < 20 nm) so that 10 nm is obtained in the visible (lambda/60). A resolution of lambda/500 has been obtained in the mid-infrared at lambda = 10 microm. The advantage of infrared, terahertz and even microwave illumination is that specific excitations can be exploited to yield specific contrast, e.g. the molecular vibration offering a spectroscopic fingerprint to identify chemical composition. S-SNOM can routinely acquire simultaneous amplitude and phase images to obtain information on refractive and absorptive properties. Plasmon- or phonon-resonant materials can be highlighted by their particularly high near-field signal level. Furthermore, s-SNOM can map the characteristic optical eigenfields of small, optically resonant particles. Lastly, we describe theoretical modelling that explains and predicts s-SNOM contrast on the basis of the local dielectric function.     

Optical properties of reactively sputtered TeOx amorphous films

We report on the linear optical properties of TeOx films deposited by radio-frequency reactive sputtering on fused-silica substrates. The oxygen stoichiometry ranges from x = 1.95 to x = 2.75, as experimentally determined by Rutherford backscattering. The complex dielectric function of TeOx samples has been measured in the range from lambda = 260 nm to lambda = 1700 nm by variable angle spectroscopic ellipsometry. All samples are transparent in the visible and near infrared. Regarding the refractive index measured at lambda = 1.5 microm, delta n variations from 0.5% to 7% were found, with the general trend monotonically decreasing with respect to the oxygen content. This opens the possibility to easily implement TeOx-based multilayer structures, with a fine tuning of the index, which could be of particular interest for applications in optical communications.     

Phase retarders highly insensitive to the input angle

In the few exceptional cases of total internal reflection phase retarders that are weakly sensitive to variations in the input angle of incidence i, the devices are of increasingly larger size; deviate or translate the emergent beam; are difficult to align in optical systems; or, in coated rhombs, have an impermanent stability of the retardance. Based on new compensating effects, novel devices of high retardance stability and advantageous characteristics are presented. One device is stable to within 0.09 degrees of 90 degrees for i ? 3 degrees . It is a two-reflection quarter-wave retarder that does not alter the path of the compact size light beam, is of compact size (one seventh the size occupied by the achromatic device AD-1 for equal aperture lengths), and can be easily aligned in optical systems or used as a rotating element. The path length of the beam inside the device is less than one third the corresponding length inside the achromatic device AD-1.     

Real-time and full-field detection of near-wall salinity using surface plasmon resonance reflectance

An idea of real-time and full-field detection of near-wall salinity is presented to use the surface plasmon resonance (SPR) reflectance that changes with refractive index variations of the tested saline fluid. The laboratory-designed SPR system, based on the Kretschmann's configuration, uses a 47.5 nm thick gold layer as the SPR resonator, coated on a BK7 prism (n=1.515), and requires a one-time system calibration to establish a correlation of the specified saline mass concentration levels to the corresponding CCD (charge-coupled device) pixel gray levels. As a gravity-falling saline drop in water reaches the bottom and diffuses thereafter, the SPR system quantitatively maps the evolution of the salinity distributions in the near-wall region (less than 1 microm). An elaborate uncertainty analysis shows that the overall measurement uncertainties critically depend on the uniformity of the metal film thickness and the accuracy of its dielectric constant.     

Angular range for reflection of p-polarized light at the surface of an absorbing medium with reflectance below that at normal incidence.

The range of incidence angle, 0 < phi < phi(e), over which p-polarized light is reflected at interfaces between transparent and absorbing media with reflectance below that at normal incidence is determined. Contours of constant phi(e) in the complex plane of the relative dielectric constant epsilon are presented. A method for determining the real and imaginary parts of the complex refractive index, epsilon(1/2) = n + jk, which is based on measuring phi(e) and the pseudo-Brewster angle phi(pB), is viable in the domain of fractional optical constants, n, k < 1.     

Optimization of holographic storage with modulated recording beams in a thick polyvinyl alcohol/acrylamide photopolymer

In a holographic photopolymer system, the storage properties were often limited due to the attenuation in depth of light during the recording step. To obtain smaller values of the depth attenuation profiles in 1 mm thick polyvinyl alcohol/acrylamide (PVA/acrylamide) photopolymers, we used a triangle prism, sitting one face tilted at 13.7 degrees to the axis within the focus of a lens, to modulate the distribution of recording beams. Doing this permitted larger refractive index modulation depth to be achieved, and larger dynamic range (M#=9.2) was obtained in the PVA/acrylamide photopolymers.     

Complex reflection coefficients for the parallel and perpendicular polarizations of a film-substate system

The complex reflection coefficients Rv(phi,zeta) of a film-substrate system for the parallel (v = p) and perpendicular (v = s) polarizations are examined in detail as functions of the angle of incidence phi(0 相似文献   

Quenches of formvar - coated NbTi/Cu caused by step input in power

We have investigated the stability of the composite Nb48Ti/Cu coated with a formvar layer (30 μm thick). Starting from thermal equilibrium in the superfluid liquid He II range below the lambda temperature (T = Tλ), the composite temperature is found to rise first monotonically with time t, upon onset of energy dissipation. However, restricted stability is visible as a relative temperature maximum (Tmax) of the composite at the time tmax, followed by a relative minimum in T at tmin. These coated composite phenomena are similar to stability conditions of bare composites in the same "conductor-in-box " geometry employed. However at a specified power the times tmaxand tminare shifted in comparison to the bare composite. Diagnosis is based on power-time functions whose tangents are characterized by power law exponents (m) . The m-values found are re - presentative of strong, localized solid - coolant interaction, of a caloric condition, or of locally turbulent fluid motion. In the range covered by the present transients, stability is available by creation of entropy - rich buffer domains of fluid, below the superconducting transition temperature, between He II and the heated composite. The latter is quench - protected in an intermediate power range.     

Lipid bilayer microarray for parallel recording of transmembrane ion currents

This paper describes a multiwell biochip for simultaneous parallel recording of ion current through transmembrane pores reconstituted in planar lipid bilayer arrays. Use of a thin poly(p-xylylene) (parylene) film having micrometer-sized apertures (phi=15-50 microm, t=20 microm) led to formation of highly stable bilayer lipid membranes (BLMs) for incorporation of transmembrane pores; thus, a large number of BLMs could be arrayed without any skillful technique. We optically confirmed the simultaneous formation of BLMs in a 5x5 matrix, and in our durability test, the BLM lasted more than 15 h. Simultaneous parallel recording of alamethicin and gramicidin transmembrane pores in multiple contiguous recording sites demonstrated the feasibility of high-throughput screening of transmembrane ion currents in artificial lipid bilayers.     

A New Method for Spectral Performance Evaluation of a Chromatic and Achromatic Quarter-Wave Retarder

When a polarized polychromatic beam passes through a quarter-wave retarder, the constituent spectral components suffer different changes in the state of polarization. As a result, when the beam passes through an analyzer, the intensity of the resultant beam changes, depending on the orientation of the analyzer, state of polarization of the input beam, spectral and spatial intensity distribution of the source and the wavelength-dependent retardance of the quarter-wave retarder. The intensity variation of the resulting beam is theoretically and experimentally observed, with the variation of the azimuthal angle of the analyzer for film-type chromatic and prism-type achromatic quarter-wave retarders. The spectral performances of achromatic retarders are generally evaluated by measuring retardances at discrete wavelengths by using a monochromatic beam of light over the wavelength range of interest. In this study, a simple method is used for computing the fractional nonlinear polarization (FNLP) from theoretically and experimentally obtained intensity variations for evaluating the spectral performance of both achromatic and chromatic quarter-wave retarders operating over a broad spectral range in the visible region using a polychromatic beam of light. FNLP variation is also shown for a film-type chromatic quarter-wave retarder using a monochromatic source of light. The experimentally obtained values are compared with theoretical values and a good agreement is observed. The applications of the method for the performance evaluation of quarter-wave retarders are discussed.     

Optical excitation of surface plasma waves in an indium film bounded by dielectric layers

The method of attenuated total reflection (ATR) was used to excite optically surface plasma waves (SPWs) in thin indium films. Three successive layers of MgF₂/In/MgF₂ were evaporated onto the base of a glass prism which had a high refractive index. Continous thin films of indium were obtained by maintaining the substrate at liquid nitrogen temperature during deposition. The ATR angular spectra and associated resonant oscillations were studied at three different wavelengths in the visible region and good agreement was obtained between the experimental and the calculated spectra. The symmetric SPW of the indium film was more highly attenuated than the antisymmetric SPW. Owing to the high damping of the plasma in indium only the antisymmetric SPW could be excited via an optical reflectance resonance when the indium slab was isolated by thick dielectric layers. With thinner bounding dielectrics two SPW-type resonances were observed. Complete calculations of the magnetic field oscillations within the variousmedia, as well as calculations of the current distributions and surface charge densities of the indium film, showed resonant oscillations of mixed symmetry.