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An optical sensor for the dual sensing of oxygen (Osub2/sub) and carbon dioxide (COsub2/sub) based on sensing films coated on filter paper is proposed. Ethyl cellulose (EC) doped with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and 7-amino-4-trifluoromethyl coumarin serve as the oxygen sensing material and reference blue emission dye for the pH indicator, respectively. The COsub2/subsensing layer includes the pH-sensitive fluorescent indicator 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt immobilized within the EC. The Osub2/sub- and COsub2/sub-sensitive materials can both be excited with a 405 nm LED, and the two emission wavelengths can be detected separately. The experimental result reveals that the optical Osub2/suband COsub2/subsensors have sensitivities of IsubNsub2/sub/sub/Isub100%Osub2/sub/sub=22.8 and IsubNsub2/sub/sub/Isub100%COsub2/sub/sub=3.6, respectively. The response times of the optical Osub2/subsensor were 15 s upon switching from nitrogen to Osub2/suband 41 s when moving from Osub2/subto nitrogen (Nsub2/sub). The response times of the optical COsub2/subsensor were 7 s upon switching from 100% Nsub2/subto 100% COsub2/suband 39 s when moving from 100% COsub2/subto 100% Nsub2/sub. The proposed optical dual sensor can be used for the simultaneous sensing of Osub2/suband COsub2/subconcentrations in environmental applications.

In this paper, we show that laser speckle analysis (LSA) can provide valuable information about the structure of crumpled thin sheets. Crumpling and folding of slender objects are present in several phenomena and in various ranges of size, e.g., paper compaction, cortical folding in brains, DNA packing in viral capsids, and flower buds, to name a few. The analysis of laser speckles, both numerical and graphical, is a source of information about the activity of biological or non-biological materials, and the development of digital electronics, which brought the ease of image processing, has opened new perspectives for a spectrum of LSA applications. LSA is applied on randomly crumpled and one-, two-, and three-times folded papers, and appreciable differences in LSA parameters are observed. The methodology can be applied for easy-to-implement quantitative assessment of similar phenomena and samples.

Quantifying the coloration and luminous transmittance of eyewear filters is essential to understand their impact on human visual performance. Accurate measurements require the use of a spectrophotometer, with such equipment often being prohibitively expensive for wide-scale use. This paper details a new technique to characterize eyewear filters using only a digital camera and a sheet of white paper. Images of the paper are captured with and without the filter in front of the camera lens, and then subsequent analysis of pixel intensities allows the filter coloration and luminous transmittance to be determined. The technique has been applied to six different eyewear filters using three different camera and illumination configurations, demonstrating a reasonable match to the spectrophotometer data. This technique is suited to implementation in a smartphone app, in order to provide a low-cost and widely deployable solution to monitor the ageing of eyewear inventory.

We present a low-cost terahertz wave plate based on form birefringence fabricated using ordinary paper. Measurements of the transfer function of the wave plate between polarizers closely agree with predictions based on the measured complex indices of refraction of the effective medium. For the design frequency, the dependence on wave plate angle also agrees with theory.

We explore the application of terahertz spectroscopic techniques for the remote determination of the water content of paper. The aim is the development of a rapid diagnostic imaging tool applicable in paper fabrication processes. THz radiation offers a high sensitivity for water, a good spatial resolution, and insensitivity to scattering at the paper surface. The advent of THz cameras makes fast large-area image detectors feasible. In this paper, we show for the case of a 0.6-THz fixed-frequency system, that the water content of paper can be determined with high accuracy. We demonstrate a quantitative (calibrated) method for determining the moisture content in paper based on extinction and phase measurements in the lower THz range with a spatial resolution in the mm-range and scanning times below two minutes.

We present a disposable low cost paper-based metamaterial for sensing liquids based on their dielectric properties. The sensor is based on resonance shift due to the change in the effective capacitance of each resonator in the metamaterial array. Key novelty in the design is the implementation of metamaterial on low cost and ubiquitous paper substrate. This metamaterial-on-paper sensor is fabricated in a totally cleanroom-free process using wax printing and screen printing. Wax patterning of paper enables creation of microfluidic channels such that liquid analytes can be delivered to each metamaterial unit cell for sensing. Screen printing is used to implement disc shaped resonator unit cells. We demonstrate sensing of liquids: Oil, methanol, glycerol and water each showing an average resonance frequency shift of 1.12 (9.6%), 4.12 (35.4%), 8.76 (75.3%) and 11.63 GHz (100%) around the center frequency of around 94 GHz respectively. Being label-free, this approach can be expanded to sense other liquids based on their dielectric constants.

Editor-in-Chief Ron Driggers explains the standards that must be met by a simulation paper in order to be peer reviewed for publication in Applied Optics.

Editor-in-Chief Ron Driggers details the Applied Optics policy of not considering papers that have been rejected twice by OSA journals.

Applied Optics Editor Ron Driggers explains the new policy for considering expanded conference papers in OSA journals.

In this work pulse generation in both the 1.5 and 2 μm spectral ranges using a graphene oxide (GO)-paper-based saturable absorber in Er- and Tm-doped fiber lasers is presented. The article describes the fabrication method of GO paper and its characterization. The performance of both lasers is discussed in detail. Stable, mode-locked operation provides 613 fs and 1.36 ps soliton pulses centered at 1565.9 and 1961.6 nm in Er- and Tm-doped fiber lasers, respectively. Furthermore, scaling of spectral width, and hence the pulse duration, by increasing the number of GO paper layers in the Er-doped laser is described. The versatility and simplicity of GO paper fabrication combined with the possibility of scaling the optical spectrum full width at half-maximum are essential features that make it a good candidate for ultrafast low-power mode-locked lasers operating in different spectral regions.

In situ ablation of thin metal films on fused silica substrates by picosecond class lasers was investigated as a method of characterizing the beam at the sample plane. The technique involved plotting the areas enclosed by constant fluence contours identified in optical microscope images of the ablation sites versus the logs of the pulse energies. Inconel films on commercially available neutral density filters as well as magnetron sputtered gold films were used. It was also shown that this technique could be used to calibrate real-time beam profile diagnostics against the beam at the sample plane. The contours were shown to correspond to the boundary where part or all of the film was ablated.

The objective of this work was to establish the relationship between the calculated subsurface scattered-photon distribution and the mathematical quantity known as point-spread function (PSF). Photon distribution of subsurface scattered light was calculated using the Monte Carlo method developed for describing reflectance and opacity of paper and of images printed on paper. The obtained normalized photon distribution made it possible to separate optical and mechanical components of dot gain for the paper-ink system. In the presented method of obtaining the reflectance profile of a screen element, the PSF convolves with a modelled reflectance profile of that element. It was found that the PSF can be better approximated by means of the Lorentzian function when compared to the Gaussian profile that was used in the past research on this topic.

Edge mis-figure is regarded as one of the most difficult technical issues for manufacturing the segments of extremely large telescopes, which can dominate key aspects of performance. A novel edge-control technique has been developed, based on 'Precessions' polishing technique and for which accurate and stable edge tool influence functions (TIFs) are crucial. In the first paper in this series [D. Walker Opt. Express 20, 19787-19798 (2012)], multiple parameters were experimentally optimized using an extended set of experiments. The first purpose of this new work is to 'short circuit' this procedure through modeling. This also gives the prospect of optimizing local (as distinct from global) polishing for edge mis-figure, now under separate development. This paper presents a model that can predict edge TIFs based on surface-speed profiles and pressure distributions over the polishing spot at the edge of the part, the latter calculated by finite element analysis and verified by direct force measurement. This paper also presents a hybrid-measurement method for edge TIFs to verify the simulation results. Experimental and simulation results show good agreement.

When a transparency printed with a first halftone color is deposited on top of a paper printed with a second halftone color, we obtain a third color that we are able to predict in both reflectance and transmittance modes, thanks to a spectral prediction model. The model accounts for the multiple reflections of light between the printed paper and the printed transparency, which are themselves described by specific reflectance and transmittance models, each one being calibrated using a small number of printed colors. The model can account for light scattering by the inks. The measuring geometry and the orientations of light in the transparency are taken into account on the basis of radiometric rules and geometrical optical laws. Experimental testing carried out from several inkjet-printed CMY halftones shows fairly good agreement between predictions and measurements.

Passive terahertz (THz) setups require optical elements with large diameters for optimal harvesting of weak signals. High f-number implies sophisticated aspheric designs to ensure optimal resolution and good energetic efficiency. Trial and error testing of such optics is expensive and numerical modeling is time consuming; hence, we propose extremely cheap diffractive lenses for THz made of regular paper. They are easy to manufacture even with large diameters, and the optical function can be easily customized, which can be used for initial experimental testing of THz setups. Characterization of the proposed diffractive lenses with time-domain spectroscopy is presented and discussed.

Segment-edges for extremely large telescopes are critical for observations requiring high contrast and SNR, e.g. detecting exo-planets. In parallel, industrial requirements for edge-control are emerging in several applications. This paper reports on a new approach, where edges are controlled throughout polishing of the entire surface of a part, which has been pre-machined to its final external dimensions. The method deploys compliant bonnets delivering influence functions of variable diameter, complemented by small pitch tools sized to accommodate aspheric mis-fit. We describe results on witness hexagons in preparation for full size prototype segments for the European Extremely Large Telescope, and comment on wider applications of the technology.

The measurement of the bonded area of pulp fibers has been an unsolved issue in paper science for more than 40 years. By the use of an established pulp fiber model, and a 4 × 4 transfer matrix formalism we simulated the optical behavior of pulp fibers in a modified imaging ellipsometer, and we demonstrate that there are rather strong symmetries in the ellipsometric angles Ψ and Δ when comparing single fibers, unbonded fiber crossings, and fiber-fiber bonds. Based on these symmetries we propose and test an algorithm that allows to distinguish the three cases (single fibers, unbonded fiber crossings, and fiber-fiber bonds) in the analysis of ellipsometric data.

We have used Laser Speckle Contrast Imaging (LSCI) to investigate the statistical properties of dynamic speckle reflected from an obscuring scattering surface in order to reveal drawings that are hidden beneath. Here we explore the limitations of this method used with various algorithms when applied to a selection of paper samples. These samples consist of a sketch executed in an assortment of media laid on a base surface that are then hidden beneath a subsequent top layer. The ability to resolve gray scale images was examined as well as the contrast surface temperature relationship. A book with glued pages was investigated in order to demonstrate the technique's applicability to the non-destructive examination of cultural materials. While being shown as a useful tool in revealing obscured drawings the scattering properties of the surface layer present a limitation in its general applicability.

International audience; We show that conventional paper can be cut using a 1W laser diode, provided the cutting lines are first traced using a proper ink. The ink should absorb the laser light, and penetrate deep into the paper. An " invisible ink " that is transparent in the visible range and absorbing in the infrared has been successfully tested. The paper is tidily cut. The laser power required to cut the paper is proportional to the displacement speed of the paper. Cutting speeds exceeding 3 cm.s-1 .W-1 have been demonstrated. At higher speeds, the paper is not cut through, but easy-tearable lines and easy-folding lines are obtained. The whole inking and laser cutting process may be integrated into next generations of personal inkjet printers and expand document creation abilities.

A long plasma channel, formed due to the dynamic balance between the nonlinear self-focusing and the plasma defocusing in the propagation of intense femtosecond laser pulses in air, is demonstrated to be able to continuously propel a paper airplane without complicated focusing optics. The maximum coupling coefficient generated by the plasma channel is found to be more than 8.5 dyne/W. In the plasma channel, the detonation wave generation with the air ionization is found to be the propulsive source.

A critical factor that affects the appearance of printed paper surfaces is gloss uniformity, which is usually assessed visually. To relate gloss uniformity to nonvisual quantities, we first visually identified areas of either high or low gloss on the same sample for two different types of paper. We then measured the roughness and the reflectance of these areas. Microroughness was measured with an atomic-force microscope, and roughness was measured over a larger area with a confocal laser scanning microscope. The local reflectance of the high-gloss and the low-gloss areas was obtained from images taken with a gloss-imaging instrument and compared with the roughness of each area. This correlation is nonlinear, and roughness is insufficient to predict the local reflectance. Light-scattering measurements were made in the specular direction to map the gloss uniformity over larger areas than was possible with the gloss-imaging instrument. These maps were used to show the possibility of using both the spatial frequency and the fan filters, which together form a set of cortex filters, to analyze the variation of the gloss about the mean value and its spatial distribution on the surface in terms of spatial frequency and azimuthal orientation.

Over the past several years, metamaterials have been introduced and rapidly been adopted as a means of achieving unique electromagnetic material response. In metamaterials, artificially structured—often periodically positioned—inclusions replace the atoms and molecules of conventional materials. The scale of these inclusions is smaller than that of the electromagnetic wavelength of interest, so that a homogenized description applies. We present a homogenization technique in which macroscopic fields are determined via averaging the local fields obtained from a full-wave electromagnetic simulation or analytical calculation. The field-averaging method can be applied to homogenize any periodic structure with unit cells having inclusions of arbitrary geometry and material. By analyzing the dispersion diagrams and retrieved parameters found by field averaging, we review the properties of several basic metamaterial structures. © 2006 Optical Society of America OCIS codes: 160.0160, 160.1190, 260.2110, 350.5500.

A simplified stochastic model for the fiber structure of paper is introduced. The packing density and optical thickness of the fiber network are derived analytically, and their dependence on fiber characteristics can be seen. We undertake a Monte Carlo simulation of light scattering that is based on geometrical optics, using a realization of the model, which gives packing densities and optical thicknesses well in accordance with those given by the stochastic model and the scattering quantities as functions of three angles.

A method for time-resolved recording of light scattering in thin, highly scattering media is described. Subpicosecond pulses from a high-power Ti:sapphire laser are used, and single-shot recordings of the scattered light are made with a fast streak camera. The method is applied to the study of light scattering in paper, and a 1-ps resolution is demonstrated. The dependence of the light scattering on the basis of weight and density of the paper has been studied. A white-light continuum generated from the high-power pulses by the use of self phase modulation in water is used to study the wavelength dependence of the scattering process. A model for the propagation of light in paper has been developed and used in Monte Carlo simulations. The experimental results are used for testing this model, and absorption and scattering parameters are determined from that comparison.

The application of angle-resolved light scattering (ARLS) to the measurement of the surface roughness of glossy coatings on paper was investigated. To this end, ARLS patterns were measured for laser light scattered from several glossy paper samples, and these patterns were compared with those calculated using a theoretical model based on plane-wave scattering from an isotropic rough surface. Mechanical stylus profilometry data for the rms roughnesses and the autocorrelation functions of the coatings were used as input to calculate the patterns. For all the paper samples measured, as well as for all the incidence angles used, there was good agreement between the experimental and the calculated patterns when all the rms roughnesses measured by profilometry were reduced by 30%. The indication from these experiments is that ARLS may be used to determine the roughness parameters of the coatings. As a check on these results, measurements were also performed with a commercial optical surface probe; these data agreed well with both the ARLS and the stylus profilometry results.

Arend and Reeves [J. Opt. Soc. Am. A 3, 1743 (1986)] described measurements of color constancy in computer simulations of arrays of colored papers of equal Munsell value under 4000-, 6500-, and 10,000-K daylight illuminants. We report an extension of those experiments to chromatic arrays spanning a wide range of Munsell values. The computer-simulated scene included a standard array of Munsell papers under 6500-K illumination and a test array, an identical array of the same papers under 4000 or 10,000 K. Observers adjusted a patch in the test array in order to match the corresponding patch in the standard array by one of two criteria. They either matched hue and saturation or they made surface-color matches, in which the test patch was made to "look as if it were cut from the same pice of paper as the standard patch." The test and the standard patches were surrounded by a single color (annulus display) or by many colors (Mondrian display). The data agreed with those of our previous equal-value experiment. The paper matches were often approximately color constant. The hue-saturation matches were in the correct direction for constancy but were always closer to a chromaticity match (no constancy) than to the chromaticity required for hue-saturation constancy.

An equation to describe the granularity of an electrophotographic imaging system has been developed to include the density variance attributed to the reflectance of paper and toner surfaces. Granularity measurements from two conventional electrophotographic copiers were used to validate the relationship. The results show good agreement with the overall shape of the granularity-versus-density curve; however, the values are not consistent with estimated toner particle size. Clustering of the toner particles is suggested as the cause of the high granularity values.

Glossiness ranking of photographic paper samples by observers was found to have a slightly higher correlation with gloss measurement at 2212° and 45° than at 75°. The magnitude of a usually just noticeable gloss difference was determined.

Both sector photometer and microphotometer analyses were carried out on the Hg spectrum transmitted by papers popularly used as window materials in Chinese homes. The intensity distribution of transmitted radiation, after normal incidence, through samples of twelve different kinds of paper has been studied, and the total transmission calculated for various wavelengths. The total transmission of visible light (4354A) ranges from 38 percent to 72 percent, and of ultraviolet light (2967A) from 16 percent to 41 percent for the papers studied. Oiling the papers with vegetable oil (“tung yu”) increases the transmission by about 50 percent, at the same time narrowing the distribution curve and strengthening the paper against the effects of moisture.

The recording and measurement of wavelengths shorter than about 3300A has generally involved the use of equipment to isolate this region, such as quartz spectrographs and photoelectric meters, The present work has resulted in photosensitive papers that respond only to the shorter wave ultraviolet and thus provide materials for recording and measuring this region with the ease of a photographic printing out process. The basis of the new papers lies in the activation of triphenylmethane dye cyanides so that they will react to ultraviolet with the formation of the associated dyes. Activators have been found that produce photosensitive mixtures suitable for use on paper. The sensitized papers print out fully formed, permanent images. Materials are described that are sensitive to 3250A and shorter and to 3350A and shorter wavelengths but are quite unaffected by sunlight through such a colorless glass as Corning No. 7380. Actinometers may be prepared to measure the short wave ultraviolet output of lamps, the erythemal component of sunlight and dosages of therapeutic ultraviolet. Another use for the papers is in recording instruments where a beam of ultraviolet may be employed to trace a line on the moving paper, which is fully visible behind a window of colorless ultraviolet-absorbing glass.

This article is a review of a reprint of the 1890 commemoration edition of The Scientific Papers of James Clerk Maxwell (Dover Publications, Inc., New York), $12.50. Vol. 1, 607 pp.; Vol.2, 806 pp. One hundred and one of Maxwell's shorter papers, articles, speeches, and reviews on electricity and magnetism, the dynamical theory of gases, theory of light, color vision and other optical problems, elastic solids, molecular physics, etc., are in this reprint; his longer treatises on electricity and magnetism, heat, and matter and motion are not included. This review is illustrated with photographs from the Maxwell family archives which have not been published before.

A brief summary is given of the paper by Stiles. The line-element suggested by Stiles is shown to be the sum of the squares of total differentials of three magnitudes. Therefore, the corresponding color threefold is Euclidean. For the same reason, the line-element originally proposed by Helmholtz also defined a Euclidean color space. The customary parameters of colorimetry correspond to curvilinear coordinates in the color space of both Helmholtz and Stiles. In both of those spaces, constant luminosity is represented by curved surfaces. The forms of the line-elements of both Helmholtz and Stiles imply that geodesics, representing series of colors which exhibit the least number of just-perceptible differences between any two colors, are straight lines in the Euclidean spaces defined by those line-elements. They also imply that ordinary length measured along these lines is proportional to the number of just-perceptible differences between the colors represented by the terminal points. No direct tests of these implications are known. MacAdam’s data on the discrimination of equiluminous colors determine a surface of constant luminosity in the color discrimination space for at least one observer (PGN). This surface exhibits such severe (and irreducible) curvature that the straight lines drawn between most pairs of considerably different equiluminous colors are, at their midpoints, far from the surface of constant luminosity. The line-elements of both Stiles and Helmholtz, therefore, imply that the series of colors exhibiting the least number of just-perceptible differences between two equiluminous colors includes many colors of very different luminosity. Although no observational tests are known, it seems unreasonable to expect that considerable departures from the common luminosity of the terminal colors will reduce the number of differences perceptible in any series between them. Attention is called to the criterion of probability of errors in color matching as an alternative to just-perceptible differences for investigations of visual sensitivities to color differences. This concept leads to a definition of the line-element independently of any assumption of the applicability to color discrimination of Fechner’s law or its modifications.

Writing tests were made on commercial Electrofax paper using an all glass thin window cathode ray tube. Developed line widths from 5 mil to 15 mil could be obtained by varying beam current. Writing speeds of up to 790,000 in./sec were achieved. Electron beam current appeared to vary linearly with writing speed.

The equation relating dot area to half-tone density, when sideways scattering of light takes place in the paper, has been modified to take into account multiple internal reflections. Curves showing the relationship between dot area and density for various ink densities and amounts of first-surface reflectance are given. Callahan’s conclusion that these effects are negligible is not in accordance with the authors’ experience, and the new equations indicate the possibility of densities much higher than the limiting values derived from Callahan’s equations and from our earlier equation which neglected multiple internal reflectance.

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