Optical Research Papers - Academia.edu (original) (raw)

This paper reports on the use of cellulose paper simultaneously as electrolyte, separation of electrodes, and physical support of a rechargeable battery. The deposition on both faces of a paper sheet of metal or metal oxides thin layers... more

This paper reports on the use of cellulose paper simultaneously as electrolyte, separation of electrodes, and physical support of a rechargeable battery. The deposition on both faces of a paper sheet of metal or metal oxides thin layers with different electrochemical potentials, respectively as anode and cathode, such as Cu and Al, lead to an output voltage of 0.70 V and a current density that varies between 150 nA/cm 2 and 0.5 mA/cm 2 , subject to the paper composition, thickness and the degree of OH x species adsorbed in the paper matrix. The electrical output of the paper battery is independent of the electrodes thickness but strongly depends on the atmospheric relative humidity (RH), with a current density enhancement by more than 3 orders of magnitude when RH changes from 60% to 85%. Besides flexibility, low cost, low material consumption, environmental friendly, the power output of paper batteries can be adapted to the desired voltage-current needed, by proper integration. A 3-V prototype was fabricated to control the ON/OFF state of a paper transistor.

The maximum distance to which the secondary mirror can be moved with respect to its primary in a true Cassegrain telescope with limited image deterioration is found to be proportional to the fourth power of the focal ratio of the primary... more

The maximum distance to which the secondary mirror can be moved with respect to its primary in a true Cassegrain telescope with limited image deterioration is found to be proportional to the fourth power of the focal ratio of the primary mirror. This limit is independent of all other parameters describing the system when the magnification of the secondary is greater than about 3.

It is shown that the Fraunhofer diffraction pattern of a tilted aperture screen can be interpreted as a ' monocular view of the Ewald sphere. Two of those patterns recorded at opposite tilting angles are used to give a stereoscopic... more

It is shown that the Fraunhofer diffraction pattern of a tilted aperture screen can be interpreted as a ' monocular view of the Ewald sphere. Two of those patterns recorded at opposite tilting angles are used to give a stereoscopic impression of the Ewald sphere. Experimental results are shown, and the approximations involved are discussed.

An hybrid atomic force-scanning near-field optical microscope (AFM-SNOM) has been realized starting from a home-built AFM. The instrument uses a tetrahedral SiN tip for force and near field detection and is designed to provide, besides... more

An hybrid atomic force-scanning near-field optical microscope (AFM-SNOM) has been realized starting from a home-built AFM. The instrument uses a tetrahedral SiN tip for force and near field detection and is designed to provide, besides simple imaging, a full three-dimensional (3-D) mapping of force, friction and light intensity on the sample. High-resolution optical images of dielectric samples are presented together with curves describing the behavior of the collected optical intensity as a function of tip-object distance. AFM images and forcedistance curves are reported as well and are compared with those obtained from the optical channel. Subwavelength features of the samples can be easily appreciated in both kinds of images, and the refractive index of the object can be computed from the attenuation constant of the tunneling light detected by the tip, with the AFM curve providing a convenient way of detecting the contact point. The spatial resolution of this kind of measurement is far better than that obtainable with any other index-measuring device. Homogeneous glass samples as well as monomode channel waveguides were analyzed in our experiments. The refractive index of several different prisms, made either of BK7 (n = 1:519 at = 532 nm) or of SF58 (n = 1:932) glass, could be measured with our near-field technique. As for the channel waveguides, the accuracy of our measurements lets us detect their presence and lateral extension in the substrate but is not yet sufficient to allow the reconstruction of their index profile.

We have compared different loop buffer switch architectures in terms of their functionality. Some of these architectures have already been proposed with only their description and operation. The performance evaluation of the switches has... more

We have compared different loop buffer switch architectures in terms of their functionality. Some of these architectures have already been proposed with only their description and operation. The performance evaluation of the switches has been done in terms of packet loss probability for random and bursty traffic. A new architecture has been proposed, which incorporates the good features of the existing architectures.

A theory is presented which relates the minimum detectable contrast level for an object in the presence of noise to the statistics of the speckle. Consideration is given to smoothing of the noise by multiple looks and by area.... more

A theory is presented which relates the minimum detectable contrast level for an object in the presence of noise to the statistics of the speckle. Consideration is given to smoothing of the noise by multiple looks and by area. Measurements of the minimum detectable contrast are made for two types of speckle noise. First, a coherent, plane wave is added to an ideal diffuse wave and the threshold of detection is established as a function of the beam ratio. Secondly, these results are compared to the technique of speckle smoothing using an N-fold intensity superposition of fully developed theory is observed.

A theory of the influence of measurement conditions on temperature measurement accuracy with infrared systems has been recently presented. A comparison study of the shortwave 13-5-µm2 and longwave 18-12-µm2 measuring IR cameras was... more

A theory of the influence of measurement conditions on temperature measurement accuracy with infrared systems has been recently presented. A comparison study of the shortwave 13-5-µm2 and longwave 18-12-µm2 measuring IR cameras was conducted on the basis of this theory. The results of the simulations show that the shortwave systems in typical measurement conditions generally offer better accuracy in temperature measurement than do the longwave systems. Some experiments that use a commercially available IR camera were carried out to verify the theory. The results of these experiments and a discussion about the theory limitations are presented.

We model the double phase-conjugate mirror (DPCM) as a function of time, the average direction of propagation of the two beams forming the DPCM, and one transverse coordinate. Calculations show that the conjugation fidelity and... more

We model the double phase-conjugate mirror (DPCM) as a function of time, the average direction of propagation of the two beams forming the DPCM, and one transverse coordinate. Calculations show that the conjugation fidelity and reflectivity have different dependencies on the photorefractive coupling coefficient times length; the fidelity turns on abruptly with a threshold, whereas the reflectivity increases smoothly. The DPCM behaves as an oscillator at and above threshold: the time required for the reflectivity to reach the steady state dramatically slows down near threshold (like critical slowing down in lasers); above threshold the DPCM is self-sustaining even if the random noise terms used to start the process are set to zero. A decrease in the noise level improves the fidelity but increases the response time. The use of unbalanced input beam ratios results in asymmetric conjugation such that the fidelity obtained on the side of the weaker input beam is significantly reduced. The slowing down diminishes with increasing noise level or unbalanced input intensities.

A coherent processor is presented which is capable of performing a large class of 1-D linear space-variant operations. The only components of the processor are a 1-D input, a mask whose transmittance is specified by the desired linear... more

A coherent processor is presented which is capable of performing a large class of 1-D linear space-variant operations. The only components of the processor are a 1-D input, a mask whose transmittance is specified by the desired linear operation, and an output plane. Compared with other 1-D processors, this processor has advantages of real space compactness and total elimination of vignetting. Experimental results are presented for the specific operations of convolution and spectrum scaling.

The possibility of improving the discrimination capability (DO in color pattern recognition is analyzed. In each channel, red, green and blue (R, G, B), a region of support is designed to improve the behavior of the Phase Only Filter... more

The possibility of improving the discrimination capability (DO in color pattern recognition is analyzed. In each channel, red, green and blue (R, G, B), a region of support is designed to improve the behavior of the Phase Only Filter matched to the corresponding component of the target. The procedure of optimization is based on the analytical expressions which give the DC in R, G, B channels, for real valued input scenes. Computer simulation results are presented and discussed.

An experiment to investigate the potential of a laser-induced plasma method for determining concrete compressive strength was conducted by focusing a Nd:YAG laser on concrete samples with different degrees of compressive strength. This... more

An experiment to investigate the potential of a laser-induced plasma method for determining concrete compressive strength was conducted by focusing a Nd:YAG laser on concrete samples with different degrees of compressive strength. This technique was developed in light of the role of the shock wave in the generation of a laser-induced plasma. It was found that the speed of the shock front depends on the hardness of the sample. It was also found that a positive relationship exists between the speed of the shock front and the ionization rate of the ablated atoms. Hence, the ratio of the intensity between the Ca(II) 396.8 nm and Ca(I) 422.6 nm emission lines detected from the laser-induced plasma can be used to examine the hardness of the material. In fact, it was observed that the ratio changes with respect to the change in the concrete compressive strength. The findings also show that the ratio increases with time after the cement is mixed with water.

The wave-splitting phase-shifting digital holography using a pixelated microretarder array is proposed. By using four intensity images recorded by the pixelated microretarder array, Stokes parameters of the incident wave can be... more

The wave-splitting phase-shifting digital holography using a pixelated microretarder array is proposed. By using four intensity images recorded by the pixelated microretarder array, Stokes parameters of the incident wave can be calculated. The fully complex amplitude distribution of the object wave can be obtained by using Stokes parameters, if the polarization states of the object and reference waves are linear and orthogonal. Two sets of experimental results are provided to verify the feasibility of the proposed method. One is the result for a movie recording using a CW laser and the other is the result for instant recording using a single pulsed laser.

An external reflection scanning near-field optical microscope with shear force regulation of the tip-surface distance is described. Near-field optical and shear force topographical images are compared for various samples. It is shown that... more

An external reflection scanning near-field optical microscope with shear force regulation of the tip-surface distance is described. Near-field optical and shear force topographical images are compared for various samples. It is shown that the most important correlative relationships between these images can be deduced from symmetry considerations. The possibility of extracting additional information from the optical images is demonstrated on images of human blood cells.

We present a model of energy consumption in IP networks. Using this model, we identify energy ldquohotspotsrdquo and estimate how energy consumption will grow with increasing network capacity. Todaypsilas Internet uses less than 1% of the... more

We present a model of energy consumption in IP networks. Using this model, we identify energy ldquohotspotsrdquo and estimate how energy consumption will grow with increasing network capacity. Todaypsilas Internet uses less than 1% of the available electricity supply. However, network energy consumption could grow substantially as access rates increase.

By having a single optical element combine the light of several high luminance LEDs, a high luminance light source can be formed, with shape and emission characteristics adaptable to nearly all illumination problems. The illuminance... more

By having a single optical element combine the light of several high luminance LEDs, a high luminance light source can be formed, with shape and emission characteristics adaptable to nearly all illumination problems. The illuminance distribution of this virtual source facilitates the generation of the desired intensity pattern via its imaging-stye projection into the far field. This projection is achieved by one refractive and one reflective freeform surface, both calculated simultaneously by the 3D SMS method, which is herein demonstrated for an LED automotive headlamp.

Next-generation switches and routers may rely on optical switch fabrics to overcome cost, power, space, and scalability problems that arise in sizing traditional electrical backplanes into the terabit regime. However, several... more

Next-generation switches and routers may rely on optical switch fabrics to overcome cost, power, space, and scalability problems that arise in sizing traditional electrical backplanes into the terabit regime. However, several technological and architectural problems must be overcome to be able to use such an approach. The reconfiguration times of optical packet fabrics are longer than those of electronic fabrics. Even though we can relax some of the constraints in switching speed by using appropriate packetization and scheduling mechanisms, we need to adapt optical technology to the needs of packet switching. We present an optical packet fabric design, based on arrayed waveguide gratings and fast wavelength tuning, and present methods for solving the technical problems of fast switching.

Background: Super-resolution optical fluctuation imaging (SOFI) achieves 3D super-resolution by computing temporal cumulants or spatio-temporal cross-cumulants of stochastically blinking fluorophores. In contrast to localization... more

Background: Super-resolution optical fluctuation imaging (SOFI) achieves 3D super-resolution by computing temporal cumulants or spatio-temporal cross-cumulants of stochastically blinking fluorophores. In contrast to localization microscopy, SOFI is compatible with weakly emitting fluorophores and a wide range of blinking conditions. The main drawback of SOFI is the nonlinear response to brightness and blinking heterogeneities in the sample, which limits the use of higher cumulant orders for improving the resolution. Balanced super-resolution optical fluctuation imaging (bSOFI) analyses several cumulant orders for extracting molecular parameter maps, such as molecular state lifetimes, concentration and brightness distributions of fluorophores within biological samples. Moreover, the estimated blinking statistics are used to balance the image contrast, i.e. linearize the brightness and blinking response and to obtain a resolution improving linearly with the cumulant order. Results: Using a widefield total-internal-reflection (TIR) fluorescence microscope, we acquired image sequences of fluorescently labelled microtubules in fixed HeLa cells. We demonstrate an up to five-fold resolution improvement as compared to the diffraction-limited image, despite low single-frame signal-to-noise ratios. Due to the TIR illumination, the intensity profile in the sample decreases exponentially along the optical axis, which is reported by the estimated spatial distributions of the molecular brightness as well as the blinking on-ratio. Therefore, TIR-bSOFI also encodes depth information through these parameter maps. Conclusions: bSOFI is an extended version of SOFI that cancels the nonlinear response to brightness and blinking heterogeneities. The obtained balanced image contrast significantly enhances the visual perception of super-resolution based on higher-order cumulants and thereby facilitates the access to higher resolutions. Furthermore, bSOFI provides microenvironment-related molecular parameter maps and paves the way for functional super-resolution microscopy based on stochastic switching.

Most confocal microscopes do not produce images in real time with nonlaser light sources. The tandem scanning confocal microscope does produce such images but, because the pinhole apertures of the Nipkov disk must be placed far apart to... more

Most confocal microscopes do not produce images in real time with nonlaser light sources. The tandem scanning confocal microscope does produce such images but, because the pinhole apertures of the Nipkov disk must be placed far apart to reduce cross talk between neighboring pinholes, only 1% or less of the light available for imaging is used. We show that, by using aperture correlation techniques and relaxing the requirement to obtain a pure confocal image directly, one can obtain real-time confocal images with a dramatically increased (25% or even 50%) light budget.

The Fraunhofer diffraction pattern of an aperture function, which can be described in terms of the superposition of a known aperture function with a half plane, has an amplitude distribution which is real along one direction and complex... more

The Fraunhofer diffraction pattern of an aperture function, which can be described in terms of the superposition of a known aperture function with a half plane, has an amplitude distribution which is real along one direction and complex along the orthogonal direction. The real and imaginary parts of the amplitude distribution are related by Hubert transforms (dispersion relations). These disper sion relations can be used to arrive at the diffraction patterns of a variety of apertures having symmetry properties. Theoretical results are presented to illustrate the diffraction pattern of various apertures.

Using our new negative Δ LC material in a fringing field switching (n-FFS) cell, we demonstrated superior performances to conventional positive Δ FFS (p-FFS) LCD in transmittance, viewing angle, cell gap sensitivity, gamma curve, while... more

Using our new negative Δ LC material in a fringing field switching (n-FFS) cell, we demonstrated superior performances to conventional positive Δ FFS (p-FFS) LCD in transmittance, viewing angle, cell gap sensitivity, gamma curve, while keeping a comparable operation voltage and response time. Therefore, n-FFS has potential to replace p-FFS for next-generation mobile displays.

Following the development and publication of the JCAMP-DX protocol 4.24 and its successful implementation in the field of infrared spectroscopy, data exchange without loss of information, between systems of different origin and internal... more

Following the development and publication of the JCAMP-DX protocol 4.24 and its successful implementation in the field of infrared spectroscopy, data exchange without loss of information, between systems of different origin and internal format, has become a reality. The benefits of this system-independent data transfer standard have been recognized by workers in other areas who have expressed a wish for an equivalent, compatible standard in their own fields. This publication details a protocol for the exchange of Nuclear Magnetic Resonance (NMR) spectral data without any loss of information and in a format that is compatible with all storage media and computer systems. The protocol detailed below is designed for spectral data transfer, and its use for NMR imaging data transfer has not as yet been investigated.

A simple apparatus for time-correla ted single photon counting (TCSPC) m easurements in the near-infrared (near-IR) region for scanning-type applications has been constructed and examined. The apparatus consisted of ® ve m ajor com... more

A simple apparatus for time-correla ted single photon counting (TCSPC) m easurements in the near-infrared (near-IR) region for scanning-type applications has been constructed and examined. The apparatus consisted of ® ve m ajor com ponents including a pulsed diode laser source (lasing wavelength 5 780 nm; rep etition rate 5 80 MHz; power 5 5 mW ; pulse width 5 150 ps), an integrated m icroscope, a large-photoactive-area avalanche photodiode (APD), a TCSPC PC-board including the electron ics, and a Windows-based software package for accu mulating the¯uorescen ce decay pro® les. The instrument response function (IRF) of this assembly was found to be 460 ps, which is adequate for measuring lifetim es with t f $ 500 ps. Due to the sm all size of the device, it also allowed implem entation into scanning experim ents where lifetimes were measured. To dem onstrate this capability, we scanned a three-well microscope slide containing a near-IR dye. The decay pro® le of the near-IR dye, aluminum 2,3-naphthalocyanine, was collected and analyzed to obtain its lifetime, which was found to be 2.73 ns, in close agreement with the literature value for this particular dye. In addition, a three-dim ensional plot showing the decay pro® les (tim e vs. photocounts) and scan position of aluminum 2,3-naphthalocyaninē uorescence was acquired by scanning the m icroscope head over this three-well glass slide. In the scanning m ode, the IRFs as well as the decays of the dyes were found to be very stable. The device dem onstrated a concentration detection sensitivity of 0.44 nM; however, the dynamic range was limited due to the slow tim e constant (passive quenching) associated with the APD.

The necessary and sufficient conditions on the gain of the linear amplifier are determined under which the light output exhibits sub-Poissonian photon statistics or squeezing. It is found that for these effects the intensity gain must not... more

The necessary and sufficient conditions on the gain of the linear amplifier are determined under which the light output exhibits sub-Poissonian photon statistics or squeezing. It is found that for these effects the intensity gain must not exceed 2 under any circumstances. It is also shown that there exists a weaker sufficiency condition on the gain above which all nonclassical features of the field disappear. This suggests the possibility that other quantum effects may persist in the intermediate, still unexplored, domain of operation of the amplifier.

Mean-variance analysis is described as a method for characterization of the read-noise and gain of focal plane array (FPA) detectors, including charge-coupled devices (CCDs), charge-injection devices (CIDs), and complementary... more

Mean-variance analysis is described as a method for characterization of the read-noise and gain of focal plane array (FPA) detectors, including charge-coupled devices (CCDs), charge-injection devices (CIDs), and complementary metal-oxide-semiconductor (CMOS) multiplexers (infrared arrays). Practical FPA detector characterization is outlined. The nondestructive readout capability available in some CIDs and FPA devices is discussed as a means for signal-tonoise ratio improvement. Derivations of the equations are fully presented to unify understanding of this method by the spectroscopic community.

To investigate the effect of exposure duration on stereopsis and its spatial frequency dependency, we measured disparity threshold for the depth discrimination varying stimulus exposure duration between 0.05 and 2 s for three spatial... more

To investigate the effect of exposure duration on stereopsis and its spatial frequency dependency, we measured disparity threshold for the depth discrimination varying stimulus exposure duration between 0.05 and 2 s for three spatial frequencies (0.23, 0.94 and 3.75 c/deg). The results showed that disparity threshold decreased with increase in exposure duration up to a certain duration, beyond which it was approximately constant (the duration is called critical duration). The critical duration was about 150 ms for gratings with low and middle spatial frequencies (0.23 and 0.94 c/deg) while the duration was about 750 ms for gratings with high spatial frequency (3.75 c/deg). This suggests that temporal integration property varies dependently on stimulus spatial frequency. We also attempted to relate the spatial frequency dependency of the temporal integration property to the differences in temporal frequency tuning to different spatial frequency stimuli.

We consider how absorption-induced material heating alters the phase profile, the scale, the orientation, and the Bragg matching of volume holograms. We derive theoretical equations that consider the prisming, the lensing, and the Bragg... more

We consider how absorption-induced material heating alters the phase profile, the scale, the orientation, and the Bragg matching of volume holograms. We derive theoretical equations that consider the prisming, the lensing, and the Bragg mismatching that occur during material heating and compare these with experimental observations. From our Bragg-mismatching considerations we show how both read beam angle and wavelength need to be dithered for proper compensation of volume holograms for material-heating effects. Our results indicate that material heating in volume-holographic memory systems poses a severe threat to system performance. This threat is shown to be very significant in Fourier plane holograms but only moderately significant in image plane holograms.

In this paper, we deal with the subject of cross-gain modulation (XGM) and cross-phase modulation (XPM) semiconductor optical amplifier-based wavelength conversion of optical channels carrying subcarrier multiplexing signals in a... more

In this paper, we deal with the subject of cross-gain modulation (XGM) and cross-phase modulation (XPM) semiconductor optical amplifier-based wavelength conversion of optical channels carrying subcarrier multiplexing signals in a comprehensive way. The equations and models that describe the conversion process and the resulting harmonic and intermodulation distortions are obtained showing the superior performance of XPM over XGM in terms of second-and third-order distortion and contrast ratio. Experimental results for XGM-based wavelength conversion that confirm the results predicted by our theoretical models are presented, and finally, we consider the specific application of wavelength conversion of optical channels carrying full frequency plans such as that of cable television applications.

The points at which two-dimensional spectra of band-limited functions are zero can be used to generate a polynomial approximation of the complex spectrum. These point-zero locations are common to both the spectrum and the associated power... more

The points at which two-dimensional spectra of band-limited functions are zero can be used to generate a polynomial approximation of the complex spectrum. These point-zero locations are common to both the spectrum and the associated power spectrum. The phase of the complex-valued polynomial along with the measured intensity data is used to generate an initial guess for the function that an error-reduction algorithm can improve. This approach has practical utility for Fourier phase retrieval as well as for blind deconvolution. The limitations of the model are discussed, and examples are given.

Metal-organic semiconductor films are fabricated as co-evaporated films. It is demonstrated that the technique can be used to fabricate metalsemiconductor surface-enhanced Raman scattering (SERS) or surfaceenhanced resonance Raman... more

Metal-organic semiconductor films are fabricated as co-evaporated films. It is demonstrated that the technique can be used to fabricate metalsemiconductor surface-enhanced Raman scattering (SERS) or surfaceenhanced resonance Raman scattering (SERRS) substrates or to attain SERS or SERRS of highly insoluble pigments. The experiments are carried out using three different pigments: iron phthalocyanine (FePc) and two substituted tetracaboxylic perylenes (PTCDs). The structure of the co-PVD films was characterized at the nanoscale by scanning electron microscopy through field-emission gun (SEM-FEG), revealing a fairly homogeneous spatial distribution of the silver-pigment nanoparticles. The fabricated mixed nanostructures show a homogenous distribution of plasmon enhancement as observed in the point-by-point mapping of the SERRS spectra recorded with micrometer spatial resolution in Raman microscopy.

Optical characterization of three red pigments, two organic and one inorganic, was studied in order to provide important and reliable parameters for research and applications. The pigments were C.I. Pigment Red 176, C.I. Pigment Red 57:1,... more

Optical characterization of three red pigments, two organic and one inorganic, was studied in order to provide important and reliable parameters for research and applications. The pigments were C.I. Pigment Red 176, C.I. Pigment Red 57:1, and C.I. Pigment Red 101. All three pigments were used in their transparent form, that is, their radius of gyration was smaller than 250 nm. The particles were suspended in an apolar solvent and absorption, reflection, and scattering of the suspensions were measured by means of a single spectrophotometer and the effective complex refractive index was determined.

A novel fiber Bragg grating (FBG) sensing multiplexing system based on the combination of InGaAs spectrometer and Fabry-Perot (F-P) filter (InGaAs/F-P) is proposed. The multiplexing system only demodulates FBG sensors whose peak... more

A novel fiber Bragg grating (FBG) sensing multiplexing system based on the combination of InGaAs spectrometer and Fabry-Perot (F-P) filter (InGaAs/F-P) is proposed. The multiplexing system only demodulates FBG sensors whose peak wavelengths are shifting. The demodulation can be sequenced according to each sensor's priority, latency time and wavelength shifting. What is more, the monitor section of that system is not influenced by environmental temperature and source intensity fluctuations. At the average signal repeat rate of 6Hz, the average delay time of the conventional wavelength-and spatial-division combined system, the long period grating (LPG) combined system and the InGaAs/F-P system are 303, 97, and 6 ms, respectively. Simulation analysis and experiment work demonstrated that the InGaAs/F-P system is more rational and smart than other counterparts.

The fixed oil of Laurus novocanariensis (previously L. azorica) contains mostly glycerides together with minor non-saponifiable compounds. The direct identification and quantitative determination of costunolide and dehydrocostuslactone,... more

The fixed oil of Laurus novocanariensis (previously L. azorica) contains mostly glycerides together with minor non-saponifiable compounds. The direct identification and quantitative determination of costunolide and dehydrocostuslactone, two sesquiterpene lactones components of the oil that exhibit biological activities, is described. The analysis was carried out using 13 C-NMR spectroscopy (signal acquisition with inverse gated decoupling of protons; diglyme as internal standard) without separation, derivatisation or any sample preparation.

Measuring the modulation transfer function (MTF) of digital imagers focused at or near infinity in laboratory or field settings presents difficulties because the optical path is longer than a typical laboratory. Also, digital imagers can... more

Measuring the modulation transfer function (MTF) of digital imagers focused at or near infinity in laboratory or field settings presents difficulties because the optical path is longer than a typical laboratory. Also, digital imagers can be hindered by low-resolution detectors, resulting in the resolution of the optics surpassing that of the detector. We measure the MTF for a short-wave infrared hyperspectral imager developed by Resonon, Inc., of Bozeman, Montana, which exhibits both characteristics. These difficulties are overcome with a technique that uses images of building rooflines in an oversampled, tilted knife-edge-based MTF measurement. The dark rooftops backlit by a uniformly cloudy sky provide the high-contrast edges required to perform knife-edge MTF measurements. The MTF response is measured at five wavelengths across the imager's spectral band: 1085, 1178, 1292, 1548, and 1629 nm. The MTF also is observed at various distances from the roof to investigate performance change with distance. Optimum imaging is observed at a distance of 150 m, potentially a result of imperfect infinity focus and atmospheric turbulence. In a laboratory validation of the MTF algorithm using a monochrome visible imager, the roofline MTF results are similar to results from point-source and sine-card MTF measurements. C 2010 Society of Photo-Optical Instrumentation Engineers.

This paper is concerned with the development of Fourier transform spectroscopy from its beginnings in Michelson's visibility technique through the present day application using modern digital computers. Methods used in maximizing the... more

This paper is concerned with the development of Fourier transform spectroscopy from its beginnings in Michelson's visibility technique through the present day application using modern digital computers. Methods used in maximizing the efficiency of the computation, as well as the interferometer, are discussed.

An improved photoelastic modulator (PEM) employing two piezoelectric transducers and incorporating a new ir zinc selenide (ZnSe) optical element is described. The 0.64-cm thick PEM is capable of obtaining quarter-wave retardation from... more

An improved photoelastic modulator (PEM) employing two piezoelectric transducers and incorporating a new ir zinc selenide (ZnSe) optical element is described. The 0.64-cm thick PEM is capable of obtaining quarter-wave retardation from 0.55 im to 13.0 ,um. Previously no single, high quality, low static strain PEM element existed for this wavelength range. We have also constructed other PEM's using optical elements composed of fused quartz, calcium fluoride, and KRS-5. The important optical and mechanical properties are measured and compared.

We describe a local linear grating model that permits estimation of the diffraction efficiency of high-numericalaperture two-dimensional circular lenses with one-dimensional rigorous coupled-wave analysis. The model is self-consistent and... more

We describe a local linear grating model that permits estimation of the diffraction efficiency of high-numericalaperture two-dimensional circular lenses with one-dimensional rigorous coupled-wave analysis. The model is self-consistent and is consistent with the scalar theory that results for low-numerical-aperture lenses. The accuracy of the model increases with the number of Fresnel zones of the lens. On the basis of this model we optimize the discrete phase profile of the lens for the maximum diffraction efficiency, using the random search method. The TE and the TM modes are optimized simultaneously. Their phase variations as functions of local grating periods are removed by cyclic shifts of the grating profiles, resulting in constructive summation at the focus and high diffraction efficiency. © 1997 Optical Society of America [S0740-3232

erratum min max THz 10 18 10 17 n≈10 16 cm -3

In this paper, we present the impact of swift heavy ion beam irradiation on the structural, optical and electronic properties of SnO 2 thin films. Thin films were deposited using the pulsed laser deposition technique on Al 2 O 3... more

In this paper, we present the impact of swift heavy ion beam irradiation on the structural, optical and electronic properties of SnO 2 thin films. Thin films were deposited using the pulsed laser deposition technique on Al 2 O 3 substrates. Atomic force microscopy, X-ray diffraction, UV-visible absorption and temperature-dependent resistivity measurements were performed to explore the morphological, structural, optical and electronic properties of the as-deposited and irradiated samples. The peak intensity of the (200) peak was found to decrease monotonously with increasing irradiation fluence. The band gap energy of the 1 × 10 11 ion/cm 2 irradiated sample was found to increase. The electrical resistivity of the samples showed a continuous increase with the irradiation fluence.

We show that material and guide dispersion may be used effectively in an optical fiber to convert an FM signal to an AM signal after it traverses a certain minimum fiber length. This length depends on material and modal dispersion of the... more

We show that material and guide dispersion may be used effectively in an optical fiber to convert an FM signal to an AM signal after it traverses a certain minimum fiber length. This length depends on material and modal dispersion of the guide. An upper limit to the fiber length is established and is shown to be related to laser linewidth.

This paper investigates optical coherent systems based on polarization multiplexing and high-order modulations such as phase-shift keying (PSK) signals and quadrature amplitude modulations (QAM). It is shown that a simple linear receiver... more

This paper investigates optical coherent systems based on polarization multiplexing and high-order modulations such as phase-shift keying (PSK) signals and quadrature amplitude modulations (QAM). It is shown that a simple linear receiver processing is sufficient to perfectly demultiplex the two transmitted streams and to perfectly compensate for group velocity dispersion (GVD) and polarization mode dispersion (PMD). In addition, in the presence of a strong phase noise of the lasers at the transmitter and receiver, a symbol-by-symbol detector with decision feedback is able to considerably improve the receiver robustness with a limited complexity increase. We will also discuss the channel estimation and the receiver adaptivity to time-varying channel conditions as well as the problem of the frequency acquisition and tracking. Finally, a new two-dimensional (polarization/time) differential encoding rule is proposed to overcome a polarization-ambiguity problem. In the numerical results, the receiver performance will be assessed versus the receiver complexity.