Applied Optics Research Papers - Academia.edu (original) (raw)

A new method of designing nonimaging concentrators is presented and two new types of concentrators are developed. The first is an aspheric lens, and the second is a lens-mirror combination. A ray tracing of three-dimensional concentrators (with rotational symmetry) is also done, showing that the lens-mirror combination has a total transmission as high as that of the full compound parabolic concentrators, while their depth is much smaller than the classical parabolic mirror-nonimaging concentrator combinations. Another important feature of this concentrator is that the optically active surfaces are not in contact with the receiver, as occurs in other nonimaging concentrators in which the rim of the mirror coincides with the rim of the receiver.

- by Juan C Miñano
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- Mechanical Engineering, Optics, Ray Tracing, Applied Optics

Technological innovation in all areas has led to the appearance in recent years of new metallic and pearlescent materials, yet no exhaustive studies have been conducted to assess their colorimetric capabilities. The chromatic variability of these special-effect pigments may largely be due to the three-dimensional effect of their curved shapes and orientations when they are directionally or diffusely illuminated. Our study examines goniochromatic colors using the optimal colors (MacAdam limits) associated with normal colors (photometric scale of relative spectral reflectance from 0 to 1) under certain conventional illuminants and other light sources. From a database of 91 metallic and interference samples and using a multigonio-spectrophotometer, we analyzed samples with lightness values of more than 100 and others with lightness values of less than 100, but with higher chromaticities than optimal colors, which places them beyond the MacAdam limits. Our study thus demonstrates the existence of chromatic perceptions beyond the normal solid color associated with these materials and independent of the light source. The challenge for future research, therefore, is to replicate and render these color appearances in current and future color reproduction technologies for computer graphics.

We present a survey on five years of experiments of excimer laser irradiation of linen fabrics, seeking a coloration mechanism able to reproduce the microscopic complexity of the body image embedded onto the Shroud of Turin. We achieved a superficial, Shroud-like coloration in a narrow range of irradiation parameters. We also obtained latent coloration that appears after artificial or natural aging of linen following laser irradiations that, at first, did not generate any visible effect. Most importantly, we have recognized photochemical processes that account for both coloration and latent coloration.

- by Giuseppe Baldacchini and +2
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- Mechanical Engineering, Science and Religion, Holy Shroud of Turin, Shroud

We have demonstrated a one-dimensional array of individually addressable electrowetting tunable liquid lenses that compensate for more than one wave of phase distortion across a wavefront. We report a scheme for piston control using tunable liquid lens arrays in volume-bound cavities that alter the optical path length without affecting the wavefront curvature. Liquid lens arrays with separately tunable focus or phase control hold promise for laser communication systems and adaptive optics.

- by Robert Niederriter
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- Mechanical Engineering, Optics, Applied Optics, Optical physics

This paper presents a method of eliminating the error introduced by the nonuniform diffraction halo in speckle photography. It is shown that, by proper aperturing of the imaging lens, the intensity distribution in the diffraction halo can be made constant over a certain frequency range. The measurements made on Young's fringes, present in this region, would be free from error due to varying intensity in the diffraction halo.

- by Rajpal S Sirohi
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- Mechanical Engineering, Physics, Medicine, Error Correction

The retrieval sensitivity in regard to the recovery of aerosol size distributions using particle angular scattering properties is investigated. Previous retrieval methods have all assumed that the scattering characteristics of spheres is adequate to retrieve size distributions. The present results show that particle nonsphericity can have a significant effect upon the retrieval. In particular assumptions based upon Mie spheres may lead to interpretations of spurious multimodal distributions. Furthermore, it is also shown that shape effects cannot be separated from composition effects. The effect on retrieved size distributions is investigated due to (1) variations in the particle index of refraction, (2) truncation of angular scattering intensities due to measurement limitations, (3) the use of two-component shell particles, (4) nonsphericity using the semiempirical approach, and (5) the replacement of spherically shaped particles by cylindrically shaped fibeis.

- by Jost Heintzenberg
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- Mechanical Engineering, Information Retrieval, Physics, Medicine

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.

- by Roger Clark
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

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.

- by R. Bamler
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

A simplified mathematical model for the far field of a monomode diode laser is employed for easy but fairly accurate computations of the optical field in the focal region. The present treatment is concerned with laser junctions significantly narrower than the wavelength. The field distribution in the plane perpendicular to the diode junction is considered in detail. The results of computations are shown to agree well with the measurements. Hence, the computational code is valuable for the designing of optical devices, such as diodefiber couplings and laser Doppler anemometers. The present work is not concerned with design calculations for specific applications. Instead, it is intended to illustrate the general features of the proposed mathematical model of monomode diode laser beams.

- by Franz Durst
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- Mechanical Engineering, Applied Optics, Optical physics, Mathematical Model

Conoscopic holography is an interferometric technique that permits the recording of three-dimensional objects. A two-step scheme is presented to recover an opaque object's shape from its conoscopic hologram, consisting of a reconstruction algorithm to give a first estimate of the shape and an iterative restoration procedure that uses the object's support information to make the reconstruction more robust. The existence, uniqueness, and stability of the solution, as well as the convergence of the restoration algorithm, are studied. A preliminary experimental result is presented.

- by Laurent Mugnier
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- Mechanical Engineering, Computer Vision, Image Analysis, Optical Flow

We introduce length-sensing and control schemes for the dual-recycled cavity-enhanced Michelson interferometer configuration proposed for the Advanced Laser Interferometer Gravitational Wave Observatory ͑LIGO͒. We discuss the principles of this scheme and show methods that allow sensing and control signals to be derived. Experimental verification was carried out in three benchtop experiments that are introduced. We present the implications of the results from these experiments for Advanced LIGO and other future interferometric gravitational-wave detectors.

- by Kenneth Strain
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- Mechanical Engineering, Signal Processing, Sensitivity Analysis, Interferometry

A depth-enhanced three-dimensional integral imaging system with electrically variable image planes is proposed. For implementing the variable image planes, polymer-dispersed liquid-crystal (PDLC) films and a projector are adopted as a new display system in the integral imaging. Since the transparencies of PDLC films are electrically controllable, we can make each film diffuse the projected light successively with a different depth from the lens array. As a result, the proposed method enables control of the location of image planes electrically and enhances the depth. The principle of the proposed method is described, and experimental results are also presented.

- by Joohwan Kim
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- Mechanical Engineering, Electrochemistry, Liquid Crystals, Polymers

The output characteristics of a toric unstable resonator fitted to a multichannel stripline excitation system are presented. The resonator is shown to possess the usual advantages of a conventional unstable resonator plus the ability to modify the profile of the output beam by a simple change in the coupling aperture. Laser output parameters have been studied as a function of coupling fraction, magnification, and internal loss factors. Variations in the focal spot size as a function of the coupling aperture as well as resonator alignment sensitivity and polarization properties have been investigated.

- by Suwas Nikumb
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- Mechanical Engineering, Experimental Study, Applied Optics, Optical physics

We discuss an optical system that encodes an input signal to a polarization state, using a spatial light modulator (SLM). Using two SLMs the optical system multiplexes two 2D signals in the polarization domain, and we demonstrate the multiplexing of two binary images. The encryption and decryption of two binary images using an XOR operation is also presented.

- by john sheridan
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- Mechanical Engineering, Computer Science, Optics, Encryption

To study the optical properties of materials, one needs a complete set of the angular distribution functions of surface scattering from the materials. Here we present a convenient method for collecting a large set of bidirectional reflectance distribution function ͑BRDF͒ samples in the hemispherical scattering space. Material samples are wrapped around a right-circular cylinder and irradiated by a parallel light source, and the scattered radiance is collected by a digital camera. We tilted the cylinder around its center to collect the BRDF samples outside the plane of incidence. This method can be used with materials that have isotropic and anisotropic scattering properties. We demonstrate this method in a detailed investigation of shot fabrics. The warps and the fillings of shot fabrics are dyed different colors so that the fabric appears to change color at different viewing angles. These color-changing characteristics are found to be related to the physical and geometrical structure of shot fabric. Our study reveals that the color-changing property of shot fabrics is due mainly to an occlusion effect.

- by Jan Koenderink
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- Mechanical Engineering, Physics, Image Analysis, Medicine

The principles of operation of a novel laser displacement sensor are described. The intended application of the sensor is to measure displacements induced by gravitational radiation. The laser sensor is composed of three coupled cavities, defined by two laser mirrors and the mirrors of a Fabry-Perot etalon placed inside the laser cavity. The laser is forced to oscillate in two longitudinal modes by a Fox-Smith internal mode selector. It is shown that the laser system can be made to operate in a condition where the beat frequency between these modes has an enhanced sensitivity to relative displacements between the etalon mirrors. A He-Ne laser displacement sensor was constructed, and a displacement sensitivity of 4.6 X 1012 Hz/cm was obtained. This value is shown to be in good agreement with the value predicted by a theoretical analysis of the sensor performance.

- by meir weksler
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- Mechanical Engineering, Physics, Medicine, Applied Optics

We are combining two optical techniques, pulsed photothermal radiometry (PPTR) and diffuse reflectance spectroscopy (DRS), for noninvasive assessment of the structure and composition of human skin in vivo. The analysis involves simultaneous multidimensional fitting of the measured PPTR signals and DRS spectra with predictions of a numerical model of light transport (Monte Carlo) in a four-layer model optical model of human skin, accounting for the epidermis, papillary and reticular dermis, and subcutis. The assessed epidermal thickness values were tested by coregistration with a multiphoton microscope, which provides vertical sectioning capability based on two-photon excited fluorescence and second-harmonic generation in selected skin components. The comparison shows that these values correspond well to the maximal epidermal thicknesses measured in the multiphoton microscopy images, the rete ridges.

Transmittance spectra of four gaseous hydrocarbons were measured by using a Fourier transform infrared spectrometer. The analyzed substances are propane, n-butane, ethanol, and iso-octane (2,2,4-trimethyl-pentane). Mixtures of hydrocarbons and nitrogen were prepared and analyzed in an optical cell between 298 and 473 K at pressures up to 1800 kPa. Molecule specific absorption cross sections were calculated for different temperatures and pressures that are relevant for technical absorption measurements. Dependences of the spectral absorption cross sections, as well as the integrated absorption cross sections on temperature and pressure, were investigated.

- by Hainer Wackerbarth
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- Mechanical Engineering, Spectroscopy, Applied, Applied Optics

A novel approach for three-dimensional ͑3-D͒ display systems implemented with a micromirror array was proposed, designed, realized, and tested. The major advantages of this approach include the following: ͑1͒ micromirrors are reflective and hence achromatic ͑panchromatic͒, ͑2͒ a wide variety of displays can be used as image sources, and ͑3͒ time multiplexing can be introduced on top of space multiplexing to optimize the viewing zone arrangements. A two-view ͑left and right͒ 3-D autostereoscopic display system was first constructed. Left-and right-eye views in the forms of both still and motion 3-D scenes were displayed, and viewers were able to fuse the stereo information. A multiview ͑two left and two right͒ 3-D autostereoscopic display system was then simulated.

- by Jefrey Kulick
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- Mechanical Engineering, Applied, Applied Optics, Optical physics

In this paper, we explore the potential benefits and limitations of using transmitter lenses in an orbital-angular-momentum (OAM)-multiplexed free-space optical (FSO) communication link. Both simulation and experimental results indicate that within certain transmission distances, using lenses at the transmitter to focus OAM beams could reduce power loss in OAM-based FSO links and that this improvement might be more significant for higher-order OAM beams. Moreover, the use of transmitter lenses could enhance system tolerance to angular error between transmitter and receiver, but they might degrade tolerance to lateral displacement.

- by Solyman Ashrafi
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- Mechanical Engineering, Lenses, Applied Optics, Optical physics
- by Kevin Lehmann
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- Mechanical Engineering, Resonators, Applied Optics, Optical physics

We achieve the analysis and design of optical attenuators with double-prism neutral density filters. A comparative study is performed on three possible device configurations; only two are presented in the literature but without their design calculus. The characteristic parameters of this optical attenuator with Risley translating prisms for each of the three setups are defined and their analytical expressions are derived: adjustment scale (attenuation range) and interval, minimum transmission coefficient and sensitivity. The setups are compared to select the optimal device, and, from this study, the best solution for double-prism neutral density filters, both from a mechanical and an optical point of view, is determined with two identical, symmetrically movable, no mechanical contact prisms. The design calculus of this optimal device is developed in essential steps. The parameters of the prisms, particularly their angles, are studied to improve the design, and we demonstrate the maximum attenuation range that this type of attenuator can provide.

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.

- by Krzysztof Chrzanowski
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- Mechanical Engineering, Optics, Medical Imaging, Remote Sensing

We develop a regularized phase-tracking ͑RPT͒ technique to unwrap phase maps. The phase maps that can be unwrapped with this new method may be bounded by arbitrarily shaped boundaries. Moreover, the RPT unwrapper has a higher noise... more

Nanoparticle-based photonic explorers have been developed for intracellular sensing and photodynamic therapy (PDT). The design employs nanoparticles made of various matrices as multifunctional nanoplatforms, loading active components by encapsulation or covalent attachment. The nanoplatform for biosensing has been successfully applied to intracellular measurements of important ionic and molecular species. The nanoplatform for PDT has shown high therapeutic efficacy in a rat 9L gliosarcoma model. Specifically, a multifunctional nanoplatform that encompasses magnetic resonance imaging (MRI) and PDT agents inside, as well as targeting ligands on the surface, has been developed and applied in vivo, resulting in much improved MRI contrast enhancement and PDT efficacy.

- by Raoul Kopelman
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- Mechanical Engineering, Photodynamic Therapy, Applied, Nanostructures

Keratometry is currently achieved by projecting a circular mire onto the patient's cornea and analyzing the size and shape of its reflected image. The projection mires are decisive for the precision of the measurement. We have previously developed a keratometric module for slit lamps, and the development of four projection mires are presented. Mire 1 is composed of optical fibers and electrical cables; Mire 2, 48 LEDs; Mire 3, optical fibers and no electrical cables; and Mire 4, mechanical parts--cable free. Mires 2-4 provide accurate keratometry measurements at slit lamps. Mire 4 is the most adequate for the clinical environment.

- by Liliane Ventura
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- Mechanical Engineering, Ophthalmology, Research Design, Cornea

Rayleigh-Brillouin (RB) scattering profiles for air have been recorded for the temperature range from 255 to 340 K and the pressure range from 640 to 3300 mbar, covering the conditions relevant for the Earth's atmosphere and for planned atmospheric light detection and ranging (LIDAR) missions. The measurements performed at a wavelength of λ 366.8 nm detect spontaneous RB scattering at a 90°s cattering angle from a sensitive intracavity setup, delivering scattering profiles at a 1% rms noise level or better. The experimental results have been compared to a kinetic line-shape model, the acclaimed Tenti S6 model, considered to be most appropriate for such conditions, under the assumption that air can be treated as an effective single-component gas with temperature-scaled values for the relevant macroscopic transport coefficients. The elusive transport coefficient, the bulk viscosity η b , is effectively derived by a comparing the measurements to the model, yielding an increased trend from 1.0 to 2.5 × 10 −5 kg · m −1 · s −1 for the temperature interval. The calculated (Tenti S6) line shapes are consistent with experimental data at the level of 2%, meeting the requirements for the future RB-scattering LIDAR missions in the Earth's atmosphere. However, the systematic 2% deviation may imply that the model has a limit to describe the finest details of RB scattering in air. Finally, it is demonstrated that the RB scattering data in combination with the Tenti S6 model can be used to retrieve the actual gas temperatures.

Two anamorphic and achromatic Fourier processors were designed and constructed using diffractive and refractive cylindrical lenses. The diffractive lenses are holographic lenses recorded on silver halide material. In both processors the achromatic one-dimensional Fourier transform plane was obtained with two holographic lenses and one refractive cylindrical lens. The image with the same magnification in both directions at the output plane was formed with two different combinations of lenses. The differences between the two processors are analyzed, and in both cases the chromatic aberration in the Fourier plane and in the output plane is evaluated. Even though single cylindrical refractive lenses were used to image in one direction, good results were obtained.

- by Jesús Atencia
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- Mechanical Engineering, Optical Signal Processing, Applied Optics, Optical physics

The mode spectrum in an optical nanowaveguide consisting of a dielectric-core layer surrounded by two identical metal layers is investigated. A simple model based on mode matching to predict the properties of mode propagation in such optical nanowaveguides is proposed. It is shown that quasi-TM 00 and quasi-TM 10 modes supported by an optical microstrip line do not have a cutoff frequency, regardless of the size of the metal strips, the thickness of the dielectric slab, and the cross-sectional shape. The transverse size of the TM 00 mode supported by a nanosized microstrip line was found to be approximately equal to the transverse dimension of the microstrip line. In closed rectangular and elliptical nanowaveguides, i.e., in which all dielectric surfaces are covered with metal films, the cross-sectional shape of the waveguide should be stretched along one side to produce propagation conditions for the fundamental mode.

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.

- by John F. Walkup
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

A multiple-prism grating solid-state dye laser oscillator was demonstrated with its grating, deployed in a Littrow configuration, under total illumination at reduced intracavity beam expansion. This compact cavity yields laser linewidths... more

- by Francisco Duarte
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- Mechanical Engineering, Oscillations, Applied Optics, Optical physics

Vacuum-UV radiation from Xe jet-target laser-produced plasmas has been produced, spectrally dispersed, and efficiently focused onto a line-shaped interaction volume by adopting an embedded-in-thechamber spectrograph geometry. Time-resolved 2D Rayleigh light scattering imaging has been carried out for visualizing the gas jet-laser plasma interaction and optimizing the emission intensity and the spectral resolution. We have calibrated the measured photon fluxes, reaching values higher than 10 13 photons͞pulse cm 2 nm in the 100-200 nm wavelength range within the first 20 ns from the laser pulse onset. The vacuum-UV light source is predicted to enable sensitive and selective single-photon ionization for time-of-flight mass spectrometry and similar vacuum-UV spectroscopy applications.

The optical responses of two sides of float glass in the soft-x-ray region were studied at the Indus-1 synchrotron facility. To the best of our knowledge these are the first experimentally obtained optical data for both sides of float glass in the soft-x-ray region. Optical constants ␦ and ␤ were determined by use of angle-dependent reflectance techniques in the wavelength range 80 -200 Å. On the side of the glass that was tin indiffused, a significant difference in ␦ value from that of the non-tin-side surface was observed. The measured data were compared with Henke's tabulated value of SiO 2 . The surface roughness of float glass was separately determined by hard-x-ray reflectivity to minimize the number of fitting variables. The effect of a contamination layer on the determination of optical constants was avoided by an appropriate sample-cleaning method.

- by Gyanendra Lodha
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- Mechanical Engineering, Applied Optics, Optical physics, Soft X Ray

We focus our efforts on development of an advanced monochromatic monitoring strategy to assist the optical coating engineer in finding a single wavelength or a sequence of monitoring wavelengths that meet simultaneously several practical demands, namely, specified input and output swing values, specified amplitude of a monitoring signal variation, and the distance between trigger point and the last signal extremum. Additionally, the most important demand is that the number of different monitoring wavelengths must be as small as possible. Manual construction of such a monitoring strategy is almost impossible because of a large number of conditions to be satisfied. We propose an algorithm that automatically generates a monitoring spreadsheet so that all demands can be satisfied as closely as possible. We consider six typical design problems and obtain a series of solutions for each of them. Then, we provide computational simulations of deposition processes assuming that they are controlled by monochromatic monitoring with the monitoring strategy generated by our algorithm, and we demonstrate how an optical coating engineer can select design solutions that exhibit the highest production yields.

. Comparison measurements of 0 : 45 radiance factor and goniometrically determined diffuse reflectance. Applied Optics, volume 48, number 15, pages 2947Optics, volume 48, number 15, pages -2957 A comparison between the absolute gonioreflectometric scales at the Helsinki University of Technology (TKK) and the Physikalisch-Technische Bundesanstalt (PTB) has been accomplished. Six different reflection standards were measured for their 0∶45 spectral radiance factor between 250 and 1650 nm in 10 nm intervals. Also, the 0∶d reflectance factor between 400 and 1600 nm in 100 nm intervals was determined from goniometric reflectance measurements over polar angles with subsequent integration within the hemisphere above the sample. Goniometric comparisons covering such an extensive wavelength range and also several different sample materials are rarely implemented. For all but one sample, the difference between the results obtained at the TKK and the PTB was, with the exception of a couple of measurement points, within the expanded uncertainty (k ¼ 2) of the comparison at least up to a wavelength of 1400 nm. All differences between the measurement results can be understood, except for one translucent sample in the visible wavelength range. The effect of sample translucency was found to be significant in the NIR wavelength region. Also, a general tendency of an increase of the TKK values relative to the PTB values in the UV region was observed. Possible causes for this phenomenon are discussed.

- by Silja Holopainen
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- Mechanical Engineering, Applied Optics, Optical physics, Diffuse reflectance

Gas phase diagnostics with multispecies diatomic spectra is discussed. Analyses of spectra from the A 3 ⌸ i 7 X 3 ⌺ Ϫ system of NH and the C 3 ⌸ u 7 B 3 ⌸ g second-positive system of N 2 are presented. Multispecies spectroscopy is applied to experimental spectra obtained from laser-induced breakdown plasmas in anhydrous ammonia gas and a low-pressure discharge lamp.

- by Christian Parigger
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- Mechanical Engineering, Spectroscopy, Plasmas, Applied Optics

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.

- by Igor Smolyaninov
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

Turbulent inhomogeneities of fluid flow have the effect of scattering light in near-forward angles, thus providing an opportunity to use optics to quantify turbulence. Here we report measurements of the volume-scattering function in the range of 10 Ϫ7 to 10 Ϫ3 rad using a wave-front sensing technique. The total scattering coefficient b, due to scattering on turbulent inhomogeneities, is between 1 and 10 m Ϫ1 under typical oceanographic conditions. The numerical calculations of turbulent volume-scattering functions compare well with the laboratory measurement. These results suggest that optical measurements at small angles are affected by turbulence-related scattering, and their effects can be well modeled with numerical calculations.

- by C. Randall Truman
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- Mechanical Engineering, Light Scattering, Applied Optics, Optical physics

An optimal algorithm for detecting a target using a ladar system employing Geiger-mode avalanche photodiodes (GAPDs) is presented. The algorithm applies to any scenario where a ranging direct detection ladar is used to determine the presence of a target against a sky background within a specified range window. A complete statistical model of the detection process for GAPDs is presented, including GAPDs that are inactive for a fixed period of time each time they fire. The model is used to develop a constant false alarm rate detection algorithm that minimizes acquisition time. Numerical performance predictions, simulation results, and experimental results are presented.

We have designed and fabricated a 2D photonic crystal (PhC) asymmetric Mach-Zehnder (M-Z) device structure using W1 channel waveguides oriented along ⌫K directions in silicon-on-insulator material. The asymmetric structure was designed using a PhC lattice with different filling factors. The asymmetry is obtained as a difference of two periods in the physical path length (⌬L ϭ 2a) between the arms, and it was sufficient to produce a phase shift in the region of operation around ϭ 1500 nm. The asymmetric M-Z structure is more sensitive than a symmetric M-Z structure to changes in the refractive index and therefore becomes an interesting platform for switching and sensor devices.

- by Richard De La Rue
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- Mechanical Engineering, Photonic Crystal, Applied Optics, Optical physics
- by D B Brumm
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- Mechanical Engineering, Data Reduction, Applied Optics, Optical physics

We utilize spatial and angular diversity to achieve speckle reduction in laser illumination. Both free-space and imaging geometry configurations are considered. A fast two-dimensional scanning micromirror is employed to steer the laser beam. A simple experimental setup is built to demonstrate the application of our technique in a two-dimensional laser picture projection. Experimental results show that the speckle contrast factor can be reduced down to 5% within the integration time of the detector.

- by M. Nadeem Akram
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- Mechanical Engineering, Displays, Applied, Applied Optics

We have developed a numerical code that, starting from far-field intensity measurements, is able to evaluate the excitation coefficients of the transverse modes in a laser system.Both the coherent and incoherent mode cases are addressed, and, while the incoherent case is shown to be equivalent to a linear problem, the coherent case is discussed through its equivalence to the phase-retrieval problem. Problems arising from both ill posedness and the nonlinearity are discussed in detail.The validity of our approach is confirmed by several numerical simulations and some experimental results on the characterization of a Q-switched Nd:YAG laser.

- by alessandra esposito
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- Mechanical Engineering, Materials Science, Optics, Laser

High-performance coatings for micromechanical mirrors were developed. The high-reflective metal systems can be integrated into the technology of MOEMS, such as spatial light modulators and microscanning mirrors from the near-infrared down to the vacuum-ultraviolet spectral regions. The reported metal designs permit high optical performances to be merged with suitable mechanical properties and fitting complementary metal-oxide semiconductor compatibility.

- by Jan-Uwe Schmidt
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- Mechanical Engineering, Near Infrared, Optical Design, Thin Films
- by David Stodolsky
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

Transparent and optical-grade TiO 2 coatings were prepared by sol-gel spinning and ion-beam sputtering techniques. We investigate process parameters for the fabrication of sol-gel spin-coated TiO 2 films exhibiting high optical quality comparable with that of ion-beam-sputtered TiO 2 films. X-ray diffraction studies showed the sol-gel-deposited films to be amorphous for heat treatments below 350°C, whereas the ion-beamsputtered films were slightly crystalline and exhibited the anatase structure. The refractive index and the extinction coefficient were evaluated from transmittance characteristics in the ultraviolet, visible, and nearinfrared regions. Transmission spectra and ellipsometric measurements showed that spin-coated films were essentially optically equivalent to those prepared by ion-beam sputter deposition.

- by Hulya Demiryont
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- Mechanical Engineering, Thin Films, Thin Film, Optical Properties
- by Dario Cabib
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- Mechanical Engineering, Infrared spectroscopy, Error Analysis, Applied Optics

Beat frequencies between the transverse modes of an unstabilized CW CO2 laser were studied by detecting the homodyne signals emitted by the laser. Frequency pulling was observed and a resulting mode spacing reduction of up to 8 percent was measured. The dependence of mode pulling on total gas pressure was measured and was found to be in fair agreement with theory. The observed effect is important in some laser tuning techniques where it leads to a reduction of the tuning range and a nonlinear dependence of the laser frequency on cavity length.

- by Mira Naftaly
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- Mechanical Engineering, Carbon Dioxide, Applied Optics, Optical physics