bluuebunny/crossref_metadata_2025 huggingface dataset:
BACKSCAT Lidar Simulation
Authors: Cheifetz Michael G. , Longtin David R.
Published: February 2023

Different lidar systems are used to probe the atmosphere and these systems typically measure the backscattered return as a way of studying aerosol profiles. Some of the lidar systems have the additional capability of measuring the Doppler return from aerosols and molecules for use in determining wind profiles. Other lidar systems have been designed to detect the Raman scattering phenomenon as a way of studying the distributions of molecular species.
Remote sensing of oil films on the sea surface using satellite lidar
Authors: Belov M.L. , Gorodnichev V.A. , Kozintsev V.I.
Published: February 2023

Lidar remote sensing is one of the most promising ways of the sea exploration. Lidar reliably detects oil films on the sea surface at vertical sounding. However, when scanning devices are used for remote sensing of the sea surface and the lidar optical axis deviates from the vertical direction, the received echo-pulse strongly depends on the sea state (wind speed) and the angle of scanning [1]. This effect can make interpretation of the lidar data difficult.
Coherent Doppler Lidar Edge Technique
Authors: Werner Christian
Published: February 2023

With a coherent Doppler lidar one can measure both, the aerosol and the velocity profile. For direct detection the edge technique was proposed (Korb et al. 1994) to get information on the velocity too.
Multiple Scattering and Lag Angle in Cloud Returns
Authors: DiMarzio Charles A. , Lindberg Scott C.
Published: February 2023

A Monte-Carlo model was used to investigate the effects of multiple scattering on coherent lidar returns from clouds. Effects on signal time history and lag angle will be shown.
Range/Doppler Imaging with a Coherent Laser Radar based on Optical Fiber Amplifiers
Authors: Phillips Mark W. , Hannon Stephen M. , Wanninger Peter G. , Suni Paul J.M. , Thomson J. Alex L. , Richmond Richard D.
Published: February 2023

Coherent Technologies, Inc., under funding from a Wright Laboratory SBIR contract, has developed a coherent laser radar based on waveform amplification in single mode erbium-doped fiber amplifiers. The transceiver emits a waveform with a large time-bandwidth product that allows imaging with simultaneous high resolution in both range and velocity for enhanced hard target recognition. The ladar is designed for range-resolved measurement rather than range- precise measurement in order to overcome military imaging countermeasures such as camouflage netting. A number of mechanisms are capable of generating wideband signals, such as amplitude mode-locking and intracavity phase modulation (frequency chirping). For the purposes of coherent ladar, most of these approaches require the injection-locking of the ladar transmitter to the master/local oscillator frequency and are therefore sensitive to transmitter perturbations. A more rugged approach adopted by CTI is to use frequency-shifted feedback (FSF) in a multi-pass amplifier to generate a wideband frequency comb on one side of the input master oscillator frequency. The amplifier can be operated in cw mode (below laser threshold) or in quasi Q- switched mode (above laser threshold) without resonator frequency-pulling effects since the axial mode structure of the laser/amplifier resonator is eliminated by FSF. This allows simple and controlled frequency generation which is insensitive to transmitter perturbations.
High Energy, Diode-Pumped Tm,Ho:YLF Laser Transmitter
Authors: Flint John H. , Rines David M.
Published: February 2023

We have recently reported efficient operation of a Tm,Ho:YLF laser pumped by quasi-CW diode-laser arrays [1]. This laser has been converted to a ring resonator, Q-switched, and injection seeded. Whereas we had obtained 50 mJ (2 W@40 Hz) of normal-mode TEM00 output from a single-crystal linear cavity, the ring has produced up to 86 mJ using polarization out-coupling. Although conventional Q-switching of this laser is limited to 10-mJ by optical damage, we have extracted up to 41 mJ using active Q-switch voltage control. The ring laser has been injection-seeded at the 10-mJ level using a "ramp-and-fire" approach, and we will report on seeding experiments now underway using active Q-switching.
Signal Fluctuations in Coherent Laser Radar
Authors: Pearson G.N. , Harris M. , Hill C.A. , Vaughan J.M.
Published: February 2023

It is well known that there are several advantages inherent in the coherent mode of operation. These include the ability to achieve near quantum-limited performance in the thermal IR where detectors are intrinsically noisy, and the availability of Doppler information. There are however some additional properties of this mode of operation which to date have not been fully exploited.
Autoregressive Moving Average Spectral Estimation of Coherent Lidar Signal
Authors: Adam O. , Zarader J.-L. , Dabas A. , Flamant P.H.
Published: February 2023

The frequency estimators that perform the best on Doppler lidar signals are somehow matched to the signal characteristics like spectral width or SNR. In the Levin estimator for instance, the fitted filter is tuned in height and width to be as close as possible to the expected signal power spectrum. In practical applications, the tunable estimator parameters are set to values corresponding to the atmospheric conditions that are most likely to be met (clear air stable conditions without significant shear and low turbulence level). Other conditions are however often met that unpredictably broaden or alter the returned spectrum. This may be particularly true for dedicated applications like wake vortex or wind shear detections. The performance of the estimation may then be highly degraded. The coupled estimation of both the signal mean frequency and width could then improve the radial velocity retrieval. Such a co-estimation is possible using an autoregressive moving average (ARMA) type of filter.
3D windfield analysis from airborne Doppler lidar data
Authors: Dabas Alain , Perin Julie , Flamant Pierre
Published: February 2023

Windfield analysis consists in retrieving the 3D wind vectors on a space grid using the observations (i.e. the measured radial velocities) provided by a conically scanned airborne Doppler lidar. The purpose of this presentation is to show that analysis techniques currently used by meteorologists can be a powerfull solution to this problem capable of extracting more information from the observed data than the usual VAD.
Processing of Wideband Doppler Lidar Signals by Digital Undersampling (Simulation)
Authors: Stoykova E.V. , Stoyanov D.V.
Published: February 2023

Undersampling is an effective way to simplify the wideband CO2 Doppler lidar hardware as shown in [1,2] offering several times lower sampling frequency. Its application assumes precise analysis for the optimal choice of the sampling frequency and filtering parameters because of the possible aliasing causing a decrease of the SNR. In this work, on the base of simulation and processing of the identical signals, two proposed by us undersampling schemes of wideband detection are compared with the conventional quadrature detection and with sampling at Nyquist frequency directly after the photomixer. Using as a model output the Doppler frequency estimate characteristics, we obtain by the undersampling the same accuracy as with the known methods. The proposed schemes use filters with constant frequency characteristics and do not require a knowledge of reference frequency before the laser shot.
Characterization of Semiconductor Detectors for Operation in 2-micron Coherent Lidars
Authors: Amzajerdian Farzin , Jones Brian F. , Kavaya Michael J.
Published: February 2023

Most earlier work on optical heterodyne receivers has concentrated on detection devices operating in the 10-micron region1–4. In view of the growing interest in eye-safe, solid state coherent laser radars using Thulium and Holmium based lasers, we have investigated the heterodyne detection characteristics of room-temperature semiconductor detectors operating in the 2-micron wavelength region. A detector characterization system has been designed and developed at NASA/MSFC that enables the accurate characterization of 2-micron detection devices for evaluating their performance as heterodyne detectors and determining their optimum operating parameters. The measured quantities will provide all the necessary detector parameters for specifying the optimum optical local oscillator power incident on the detector, the detector optimum bias voltage, and the parameters of the detector interface electronics. The detector characterization system is also capable of direct measurement of the detector heterodyne quantum efficiency ηHQE as a function of the IF signal frequency. In a coherent lidar, the signal-to-noise ratio is directly proportional to the detector heterodyne quantum efficiency, therefore knowledge of the detector heterodyne quantum efficiency is necessary for initial calibration of coherent lidars and predicting their performance.
The Antenna Properties of Optical Heterodyne Detector Arrays
Authors: Bennett C.A. , Hutchinson D.P. , Sitter D.N. , Richards R.K. , Simpson M.L.
Published: February 2023

A single-detector heterodyne receiver is usually assumed to be illuminated by a gaussian-profile local oscillator beam. The reverse projection of this beam, usually called the antenna beam, completely specifies the field of view of the receiver system [1]. A receiver array requires an array of such local oscillator beams, and the resulting antenna beam array must behave so as to efficiently sample the image field. For example, an object in the far-field should be sampled by non-overlapping antenna beams, as should all objects beyond this plane. Furthermore, these non-overlapping beams should be spaced with the same geometry as the detector array for all points on the object plane and beyond.
Kinetics and Mechanism of Proximal Probe-Induced Local Oxidation of Si and Metals
Authors: Hertel T. , Martel R. , Avouris Ph.
Published: February 2023

Current efforts in electronic device miniaturization involve the development of techniques to fabricate stable, three-dimensional structures, accessible to the outside world, e.g. through electrical contacts. Here the aim is to fabricate structures with dimensions in the range of 10-50 nm utilizing materials compatible with those of current technologies, i.e. Si, SiO2 and metals. A promising proximal probe-based technique for achieving this goal appears to be tip-induced oxidation. This process was first described by Dagata et al.1, and further developed by Snow and co-workers,2 and others. The lateral dimensions of the oxide patterns produced can be as small as 10 nm, while the thickness of the oxide is believed to be less than about 5 nm. Using this process Minne et al.3 were able to fabricate sub-1.0µm Si field-effect transistors, while Matsumoto et al.4 fabricated Ti-based single electron transistors. With respect to the oxidation mechanism, initially, it was thought that it involves an electric field-induced reaction between atmospheric oxygen and silicon,1 but later work established that H2O, not O2, is essential for the oxidation.5
Atom-Tracking STM Measurements of Surface Dynamic Processes
Authors: Swartzentruber B. S.
Published: February 2023

The kinetics of Si monomers, at submonolayer coverage, are measured using STM. Si monomers are observed in empty-state images acquired between room temperature and 115 C. The monomers become trapped at the ends of rebonded-SB type dimer rows, while substrate defects and SA type steps act as reflection barriers. At elevated temperatures, monomers thermally escape from the traps and diffuse one-dimensionally along the substrate dimer row until they find another unoccupied trap or return to their original trap. From the rate at which the monomers escape from the traps, the binding activation barrier at isolated traps is estimated to be ~ 1.0 eV. A slightly lower barrier exists for monomers to hop between traps located at the ends of neighboring dimer rows -- a process facilitating diffusion along segments of the SB type steps.
Atomic-Scale FTIR Spectroscopy of Silicon Nucleation and Growth on H-Terminated and Oxide Covered Si(111)
Authors: Knobloch J. , Hess P.
Published: February 2023

The photon-controlled nucleation and growth of amorphous hydrogenated silicon (a-Si:H) was investigated on different silicon surfaces. The 7.9 eV photons of a 157 nm F2 laser initiated the growth process by photolyzing disilane in the gas phase. The short laser pulses allowed a digital control of growth by a small fraction of a monolayer with promt operation and cessation of deposition as monitored by a quartz-crystal microbalance. Mainly the initial stage of growth up to steady state deposition of bulk material was studied yielding information on the binding configuration and structure of the interface region. Fig. 1 shows the experimental setup with the F2 laser beam in parallel configuration and the IR beam passing the substrate holder through a hole in perpendicular configuration.
Silicon Tunneling Devices Fabricated on SOI
Authors: Toriumi Akira
Published: February 2023

The tunneling is a very promising operation principle for the future electron devices, because it is very sensitive to the applied voltage, little dependent on the ambient temperature, and becomes more evident with the size miniaturization. We will discuss two kinds of tunneling devices fabricated on SOI (Silicon-On-Insulator).
Photonic Crystals for the Visible Spectrum Based on Two-Dimensional Solid-State Arrays
Authors: Rosenberg A. , Tonucci R. J.
Published: February 2023

Photonic crystals have been fabricated from dielectric arrays having periodicities of 0.188 to 0.278 µm. At these sizes, the visible spectrum transmission exhibits attenuations originating in the associated photonic band structure. The properties of these attenuations are controlled by the compositions and geometries of the arrays.
Optical Microscopy Near Atomic Resolution
Authors: Wickramasinghe Kumar , Martin Y.T.
Published: February 2023

Recently, we introduced a microscope—the Scanning Interferometric Apertureless Microscope (SIAM) whereby the Abbe limit is surpassed by almost three orders of magnitude and an optical resolution of 8 Å was demonstrated. We present results on applications of this technique to microscopy, spectroscopy and storage, including a basic theory underlying its performance.
Self-Assembled Inorganic-Organic Multilayer Thin Films
Authors: Page Catherine , Ansell Michael , Cogan Betsy , Neff Grace , Hommel Lisa
Published: February 2023

Self-assembly of inorganic-organic multilayer thin films allows the construction of materials with control of thickness, chemical composition, properties and proximity of different layers for use in a variety of applications. By developing different types of organic-inorganic bonding which can be exploited to self-assemble multilayer films we are able to prepare superstructure multilayers consisting of, for example, alternating hafnium-bisphosphonate layers and cobalt diisocyanide layers. The ability to make superstructures with different types of metal-ligand interactions allows more flexibility in the choice of organic linkers, the selection of interesting metal ions, and the properties associated with various combinations of components. Different approaches to incorporating nonlinear optical properties into these multilayers will be presented. Examples of these types of multilayers grown on silicon wafers and their characterization by grazing-angle x-ray diffraction, ellipsometry and second harmonic generation will be discussed. Preliminary results of lithographic approaches to patterning these multilayers in the lateral dimension will also be presented.
Athermalization with Diffractive Optica
Authors: Londoño Carmiña , Plummer William T. , Clark Peter P.
Published: February 2023

We athermalize a single-material lens element by using a kinoform on one surface to keep its focal length and aberrations constant with temperature to the first order.
Thermal Effects In Diffractive Lenses
Authors: Behrmann Gregory P. , Bowen John P.
Published: February 2023

For military and aerospace applications, temperature is one of the more important environmental influences on optical systems. For example, some systems are required to operate over a temperature range of -30°C to 50°C. However, little has been reported in the open literature on the effects of temperature on diffractive optical elements1,2.
On the Convergence of the Coupled-Wave Approach for Lamellar Diffraction Gratings
Authors: Li Lifeng , Haggans Charles W.
Published: February 2023

Among the many existing rigorous methods for analyzing diffraction of electromagnetic waves by diffraction gratings, the coupled-wave approach1 stands out because of its versatility and simplicity. It can be applied to volume gratings and surface relief gratings, and its numerical implementation is much simpler than others. In addition, its predictions have been experimentally validated in several cases2-4. These facts explain the popularity of the coupled-wave approach among many optical engineers in the field of diffractive optics. However, a comprehensive analysis of the convergence of the model predictions has never been presented, although several authors5,6 have recently reported convergence difficulties with the model when it is used for metallic gratings in TM polarization.
Design and Fabrication of Resonance Domain Diffractive Optical Elements
Authors: Miller J. Michael , Noponen Eero , Vasara Antti , Turunen Jari , Taghizadeh Mohammad R.
Published: February 2023

The design of computer generated diffractive optical elements has traditionally relied upon Fourier optics [1], i.e. the Fresnel or Fraunhofer diffraction theories encompassing the paraxial approximation. Fourier optics, however, is not valid if the surface relief profile contains transverse features that are less than an order of magnitude larger than the incident wavelength. In this regime, non-paraxial theories based on Kirchhoff boundary conditions should be used [2]. Even these theories fail in the resonance domain where, by definition, features of the order of one wavelength are critical [3], and so rigorous electromagnetic theory is required. The fabrication of such resonance domain diffractive optical components is becoming more plausible with the development of microlithographic fabrication technology, which can already achieve sub-micron features with a positional accuracy of about 0.1 µm.
MacBEEP: A Desktop System for Binary Optics*
Authors: Levin Philip S. , Domash Lawrence H.
Published: February 2023

Binary optics is widely recognized as an important advance, but the full development of applications has been inhibited by the limited availability of the necessary software and hardware tools to experiment with binary elements. Special purpose scientific binary optic design software and e-beam fabrication facilities are found in only a few laboratories, to which most university or government researchers or industrial designers have little access.
Microlens arrays formed by crossed thin-film deposition of cylindrical microlenses
Authors: Grunwald R. , Ehlert R. , Woggon S. , Pätzold H.-J. , Witzmann H.-H.
Published: February 2023

Crossed 1D patterning allows to generate regular 2D optical microstructures like refractive microlens arrays with high fill factors which are of interest for photonics and laser applications (image sensing / processing, coupling, beam shaping, mode selection [1]). In general, a surface can be treated sequentially or simultaneously by (a) subtractive, (b) additive or (c) modifying processes thus forming a deepened or elevated relief or a periodically changed refractive index. Type (a) has been published for excimer laser ablation by means of crossed linear scans with laser spots or contour masks [2] and by direct writing laser lithography with two subsequent (crossed) exposures by linear intensity arrays followed by a tranfer into the substrate by ion etching [3]. Problems emerge from the unwanted deposition of debris, nonlinearities and the necessary control of the laser beam quality during a sufficiently long time. A well-known approach is the holographic method of Cowan [4,5] with three beam interference in a recording photoresist medium. By this method, high-definition, replicable hexagonal hole arrays with extremely small element diameters have been found. On the other hand, the set-up is not flexible enough for a fast change of the geometry and requires a proper adjustment, a homogeneous beam and the knowledge of the nonlinearities. Direct changes of the refractive index (e.g. in photorefractive media) can be used for a process of type (b). We report on an alternative, relatively simple technology of type (c) for the fabrication of close-packed arrays (orthogonal, hexagonal) based on the crossed vapour deposition which is preferentially suitable for moderate microlens parameters (pitches, focal lengths).
Focusing Waveguide Grating Coupler Using Diffractive Doublet
Authors: Sheard Stephen , Liao Tingdi , Yang Guoguang , Prewett Philip , Zhu Jianguo
Published: February 2023

A focusing waveguide grating coupler (FWGC)[1] implements simultaneously two optical functions. One is to couple out the guided-wave propagating in the waveguide structure; the other is to focus the outgoing beam into a small spot. Although combining two optical functions into a single diffractive optical element is quite attractive, the submicron feature sizes necessary to implement high–numerical–aperture focusing elements impose a significant burden on the lithography. Therefore, focusing waveguide grating couplers with high numerical aperture (NA> 0.25) have been rarely reported[2]. Furthermore, fabrication of such FWGCs usually relies upon direct–write electron beam lithography.
The way of diffractive optics into the laser resonator
Authors: Schwarzer Heiko , Wyrowski Frank
Published: February 2023

The effect of microstructured profiles on electromagnetic waves is the basic issue of diffractive optics. These profiles represent a significant extension of the possibilities to realize optical functions. Laser optics is of special importance for diffractive optics. In this paper examples of the use of diffractive elements outside and inside the laser resonator are given. Theoretical and experimental results are presented.
Laser Beam Relaying with Phase-Conjugate Diffractive Optical Elements
Authors: Makki Siamak , Leger James
Published: February 2023

In many high power optical systems, it is necessary to relay a beam from one component to another or from the laser output to the target Simple Gaussian beams can be easily relayed with conventional optics; however more complex profiles, such as a flat-top laser mode, require an afocal imaging system to reproduce the mode profile and phase front. Fig. 1a shows a conventional afocal system. For high Fresnel number applications, the intermediate focal point can result in undesirable concentration of light and subsequent air breakdown.
Fabrication of Submicron Feature Diffractive Elements using Near-Field Direct-Write Ultra-Violet Lithography
Authors: Smolyaninov Igor I. , Mait Joseph N. , Mazzoni David L. , Davis Christopher C.
Published: February 2023

The fabrication of surface relief diffractive elements using a series of binary exposures and etches in photo-resist is attractive because it relies upon standard lithographic techniques [1]. Disadvantages of this process include the necessity for mask generation prior to photoresist exposure and the logarithmic relationship between the desired number of phase levels and number of exposures. To overcome the latter restriction, the generation of gray level masks has been proposed [2]. However, both restrictions can be overcome if the photoresist is exposed directly. Electron beam [3] and laser beam direct-write [4] procedures have been proposed. Electron beam writing is attractive for its high resolution and laser beam writing for its cost. Both high resolution and low cost are possible if a tapered fiber is used to deliver energy to the photoresist [5,6]. We report on the fabrication of diffractive gratings with submicron features using a tapered fiber to deliver ultra-violet (UV) energy to a layer of photoresist.
One-step lithography for mass production of multilevel diffractive optical elements using High Energy Beam Sensitive (HEBS) gray-level mask
Authors: Däschner Walter , Stein Robert , Long Pin , Wu Chuck , Lee Sing H.
Published: February 2023

In order to satisfy the growing industrial need for Diffractive Optical Elements (DOEs), fabricated at a low price, we investigated the gray level mask fabrication aproach. Our apoach allows mask fabrication by a single e-beam direct write step without any involved resist processing. The mask can then be used in a optical lithography tool to generate a DOE structure in photoresist. This DOE structure will then be transfered into the substrate material by the use of a chemically assisted ion beam etching (CAIBE) process.
Fabrication of Fresnel zone plates for x-ray microscopy: diffractive optics for soft x-rays
Authors: Spector S. J. , Jacobsen C. J. , Tennant D. M.
Published: February 2023

Fresnel zone plates are diffractive optical elements which are currently being used for high resolution x-ray microscopy. Several groups fabricate zone plates for use in specific microscopes [1] and we present here a summary on the fabrication of zone plates for use in the Scanning Transmission X-ray Microscope at the National Synchrotron Light Source. X-ray microscopy has demonstrated imaging with resolution five times superior to that which can routinely be achieved by visible light microscopy. In addition, x-rays with wavelengths between the carbon (4.2 nm) and oxygen (2.3 nm) K absorption edges are absorbed nearly an order of magnitude more strongly by organics than by water. This creates a natural absorption contrast mechanism and allows the viewing of many biological specimens wet and intact (without sectioning) and at atmospheric pressure [2]. By taking advantage of the spectroscopic properties of x-rays, x-ray microscopy can be used to map chemical elements and their binding states. Fluorescent chemical labels and gold labels can also be imaged at high resolution. Furthermore, several labs including ours are developing the capability to view radiation-tough frozen hydrated specimens in x-ray microscopes.
Ultrahigh Spatial-Frequency, High-Contrast Periodic Structures Produced by Interference Lithography
Authors: Nguyen H.T. , Britten J.A. , Boyd R.D. , Shore B.W. , Perry M. D.
Published: February 2023

During efforts to produce multilayer high efficiency dielectric reflection gratings in oxides, 351nm high efficiency transmission gratings, and other development work, we required very high-contrast grating profiles in photoresist. High-contrast profiles are profiles with very steep sidewalls, greater than 80 degrees. It is quite difficult to achieve high-contrast profiles using interference lithography. The electric field distribution is sinusoidal. Therefore, one would conclude that the profile would resemble a sinusoid, as shown in Figure 1a. Early work with interference lithography produced grating profiles similar to the ones shown in Figure 1a.1-3 We have learned that if great care is taken in the processing steps, very different profiles can be achieved. Figure 1b shows a very high-contrast, high-aspect ratio grating profile in photoresist. The difference between Figure 1a and Figure lb is that 1) the photoresist profile in Figure lb has completely developed through to the substrate, and 2) the contrast characteristics of the photoresist used in Figure 1b are superior over the photoresist used in Figure 1a.
Surface-relief Gratings with Sharp Edges: Improvement of the Convergence of the Coordinate Transformation Method
Authors: Li Lifeng
Published: February 2023

Since it was first proposed one and a half decades ago, the coordinate transformation method of Chandezon et al.1 (the C method) for analyzing surface-relief gratings has gone through many stages of improvement and extension.2-10 By now, it is truly one of the most efficient and versatile theoretical tools for modeling gratings of arbitrary permittivity and (reasonably) arbitrary profiles. The most distinctive features of the C method, not shared with any other rigorous grating methods, are its virtually uniform convergence with respect to the incident polarization (TE, TM, or conical) and the medium permittivity (dielectric or metal), and its perfect suitability for modeling multilayer-coated gratings.
Liquid Crystal Phase Modulation Technique to Reduce the Spatial Frequency of Interferometric Fringes
Authors: Knight P. Douglas
Published: February 2023

Interferometric surface analysis involves looking at a fringe pattern and deriving information concerning the surface being imaged. By counting the fringes, one is able to find the surface deformation relative to a reference point. But a problem is encountered when the fringes are too dense for the fringe analysis software to count them. This limits the resolution of the system. But if a spatial light modulator (SLM) could modulate the phase profile in one arm of the interferometer so that the spatial frequency of the fringes is decreased enough to be counted, this problem would be solved.
Simplified Processing Method of Dichromated Gelatin Derived from Agfa 8E75HD Plates
Authors: Im Yong Seok , Lee Young Lak , Kwak Chong Hoon , Choe Ok Shik , Kim Sang Cheol
Published: February 2023

Dichromated gelatin (DCG) is one of the best recording materials for phase volume holograms. Since DCG has large refractive-index modulation, high resolution, high diffraction efficiency (DE), and good signal-to-noise ratio, it is suitable for preparing holographic optical elements. Several papers on the hologram formation mechanism in DCG have been reported in the literature.[1-5] The simplest way to obtain a good hologram is by use of photographic plates, dissolving the silver halide in a fixing bath, and sensitizing it with a solution of ammonium dichromate. Upto now, most of the works has been done using the gelatin layer of Kodak 649F plates. Oliva et al.,[8] presented the holographic characteristics of the DCG plates obtained from Agfa 8E75HD plates. The processing procedures for preparing high-quality DCG holographic optical elements (HOEs) developed by Oliva, however, are tedious, since it takes at least 12 hours to process one HOEs. In this work, we present very simple method for making highly efficient DCG hologram starting with Agfa 8E75HD plates. Beginning with Agfa 8E75HD plates, the complete processing time including preprocessing, sensitization, and development is just 2 hours. In addition, DCG hologram has a high DE of 81.5%.
Electric Fields and Poynting Vectors in Dielectric Gratings
Authors: Shore Bruce W. , Li Lifeng , Feit Michael D.
Published: February 2023

The electric field E is the most significant of the several fields of electromagnetic radiation, because it indicates regions of dielectric response. The nodes and antinodes of plane wave structure are clearly visible in plots of the E field, as are regions of localized enhancement near grating surfaces. It is in these enhanced field regions that one expects to find the strongest photoelectric response, or the first damage as the field is increased.
Diffractive-refractive achromatic optical processor for white-light spatial filtering
Authors: Andrés P. , Tajahuerce E. , Lancis J. , Climent V. , Fernández-Alonso M.
Published: February 2023

White-light Fourier processing techniques allow to improve the signal-to-noise ratio, to use non-laser sources, and, of course, to deal with color input signals. Nevertheless, conventional optical processing operations performed with broadband illumination are severally limited due to the wavelength dependence of the diffraction phenomenon. In this way, the Fraunhofer diffraction pattern of the input transparency is chromatic dispersed, both axial and laterally and, furthermore, the insertion of spatial filters at the frequency plane produces additional chromatic effects at the output plane.
Diffraction Optics - A century from basic studies to mass production
Authors: Loewen Erwin G.
Published: February 2023

Diffractive Optics, defined as the use of diffraction to aid or perform the imaging process, belongs to the large familiy of 19th century concepts in optics that have moved from obscurity to important technology thanks to a fascinating confluence of recently discovered needs with development of a whole collection of new enabling technologies. These include computational methods, optical materials, and finally precision engineering processes that convert the impossible into the possible. Not one of these basic developments originated because of demands from the Diffraction Optics community. They came from the outside world and were conveniently appropriated as needs arose.
Diffractive Optical Elements for 3-D Displays Based on the Partial Pixel 3-D Display Architecture
Authors: Nordin G. P. , Jones M. W. , Lindquist R. G. , Kulick J. H. , Kowel S. T.
Published: February 2023

Real-time holographic display architectures are currently of significant interest,1-2 in part due to intense international competition to develop advanced displays for high definition television, three-dimensional (3-D) workstations, and virtual reality systems. We have recently invented an alternate approach to holographic displays for such applications. Our 3-D display architecture (referred to as the “partial pixel architecture”) is functionally equivalent to a holographic stereogram, yet lends itself to real-time implementation using flat panel liquid crystal technology in conjunction with diffractive optical elements.3 A key innovation of the architecture is the encoding of very high space-bandwidth product components typical of holographic displays into a fixed diffractive optical element (DOE), while the lower space-bandwidth product components of actual images are displayed in real-time on a conventional liquid crystal display (LCD). In this paper we discuss diffractive optical element design considerations and implementation issues for real-time 3-D displays based on the partial pixel architecture.
Grating diffraction analysis: Maxwell’s or Kirchhoff diffraction integrals
Authors: Moharam M. G. , Dunn S.
Published: February 2023

Scalar diffraction theory is widely used to design and analyze diffractive optical elements. This approach has been the approach of choice for it is easy to use, lacks computation strain, and more importantly, offer some direct approach for the design of diffractive elements. The validity and, therefore, the usability of the scalar diffraction approaches are based on the assumption that the smallest feature in the diffractive element is much greater than the wavelength of incident light. However, recent advances in the fabrication techniques have resulted in producing diffractive optical elements with small feature sizes of wavelength and subwavelength dimensions and scalar diffraction approaches may not be applicable. Rigorous diffraction analysis techniques have been developed and/or refined to analyze these wavelength size structures. These methods include rigorous coupled-wave theory, modal approach, method of moments, and other differential and integral methods. These electromagnetic theory based approaches provide powerful, accurate, and relatively efficient analysis methods. However, they do not provide satisfactory tools for the systematic design of diffraction elements.
Guided-mode resonant filters incorporating the Brewster effect
Authors: Magnusson R. , Shin D. , Liu Z. S.
Published: February 2023

Guided-mode resonance (GMR) effects are observed in dielectric and semiconductor thin-film structures comprising diffractive and waveguide layers1,2. High-efficiency resonances are realizable under zero-order conditions imposed by a diffractive element with suitably high spatial frequency such that all higher-order diffracted waves are evanescent. For parametric conditions such that one of these evanescent waves couples to a (leaky) waveguide mode, a resonance occurs with associated strong power exchange between the propagating zero-order waves. This resonance coupling effect is typically represented as spectral (with constant angle of incidence) or angular (with constant wavelength) variation of the diffraction efficiency of the transmitted and reflected waves. Theoretical and experimental studies1–10 have illustrated the feasibility of utilizing this basic effect for numerous applications11.
Guided-mode resonance filters generated with genetic algorithms
Authors: Tibuleac S. , Shin D. , Magnusson R. , Zuffada C.
Published: February 2023

This paper focuses on the application of genetic algorithms to the study and design of reflection and transmission filters based on the guided-mode resonance (GMR) effect in waveguide gratings.1–3 As genetic algorithms are well suited for problems with multidimensional, large search spaces4, they may be used effectively for optical filter design involving multiple periodic and homogeneous layers. In this work, the genetic algorithm library PGAPACK5 is combined with a forward code based on rigorous coupled-wave analysis6 in a new computer program that optimizes the merit function of a multilayer diffractive optical structure. Thus, a GMR-filter response with a given central wavelength, linewidth and sideband levels can be specified with a corresponding diffractive structure yielding approximately the specified response provided by the program. The net effect of this approach is that the inverse problem of finding a structure (i. e., layer thicknesses, refractive indices, fill factors, grating period) that yields a given filter response can be solved. In addition to providing useful filter designs, this approach may aid in the discovery of diffractive structures with profiles that may differ significantly from those ordinarily treated.
Multilevel diffraction gratings in the resonance domain: rigorous optimization by simulated annealing
Authors: Noponen Eero
Published: February 2023

In the design of diffractive optical elements sophisticated optimization algorithms are required that are capable of finding the optimum structure of the element, described by a set of parameters that define, e.g., the surface profile of one grating period. For binary and multilevel profiles the parameters to be optimized include the profile depth and the positions of the steps or transition points. A wide range of methods exist that are suitable for the solution of this kind of parametric optimization problems, such as direct binary search, conjugate gradient method, steepest-descent method, iterative Fourier-transformation algorithm, simulated annealing, and genetic algorithms.
Stratified diffractive optic approach for creating high efficiency gratings
Authors: Chambers Diana M. , Nordin Gregory P.
Published: February 2023

Gratings with high efficiency in a single diffracted order can be realized with both volume holographic and diffractive optical elements. However, each method has limitations that restrict the applications in which they can be used. For example, high efficiency volume holographic gratings require an appropriate combination of thickness and permittivity modulation throughout the bulk of the material. Possible combinations of those two characteristics are limited by properties of currently available materials, thus restricting the range of applications for volume holographic gratings. Efficiency of a diffractive optic grating is dependent on its approximation of an ideal analog profile using discrete features. The size of constituent features and, consequently, the number that can be used within a required grating period restricts the applications in which diffractive optic gratings can be used. These limitations imply that there are applications which cannot be addressed by either technology. In this paper we propose to address a number of applications in this category with a new method of creating high efficiency gratings which we call stratified diffractive optic gratings. In this approach diffractive optic techniques are used to create an optical structure that emulates volume grating behavior.
Grating Coupler utilizing third-order Diffraction
Authors: Ura Shogo , Fujii Takayoshi , Suhara Toshiaki , Nishihara Hiroshi
Published: February 2023

A grating coupler [1,2] is useful for exciting a guided wave or taking out a guided wave into the air, and is one of the key components in constructing integrated optic devices [3]. A grating coupler utilizing higher-order diffraction has much longer grating period than that of a 1st-order grating coupler, and is attractive from a view point of fabrication and design flexibility especially for a case using a short wavelength or a high guided-mode index. However, a coupling efficiency of the usual higher-order diffraction is too low to be utilized in practical applications. We reported [4] a proposal and design consideration of a high-efficiency 3rd-order grating coupler for application to a GaAs/AlGaAs waveguide. In this report, an efficiency enhancement technique for 3rd-order grating coupler is demonstrated experimentally for the first time. Wavelength of 0.82μm and a glass waveguide are used for the demonstration.
Two-level binary diffractive optical elements for symmetric line-patterns generation from laser diodes
Authors: Golub Michael A.
Published: February 2023

Numerous tasks of laser pointing, visual adjustment, targeting and laser radar require shaping of laser diode beam into the line contour patterns. The examples of the line patterns are straight-line segment, cross, contour of rectangle, system of points. One more task is to circularize the elliptical beam that is typical for laser diodes even after passing through standard collimators. The traditional approach is either to use cylindrical lenses1 or to apply computer-generated phase holograms reconstructing the system of points2. The usual problem in computer-generated holograms is the dot-type structure of the image, limited possibilities to achieve uniform intensity distribution along lines. Patterns containing several lines can be formed by faceted diffractive optical elements (DOEs), which use some part of clear aperture for line segment generation. However splitting the aperture adds problems in line uniformity, width, interference between lines. Other way is to use multi-channel DOEs3 utilizing several diffraction orders of DOE at once. We propose a special way to generate symmetrical patterns based on the full use of symmetrical diffraction orders of binary diffraction grating. Full cycle of design, computer simulation, fabrication and experimental investigation of DOEs for laser diodes is described in this report.
Neural networks as a statistical model for optical scatterometry
Authors: Kallioniemi Ilkka , Saarinen Jyrki , Oja Erkki
Published: February 2023

The advancement of new lithography techniques, such as electron-beam lithography and x-ray lithography, has enabled the fabrication of diffractive optical elements (DOEs) with feature sizes of the order of hundreds of nanometers and even less. There is also a continuous trend towards smaller line widths and higher packaging densities in memory cells and other semiconductor devices. Most of the elements are still done successfully by UV lithography which is still in the development stage in the deep UV region.
One-Step fabrication of a high-efficiency flat-top beam shaper
Authors: Huang Xu Guang , Wang Michael R.
Published: February 2023

A compact beam shaper is required to efficiently convert coherent Gaussian beam into a flat-top beam for applications such as optical processing, laser radar, laser microfabrication, and laser scanning. A number of techniques for laser beam shaping have been developed so far [1-3]. Directly truncating the Gaussian beam with an aperture and weighting the Gaussian beam with a neutral density filter of proper amplitude transmittance profile have very poor energy efficiency. Binary shaper based on interlaced diffraction gratings suffers from its limited diffraction efficiency. Diffractive optics beam shaper fabricated by computer-generated hologram technique, by only changing the propagation phase patterns prior to diffraction focusing, is an effective beam shaper method.
Effects of fabrication errors on Talbot array illuminators
Authors: Suleski Thomas J.
Published: February 2023

Talbot array illuminators (TAI’s) were first proposed by Lohmann as a means of creating optical interconnections.1 TAI’s are phase gratings that, under coherent, plane wave illumination, give rise to 100% modulated, square wave field and irradiance patterns. These patterns bear a strong resemblance to the spatial structure of the phase grating itself (Figure 1). Such patterns are referred to as Lohmann images2 to distinguish them from Talbot images. Talbot images are replicas of the complex field distribution immediately behind a periodic structure. Talbot images occur at integer multiples of the Talbot distance ZT = 2d2/λ, where d is the grating period and λ is the wavelength of the illuminating radiation. By comparison, only a limited number of combinations of grating duty cycle w/d, phase depth ϕ, and propagation distance z will generate Lohmann images.
Analysis and modeling of nonparaxial diffractive optical elements on curvilinear surfaces
Authors: Golub Michael A. , Grossinger Israel
Published: February 2023

Increasing possibilities of precision diamond turning and lithography bring to reality diffractive micro-relief on spherical, aspherical and other curvilinear surfaces. Contact lenses, plastic aspherical, and collimator lenses, aberration correction plates on ZnSe and other materials give the practical examples. Creation of means for design and computer modeling of curvilinear-substrate DOEs are felt essential.
Fabrication of Functional Optical Structures Based On Photonic Crystals
Authors: Scherer A. , Yariv A. , Fainman Y. , Yablonovitch E. , D’Urso B. , Painter O. , Cheng C.C.
Published: February 2023

We have developed techniques to fabricate photonic crystals within functional semiconductor materials to reflect, polarise, and filter light. These manufacturable structures have now allowed us to define high-contrast polarizing beam-splitters and ultra-small optical cavities, and hold the promise of many exciting new applications. Polarizers with over 820:1 TE/TM transmission ratios have been fabricated by microfabricating gratings through a 1-D multilayer Bragg mirror, thereby forming an in-plane 2-D photonic bandgap crystal. Ultra-small optical cavities have also been defined by perforating very thin InGaAsP/InGaAs membranes with 2-D photonic crystals to define in-plane optical resonators. Here, we will describe the fabrication methods and the observed performance of these devices.
Beam-Steering in the Spectrum of a Liquid Crystal Spatial Light Modulator
Authors: Rodhe Peder
Published: February 2023

In this report we take up some new aspects of optical beam-steering by means of liquid crystal spatial light modulators (SLM's). Our starting-point is that any form of modulation should modify the spectrum of an applied "carrier" [1]. To this end, we devote our interest to diffraction in the spectrum established by these SLM's [2], focussing on applications of smectics (either A* or C* [3]), because these materials have shown their potential, e.g., for rapid switching and small pixel size.
A Contribution to the Analysis of Relief Diffraction Gratings
Authors: Richter I. , Ryzí Z. , Fiala P.
Published: February 2023

In the last years, modeling in diffractive optics have been of great interest due to increasing amount of applications of diffractive optical elements in many different optical areas [1]. As far as the analysis problem is of interest, originally-used scalar methods became inapplicable, and more complicated (i.e. rigorous) treatments had to be developed. Among several rigorous methods (integral, modal) for the analysis of diffraction characteristics of dielectric gratings proposed, the rigorous coupled-wave analysis (RCWA) has been employed the most since it is a deterministic, noniterative, relatively straightforward technique for obtaining the exact solution from the exact electromagnetic formulation [2].