bluuebunny/crossref_metadata_2025 huggingface dataset:
Coherent laser radar for vibrometry
Authors: Letalick Dietmar , Karlsson Christer , Renhorn Ingmar
Published: February 2023

Coherent laser radar (CLR) systems have been investigated over several decades primarily for military applications. Depending on the application, several design parameters, e.g. the choice of system technology and wavelength, have to be considered. A short wavelength system can give advantages in robustness and size whereas a long wavelength system can give advantages in a lower attenuation by aerosols, which results in a longer range. Applications for a multi-purpose system a CO2-ladar include, e.g., range finding, vibrometry, and 3-D imaging. A CLR system is very useful for remote sensing of vibrational and rotational characteristics of surfaces and objects. Such information can be used in e.g. inspection and maintenance of helicopters and aircraft, and also for platform identification.
Coherent lidar efficiency enhancement using graded-reflectance resonator optics
Authors: Tratt David M. , Bowers Mark S.
Published: February 2023

For a number of years the use of graded-reflectance resonator optics has been advocated as a means of improving the overall efficiency of lidar systems. Initial efforts aimed at quantifying the degree of benefit to be expected have relied on the putative ability of such optics to impose a well-defined transverse description on the lidar transmitter output1,2. While this approach has permitted a useful insight into the question at hand, it was nevertheless recognized that there were limits to this deterministic assumption which could only properly be addressed by means of a diffractive eigenmode treatment. The purpose of this paper is to report on the results of just such an analysis.
Solid-state laser technology development at Lincoln Laboratory
Authors: Fan T. Y. , Zayhowski J. , Sanchez A.
Published: February 2023

The development of solid-state laser technology for coherent laser radar at MIT Lincoln Laboratory has been focused in the areas of frequency-modulatable, single-frequency master oscillators for chirped laser radars1,2 and Ho3+ lasers operating at 2.1 μm pumped by 1.9-μm diode lasers3. These Ho3+ lasers have the potential to scale to higher average power and energy per pulse than Tm-sensitized Ho3+ lasers pumped by 0.78-μm diode lasers.
Eye-Safe Semiconductor Lasers for Lidar: Experimental Studies of Coherence and Atmospheric Propagation
Authors: Harris M , Pearson G N , Vaughan J M , Karlsson C , Letalick D , Renhorn I
Published: February 2023

Shorter-wavelength lasers (with λ of order 1.5-2.5 μm), both semiconductor and solid-state, are showing increasing promise for lidar applications, with improved power levels and frequency stability. Advantages over existing long-wavelength systems include: compactness and robustness, compatibility with cheap components and optical fibres from the telecommunications industry, and the lack of need for cooled detectors. It is thus becoming important to investigate the primary aspects of such lasers to establish their performance characteristics. The potential for semiconductor lasers in lidar/rangefinder systems is currently limited by their relatively low output power and short coherence length (or equivalently, their broad spectral bandwidth). This reduces the level of performance in range and velocity resolution, as well as leading to a degraded signal-to-noise ratio. In fact, the two considerations of power and linewidth are closely linked, because attempts to increase the output by turning up the laser drive current eventually lead to a significant increase in bandwidth. This "rebroadening" effect is poorly understood; it imposes a limit on the coherence performance of this type of laser, and hence also on its capabilities in laser radar applications. The work reported here could benefit understanding of the serious problem of rebroadening. Further limitations to the use of semiconductor lasers may result from the increased effects of atmospheric turbulence at these wavelengths.
Airborne cw Doppler Lidar - ADOLAR
Authors: Rahm S.
Published: February 2023

For the airborne measurement of the wind field, knowledge of the exact velocity and orientation of the plane is mandatory. Any small deviation in these parameter will cause an error in the estimation of the wind field. The conical scanning airborne cw CO2 Doppler lidar ADOLAR has been designed to gain experience concerning the correction of the inertial reference system on board the aircraft using the ground return as well as for testing different signal processing algorithms. Beside this the instrument can also be used for the measurement of small scale wind phenomena e.g. valley wind or flow around a hill.
Synthetic Array Heterodyne Detection: Developments Within the Caliope CO2 Dial Program
Authors: Rehse Steven J. , Strauss Charlie E.M.
Published: February 2023

A new technique, Synthetic Array Heterodyne Detection, offers a wider field of view and improved signal to noise for coherent DIAL systems by reducing speckle interference. We have implemented a synthetic multi pixel array using a CO2 laser on a single element HgCdTe photodiode.
Heterodyne Detection for Simultaneous Range Resolved Measurements of Atmospheric Constituents and Wind Velocity
Authors: Favreau X. , Delville P. , Dabas A. , Salamitou Ph. , Flamant P. H. , Pelon J. , Loth C.
Published: February 2023

Simultaneous measurements of atmospheric constituents and wind velocity in the boundary layer is of the utmost importance for environment and pollution monitoring. A CO2 lidar is well suited for such an application for there exist a large number of coincidences between CO2 laser lines and absorption spectra of species of interest. The molecules under study will provide the absorption features while the aerosols particles will scatter the incident light giving rise to a lidar signal. Regarding such an application, a heterodyne detection is efficient at 10 μm provided the number of speckles in a transverse plane on the receiver is small (about 4). Then, it provides with improved sensitivity with respect to direct detection at the same wavelength and Doppler frequency shift measurement.
Multi-Purpose CW CO2 Autodyne Lidar
Authors: Gordov E.P. , Khmelnitskii G.S. , Fazliev A.Z.
Published: February 2023

Laser monitoring of atmospheric and polluting gas concentrations in the atmosphere as well as laser detection and imaging are still need in sensitive and at the same time simple in design and operation and inexpensive lidar instrumentation, especially in those which can perform the both tasks during one measurement sequence.
Space Industry Growth and Business Alliances
Authors: Beer C. Neil
Published: February 2023

The growth of space science and commerce is a high priority in the state of Colorado. Various alliances among federal and state government agencies and the business community will foster growth in space access and create new opportunities. Activities in this area are discussed.
Development and Performance of a CW Coherent Laser Radar for Detecting Wake Vortices*
Authors: Heinrichs R.M. , Freehart R.E. , Dasey T.J. , Mandra R.S.
Published: February 2023

A CW-coherent laser radar using a 20-Watt CO2laser has been constructed and deployed for the measurement of wake-vortex turbulence. This is part of a larger effort to understand the motion and decay of wake vortices as a function of the local atmospheric conditions. The construction and operation of the lidar and the initial fielding at Memphis International Airport are described.
Design Considerations for an Operational Wake Vortex Lidar Sensor at 2-micron Wavelengths
Authors: Koch Grady , Staton Leo , Nguyen Chi
Published: February 2023

NASA and FAA initiated a program in 1994 to develop methods for setting aircraft spacings in the air terminal area by incorporating information on the real-time behavior of aircraft wake vortices. The current wake separation standards were developed in the 1970’s when there was relatively light airport traffic and a logical break point by which to categorize aircraft. Today’s continuum of aircraft sizes and increased airport packing densities have created a need for re-evaluation of wake separation standards. The goals of this effort are to ensure that separation standards are adequate for safety and to reduce aircraft spacing for higher airport capacity. Of particular interest are the different requirements for landing under visual flight conditions and instrument flight conditions. Over the years, greater spacings have been established for instrument flight than for visual flight conditions.1
An Algorithm for the Recognition and Tracking of Aircraft Wake Vortices with a Continuous Wave Coherent Laser Radar*
Authors: Dasey Timothy J. , Heinrichs Richard
Published: February 2023

A real-time algorithm for localizing and actively following wake vortices is described. Results from an experiment at Memphis airport and from modeled data are discussed. This is the first such system to track vortices, resulting in a more efficient scan and allowing more frequent estimates of location and strength.
Investigation of Conceptual Synthetic Aperture Infrared Laser Radars
Authors: Yoshikado Shin , Aruga Tadashi
Published: February 2023

Synthetic aperture radars(SAR) have widely been used for high-resolution imaging of the earth's and planets' surfaces. In microwave remote sensing fields, aperture synthesis usually means the signal processing for obtaining an image of the area sequentially illuminated by the radar wave emitted from a single moving real aperture. It is a technique now in well-established stages for radio wavelengths.
Coherent Optical Signal Processing for a Doppler Lidar using a Michelson Interferometer
Authors: Schwiesow R. L. , Mayor S. D.
Published: February 2023

There are a number of reasons to consider operating a Doppler lidar at wavelengths near 1 µm rather than at 10.6 µm. A very important one for NCAR applications is that the shorter-wavelength lidar offers better range and velocity resolution for measurements in the turbulent boundary layer because the product of range resolution and spectral width of the velocity spectrum is proportional to the wavelength. In addition, the quantized backscattering coefficient (number of photons backscattered for a given transmitted pulse energy) may be greater near 1 µ than at 10.6 µm for particle size distributions with a relatively small mean particle size.
Formation and Chemical Reactivity of Partially Ga-terminated Si(111) Surfaces Masakazu Ichikawa
Authors: Ichikawa Masakazu , Fujita Ken , Kusumi Yukihiro
Published: February 2023

The passivation of semiconductor surfaces by adsorbates is prospective
to construct nanoscale structures such as quantum wires and dopings.
Since the adsorption and dissociation of gas molecules supplied on a
surface depend on the local chemical reactivity on the surface,
selective adsorption or growth is realized on the nanometer scale by
removing the adsorbates for the passivation with atomic accuracy.
Atomic Layer Controlled Growth of SiO2 Using Binary Reaction Sequence Chemistry
Authors: Klaus J. W. , Ott A. W. , Johnson J. M. , George S. M.
Published: February 2023

Thin SiO2 films were deposited with atomic layer control onto Si(100) and on Al2O3 films grown on Si(100) using binary reaction sequence chemistry. The atomic layer controlled growth was accomplished by separating the binary reaction SiCl4 + 2H2O --> SiO2 + 4HCl into two half-reactions: where the asterisks designate the surface species. If each half-reaction is self-limiting and goes to completion, then successive application of the A and B half-reactions in an ABAB… sequence should produce layer-by-layer SiO2 deposition. The atomic layer controlled growth of the SiO2 films was achieved at temperatures between 600-800 K and reactant pressures of 1 - 10 Torr. The SiO2 growth rates were monitored with an in-situ spectroscopic ellipsometer versus deposition temperature and reactant exposure time. The surface topography of the deposited SiO2 films was measured using atomic force microscopy (AFM). The AFM images revealed that the SiO2 films were extremely flat with a roughness nearly identical to the initial substrate surfaces.
Interface Controlled Structure Evolution in Al Thin Film Growth
Authors: Adams D.P. , Mayer T.M.
Published: February 2023

In the past, several adsorbates have been used to change thin film growth modes. This has been explained to occur by either modification of surface energetics or growth kinetics. In the present work, we study adsorbate - mediated Al film growth in order to address how initial surface chemistry can be used to tailor film microstructure, both at the early stages of growth (~1 monolayer. ML) and for thick layers(~1000MLs). For this investigation. Al thin film growth onto Si involves physical vapor deposition.
Observation of Si-Ge Alloy Formation for Germanium Growth on H-Terminated Si(111) by Real-Time Ellipsometry
Authors: Barth M. , Hess P.
Published: February 2023

The photon-controlled nucleation and growth of amorphous hydrogenated germanium (a-Ge:H) was investigated for different silicon substrate surfaces. The 6.4 eV photons of a 193 nm ArF laser initiated the deposition process by photolyzing digermane in the gas phase (parallel laser beam surface configuration). The growth process was monitored in situ by real-time spectroscopic ellipsometry (RTSE) to obtain the evolution of the optical functions and to get information on the microstructure and nucleation process.
Nanofabrication of Quantum Wires and Quantum Wells by Self-Organizing Step Flow Growth
Authors: Tersoff Jerry
Published: February 2023

Electronic devices often incorporate layers of different semiconductors, which are intended to be smooth and uniform. However, additional interesting structures sometimes develop spontaneously. These include step bunches, facets, composition modulations, and even spontaneous formation of vertical or lateral superlattices. These "accidental" structures, if they can be controlled, may have numerous applications. However, understanding and control have been hampered by the lack of simple models which describe realistic growth conditions (including strain). I will describe calculations of step-flow growth, including strain and alloy decomposition. The results point up several opportunities for controlled self-assembly and self-organization of nanostructures.
Self-assembly of Compound Semiconductor Quantum Dots For Optoelectronic Applications
Authors: Arakawa Yasuhiko
Published: February 2023

A reduction of dimensionality of the electron motions in quantum nano-structures brings new phenomena in semiconductor physics. Moreover, it allows new device concept to be considered and permits improvements in performance of the transistors and lasers. In 1982, the quantum wire laser and the quantum dot laser were proposed, predicting significant improvement of lasing characteristics[1]. When the concept was proposed, it was considered that the quantum wires and quantum dots would be realized in the 21
Self-Assembling of Silicon Quantum Dot and Its Electronic Characterization
Authors: Nakagawa K. , Fukuda M. , Miyazaki S. , Hirose M.
Published: February 2023

Formation of Si quantum dot array on ultrathin SiO2 is a key to develop a silicon-based resonant tunneling device[1] or quantum-dot floating-gate MOS memory[2]. In order to achieve room temperature operation of such quantum dot devices, the dot size should be as small as 3nm as evaluated by a simple quantum box model or coulombic charging energy. Recently it is demonstrated that Si quantum dots can be spontaneously produced on SiO2 by controlling the early stages of low-pressure chemical vapor deposition(LPCVD) of SiH4[1, 3]. For the purpose of the device application the dot size distribution should be minimized and the dot density per unit area must be as high as 1012/cm2. This paper describes a formation mechanism of nanometer-scale Si dots on SiO2 during LPCVD and a possible route to control the size distribution and the areal density of Si dots.
Self-Organized Organic Semiconductor Quantum Wires and Boxes
Authors: Jenekhe Samson A. , Chen X. Linda
Published: February 2023

The growing interest in semiconducting polymers as device materials 1-3 for applications such as thin films transistors, light-emitting diodes, lasers, and photodectors has also stimulated theoretical and experimental interest in low-dimensional organic semiconductors. 4-8 It is expected that organic quantum wells, quantum wires, quantum boxes, and superlattices may exhibit strong excitonic effects and large exciton binding energies [~0.5 -1.0 eV] in part because of the relatively small dielectric constants of organic molecules and polymers [~3 - 4].4-6 In spite of the many theoretical studies which have predicted quantum confinement effects in heterostructured semiconducting polymers,5,6 clear experimental observation of such effects was not reported until very recently. 9,10 One major experimental difficulty is the rather small exciton Bohr radii (aB) in bulk organic semiconductors (aB~1.0 - 1.5 nm) which places severe limitations on suitable techniques for preparing the nanoscale structures.10,11
Optical Spectroscopy of Single GaAs Quantum Dots
Authors: Gammon D. , Brown S.W. , Kennedy T.A. , Snow E.S. , Shanabrook B.V. , Katzer D.S. , Park D.
Published: February 2023

We discuss a number of experiments involving optical spectroscopy of excitons localized by interface fluctuations in narrow GaAs quantum wells. Monolayer-high steps at the interface lead to lateral confinement that in some cases can be described by a quantum dot (Qdot) potential. We focus on Qdots that are 3 - 5 nm thick, as determined by the quantum well thickness, and an order of magnitude larger in the lateral dimensions, as determined by the sizes of the monolayer-high islands at the interfaces [1].
Near Field Optical Microscopy and Spectroscopy for Ultra Large Scale Integrated Circuits
Authors: Duncan Walter M.
Published: February 2023

Increases in density of integration and concomitant reductions in minimum feature size have driven requirements for spatial resolution in analytical and metrological instrumentation for microelectronic structures to well below the limit set by far field diffraction of visible light. With the exception of scanned probe microscopy, analytical and metrological instruments with spatial resolutions adequate for the current generation of complementary metal oxide semiconductor (CMOS) structures all rely on ion or electron methods. Conventional ion or electron based methods are destructive and instrumentation has a high cost of ownership. Hence it is the goal of our work to develop nondestructive near field scanning optical microscopy/spectroscopy (NSOM/S) instrumentation and applications as an alternative to electron and ion methods. Imaging capabilities of near field scanning optical microscopy approach 0.02 µm and combined with spectroscopic analysis potentially provides chemical analysis of defects, particles, and thin films with ultra high spatial resolution.
Optical Response of GaAs(001) Surfaces for Monitoring and Control of Atomic-Layer-Defined Processing
Authors: Eryiğit Resul , Herman Irving P.
Published: February 2023

Progress in the miniaturization of electronic devices, the emergence of compound semiconductors in optoelectronics applications, and the development of quantum device structures based on nanostructures can continue only with an improved understanding and control of surfaces and interfacial regions. One important way to achieve such control is by real-time measurements during growth and etching. In addition to the standard surface-analysis techniques that require near ultrahigh vacuum (UHV) conditions (such as XPS, LEED, and EELS), there is a need for noninvasive real-time surface probes with submonolayer sensitivity that will be applicable to either the UHV environment of a molecular beam epitaxy (MBE) chamber or the atmospheric-pressure environment of an organometallic vapor phase epitaxy (OMVPE) reactor. Optical probes can be used during either type of processing.
Semiconductor Nanocrystallites: Building Blocks for Quantum Dot Structures
Authors: Bawendi Moungi G.
Published: February 2023

We describe the electronic properties of nearly monodisperse CdSe nanocrystals as isolated quantum dots and in close packed structures of quantum dots.
Size Dependent Electronic Level Structure of Colloidal InAs Nanocrystal Quantum Dots
Authors: Banin U. , Lee J. C. , Guzelian A. A. , Alivisatos A. P.
Published: February 2023

Semiconductor nanocrystals serve as model systems for evolution of bulk properties from the solid state to the molecular regime.1 In this work we study a fundamental question related with quantum confinement in semiconductors - the evolution of the electronic level structure with size in InAs nanocrystals.
Ultrafast Optical Nonlinearities and Carrier Dynamics in Direct- and Indirect-Gap Semiconductor Nanocrystals
Authors: Klimov Victor I. , McBranch Duncan W.
Published: February 2023

Semiconductor nanocrystals (NCs) exhibit large and fast optical nonlinearities, and efficient photo- and electroluminescence that make them promising materials for applications in optoelectronics and ultrafast optical switching. The nonlinear optical and luminescent properties of NCs are significantly affected by carrier dynamics. Carrier trapping and a nonradiative Auger process are believed to play a major role in the early stages of carrier relaxation, resulting in ultrafast picosecond and subpicosecond dynamics measured in femtosecond pump-probe, photoluminescence (PL) up-conversion, and photoecho experiments.
”Resistance” of a molecular wire
Authors: Datta Supriyo , Tian Weidong , Kubiak Clifford P.
Published: February 2023

A number of groups have recently reported experimental studies of the electronic conduction through a monolayer of organic molecules self-assembled between two large metallic contacts [1-5]. Measured resistances to date are at least several megohms per molecule and has to be lowered by a few orders of magnitude before such wires can be considered seriously for interconnect applications. In this paper we present a simple model that lends insight into the factors affecting the molecular resistance and suggests possible schemes for designing molecular wires with lower resistance that can be truly said to 'conduct'.
Photo- and Cathodoluminescence in Quantum-Confined Semiconductor Intercalates
Authors: Phillips MarkL. F. , Shea Lauren E. , Nenoff Tina M. , Tallant David R. , Walko Robert J.
Published: February 2023

New vacuum ultraviolet (VUV) and cathodoluminescent (CL) phosphors are needed for a variety of display applications. Plasma display panels, which use VUV phosphors to convert short wavelengths (< 200 nm) to visible or near-UV light, need materials with high energy conversion efficiencies. This, in turn, requires high quantum yields and good VUV absorption. CL phosphors that can be operated at low voltages are needed for flat panel displays based on field emission and vacuum fluorescence.
Optical Characterization of Silica Aerogels
Authors: Cahill Glauser Sally A. , Lee Howard W. H.
Published: February 2023

Aerogels are a unique class of ultra low density solid materials with interconnected pores and porosities up to 98%. Their nanometer-sized structures create remarkable optical, electrical, thermal, and structural properties. We studied the optical properties of silica aerogels with densities ranging from 8 mg/cc to 172 mg/cc. The preparation of the aerogels studied in this paper is discussed in detail in reference 1. We report on the photoluminescence and the lifetime decay of the luminescence as well as correlate the absorption and excitation spectra. The luminescence ranges from the ultraviolet to the visible and the absorption occurs well below the bandgap of amorphous silica. The results are discussed in terms of implications for the electronic structure of aerogels as well as similarities and differences with the optical and electronic properties of amorphous silica which has densities near 2200 mg/cc. Aerogels have interesting optical properties that may enable a variety of optical applications.
Diffractive Optical Elements Fabricated by Electron Beam Lithography
Authors: Smith Robin
Published: February 2023

In recent years we have studied binary amplitude diffractive optical elements fabricated by means of electron beam lithography in the form of opaque chrome rulings on glass substrates and binary phase elements produced from these by contact copying into photoresist. We have investigated a range of imaging structures including zone plates, diffractive axicons, Dammann gratings and elements designed for optical testing. We are currently developing elements to generate particular aberrated wavefronts for the direct recording of volume diffractive elements in DCG and elements to generate curved line patterns for single shot CO2 laser machining.
Pure Silica Diffraction Gratings and Mocrolens Arrays Made by the Sol-Gel Process
Authors: Nogues Jean-Luc
Published: February 2023

Surface feature optics, including binary optics, sinusoidal gratings, and high-fill factor microlens arrays, are being intensively developed for use in beam splitting and optical computing. Most are fabricated in plastics, and are therefore subject to such general disadvantages as limited optical transmission and high CTE. Some can be scribed in silica but dimensions are limited and fabrication costs are extremely high. Using the sol-gel process, it is possible to fabricate surface feature optics in pure silica by a room-temperature molding technique. This technique provides the advantage of the highly favorable optical qualities of silica, such as broadband transmission, low CTE and exceptional resistance to laser damage.
Fabrication of continuous relief diffractive optical elements by laser writing
Authors: Gale M.T. , Schütz H. , Ehbets P. , Prongué D.
Published: February 2023

The fabrication of Diffractive Optical Elements (DOEs) in the form of continuous microrelief structures with programmable, complex phase profiles is still a challenging application of modern microlithographic technology. This paper describes the status and recent results of a laser writing system which has been built-up at the Paul Scherrer Institute in Zurich (PSIZ) and constantly refined over recent years.
Diffractive optics in a free-space digital optic system
Authors: Morrison R.L. , Walker S.L. , Cloonan T.J. , Tooley F.A.P. , McCormick F.B. , Sasian J.M. , Lentine A.L. , Brubaker J.L. , Crisci R.J. , Hinterlong S.J. , Hinton H.S.
Published: February 2023

The high throughput of optical interconnections was first utilized in the long distance telecommunication network. With advances in technology, optical communication continues to penetrate to ever shorter interconnection distances. Free-space optical interconnections at the chip and gate level can enhance the performance of electrical connections since light can exploit the dimension perpendicular to the planar electronic surface and can overcome the impedance losses typically experienced by high speed electronic signals.
Review and Applications of Rigorous Coupled-Wave Analysis of Grating Diffraction
Authors: Glytsis Elias N. , Gaylord Thomas K.
Published: February 2023

The diffraction of electromagnetic waves by periodic structures continues to be of great interest and practical importance owing to numerous applications in a variety of fields such as acousto-optics, electro­optics, integrated optics, spectroscopy, optical computing, optical interconnects, and quantum electronics. Optical gratings may be planar (slab, volume gratings) or surface-relief (corrugated gratings). The periodic modulation may be in the permittivity (resulting in index of refraction gratings), or in conductivity (absorption) or in a combination of these. Diffraction gratings can be fabricated in dielectrics, semiconductors, metals, or even plasmas. They can be characterized as isotropic, uniaxial-, biaxial-anisotropic or gyrotropic depending on the properties of their materials. They can be of constant or of varying modulation and can be cascaded or multiplexed. The grating diffraction methods of analysis can be divided into two major categories, the integral methods,1 and the differential methods.1–7 The most common and accurate differential methods are the coupled-wave approaches2–5 and the modal approaches.6,7
Filter Properties of Dielectric Waveguide Gratings
Authors: Magnusson R. , Wang S. S.
Published: February 2023

By using an exact electromagnetic model (rigorous coupled-wave theory) to analyze periodic dielectric waveguides, sharp resonance phenomena where 100% switching of light energy between waves occurs over small parameter ranges have been discovered.1 Physically, this is due to coupling of external diffracted fields with the modes of the waveguide. Several interesting applications and devices based on this resonance effect can be envisioned. For example, efficient, low-power switching elements appear to be feasible using this concept. Lossless spectral filters (static and tunable) with arbitrarily narrow, controllable linewidth may also be feasible. Using a high spatial frequency dielectric waveguide grating may lead to 100% reflective narrow-band spectrally selective mirrors. These elements can then be used to line-narrow lasers in bulk systems and possibly in integrated optics. Improved thin-film structures and high-precision sensor applications may also be feasible.
Recent Progress in Hoe Optical Pickup
Authors: Lee Wai-Hon
Published: February 2023

The popularity of the compact disc players today indicates that the era for optical recording is here to stay. For this reason many improvements made on the optical pickups are being incorporated by manufacturer of compact disc players, especially those in JAPAN. In this short article I will review some of the progress in the HOE pickups(Ref. 1) as developed at HOETRON INC.
On the Limits of Scalar Diffraction Theory for Conducting Gratings
Authors: Gremaux Douglas A. , Gallagher Neal C.
Published: February 2023

Many diffractive elements such as computer generated holograms and periodic gratings are designed by using scalar diffraction theory. The Lohmann hologram is an example of this [1]. The Lohmann method utilizes a two dimensional planar array of square cells each containing a rectangular aperture. Ideally by choosing the proper size and position of each aperture, any arbitrary wavefront can be created. The number of cells in the hologram determine how accurately it can produce the desired wavefront. So in order to reduce error, one would want as many cells in as small a space as necessary to achieve the desired accuracy. In the past, these holograms, as well as other diffractive elements, were limited by the manufacturing process which prevented very small cell sizes, or in more general terms, limited the space bandwidth product of the element. Many of the early computer generated holograms were plotted on paper or even laid out by hand, and then photo-reduced to the proper size. But today, thanks to advances in computer technology and microlithography devices such as electron beam machines, these diffractive elements can be made with micron or sub-micron feature sizes. Some devices made with very small features do not perform as expected. This is not due to fabrication constraints, but rather due to the design process itself. Scalar diffraction theories are used to describe the interaction of light with these diffractive elements [2]. But scalar diffraction theory begins to break down as feature sizes shrink to the order of a few wavelengths or less.
Diffraction Efficiency of a Grating as a Function of the State of Polarization of Incident Light
Authors: Azzam R. M. A.
Published: February 2023

For light of a given wavelength incident on a grating in an arbitrary orientation the distribution of light among the various (reflected and/or transmitted) diffracted orders depends on the incident wave polarization. Such polarization effects of gratings, first discovered by Fraunhofer1, require a full electromagnetic approach2 for their explanation.
A Diffraction Grating Photopolarimeter
Authors: Azzam R. M. A. , Giardina K. A.
Published: February 2023

A new division-of-amplitude photopolarimeter1 with no moving parts or modulators is described that employs the conical diffraction of light from a grating which is set for oblique incidence with the grating lines inclined with respect to the plane of incidence, Fig. 1. The grating G splits the incident light beam, whose state of polarization is to be measured, into four or more beams that are intercepted by linear photodetectors Dm (m = 0, 1, 2, …). This produces four or more signals im that represent multiple projections of the unknown Stokes vector S. S is reconstructed from its projections by matrix inversion. We have built a prototype photopolarimeter of this type using an Al-coated, 600-grooves/mm, holographic grating set at 65° angle of incidence with the grooves oriented at 45° with respect to the plane of incidence, and a 633-nm He-Ne laser as the light source. This novel photopolarimeter has been calibrated and tested, with and without the linear polarizers Pm in front of the photodetectors, using the same procedures recently established for the four-detector photopolarimeter2,3 . This polarization-analysis scheme has several advantages and degrees of flexibility. In particular, it can be adapted using detector arrays so as to perform time-resolved spectropolarimetry.
Holographic Optical Elements for Incoherent Spatial Filtering with Longitudinal Periodicity
Authors: Hanson S. Grüner
Published: February 2023

Self-imaging without conventional optical elements has been studied extensively. A good overview of the field has recently been published1. Diffraction by white light by two equal periodic structures is usually referred to as the Lau effect, and will form the basis for the structures which are considered in this investigation.
Ultra Lightweight Diffractive Eyepiece
Authors: Aldrich Robert E.
Published: February 2023

Many have suggested the use of diffractive optics as color correctors in the IR, some have never built such devices. Plastic aspheric eyepieces are lighter weight than conventional glass spherical optics due to plastics smaller specific gravity and the superior correction of aspheres, which allows for fewer elements.
A Holographic-Element-Array-Based Laser Directional and Wavelength Discrimination Device
Authors: Chen Jenkins , Lin Freddie , Liu William
Published: February 2023

Laser directional and wavelength sensing devices which can be mounted on a variety of military platforms are needed for possible future optical countermeasure systems. Presently, extremely sensitive and rugged photodetectors operating from NUV to FIR are commercially available. However, determining the direction and wavelength of the illumination is more difficult than merely detecting its presence. What is required is a compact low-power device that quickly gives an unambiguous directional and wavelength indication of laser illumination and makes good estimates of the laser energy's temporal characteristics (pulse frequency and type of modulation), preferably for several wavelengths.
A Hybrid Diffractive/Refractive Lens for Use in Optical Data Storage
Authors: Kubalak David , Morris G Michael
Published: February 2023

Optical data storage (ODS) lenses are mounted with an automatic refocusing mechanism to account for possible variations in the lens-disk distance, e.g., disk wobble. This auto-focus system, however, cannot compensate for laser mode hopping, which occurs on a nanosecond scale. One possible solution is to use frequency stabilized lasers, but these tend to be very expensive. Another option is to correct the longitudinal chromatic aberration of the lens over the spectral bandwidth of the source. Unfortunately, achromatizing the lens using conventional glass requires a positive and negative element, which significantly increases the size and weight of the lens, neither of which is desirable for optical data storage. An alternative option is the use of gradient index glass, and a fourth possible solution is to use a diffractive/refractive hybrid lens, which is the focus of this paper.
Diffractive properties of gelatin as an aerogel
Authors: Rallison Richard D. , Bialkowski Stephen E.
Published: February 2023

Shankoff had discovered that dichromated gelatin could have an index modulation as high as .26 as far back as 19681 and Meyerhofer showed that this implied a reduction of effective index of refraction (n) from 1.54 to 1.27 as well as explaining the increase in thickness (T) of a developed hologram of from 1.3 to 1.4 times the original thickness before exposure.2 The results or effects of the expansion are touched on but the implications of the change in bulk index are not discussed at all. Figure 1 shows the usual result of making a transmission grating with slanted planes, the developed hologram will playback at an angle that indicates that the planes have changed to a smaller angle due simply to the expansion of the film. This is also the special case where the light makes a 90 degree turn in the grating and no P polarized light can be diffracted. If only the planes were tipped then the internal angle of 90 degrees would be approximately maintained in spite of a changed external angle but in fact the angle changes to an angle less than 90 degrees because as the bulk index went down the effective spatial frequency went up and P light is still diffracted at lambda 1. 45 degree slants are difficult.
Blazed Diffracting Optical Components
Authors: Hutley M.C.
Published: February 2023

1. The blazed profile effectively "unwraps the cann spiral," i.e., it provides just the right amount of phase lag to compensate for the change in path difference as one goes from one side of a groove to the other. This description is helpful in understanding the performance of various approximations to a triangular profile (e.g., discrete steps and rounded edges).
Signal Synthesis and Coding in Diffractive Optics
Authors: Wyrowski Frank
Published: February 2023

Diffractive elements (DE) allow the manipulation of an electromagnetic wave by diffraction. Dependent on the choice of the diffraction theory employed to calculate the DE, different parts of diffractive optics can be defined. Digital holography is the part that is based on the use of scalar diffraction theory.1 The transmittance or reflectance of the DE is calculated by geometrical optics and the wave propagation by paraxial wave optics. Of particular importance are the Fresnel- and the Fourier transform.
Diffractive optical elements for optoelectronics
Authors: Streibl Norbert
Published: February 2023

Diffractive optical elements (DOEs) rely on the deflection of light waves by diffraction on microstructures rather than on refraction by smooth surfaces. They are well-suited for applications involving monochromatic light and lasers: They are flexible in design (synthetic holograms are designed by CAD), it is possible to fabricate array-optics (several elements precisely positioned side by side on one single substrate). DOEs may perform several functions at the same time (for example focusing, deflecting and beam splitting can be integrated into one component), they are often fabricated by planar technologies well known from microelectronics and they can be replicated, once one master has been made. Often DOEs are smaller and lighter in weight than conventional optical elements. Typical problems with DOEs are their wavelength dependence and the achievement of high diffraction efficiencies and low levels of straylight. Since DOEs usually have only very few optical surfaces (often just one) for diffractive lens systems the correction for aberrations, the field of view or tolerances against wavelength detuning are in many cases insufficient.
Analysis of Weighted Fan-out/Fan-in Volume Holographic Interconnections
Authors: Nordin Gregory P. , Asthana Praveen , Tanguay Armand R. , Jenkins B. Keith
Published: February 2023

Volume holography has often been proposed as an interconnection technology for photonic neural network implementations [1] because it appears to potentially meet the critical requirements of providing both large numbers of interconnections and a weighted fan-out/fan-in topology. The feasibility of using volume holograms for large-scale weighted fan-out/fan-in interconnection applications depends in part on the fidelity with which the interconnection weights can be implemented, and on the throughput that can be achieved in the volume holographic interconnection system. In addition, an important implementation issue is the number of exposures required to record a particular interconnection configuration because this can impact the total writing time and required exposure schedule.
Acoustooptic Programmable Spot Array Generator
Authors: Mait Joseph N. , Prather Dennis W. , Athale Ravindra A.
Published: February 2023

In some optical computing architectures [1] array generators are used to establish an array of fixed, regular interconnects between two planes. Because system programmability is achieved elsewhere, the ability to reconfigure the array is not a requirement and the array generator can be fabricated as a fixed phase filter. In contrast, for optical processing applications such as optical morphology [2] reconfigurability and programmability of the spot array are essential, for which purpose magneto-optic spatial light modulators [3] and acoustooptic (AO) modulators [4] have been employed.
Multiple Beam Splitter Characteristics of Holographic Surface-Relief Gratings Recorded Nonlinearly
Authors: Langlois P. , Beaulieu R. , Beauregard A.
Published: February 2023

It has been recently reported that dielectric surface-relief gratings with conic cross- sectional shapes have high diffraction efficiency and produce several beams of similar intensities1. Although conic gratings give reasonably good characteristics, other surface- relief are worth considering.
Compact Micro-Optical Diode Laser Assembly Using Mass-Transported Large-Numerical-Aperture Refractive Microlenses
Authors: Tsang D. Z. , Liau Z. L. , Walpole J. N.
Published: February 2023

The advancement of semiconductor laser materials growth and device fabrication technology has brought the cost of the laser chip well below the cost of the associated optics, precision alignment, and packaging required to effectively utilize the device in systems applications.1 We report here a novel compact packaging approach that utilizes unique microlenses for simplified lens support and alignment In this scheme, a microlens fabricated on a planar substrate is directly attached to the laser/heatsink to form a precision optical assembly providing a collimated (or focused) output beam. The approach is applicable to either single lasers or laser arrays.
Diffractive Spot-Array Generation Using Multimode Surface-Emitting Lasers and Light-Emitting Diodes
Authors: Hoch John S. , Grot Annette , Tan T. S. , Kahn Joseph M.
Published: February 2023

The ability to shape the diverging beam from a surface-emitting laser or a light-emitting diode is important for future micro-optic illumination systems. In this paper, we consider using two surface-relief diffractive optical elements (DOEs) to shape the output from a 980-nm multimode vertical-cavity surface-emitting laser (VCSEL) into a closely spaced rectangular spot array in the near field (approximately 10 mm from the laser). We also describe a similar system for illumination by an 850-nm resonant-cavity light-emitting diode (RCLED). With small intensity variation from spot to spot, the rectangular spot array is intended to approximate a profile that is completely uniform from point to point. This design strategy is particularly valuable with the VCSEL, as its complicated multimode emission profile makes it nearly impossible to guarantee absolute uniformity within the rectangle, but creating a rectangular array of light spots spaced very close together is still feasible.
3 X 3 Optoelectronic Cross-Bar Switch Using Vertical Cavity Surface Emitting Laser Arrays
Authors: Rajkumar N. , McMullin J. N. , Keyworth B. P. , MacDonald R. I.
Published: February 2023

In an electronic space division switch matrix, the system performance at high frequencies is subject to degradation because of crosstalk due to electromagnetic coupling in adjacent signal paths. A substantial improvement in performance can be obtained if the incoming signals were optical and the outgoing electrical with optical detectors acting as the cross points[1,2]. As the incoming paths are optical, a great degree of immunity to crosstalk can be gained, and the crosstalk that may arise in the outgoing electrical lines could be reduced by proper shielding as the adjacent conductor lines are no longer electrically connected. Such switching matrices may also be applied in high speed analog and digital signal processing applications [3,4]. The signal distribution in optoelectronic switches has been done in the past using 1:N multimode fibre splitters and butt-coupling the fibres to the MSM detectors by prealigning the fibres in etched silicon V-groove arrays. Two drawbacks of the fibre distribution method are that it is very fragile and handling large number of fibres is difficult and time-consuming. Alternative approaches are the use of integrated waveguide devices for power division or free space interconnect. A 3X3 free space switch prototype using three discrete lasers has been previously reported [5]. In this paper a modified version using vertical cavity surface emitting lasers (VCSEL’s) driven by electrical inputs is described.
Foundry fabrication for diffractive optical elements
Authors: Athale Ravi , Raj Kannan
Published: February 2023

Batch fabrication of multiple projects to spread the non-recurring costs and therefore reducing the cost of prototype custom circuits has been carried out for silicon integrated circuits (MOSIS). Recent efforts along this line include batch fabrication of optoelectronic devices through the CO-OP program. In this talk, we will discuss issues involved in providing multi-project foundry fabrication of diffractive optical elements through the binary optics approach. Cost comparison with other competing technologies will be made.
Diamond Turning and Replication of High-Efficiency Diffractive Optical Elements
Authors: Blough C. G. , Mack S. K. , Michaels R. L. , Rossi M.
Published: February 2023

Diffractive optical elements can provide a significant advantage in the design of many optical systems that require aspheric or chromatic correction. For high-numerical aperture systems that have tight size and weight constraints, a diffractive element can often provide the necessary leverage to obtain a suitable optical design. For extremely narrow wavelength applications, a diffractive singlet can be used to produce the desired aspheric wavefront; however, for large wavelength range applications the diffractive asphericity must be tempered to reduce spherochromatism. The unique dispersion characteristics of diffractive surfaces provide the ability to correct primary or secondary chromatic aberrations.[1,2] Recent literature has shown that there are numerous potential optical designs that could benefit from the application of diffractive optical elements.[3] The main impediments that inhibit system engineers from manufacturing more optical designs containing diffractive elements is uncertainty about predicted performance and cost. We have developed manufacturing techniques that utilize the accurate machining potential of single-point diamond turning (SPDT) to generate robust metal master surfaces suitable for replication. By utilizing several replication techniques, a variety of different optical component configurations can be efficiently manufactured to provide exceptional wavefront performance and high diffraction efficiency.