High resolution measurements in space astronomy and the requirements for diffraction limited optics
High resolution measurements and diffraction limited optics of large space telescope
Spitzer, L., Jr.↗
SEARCH · Engineering Papers
Results for “diffractive optics”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Method and system for homogenizing diode laser pump arrays
An optical amplifier system includes a diode pump array including a plurality of semiconductor diode laser bars disposed in an array configuration and characterized by a periodic distance between adjacent semiconductor diode laser bars. The periodic distance is measured in a first direction perpendicular to each of the plurality of semiconductor diode laser bars. The diode pump array provides a pump output propagating along an optical path and characterized by a first intensity profile measured as a function of the first direction and having a variation greater than 10%. The optical amplifier system also includes a diffractive optic disposed along the optical path. The diffractive optic includes a photo-thermo-refractive glass member. The optical amplifier system further includes an amplifier slab having an input face and position along the optical path and separated from the diffractive optic by a predetermined distance. A second intensity profile measured at the input face of the amplifier slab as a function of the first direction has a variation less than 10%.
36 MATERIALS SCIENCE↗
Piezoelectric Diffraction-Based Optical Switches
Piezoelectric diffraction-based optoelectronic devices have been invented to satisfy requirements for switching signals quickly among alternative optical paths in optical communication networks. These devices are capable of operating with switching times as short as microseconds or even nanoseconds in some cases.
Spremo, Stevan↗
Micro-Fresnel Zone Plate Optical Devices Using Densely Accumulated Ray Points
An embodiment generally relates to an optical device suitable for use with an optical medium for the storage and retrieval of data. The optical device includes an illumination means for providing a beam of optical radiation of wavelength .lamda. and an optical path that the beam of optical radiation follows. The optical device also includes a diffractive optical element defined by a plurality of annular sections. The plurality of annular sections having a first material alternately disposed with a plurality of annular sections comprising a second material. The diffractive optical element generates a plurality of focal points and densely accumulated ray points with phase contrast phenomena and the optical medium is positioned at a selected focal point or ray point of the diffractive optical element.
Choi, Sang H.↗
Far-field measurements of short-wavelength surface plasmons
We present direct far-field measurements of short-wavelength surface plasmon polaritons (SPP) by conventional optics means. Plasmonic wavelength as short as 231 nm was observed for 532 nm illumination on a Ag−Si{sub 3}N{sub 4} platform, demonstrating the capability to characterize SPPs well below the optical diffraction limit. This is done by scaling a sub-wavelength interferometric pattern to a far-field resolvable periodicity. These subwavelength patterns are obtained by coupling light into counter-propagating SPP waves to create a standing-wave pattern of half the SPP wavelength periodicity. Such patterns are mapped by a scattering slit, tilted at an angle so as to increase the periodicity of the intensity pattern along it to more than the free-space wavelength, making it resolvable by diffraction limited optics. The simplicity of the method as well as its large dynamic range of measurable wavelengths make it an optimal technique to characterize the properties of plasmonic devices and high-index dielectric waveguides, to improve their design accuracy and enhance their functionality.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Design of a Large Diffraction Grating Optical Assembly
The Advanced Radiographic Capability (ARC) is a diagnostic system in the National Ignition Facility (NIF) that will enable high-speed imaging of imploding targets in the NIF Target Chamber. NIF is a multi-billion dollar project to focus 192 laser beams onto a small target (approximately the size of a pencil eraser) to generate nuclear fusion. The complete ARC system is composed of approximately 80 modular large optical assemblies known as Line Replaceable Units (LRUs). The total estimated weight of the ARC optics alone is 16,000 lbs, with an average optic weight of 200 lbs. Key to the function and performance of ARC is an optical compressor, which uses diffraction gratings known as Grating LRUs to temporally compress a total of 8 laser beams. The resulting high-power beams are focused onto a back-lighter target to create high-energy xrays for imaging. These Grating LRUs are housed inside vacuum vessels called Compressor Vessels (Figures 1-5). There are a total of 32 Grating LRUs, 16 in each Compressor Vessel.
42 ENGINEERING↗
Acousto-optic filter for electronic laser tuning
Electronically tunable lithium niobate filter utilizes acoustic-optic diffraction for tuning laser to desired frequencies. Filter placed inside laser cavity diffracts incident optical signal of one polarization into orthogonal polarization by collinearly propagating acoustic beam to desired wavelength.
Harris, S. E.↗
Entropy-mode-driven gas optics
We propose a class of gaseous diffractive optical elements created by imprinting an entropy mode in a gas. Previous approaches to gaseous diffractive optics have relied on the simultaneous excitation of a standing acoustic wave and an entropy mode to produce one-dimensional periodic structures. However, the presence of acoustic oscillations in the gas imposes stringent constraints on some of the operational parameters of these optical elements, such as their lifetime and diffraction angle. Here, in this work, we introduce an approach that eliminates the acoustic mode, relying solely on the entropy mode. This enables control of the lifetime and temporal profile of gaseous optical elements, and also allows the creation of arbitrary structures with greater contrast, including nonperiodic patterns such as chirped gratings or lenses. This approach should allow operation over a wider parameter space, including larger diffraction angles and compatibility with laser pulse durations ranging from femtoseconds to microseconds.
Optics and optical instruments↗
Even Illumination from Fiber-Optic-Coupled Laser Diodes
A method of equipping fiber-optic-coupled laser diodes to evenly illuminate specified fields of view has been proposed. The essence of the method is to shape the tips of the optical fibers into suitably designed diffractive optical elements. One of the main benefits afforded by the method would be more nearly complete utilization of the available light. Diffractive optics is a relatively new field of optics in which laser beams are shaped by use of diffraction instead of refraction.
Howard, Richard T.↗
Advances in Decommissioning Using Laser Cutting - 16035
This paper describes advancements made in laser cutting in the UK Collaborative Project 'LaserSnake2'. In particular it will focus on the use of special laser cutting heads and optics to enhance cutting performance, whilst at the same time, reducing the effects of the residual laser beam passing through the cut. The benefits of using lasers for applications in decommissioning include the high speeds available, the tolerance of the process, the lightness of the cutting head, the lack of a reaction force with the part being cut and the ease of automation of the laser cutting operation. Laser cutting, however, is a thermal process and a potential detriment, is that the residual laser beam passing through the kerf, might damage or indeed set fire to, something positioned behind the part being cut. This paper describes the use of a diffractive optical element in the laser beam forming optics, designed to extend the depth of focus of the system, without increasing the physical focal length of the optic. In this way, for cutting thick materials, the goal is to achieve the cutting performance of a long focal length lens, with the beam divergence of a short focal length lens. A design of diffractive optical element is presented, which when used with a laser power of 5 kW, in conjunction with a set of conventional beam forming optics, including a 250 mm focal length focusing lens, is able to cut 40 mm thick C-Mn steel plate at 50 mm/min, while varying the nozzle tip to plate stand-off distance by 100 mm. For the same laser power in the focusing beam, this performance can be equaled by removing the diffractive optic and 250 mm lens and replacing these with just a 500 mm lens. However, when using the diffractive optical element, the power density in the residual beam has been reduced by a factor four when compared to that from the optical arrangement using the 500 mm lens. As well as the cutting performance, the effect of the two different power density residual beams on concrete will be presented. (authors)
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Collaborative development of diffraction-limited beamline optical systems at US DOE light sources
An ongoing collaboration among four US Department of Energy National Laboratories has demonstrated key technology prototypes and software modeling tools required for new high-coherent flux beamline optical systems. New free electron laser (FEL) and diffraction-limited storage ring (DLSR) light sources demand wavefront preservation from source to sample to achieve and maintain optimal performance. Fine wavefront control was achieved using a novel, roomtemperature cooled mirror system called REAL (resistive element adjustable length) that combines cooling with applied, spatially variable auxiliary heating. Single-grating shearing interferometry (also called Talbot interferometry) and Hartmann wavefront sensors were developed and used for optical characterization and alignment on several beamlines, across a range of photon energies. Demonstrations of non-invasive hard x-ray wavefront sensing were performed using a thin diamond single-crystal as a beamsplitter.
Goldberg, Kenneth A.↗
Sub miniaturized laser doppler velocimeter sensor
A miniaturized laser Doppler velocimeter is formed in a housing that is preferably 3 mm in diameter or less. A laser couples light to a first diffractive optical element that is formed on the fiber end. The light is coupled to a lens that also includes a diffractive optical element. The same lens is also used to collect receive light, and receives includes another diffractive optical element to collect that received light.
Gharib, Morteza↗
Ultrafast photonic micro-systems
A microelectromechanical device for diffracting optical beams comprises a diffractive element suspended over a channel. The diffractive element is configured to receive an optical beam and diffract and/or transmit the optical beam based on an orientation of the diffractive element. At least one torsional actuator is operatively connected to the diffractive element. The at least one torsional actuator is configured to selectively adjust the orientation of the diffractive element. The diffractive element has a diffractive element resonant frequency that is nearly the same as a resonant frequency of the optical beam.
Wang, Jin↗
Diffraction-Based Optical Switching with MEMS
In this article, we are presenting an overview of MEMS-based (Micro-Electro-Mechanical System) optical switch technology starting from the reflective two-dimensional (2D) and three-dimensional (3D) MEMS implementations. To further increase the speed of the MEMS from these devices, the mirror size needs to be reduced. Small mirror size prevents efficient reflection but favors a diffraction-based approach. Two implementations have been demonstrated, one using the Texas Instruments DLP (Digital Light Processing), and the other an LCoS-based (Liquid Crystal on Silicon) SLM (Spatial Light Modulator). These switches demonstrated the benefit of diffraction, by independently achieving high speed, efficiency, and high number of ports. We also demonstrated for the first time that PSK (Phase Shift Keying) modulation format can be used with diffraction-based devices. To be truly effective in diffraction mode, the MEMS pixels should modulate the phase of the incident light. We are presenting our past and current efforts to manufacture a new type of MEMS where the pixels are moving in the vertical direction. The original structure is a 32 x 32 phase modulator array with high contrast grating pixels, and we are introducing a new sub-wavelength linear array capable of a 310 kHz modulation rate
36 MATERIALS SCIENCE↗
Outdoor measurements of a photovoltaic system using diffractive spectrum-splitting and concentration
In a single-bandgap absorber, photons having energy less than the bandgap are not absorbed, while those having energy larger than the bandgap lose the excess energy via thermalization. We present outdoor measurements of a photovoltaic system that overcomes these losses via spectrum splitting and concentration using a planar diffractive optic. The system was comprised of the diffractive optic coupled with GaInP and CIGS solar cells. The optic provides a geometric concentration of 3X for each solar cell. It is easily fabricated by single-step grayscale lithography and it is ultra-thin with a maximum thickness of only 2.5μm. Electrical measurements under direct sunlight demonstrated an increase of ~25% in total output power compared to the reference case without spectrum splitting and concentration. Since different bandgaps are in the same plane, the proposed photovoltaic system successfully circumvents the lattice-matching and current-matching issues in conventional tandem multi-junction solar cells. As a result, this system is also tolerant to solar spectrum variation and fill-factor degradation of constitutive solar cells.
14 SOLAR ENERGY↗
Asymmetric three-beam binary optic grating
Binary and diffractive optical components are finding many applications in optical systems and integrated optical devices. A recent application required the development of a two-dimensional diffraction grating to perform an asymmetric, three-beam fanout. In this paper, techniques are presented for the design of arbitrary fanout grating devices. Modeling and optimization processes are demonstrated for the three-beam grating. The counter-intuitive results of the initial design are discussed, and experimental data verifying performance are presented.
Kathman, Alan D.↗
Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering Microscopy
Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. In this paper, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron–phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron–phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
High-Efficiency Flexible Multilevel Photon Sieves by Single-Step Laser-Based Fabrication and Optical Analysis
Over the past several decades, the need for high-resolution, high-efficiency, lightweight, high contrast focusing optics has continued to increase due to their applications in fields such as astronomy, spectroscopy, free-space optical communications, defense, and remote sensing. In recent years, photon sieve planar diffractive optics have been developed on flexible, lightweight polyimide substrates. However, transmission efficiencies have continuously been very low (~1-4%), thus impeding the widespread use of photon sieves in practical applications. Here, we present a flexible, lightweight, N = 4 level phase photon sieve with over 25% transmission efficiency; nearly triple that of any other photon sieve reported thus far. In this study, the photon sieve was fabricated via a novel pulsed laser ablation method using an ultraviolet source, and the total time to fabricate a ~3 sq cm sample was tens of seconds. Theoretical analysis of the photon sieve was carried out via the FDTD method, and was in very good agreement with experimental results. We also calculated via FDTD modeling the behavior of higher step (N = 8, 16, 32) photon sieves for further enhanced efficiencies, and show a fundamental limit on photon sieve efficiency of 70% in the limit of increasing step number. This multilevel photon sieve represents a new step in high-resolution diffractive optics, moving towards efficiencies suitable for widespread applications.
Julian, Matthew N.↗