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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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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Large‐Area, High‐Numerical‐Aperture, Freeform Metasurfaces

Abstract Nanophotonic devices are optical platforms capable of unprecedented wavefront control. To push the limits of experimental device performance, scalable design methodologies that combine the simplicity and fabricability of conventional design paradigms with the extended capabilities of freeform optimization are required. A novel gradient‐based design framework for large‐area freeform metasurfaces is introduced in which nonlocal interactions between simply shaped nanostructures, placed on an irregular lattice, are tailored to produce high‐order hybridized modes that support customizable large‐angle scattering profiles. Utilizing this approach, multifunctional super‐dispersive metalenses are designed and experimentally demonstrated. The approach to high‐numerical‐aperture radial metalenses capable of diffraction limited focusing and the generation of donut‐shaped point spread functions is also extended. It is anticipated that these concepts will have utility in super‐resolution microscopy, particle trapping, additive manufacturing, and metrology applications that require ultra‐high numerical apertures.

Optics↗
DOE OSTI2016

Highly uniform parallel microfabrication using a large numerical aperture system

In this letter, we report an improved algorithm to produce accurate phase patterns for generating highly uniform diffraction-limited multifocal arrays in a large numerical aperture objective system. It is shown that based on the original diffraction integral, the uniformity of the diffraction-limited focal arrays can be improved from ∼75% to >97%, owing to the critical consideration of the aperture function and apodization effect associated with a large numerical aperture objective. The experimental results, e.g., 3 × 3 arrays of square and triangle, seven microlens arrays with high uniformity, further verify the advantage of the improved algorithm. This algorithm enables the laser parallel processing technology to realize uniform microstructures and functional devices in the microfabrication system with a large numerical aperture objective.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Hybrid achromatic microlenses with high numerical apertures and focusing efficiencies across the visible

Abstract Compact visible wavelength achromats are essential for miniaturized and lightweight optics. However, fabrication of such achromats has proved to be exceptionally challenging. Here, using subsurface 3D printing inside mesoporous hosts we densely integrate aligned refractive and diffractive elements, forming thin high performance hybrid achromatic imaging micro-optics. Focusing efficiencies of 51–70% are achieved for 15μm thick, 90μm diameter, 0.3 numerical aperture microlenses. Chromatic focal length errors of less than 3% allow these microlenses to form high-quality images under broadband illumination (400–700 nm). Numerical apertures upwards of 0.47 are also achieved at the cost of some focusing efficiency, demonstrating the flexibility of this approach. Furthermore, larger area images are reconstructed from an array of hybrid achromatic microlenses, laying the groundwork for achromatic light-field imagers and displays. The presented approach precisely combines optical components within 3D space to achieve thin lens systems with high focusing efficiencies, high numerical apertures, and low chromatic focusing errors, providing a pathway towards achromatic micro-optical systems.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Focus optimization at relativistic intensity with high numerical aperture and adaptive optics

Improved focusing of laser beams using high numerical aperture systems is an efficient route to increasing intensities in the ultrafast regime to relativistic levels. We experimentally demonstrate a new method of optimizing the focus of a high-power laser, using second harmonic generation at full intensity in a low-pressure gas to provide a figure of merit for optimizing the shape of a deformable mirror via a genetic algorithm. Nonlinear and thermal aberrations are corrected, and aberrations introduced by filters are avoided. Furthermore, the method is applied to focus a millijoule, short pulse (30 fs), high repetition rate laser system to relativistic intensity in both near IR and mid IR regimes.

Lin, Jinpu↗
DOE OSTI2018

Extreme ultraviolet mask roughness effects in high numerical aperture lithography

Given the reflective nature of extreme ultraviolet lithography and its extremely short operational wavelength, roughness of the optical surfaces is of significant concern. In particular, roughness in the mask multilayer leads to image plane speckle and ultimately patterned line-edge or line-width variability in the imaging process. Here we consider the implications of this effect for future high numerical aperture (NA) systems that are assumed to require anamorphic magnification projection optics. The results show significant anisotropic behavior at high NA as well as a substantial increase in relative patterned line variability in the shadowed direction when comparing 0.55 NA to 0.33 NA, despite the assumption of an anamorphic magnification system. In conclusion, the shadowed-direction patterned line variability is 2× larger than for unshadowed lines, and the majority of the increase in variability occurs in the low frequency regime.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Ion trap with in-vacuum high numerical aperture imaging for a dual-species modular quantum computer

Photonic interconnects between quantum systems will play a central role in both scalable quantum computing and quantum networking. Entanglement of remote qubits via photons has been demonstrated in many platforms; however, improving the rate of entanglement generation will be instrumental for integrating photonic links into modular quantum computers. We present an ion trap system that has the highest reported free-space photon collection efficiency for quantum networking. We use a pair of in-vacuum aspheric lenses, each with a numerical aperture of 0.8, to couple 10(1)% of the 493 nm photons emitted from a 138Ba+ ion into single-mode fibers. We also demonstrate that proximal effects of the lenses on the ion position and motion can be mitigated.

Instruments & Instrumentation↗
DOE OSTI2023

Sharp, high numerical aperture (NA), nanoimprinted bare pyramid probe for optical mapping

The ability to correlate optical hyperspectral mapping and high resolution topographic imaging is critically important to gain deep insight into the structure–function relationship of nanomaterial systems. Scanning near-field optical microscopy can achieve this goal, but at the cost of significant effort in probe fabrication and experimental expertise. To overcome these two limitations, we have developed a low-cost and high-throughput nanoimprinting technique to integrate a sharp pyramid structure on the end facet of a single-mode fiber that can be scanned with a simple tuning-fork technique. The nanoimprinted pyramid has two main features: (1) a large taper angle (~70°), which determines the far-field confinement at the tip, resulting in a spatial resolution of 275 nm, an effective numerical aperture of 1.06, and (2) a sharp apex with a radius of curvature of ~20 nm, which enables high resolution topographic imaging. Optical performance is demonstrated through evanescent field distribution mapping of a plasmonic nanogroove sample, followed by hyperspectral photoluminescence mapping of nanocrystals using a fiber-in-fiber-out light coupling mode. Through comparative photoluminescence mapping on 2D monolayers, we also show a threefold improvement in spatial resolution over chemically etched fibers. These results show that the bare nanoimprinted near-field probes provide simple access to spectromicroscopy correlated with high resolution topographic mapping and have the potential to advance reproducible fiber-tip-based scanning near-field microscopy.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

One dimensional focusing with high numerical aperture multilayer Laue lens

Multilayer Laue lenses (MLLs) capitalize on the developments in multilayer deposition technologies for fabricating reflective coatings, specifically undertaken for EUV lithography, where layer thicknesses of several nanometers can be achieved. MLLs are deposited layer by layer, with their thicknesses following the zone plate law, and then pieces are sliced and extracted for use in focusing. Rays are reflected in the Laue geometry. The efficiency of a MLL can be very high, and is maximized by making the slice equal to about a half Pendellosung period so that most energy is transferred from the undiffracted to the diffracted beam, and by ensuring that the Bragg condition is met at each point in the zone plate. This latter condition requires that the layers are tilted to the beam by an amount that varies with layer position; e.g. for focusing a collimated beam, the layers should be normal to a cylinder of radius of twice the focal length. We have fabricated such tilted-zone MLLs and find that they exhibit improved efficiency across their entire pupil as compared with parallel-zone MLLs. This leads to a higher effective NA of the optic and hence higher resolution.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Low vibration high numerical aperture automated variable temperature Raman microscope

Raman micro-spectroscopy is well suited for studying a variety of properties and has been applied to wide- ranging areas. Combined with tuneable temperature, Raman spectra can offer even more insights into the properties of materials. However, previous designs of variable temperature Raman microscopes have made it extremely challenging to measure samples with low signal levels due to thermal and positional instability as well as low collection efficiencies. Thus, contemporary Raman microscope has found limited applicability to probing the subtle physics involved in phase transitions and hysteresis. This paper describes a new design of a closed-cycle, Raman microscope with full polarization rotation. High collection efficiency, thermal and mechanical stability are ensured by both deliberate optical, cryogenic, and mechanical design. Measurements on two samples, Bi 2 Se 3 and V 2 O 3 , which are known as challenging due to low thermal conductivities, low signal levels and/or hysteretic effects, are measured with previously undemonstrated temperature resolution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Micro-lensed fiber optic plate and methods of forming thereof

A method of forming a micro-lensed fiber optic plate. The method includes obtaining a fiber optic plate that has a plurality of fibers arranged in parallel. A first end of a fiber of the plurality of fibers can have a first numerical aperture. The fiber of the plurality of fibers includes a core material running along a length of the fiber that is circumscribed by a layer of cladding material. The method also includes creating a lensed surface at a second end of the fiber of the plurality of fibers. The second end is opposite the first end. The lensed surface of the fiber of the plurality of fibers can have a second numerical aperture that is different from the first numerical aperture.

Bagwell, Brett↗
DOE OSTI2015

Solid immersion lenses for enhancing the optical resolution of thermal and electroluminescence mapping of GaN-on-SiC transistors

Solid immersion lenses (SILs) are shown to greatly enhance optical spatial resolution when measuring AlGaN/GaN High Electron Mobility Transistors (HEMTs), taking advantage of the high refractive index of the SiC substrates commonly used for these devices. Solid immersion lenses can be applied to techniques such as electroluminescence emission microscopy and Raman thermography, aiding the development device physics models. Focused ion beam milling is used to fabricate solid immersion lenses in SiC substrates with a numerical aperture of 1.3. A lateral spatial resolution of 300 nm is demonstrated at an emission wavelength of 700 nm, and an axial spatial resolution of 1.7 ± 0.3 μm at a laser wavelength of 532 nm is demonstrated; this is an improvement of 2.5× and 5×, respectively, when compared with a conventional 0.5 numerical aperture objective lens without a SIL. These results highlight the benefit of applying the solid immersion lenses technique to the optical characterization of GaN HEMTs. Further improvements may be gained through aberration compensation and increasing the SIL numerical aperture.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Antireflective Multi‐Dielectric Metasurfaces Operating in the Visible

Abstract As increasingly more demanding photonics applications are brought on‐chip, more complex design solutions are employed to deliver enhanced performance: e.g., meta‐molecules, inverse‐designed freeform structures, and multilayer metasurfaces. Instead, this study introduces anti‐reflective metasurfaces fabricated in a single nanolithography step that follows deposition of multiple dielectrics onto a substrate. Anti‐reflective metasurfaces offer fundamentally better transmission efficiencies compared to conventional equivalents. Conventional and anti‐reflective metalenses, both fabricated in the Ta 2 O 5 /SiO 2 material platform for 461 nm operation, show an improvement in focusing efficiencies from ≈ 55% to ≈ 90% at low numerical apertures and from ≈ 35% to ≈ 65% at high numerical apertures. Simulations of ideal and imperfect metalenses indicate that anti‐reflective metasurfaces not only improve transmission at the design library level, but also reduce spurious diffraction and protect against higher‐order scattering.

Optics↗
DOE OSTI2017

Single Mode Air-Clad Single Crystal Sapphire Optical Fiber

The observation of single mode propagation in an air-clad single crystal sapphire optical fiber at wavelengths at and above 783 nm is presented for the first time. A high-temperature wet acid etching method was used to reduce the diameter of a 10 cm length of commercially-sourced sapphire fiber from 125 micrometers to 6.5 micrometers, and far-field imaging provided modal information at intervals as the fiber diameter decreased. Modal volume was shown to decrease with decreasing diameter, and single mode behavior was observed at the minimum diameter achieved. While weakly-guiding approximations are generally inaccurate for low modal volume optical fiber with high core-cladding refractive index disparity, consistency between these approximations and experimental results was observed when the effective numerical aperture was measured and substituted for the theoretical numerical aperture in weakly-guiding approximation calculations. With the demonstration of very low modal volume in sapphire at fiber diameters much larger than anticipated by legacy calculations, the resolution of sapphire fiber distributed sensors may be increased and other sensing schemes requiring very low modal volume, such as fiber Bragg gratings, may be realized in extreme environment applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Preparing for the Next Generation of EUV Lithography at the Center for X-ray Optics

The introduction of EUV lithography into high-volume semiconductor manufacturing this year represents a monumental milestone for EUV technology. After nearly 30 years of development, the EUV research community has overcome many of the key obstacles required to enable the long-awaited integration of EUV lithography into the lab. These obstacles have included: the development of a stable, high-powered EUV source to ensure adequate exposure tool reliability; controlling EUV mask defects and mask contamination; and the development of EUV resists with adequate sensitivity, resolution, and line width roughness to meet the tolerances required for high-volume manufacturing. As EUV moves into its second generation, there will be new challenges facing the community as it works to push EUV technology into the future. Smaller feature sizes will be achieved using higher numerical aperture optics, which are planned to have an anamorphic geometry (asymmetric magnification and numerical aperture between horizontal and vertical axes) to overcome 3D effects at the mask. This new geometry and its larger angle ranges make understanding mask absorber and multilayer effects all the more important. New methods for high-NA wavefront metrology need to be tested to ensure that these optical systems can be aligned to operate with minimal aberrations. Mask defects need to continue to be studied, and the inclusion of EUV pellicles in the roadmap requires that mask inspection and review systems adapt accordingly. Finally, new resists must be developed to support the increased resolution of feature sizes below 8 nm half pitch. The Center for X-ray Optics (CXRO) at Berkeley Lab has been a leader in EUV research for the past 25 years. Leveraging 13.5 nm EUV light from the Advanced Light Source synchrotron facility, CXRO is home to several EUV and soft X-ray (SXR) research tools that have provided important insights into EUV resists, masks, and coatings. The 0.3 NA Microfield exposure tool (MET) and Dose Calibration Tool (DCT) have played an instrumental role in the development of the current generation of high-resolution EUV resists. The Actinic Inspection Tool (AIT) and its successor, SHARP, have enabled aerial image analysis, providing key insights into mask defects, 3D mask effects, illumination, and aberrations. And the CXRO Reflectometer continues to be the industry standard in multilayer coating and EUV mask scattering metrology. To address the new challenges facing the next generation of EUV lithography, CXRO has upgraded its suite of EUV research tools. The 0.5 NA MET5 is a newly commissioned projection lithography tool that is capable of printing feature sizes down to 8 nm half pitch. A new radiation chemistry program is deploying several techniques aimed at dissecting the role of primary photoelectrons and secondary electrons in EUV resists. The SHARP microscope has been outfitted with anamorphic zone plate lenses that can emulate the geometry of next-generation EUV scanners, and the reflectometer has been applied to new scattering experiments for the purpose of understanding the 3D effects of EUV mask multilayers, as well as determining mask properties using scattering profiles. In parallel with these tools, the CXRO High-NA Wavefront Sensing Program is developing high-resolution wavefront sensors suitable for measuring aberrations at high NA. This article presents an overview of these programs and describes how they will address the primary challenges that face the EUV community as it moves to the next generation of EUV lithography.

47 OTHER INSTRUMENTATION↗