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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

On-chip spectroscopic sensors with optical fringe suppression

An on-chip spectroscopic sensor includes a tunable diode laser. A laser driver for drives the tunable diode laser. An analyte test cavity receives a chemical sample and exposes the received chemical sample to light from the tunable diode laser. An optical detector detects light emerging from the analyte test cavity as a result of the laser exposure. A spectral analyzer determines a spectrum of the emerging light, matches and removes one or more known optical fringe patterns from the determined spectrum, and determines a composition or concentration of the chemical sample from the optical fringe pattern-removed spectrum.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

On-chip spectroscopic sensors with optical fringe suppression

An on-chip spectroscopic sensor includes a tunable diode laser. A laser driver for drives the tunable diode laser. An analyte test cavity receives a chemical sample and exposes the received chemical sample to light from the tunable diode laser. An optical detector detects light emerging from the analyte test cavity as a result of the laser exposure. A spectral analyzer determines a spectrum of the emerging light, matches and removes one or more known optical fringe patterns from the determined spectrum, and determines a composition or concentration of the chemical sample from the optical fringe pattern-removed spectrum.

Green, William↗
DOE OSTI2022

Total Internal Reflection of Two Lasers in a Single Planar Optical Waveguide

Multiplex biomarker quantitation is ideal for tracking the progression of a disease, but sensitive, specific, and quantitative multiplex biosensing remains challenging. We achieved total internal reflection with two lasers in a single planar optical waveguide by coupling 532 nm laser light into the diffraction grating of a waveguide and 635 nm laser light directly into the thin film of the same waveguide. We confirmed that the evanescent fields generated in the waveguide can excite two fluorescent dyes (Alexa Fluor 532 and Alexa Fluor 647) held to the surface of the waveguide through biotin-streptavidin chemistry. This sensing concept holds significant potential as a platform for multiplex biomarker detection.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

An attempt to simulate laser-induced all-optical spin switching in a crystalline ferrimagnet

Interest in all-optical spin switching (AOS) is growing rapidly. The recent discovery of AOS in Mn 2 RuGa provides a much needed clean case of crystalline ferrimagnets for theoretical simulations. Here, we attempt to simulate it using the state-of-the-art first-principles method combined with the Heisenberg exchange model. We first compute the spin moments at two inequivalent manganese sites and then feed them into our model Hamiltonian. We employ an ultrafast laser pulse to switch the spins. We find that there is a similar optimal laser field amplitude to switch spins. However, we find that the exchange interaction has a significant effect on the system switchability. Weakening the exchange interaction could make the system unswitchable. This provides a crucial insight into the switching mechanism in ferrimagnets.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Studies of Laser-Driven Flyer Acceleration Using Optical Fiber Coupling [Book Chapter]

An optically recording velocity interferometer system has been used to measure acceleration histories and maximum velocities for laser-driven aluminum foil targets launched from the output face of optical fibers. Peak flyer velocities have been determined as a function of various parameters, including driving laser fluence, laser pulse duration and target thickness. The results at high fluences are consistent with a nearly constant efficiency of coupling optical energy into flyer kinetic energy and a small ablated mass fraction; however, the coupling efficiency falls off rapidly at fluences < 15 J-cm -2 . Measurement of the time delay between laser pulse arrival at the target and the onset of flyer motion have also been performed. Significant delays are observed at low fluences, arising from the increased time required for plasma formation at the fiber/foil interface under these conditions.

440600 -- Optical Instrumentation-- (1990-)↗
DOE OSTI2021

An imaging refractometer for density fluctuation measurements in high energy density plasmas

In this work, we report on a recently developed laser-probing diagnostic which allows direct measurements of ray-deflection angles in one axis, whilst retaining imaging capabilities in the other axis. This allows us to measure the spectrum of angular deflections from a laser beam which passes though a turbulent high-energy-density plasma. This spectrum contains information about the density fluctuations within the plasma, which deflect the probing laser over a range of angles. We create synthetic diagnostics using ray-tracing to compare this new diagnostic with standard shadowgraphy and schlieren imaging approaches, which demonstrates the enhanced sensitivity of this new diagnostic over standard techniques. We present experimental data from turbulence behind a reverse shock in a plasma and demonstrate that this technique can measure angular deflections between 0.06 and 34 mrad, corresponding to a dynamic range of over 500.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Dopant Segregation in Single-Crystal Optical Fiber Grown via the Laser-Heated Pedestal Growth Technique

Single crystal (SC) optical fiber has promising potential to be used for optical fiber sensing applications in harsh conditions due to its robustness to high temperature, high radioactivity, and resistance to chemical corrosion as compared to optical sensors using silica fiber. However, SC fiber grown via the laser-heated pedestal growth (LHPG) technique innately does not have a core-cladding structure found in standard optical fiber, resulting in optical losses. In this work we investigate optimization of the growth parameters of a two LHPG process used to grow SC fiber with a graded index via introduction of dopants to the feedstock material. Feedstock material is fabricated with the first LHPG device, then sol-gel dip-coated to create outer films of dopant material. The dip-coated feedstock is used to grow SC fiber in which segregation of the dopant constituents occurs, resulting in a graded index of refraction across the fiber, and an effective core-cladding structure. Hardware and software improvements to both LHPG systems are presented and the growth parameters for short pieces of ~320-330 μm diameter YAG fiber has been established. Characterization techniques/procedures have also been established for future grown SC fiber. These improvements and preparations are anticipated to result in a significant increase in grown fiber quality with a similar growth rate to that previously established.

Lander, Gary↗
DOE OSTI2024

Dopant Segregation in Single-Crystal Optical Fiber Grown via the Laser-Heated Pedestal Growth Technique

Single crystal (SC) optical fiber has promising potential to be used for optical fiber sensing applications in harsh conditions due to its robustness to high temperature, high radioactivity, and resistance to chemical corrosion as compared to optical sensors using silica fiber. However, SC fiber grown via the laser-heated pedestal growth (LHPG) technique innately does not have a core-cladding structure found in standard optical fiber, resulting in optical losses. In this work we investigate optimization of the growth parameters of a two LHPG process used to grow SC fiber with a graded index via introduction of dopants to the feedstock material. Feedstock material is fabricated with the first LHPG device, then sol-gel dip-coated to create outer films of dopant material. The dip-coated feedstock is used to grow SC fiber in which segregation of the dopant constituents occurs, resulting in a graded index of refraction across the fiber, and an effective core-cladding structure. Hardware and software improvements to both LHPG systems are presented and the growth parameters for short pieces of ~320-330 μm diameter YAG fiber has been established. Characterization techniques/procedures have also been established for future grown SC fiber. These improvements and preparations are anticipated to result in a significant increase in grown fiber quality with a similar growth rate to that previously established.

Lander, Gary↗
DOE OSTI2021

Colloidal quantum dot lasers

We report semiconductor nanocrystals represent a promising class of solution-processable optical-gain media that can be manipulated via inexpensive, easily scalable colloidal techniques. Due to their extremely small sizes (typically <10 nm), their properties can be directly controlled via effects of quantum confinement; therefore, they are often termed colloidal quantum dots (CQDs). In addition to size-tunable emission wavelengths, CQDs offer other benefits for lasing applications, including low optical-gain thresholds and high temperature stability of lasing characteristics. Recent progress in understanding and practical control of processes impeding light amplification in CQDs has resulted in several breakthroughs, including the demonstration of optically pumped continuous-wave lasing, the realization of optical gain with direct current electrical injection and the development of dual-function electroluminescent devices that also operate as optically pumped lasers. The purpose of this Review is to assess the status of the field of CQD lasing and discuss the existing challenges and opportunities. A particular focus is on approaches for suppressing nonradiative Auger recombination, novel optical-gain concepts enabled by strong exciton-exciton interactions and controlled CQD charging, effects of nanocrystal form factors on light amplification and practical architectures for realizing electrically pumped CQD lasers. This overview suggests that the accumulated knowledge, along with the approaches developed for manipulating the optical-gain properties of colloidal nanostructures, perfectly position the CQD field for successfully addressing a long-standing challenge: the realization of CQD-based laser diodes. Colloidal quantum dots are promising materials for realizing versatile, wavelength-tunable, solution-processed lasers. This Review surveys recent advances in colloidal quantum dot lasing, provides an in-depth analysis of outstanding challenges and discusses a path forward to implementing technologically viable lasing devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optical properties of differing nanolayered structures of divalent europium doped barium fluoride thin films synthesized by pulsed laser deposition

Optically-active thin films are employed in a variety of applications, such as LEDs and photovoltaics, due to their ability to act as up- or down-photon energy converters. Their performance depends critically on their composition and structure; thus, the use of novel synthesis techniques that allow for their control at the nanoscale level can result in improved efficiency and practicality. Here, layered thin films consisting of Eu 2+ - doped BaF 2 nanocrystalline layers separated by amorphous Al 2 O 3 were synthesized via sequential pulsed laser deposition using three separate targets for the different components; this synthesis technique provides precise control of layer thickness at the nanoscale along with dopant distribution within the film. Cross-sectional transmission electron microscopy analysis verified the desired nano-layering. Post-deposition heat treatments in a nitrogen atmosphere resulted in samples exhibiting steady emission with a broad peak ranging from 400 to 600 nm and a shoulder at 410 nm. The CIE 1931 chromaticity coordinates are x = 0.26-0.29 and y = 0.32-0.35 and vary as a function of the sample configuration. Because the chromaticity coordinates are close to those of a pure white light (x = 0.33, y = 0.33), these films demonstrate advantageous properties for applications with UV-pumped white light LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A multi-chord, two-color interferometer using Hilbert transform phase detection for measuring electron density in spheromak plasmas

A new, four-chord, CO 2 /He–Ne heterodyne interferometer has been designed and built for measuring line-averaged plasma density in the HIT-SI3 and subsequent HIT-SIU sustained spheromak devices. The two-color system successfully eliminates vibration-induced errors caused by mirrors that are secured to the vacuum chamber and is able to resolve electron densities ne in the full operating range of 10 18 –10 20 m –3 in both experiments with an integrated error of 4.7 × 10 17 m –2 . Here, data are presented from high toroidal current plasma discharges, showing the time evolution of electron densities n e and j Φ /n e along multiple chords.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Shock formation in flowing plasmas by temporally and spatially smoothed laser beams

The cumulative impact of multiple laser speckles on a supersonic plasma flow across optically smoothed laser beams is investigated. The bending of laser beams caused by ponderomotive laser–plasma coupling, together with flow, leads to plasma a momentum-conserving response that results in a deceleration of the flow. Once the flow velocity decreases to a subsonic level, the action of the laser beams can generate a shock within the plasma. This scenario has been predicted theoretically and confirmed by hydrodynamic simulations. The conditions of shock generation are given in terms of the ponderomotive pressure, speckle size, and the flow velocity. The nonlinear properties of the shocks are analyzed using Rankine–Hugoniot relations. According to linear theory, temporally smoothed beams exhibit a higher threshold for shock generation. Numerical simulations with beams that are smoothed by spectral dispersion compare well with the linear theory results, diverging only in the nonlinear regime. The conditions necessary for shock generation and their effects on the laser–plasma coupling in the inertial confinement fusion experiments are also discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Alkali resistant optical coatings for alkali lasers and methods of production thereof

In one embodiment, a method for forming an alkali resistant coating includes forming a first oxide material above a substrate and forming a second oxide material above the first oxide material to form a multilayer dielectric coating, wherein the second oxide material is on a side of the multilayer dielectric coating for contacting an alkali. In another embodiment, a method for forming an alkali resistant coating includes forming two or more alternating layers of high and low refractive index oxide materials above a substrate, wherein an innermost layer of the two or more alternating layers is on an alkali-contacting side of the alkali resistant coating, and wherein the innermost layer of the two or more alternating layers comprises at least one of: alumina, zirconia, and hafnia.

36 MATERIALS SCIENCE↗
DOE OSTI2024

System and method for atomic layer deposition of rare-earth oxides on optical grade materials for laser gain media

A method is disclosed for doping a quantity of powder particles. A container having a central chamber is initially charged with a quantity of powder particles. A quantity of precursor is sublimed to form a heated precursor. A quantity of carrier gas is mixed with the precursor to form a mixture of heated precursor/carrier gas. The central chamber is charged with the heated precursor/carrier gas and then moved to cause interaction of the powder particles with the heated precursor/carrier gas to form a first monolayer coating on the powder particles. The heated precursor/carrier gas is then removed from the central chamber and the central chamber is charged with a O2/O3 gas under a plasma. The central chamber is then further moved to produce interaction of the O2/O3 gas with the first monolayer coating on the powder particles to modify the first monolayer coating to create a different, single monolayer coating forming an oxide coating on the powder particles.

Miller, John S.↗