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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Third harmonic generation in the short-wavelength UV range by a single plasmonic nanostructure

The nonlinear optical interaction of laser radiation with nanostructures formed in gold and aluminium nanofilms has been experimentally studied. It is shown that, despite the high susceptibility χ{sub 3} of aluminium in comparison with gold, the third-harmonic generation efficiency at a wavelength of 260 nm is much higher for the nanostructures formed in a gold nanofilm because of the efficient excitation of a localised plasmon resonance at the fundamental frequency. (extreme laser radiation: physics and fundamental applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Fractional laser microablation of skin: increasing the efficiency of transcutaneous delivery of particles

We study several regimes of fractional laser microablation using a pulsed Er : YAG laser for producing microchannels of different depth and incisions that allow transcutaneous delivery of particles of different size, namely, Al{sub 2}O{sub 3} (27 μm), ZrO{sub 2} (smaller than 5 μm) and TiO{sub 2} (smaller than 100 nm). The shock wave regime was used both for enhancing the penetration of particles into the ablation zones and as an independent method of particle delivery into the skin. Based on optical coherence tomography we assessed the coherent depth of particle detection in the skin in 2 hours, 3 days and 10 days after the administration. The maximal localisation depth (up to 450 μm) was obtained for TiO{sub 2} nanoparticles in the regime of incisions with enhancement of particle penetration by pulses of a multiple-beam hydrodynamic shock wave. The results of the study can be useful for developing new methods of transcutaneous delivery of micro- and nanocarriers of medicinal preparations. (laser biophotonics)

36 MATERIALS SCIENCE↗
DOE OSTI2016

Post-filamentation propagation of high-power laser pulses in air in the regime of narrowly focused light channels

We report the results of experimental and theoretical studies of the post-filamentation stage of nonlinear propagation of high-power pulsed radiation from a Ti : sapphire laser in air. We have for the first time obtained the experimental dependences of the angular divergence of specific spatially localised high-intensity light structures that are observed in the beam after its multiple filamentation (post-filamentation of channels) when varying the initial focusing of laser radiation and its energy. It is found that the angular divergence of the post-filamentation channels decreases with increasing pulse energy and reducing beam numerical aperture. The experimental dependences are qualitatively interpreted based on the diffraction model of the Bessel – Gaussian beam. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Scanning photoelectron microscopy using a pointed capillary probe

The possibilities of a new type of scanning probe microscopy (SPM) for two different samples are experimentally demonstrated. The method is based on the use of a pointed capillary, which can simultaneously act as a ‘classical’ SPM probe and also as a controlled thin channel for transporting charged particles emitted by the surface to the detector. In the experiment, photoelectrons pass through a dielectric hollow cone probe with an aperture radius of 1 μm and detected by microchannel plates at different points of the investigated conducting surface irradiated by the second harmonic of a femtosecond Ti : sapphire laser. As a result, the sample’s surface profile is visualised with a subwavelength spatial resolution. This method makes it possible to control spatially localised beams of electrons, ions, neutral atoms (molecules) and soft X-ray radiation, as well as opens a possibility for research in the field of nanoscale photodesorption of molecular ions. (electron microscopy)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Laser frequency stabilisation on narrow resonances of cold magnesium atoms at the {sup 1}S{sub 0} – {sup 3}P{sub 1} transition

Experimental studies aimed at developing an optical frequency standard based on ultracold magnesium atoms with a relative uncertainty of Δν/ν < 10{sup –16} are performed. The frequency of the clock laser system at a wavelength of 457 nm is stabilised to narrow optical resonances (Ramsey fringes) in time-separated laser fields interacting with cold magnesium atoms localised in a magneto-optical trap (MOT). The frequency stability of the laser system is investigated using a femtosecond comb based on a Ti:sapphire laser. Long-term frequency stability (determined by the Allan function) of ∼5 × 10{sup –15} at averaging time τ = 1000 s is obtained. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Self-action of a wave field in one-dimensional system of weakly coupled active optical waveguides

The dynamics of self-action of a wave field in an array of weakly coupled active optical waveguides is studied analytically and numerically. It is shown that the introduction of weak gain in each of the waveguides allows significant reduction of radiation losses and efficient capture of all radiation in a single optical waveguide. The possibility of controlling the radiation localisation in the desired waveguide at the expense of varying the injection angle of the wave field into the considered system is demonstrated. The dependences of the characteristic parameters of the wave field are determined. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

On the nonlocality of the reflection of an electromagnetic wave from a flat surface upon excitation of surface waves

Diffraction phenomena arising due to reflection of a plane electromagnetic wave from a metal film, which are caused by a limited size of the incident beam aperture, are considered in the Kretschmann scheme used to excite a surface plasmon wave. It is shown that the wave reflection occurs nonlocally, that is, the region of the surface on which the wave is incident and the region from which it is reflected do not substantially coincide. The localisation of the maximum field is investigated when a surface plasmon is excited on a silver film. The absolute values of the gain in terms of the amplitude of the field on the free surface of the film are calculated. The proposed theory is applied to explain the Goos – Hänchen effect. (integrated optics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Thermoplasmonic laser-induced backside wet etching of sapphire

The technology of thermoplasmonic laser-induced backside wet etching is proposed to microstructure such solid and difficult-to-process materials as sapphire. In this technology, the laser absorbing medium is silver nanoparticles obtained from a precursor (AgNO{sub 3}) and providing significant laser radiation absorption due to the presence of plasmonic absorption with the formation of a substantially localised region with extremely high temperatures and pressures. This approach makes it possible to process sapphire both in the ‘gentle’ regime with the formation of nanometre structures and in the ‘strong’ regime to allow for the formation of ‘deep’ structures with etching rates up to several micrometers per pulse and high aspect ratio. The possibility of formation of periodic structures in sapphire in the above-threshold regime is shown. (in memory of professor v.n. bagratashvili (1947 – 2018))

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Complementary bimodal approach to monitoring of photodynamic therapy with targeted nanoconstructs: numerical simulations

We propose a new approach to monitoring photodynamic therapy (PDT) of glioblastoma with the use of targeted nanoconstructs containing a photosensitiser (PS) [benzoporphyrin derivative (BPD)] and IRDye800 dye, antibodies for efficient accumulation of the drug in a tumour, and a chemotherapeutic agent for combined effect on tumour cells. Application of IRDye800 is determined by the shift of its absorption and fluorescence spectra to the near-IR range with respect to BPD that ensures a higher imaging depth. Monitoring of PDT is based on the simultaneous fluorescence and optoacoustic (OA) imaging. Fluorescence imaging provides visualisation of fluorescence agents with high molecular sensitivity and monitoring of the effectiveness of PDT by PS photobleaching. OA allows one to examine the vascular pattern of the tumour environment, as well as assess the depth of the tumour. IRDye800 is a better contrast agent in comparison to BPD due to red-shifted spectral characteristics and a higher fluorescence quantum yield. Monte Carlo simulations combined for OA simulations with K-wave modelling allowed the feasibility of the complementary approach to be studied and demonstrated that this combination allows one to localise a tumour with a size of 2 mm at depths from 100 μm to 2 mm. (paper)

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Stimulated emission of AlGaN layers grown on sapphire substrates using ammonia molecular beam epitaxy

By optimising the growth temperature of the AlGaN layers and using high-temperature AlN buffer layers, high-quality Al{sub x}Ga{sub 1 – x}N layers (x = 0.15, 0.21, 0.26, and 0.3) were obtained, in which stimulated emission in the UV spectral range 330 – 297 nm was implemented with the threshold intensity of excitation I{sub th} ≈ 0.7 – 1.4 MW cm{sup −2}, respectively. It is found that the threshold value of the stimulated emission of AlGaN layers grown by molecular beam epitaxy is largely determined by the intensity of the process of thermal decomposition of GaN, which affects the surface morphology and, consequently, the amount of optical scattering loss. It is shown that no pronounced localisation of nonequilibrium charge carriers occurs in the AlGaN layers, which is manifested in the absence of a large Stokes shift and in the realisation of optical amplification at transitions in an electron-hole plasma, and also indicates a relatively homogeneous material composition. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Balance-equation method for simulating terahertz quantum-cascade lasers using a wave-function basis with reduced dipole moments of tunnel-coupled states

A model based on a system of balance equations for localised and continuum states is developed to calculate the current − voltage (I − V) and power characteristics of quantum-cascade lasers (QCLs) operating in the terahertz (THz) range. A method for modifying the eigenbasis of the Schrödinger equation by reducing the dipole moments of tunnel-coupled states is proposed to take into account the effect of dephasing on the carrier transport. The calculated and experimental data on the current − voltage characteristics and the dependence of the integrated radiation intensity on current for the THz QCLs lasing at 2.3 THz are compared. The calculated and measured values of the threshold current, lasing current range, and maximum operating temperature T{sub max} are found to be in good agreement. It is shown that T{sub max} can be increased by 25 % by reducing the thickness of the top contact layer n{sup +}-GaAs of the laser structure under study from 800 to 100 nm. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Optical fibres and fibre tapers with an array of Bragg gratings

The properties of optical fibres with an array of fibre Bragg gratings written directly during the fibre drawing are considered. Such optical fibres offer new possibilities for producing new types of active and passive fibre elements due to the enhanced back-reflected signal of the so-called artificial Rayleigh scattering, and are of interest for modelling physical phenomena associated with the statistics of reflecting centres in optical fibres, such as, e.g., localisation of photons. We studied fibres with an array of Bragg gratings written in photosensitive fibres, ordinary single-mode optical fibre of the SMF-28 type and in fibre with a core doped with erbium ions. To control the spectrum width of the reflected signal, we used chirped phase masks, as well as writing arrays of gratings in tapered optical fibres. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Nanodiamonds with SiV colour centres for quantum technologies

Properties of silicon-vacancy (SiV) colour centres in ultra-nanosize diamonds are studied. Nanodiamonds are obtained at a high temperature and pressure, which induced transformations in mixtures of organic and hetero-organic compounds without metal-catalysts. The size distribution of grown nanodiamonds is determined by the methods of transmission electron microscopy and atomic-force microscopy, as well as by using the model of phonon spatial localisation. In addition, Raman spectra of various nanodiamonds and luminescence properties of SiV-centres are investigated. (laser applications and other topics in quantum electronics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Utilisation of spatial derivative measurements in circular diffuse optical tomographic imaging to improve image resolution and contrast

The resolution of images recovered using diffuse optical tomography without spatial prior information is inherently limited due to the diffusive nature of light transport in scattering dominated biological tissue. Several studies have previously reported an improvement in depth sensitivity in near infrared spectroscopy by considering the subtraction of two neighbouring measurements. A nearest neighbour, spatial derivative based algorithm is presented, in which the difference between neighbouring source-sharing source – detector pairs is considered for tomographic reconstruction. Using a circular, inward-facing optode geometry, it is shown that deeper abnormalities in oxyhaemoglobin, deoxyhaemoglobin and water can be recovered with better localisation and contrast as compared to reconstructing using absolute values of multi-wavelength data. Relative improvements of up to 25 % in quantitative accuracy of recovered physiological values are demonstrated at better resolution for cancerous tissue in a heterogeneous breast model, when using this proposed spatial derivative based parameter reconstruction. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Spectroscopy of atoms in an optical dipole trap using spectrally selective heating by a probe laser field

Spectral properties of atoms localised in an optical dipole trap are studied using the method of spectrally selective heating by a probe field. The method is based on measuring the number of atoms in a trap after they interact with a probe field. The dependence of the number of atoms on the frequency of the probe field fully characterises the shift and width of the spectral absorption line of trapped atoms. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Quantum cascade laser with bound-to-quasi-continuum optical transitions at a temperature of up to 371 K

Based on a matched Ga{sub 0.47}In{sub 0.53}As/Al{sub 0.48}In{sub 0.52}As heteropair, we have developed a quantum cascade laser emitting at a wavelength of 7.4 μm. The chosen heterostructure with a relatively large number of quantum wells and barriers represents two mini-bands separated by a mini-gap with a localised doublet level near the upper mini-band, which provides a wide emission band (∼100 cm{sup −1}). In a pulse regime, the maximal laser operation temperature is 371 K. Such a high temperature is explained by two factors: a large energy of the transfer from the doublet to the upper mini-band and a large volt defect. The characteristic temperatures T{sub 0} are found, which are equal to 170 K for low (less than 300 K) temperatures and 270 K for the range of 300 − 370 K. In addition, optical cavity losses are determined to be 2.5 and 7.7 cm{sup −1} at temperatures of 80 and 254 K, respectively. The pulse power is 0.3 W at 80 K and 0.05 W at 293 K. (lasers, active media)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Atom femtosecond optical trap based on spectrally filtered laser radiation

We have examined the use of alkali metal (rubidium) vapour for spectral filtering of broadband pulsed laser light that is used to produce a femtosecond pulsed optical dipole trap. It has been shown that, even at large detuning of the centre emission frequency from the frequency of atomic transitions, spectral components present in the wings of the laser emission line are capable of heating localised atoms, thus reducing their lifetime in the atomic trap. Using atomic vapour for filtering the laser emission spectrum, we have suppressed its spectral components resulting in heating. This has made it possible to increase the lifetime of atoms in the pulsed optical dipole trap to a value comparable to their lifetime in an optical trap formed by narrow-band cw laser light. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Reversible plasmonic switching in a graphene nanoresonator loaded with a core – shell quantum dot

A model of an all-plasmonic switch based on a graphene waveguide integrated with a stub nanoresonator loaded with a quantum dot is considered. Using the full-wave numerical simulation, it is shown that successive on/off switching of the control surface plasmon – polariton wave at the input of the waveguide leads to a change in the phase of the signal plasmon – polariton wave in the nanoresonator by π. This causes reversible switching of the device operation regime – from almost complete blocking to stable transmission of the signal plasmon – polariton wave through the waveguide. The effect is implemented at rates of ∼0.5 THz for infrared electromagnetic waves localised in a device with a switching region of 40 × 20 nm. (paper)

36 MATERIALS SCIENCE↗