SEARCH · Engineering Papers

Results for “MONOCRYSTALS”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,297 records · Page 72

All sources NASA NTRS DOE OSTI

DOE OSTI2016

Room-temperature Fe{sup 2+}:ZnS single crystal laser pumped by an electric-discharge HF laser

A room-temperature laser based on a Fe{sup 2+}:ZnS single crystal has been studied. The crystal was pumped by a nonchain electric-discharge HF laser with a light pulse FWHM of ∼140 ns. The pump spot diameter on the crystal surface (d) varied from 3.9 to 11.6 mm. The slope efficiency at these values of d was 37% – 39 %, respectively. The maximum laser energy was 380 mJ (at d=11.6 mm) with the total efficiency with respect to the absorbed pump energy of ∼19%. A further increase in the laser energy was not achieved because the crystal was destroyed at an incident pump energy and power of 3.4 J and ∼24 MW, respectively. The damaged region has a form of a long narrow channel shifted from the entrance surface inside the active element. (lasers)

42 ENGINEERING↗

DOE OSTI2016

IR luminescence of Fe{sup 2+} : ZnSe single crystals excited by an electron beam

Spectral-kinetic characteristics of the cathodoluminescence of Fe{sup 2+} : ZnSe single crystals are studied at T='300' and 80 K. These characteristics correspond to the IR luminescence spectrum and kinetics of Fe{sup 2+} ions in ZnSe crystals optically excited into the impurity absorption band. The obtained results open a real possibility of pumping Fe{sup 2+} : ZnSe lasers by hot electrons. (letters)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Laser nanoablation of diamond surface at high pulse repetition rates

The chemical etching of the surface of a natural diamond single crystal irradiated by subpicosecond laser pulses with a high repetition rate (f⩽500 kHz) in air is experimentally investigated. The irradiation has been performed by the second-harmonic (515 nm) radiation of a disk Yb : YAG laser. Dependences of the diamond surface etch rate on the laser energy density and pulse repetition rate are obtained. (interaction of laser radiation with matter)

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2016

Laser structuring of the diamond surface in the nanoablation regime

The possibility of using nanoablation (graphitisation-free photoinduced etching) for precise micro- and nanostructuring of the surface of a diamond single crystal has been experimentally investigated. The processing has been performed by femtosecond third-harmonic pulses of a Ti : sapphire laser (λ=266 nm). The specific features of the formation of a surface nanorelief (regularity of the newly formed structures and reduced nanoablation rate near craters) are discussed. The possibility of fabricating a diamond phase diffraction grating with a relief depth of ∼130 nm is demonstrated and the diffraction pattern recorded at λ=532 nm is compared with the results of theoretical analysis. (paper)

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2017

Study of the optical absorption and photoluminescence in (Pb,Gd){sub 3}(Al,Ga){sub 5}O{sub 12} : Ce epitaxial films grown from Pb-containing melt solutions

The optical absorption and photoluminescence properties of cerium-activated (Pb,Gd){sub 3}(Al,Ga){sub 5}O{sub 12} epitaxial films are studied. The films are grown on single-crystal (111)-oriented Gd{sub 3}Ga{sub 5}O{sub 12} substrates by liquid-phase epitaxy from supercooled PbO – B{sub 2}O{sub 3} melt solutions at different concentrations of gadolinium, cerium, and aluminium oxides in the charge. The photoluminescence band of Ce{sup 3+} ions is shown to peak at 532 nm. The highest cathodoluminescence yield of about 51500 photons MeV{sup -1} at a decay time of the slow component of 61.0 ns (light yield fraction 68%) is found for the Pb{sub 0.01}Ce{sub 0.03}Gd{sub 2.96}Al{sub 3.14}Ga{sub 1.86}O{sub 12} film, grown from melt solution with gadolinium oxide, cerium oxide, and aluminium oxide concentrations of 0.4, 0.2, and 4.5 mol % in the charge, respectively. Epitaxial films with these spectroscopic characteristics are promising for application in scintillation screens. (fluorescence and photogeneration)

36 MATERIALS SCIENCE↗

DOE OSTI2018

Defectoscopy of ZnGeP{sub 2} single crystals using a strontium vapour laser

A modified method of optical defectoscopy of ZnGeP{sub 2} single crystal plates using a strontium vapour laser (λ = 1.03 and 1.09 μm) is proposed based on shadow imaging of internal defects in plates cut parallel to the (100) plane. It is shown that the use of a strontium vapour laser with a wavelength of 6.45 mm makes it possible to study inhomogeneities in large-size ZnGeP{sub 2} samples. The possibility of fabricating a projection defectoscope for monitoring breakdown development in ZnGeP{sub 2} crystals is considered. (laser applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2017

Low-coherence interferometry as a tool for monitoring laser micro- and nanoprocessing of diamond surfaces

We have demonstrated the possibility of using low-coherence tandem optical interferometry for monitoring the local laser processing of diamond surfaces. Noncontact measurements of the optical thickness of single-crystal diamond plates were performed directly during the exposure of the surface to repetitive intense laser pulses. We investigated the dynamics of the thinning of a single crystal in two radically different regimes of laser etching: ablation (KrF excimer laser, λ = 248 nm, τ = 20 ns) and nanoablation (Ti : sapphire laser, λ = 266 nm, τ = 100 fs). (laser technologies)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Modelling of heating and photoexcitation of single-crystal silicon under multipulse irradiation by a nanosecond laser at 1.06 μm

We report a theoretical study of heating and photoexcitation of single-crystal silicon by nanosecond laser radiation at a wavelength of 1.06 μm. The proposed physicomathematical model of heating takes into account the complex nonlinear dynamics of the interband absorption coefficient of silicon and the contribution of the radial heat removal to the cooling of silicon between pulses under multipulse irradiation, which allows one to obtain a satisfactory agreement between theoretical predictions of silicon melting thresholds at different nanosecond pulse durations and experimental data (both under single-pulse and multipulse irradiation). It is found that under irradiation by nanosecond pulses at a wavelength of 1.06 μm, the dynamic Burshtein – Moss effect can play an important role in processes of photoexcitation and heating. It is shown that with the regimes typical for laser multipulse microprocessing of silicon (the laser spot diameter is less than 100 μm, and the repetition rate of pulses is about 100 kHz), the radial heat removal cannot be neglected in the analysis of heat accumulation processes. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Energy and spectral characteristics of a parametric generator based on a nonlinear ZnGeP{sub 2} crystal pumped by a Ho : YAG laser

We have experimentally realised the average generation power of a parametric generator based on a ZnGeP{sub 2} single crystal, which constituted ∼1.5 W at an efficiency of ∼28.6 % in the wavelength range of 3.5 – 4.8 μm with an average pump radiation power of ∼5.5 W and its energy density of ∼ 0.47 J cm{sup −2}. It is shown that there are threshold conditions for the average pump power, providing the realisation of parametric generation. In this case, an increase in the generation efficiency with an increase in the energy density of pump radiation to ∼ 0.4 J cm{sup −2} is observed; with its further increase, the output power increases due to a decrease in the parametric generation threshold. Parametric generators (PGs) based on ZnGeP{sub 2} single crystals with such characteristics are promising for solving many applied problems, including generation of terahertz radiation when nonlinear crystals are pumped by radiation from these PGs at difference frequency. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Generation regimes of a solid-state coupled-cavity ring laser

Based on the experimental studies we have shown that when an inhomogeneous magnetic field is applied to an active YAG : Nd crystal, a solid-state coupled-cavity ring laser is characterised by the following generation regimes: stationary unidirectional regime, self-modulation regimes of the first and second kinds, and dynamic chaos regime. Transitions between these generation regimes were carried out when the magnet was moved over the surface of the YAG : Nd single crystal, which made it possible to control the radiation dynamics. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Parametric stimulated Raman scattering in barium nitrate crystals

The spectra of multifrequency parametric stimulated Raman scattering in a barium nitrate single crystal is investigated. When this single crystal is excited by ultrashort (80 ps) YAG : Nd{sup 3+} laser pulses with a wavelength of 1064 nm, a frequency comb of eight anti-Stokes components is observed in the visible spectral range. The Raman satellites are due to the totally symmetric vibrational modes of barium nitrate single crystal. The frequencies of the corresponding Raman Stokes components in the IR range (from 1193 to 9662 nm) are calculated. The results of the study open the way to form an array of laser frequencies from the IR to green spectral range with a period of 1047 cm{sup –1}. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Acousto-optic modulators for a controlled frequency shift of light beams in optical and microwave cold-atom frequency standards

A series of specialised acousto-optic modulators/frequency shifters based on paratellurite (TeO{sub 2}) single crystals is developed for systems of laser cooling and frequency stabilisation of laser sources in optical and microwave frequency standards based on cold strontium, rubidium and caesium atoms. The methods of calculation and optimisation of the main parameters of acousto-optic modulators are considered; their basic technical characteristics are experimentally investigated in the spectral range of optical radiation 460 – 900 nm and in the frequency shift range of 5 – 400 MHz. The modulators have a high diffraction efficiency, low power consumption and the ability to work with linearly and randomly polarised optical radiation. (frequency standards)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Growth of Yb : Na{sub 2}SO{sub 4} crystals and study of their spectral – luminescent characteristics

Ytterbium-doped single crystals of the high-temperature hexagonal sodium sulphate modification are grown by the Czochralski method. It is found by energy dispersive analysis that the crystallisation occurs congruently. The Yb : Na{sub 2}SO{sub 4} crystals have additional (with respect to Yb{sup 3+} ions) absorption bands in the regions of 650, 850 and 1150 nm, which obviously belong to colour centres. The luminescence spectrum of the Yb : Na{sub 2}SO{sub 4} single crystal noticeably differs from the luminescence spectrum of Yb : YAG crystals by the presence of a broad band without a prominent peak. The luminescence decay curve for the powder is single-exponential with a time constant of 1175 μs, which is somewhat larger than that for the Yb : YAG crystal. The lifetime of the ytterbium excited state does not change during storage of the samples in air for a week. (active media)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Multifrequency stimulated Raman scattering of light in a calcite single crystal

Using pulses of multifrequency stimulated Raman scattering (SRS) in calcite, nonlinear photoluminescence in a stilbene molecular crystal is excited. When multifrequency SRS is excited by the radiation of a Nd{sup 3+} : YAG laser with a wavelength of 1064 nm, eleven anti-Stokes components are observed in the visible spectrum with an average frequency shift of 1086 cm{sup −1} between them. Using the second harmonic of the Nd {sup 3+} : YAG laser radiation allowed three anti-Stokes and four Stokes components to be recorded. The large spectral range of the frequency comb facilitated effective reduction in the duration and increase in the intensity of the radiation pulse of multifrequency SRS. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Relaxation oscillations in a bipolarised Nd : YAG laser with a Fabry – Perot cavity

Based on the model of a bipolarised laser, which takes into account real orientations of absorbing and emitting dipoles of active centres in the unit cell of an Nd : YAG single crystal, we have shown that the appearance of low-frequency relaxation oscillations requires the participation of both competing pump channels through linearly and circularly polarised dipole transitions. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2020

Influence of growth temperature of KTiOAsO{sub 4} single crystals on their physicochemical parameters and formation of domain structures

A potassium titanyl arsenate (KTiOAsO{sub 4}, KTA) crystal 50 × 80 × 60 mm in size has been grown by upgraded Czochralski method from flux (TGGS) with a decrease in temperature from 900 to 770 °C during pulling. It is shown that the spectroscopic properties of the parts of KTA crystals grown at 900 and 770 °C are close, whereas the electrical conductivity of the low-temperature (770 °C) KTA part turned out to be an order of magnitude lower than that of the high-temperature part. Visualisation of the domain structure by second-harmonic generation microscopy revealed a more efficient domain intergrowth (throughout the sample) in the low-temperature KTA, which is important for forming a regular domain structure (RDS) in a KTA-based nonlinear optical element. It is established that the quantum efficiency of parametric generation of light in the RDS formed in low-temperature KTA is several times higher than in the case of high-temperature KTA. The results obtained are important for optimising RDS parameters. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

CIRCUMSTELLAR MAGNETITE FROM THE LAP 031117 CO3.0 CHONDRITE

We report the first microstructural confirmation of circumstellar magnetite, identified in a petrographic thin section of the LaPaz Icefield 031117 CO3.0 chondrite. The O-isotopic composition of the grain indicates an origin in a low-mass (∼2.2 M{sub ⊙}), approximately solar metallicity red/asymptotic giant branch (RGB/AGB) star undergoing first dredge-up. The magnetite is a single crystal measuring 750 × 670 nm, is free of defects, and is stoichiometric Fe{sub 3}O{sub 4}. We hypothesize that the magnetite formed via oxidation of previously condensed Fe dust within the circumstellar envelope of its progenitor star. Using an empirically derived rate constant for this reaction, we calculate that such oxidation could have occurred over timescales ranging from approximately ∼9000–500,000 years. This timescale is within the lifetime of estimates for dust condensation within RGB/AGB stars.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Quantum critical fluctuations in the heavy fermion compound Ce(Ni 0.935 Pd 0.065 ) 2 Ge 2

Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experi- ments were performed on a single crystal of the heavy fermion compound Ce(Ni 0.935 Pd 0.065 ) 2 Ge 2 in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T 3/2 and γ(T) ~ γ 0 - bT 1/2 ). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

36 MATERIALS SCIENCE↗