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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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Optically pumped lasing in single crystals of organometal halide perovskites prepared by cast-capping method

A simple “cast-capping” method is adopted to prepare single-crystal perovskites of methyl ammonium lead bromide (CH{sub 3}NH{sub 3}PbBr{sub 3}). By capping a CH{sub 3}NH{sub 3}PbBr{sub 3} solution casted on one substrate with another substrate such as glass, mica, and distributed Bragg reflector (DBR), the slow evaporation of solvent enables large-size cubic crystals to grow between the two substrates. Under optical pumping, edge-emitting lasing is observed based on Fabry–Pérot resonation between parallel side facets of a strip-shaped crystal typically with a lateral cavity length of a few tens of μm. On the other hand, vertical-cavity surface-emitting lasing (VCSEL) is obtained from a planar crystal grown between two DBRs with a cavity thickness of a few μm. Simultaneous detection of those edge- and surface-emissions reveals that the threshold excitation fluence of VCSEL is higher than that of the edge-emitting lasing due to thickness gradient in the planar crystal.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Self-cavity lasing in optically pumped single crystals of p-sexiphenyl

Organic single-crystal self-cavities are prepared by solution growth of p-sexiphenyl (p-6P). Based on Fabry-Pérot feedback inside a quasi-lozenge-shaped platelet crystal, edge-emitting laser is obtained under optical pumping. The multimode lasing band appears at the 0-1 or 0-2 vibronic progressions depending on the excitation conditions which affect the self-absorption effect. Cavity-size dependence of amplified spontaneous emission (ASE) is investigated with laser-etched single crystals of p-6P. As the cavity length of square-shaped crystal is reduced from 100 to 10 μm, ASE threshold fluence is decreased probably due to size-dependent light confinement in the crystal cavity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Excitation-dependent carrier lifetime and diffusion length in bulk CdTe determined by time-resolved optical pump-probe techniques

We applied time-resolved pump-probe spectroscopy based on free carrier absorption and light diffraction on a transient grating for direct measurements of the carrier lifetime and diffusion coefficient D in high-resistivity single crystal CdTe (codoped with In and Er). The bulk carrier lifetime t decreased from 670 +/-50 ns to 60 +/- 10 ns with increase of excess carrier density N from 10 16 to 5 x 10 18 cm -3 due to the excitation-dependent radiative recombination rate. In this N range, the carrier diffusion length dropped from 14 um to 6 um due to lifetime decrease. Modeling of in-depth (axial) and in-plane (lateral) carrier diffusion provided the value of surface recombination velocity S = 6 x 10 5 cm/s for the untreated surface. At even higher excitations, in the 10 19 -3 x 10 20 cm -3 density range, D increase from 5 to 20 cm^2/s due to carrier degeneracy was observed.

14 SOLAR ENERGY↗
DOE OSTI2018

Laser induced phase transition in epitaxial FeRh layers studied by pump-probe valence band photoemission

We use time-resolved X-ray photoelectron spectroscopy to probe the electronic and magnetization dynamics in FeRh films after ultrafast laser excitations. We present experimental and theoretical results which investigate the electronic structure of FeRh during the first-order phase transition, identifying a clear signature of the magnetic phase. We find that a spin polarized feature at the Fermi edge is a fingerprint of the magnetic status of the system that is independent of the long-range ferromagnetic alignment of the magnetic domains. We use this feature to follow the phase transition induced by a laser pulse in a pump-probe experiment and find that the magnetic transition occurs in less than 50 ps and reaches its maximum in 100 ps.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Room-temperature spin-to-charge conversion in sputtered bismuth selenide thin films via spin pumping from yttrium iron garnet

We investigated spin-to-charge current conversion in sputtered Y 3 Fe 5 O 12 (YIG)/granular bismuth selenide (GBS) bi-layers at room temperature. The spin current is pumped to the GBS layer by the precession of magnetization at ferromagnetic resonance in the YIG layer. The spin-mixing conductance is determined to be as large as (13.64 ± 1.32) × 10 18 m -2 , which is larger than that of YIG/Pt and comparable or better than that of YIG/crystalline bismuth selenide indicating that GBS is a good spin-sink. The figure of merit of spin-to-charge conversion, the inverse Edelstein effect length ( λ IEE ), is estimated to be as large as (0.11 ± 0.03) nm. λ IEE shows GBS film thickness dependence, and its value is three times as large as in crystalline bismuth selenide. The λ IEE value larger than that of crystalline bismuth selenide and other topological insulators indicates that the spin-to-charge conversion is due to the spin-momentum locking. As the thickness of GBS increases, λ IEE decreases, which means the figure-of-merit of spin-to-charge conversion is influenced by grain size.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Laser-free GHz stroboscopic transmission electron microscope: Components, system integration, and practical considerations for pump–probe measurements

In this work a 300 keV transmission electron microscope was modified to produce broadband pulsed beams that can be, in principle, between 40 MHz and 12 GHz, corresponding to temporal resolution in the nanosecond to picosecond range without an excitation laser. The key enabling technology is a pair of phase-matched modulating and de-modulating traveling wave metallic comb striplines (pulsers). An initial temporal resolution of 30 ps was achieved with a strobe frequency of 6.0 GHz. The placement of the pulsers, mounted immediately below the gun, allows for preservation of all optical configurations, otherwise available to the unmodified instrument, and therefore makes such a post-modified instrument for dual-use, i.e., both pulsed-beam mode (i.e., stroboscopic time-resolved) and conventional continuous waveform mode. In this article, we describe the elements inserted into the beam path, challenges encountered during integration with an in-service microscope, and early results from an electric-field-driven pump–probe experiment. We conclude with ideas for making this class of instruments broadly applicable for examining cyclical and repeatable phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Coupling to rotational manifolds to improve gas-phase pump–probe spectroscopic models

The physical picture of gas-phase optical transitions is normally presented as an isolated two-level system balanced by upward and downward processes. Isolated models assume a phenomenological treatment of collisional dephasing but do not strictly account for collisional population exchange with the rotational baths. While this assumption is valid under low-intensity conditions, where excitation is rate-limiting, isolated models can deviate from Beer’s Law at sufficient pressures and monochromatic intensities when both collisional broadening and power broadening are comparable to (or greater than) lifetime broadening, which are not uncommon conditions for cavity enhanced spectroscopies in the mid-IR spectral range. Although this problem has been addressed by rate-equation models for linear absorption measurements, a general treatment for multi-level quantum mechanical models suitable for non-linear absorption measurements (two-photon/two-color/pump–probe) is lacking. Isolated models require physical parameter inputs that disagree with expected values by at least an order of magnitude. These non-physical models undermine the ability to predict non-linear signal strengths under untested conditions and thereby limit the potential to optimize the sensitivity of non-linear spectroscopies and to expand their analytical applications (e.g., new analytes and/or buffer gases, changes in cavity free-spectral-range, changes in intracavity powers or wavelengths, and accurate investigation of physical phenomena). In this study, we derive bath-coupled models for gaseous pump–probe spectroscopy by application of the quantum Lindblad equation and detailed balance. Bath-coupled models are shown to fit data consistently across variations in intensity and agree with all physically expected values.

Cavity ring-down spectroscopy↗
DOE OSTI2013

Linewidth-tunable laser diode array for rubidium laser pumping

To optimise the pump source for a high-power diodepumped rubidium vapour laser, we have designed a laser diode array (LDA) with a narrowed and tunable linewidth and an external cavity formed by two volume Bragg gratings (VBGs). Through controlling the temperature differences between the two VBGs, the LDA linewidth, which was 1.8 nm before mounting the two VBGs, was tunable from 100 pm to 0.2 nm, while the output power changed by no more than 4 %. By changing simultaneously the temperature in both VBGs, the centre wavelength in air of the linewidth-tunable LDA was tunable from 779.40 nm to 780.05 nm. (control of laser radiation parameters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Intracavity laser spectroscopy with a semiconductor disk laser-pumped cw Cr{sup 2+} : ZnSe laser

Absorption spectra of the air have been measured near 2.31 μm using intracavity laser spectroscopy with a semiconductor disk laser-pumped cw Cr{sup 2+} : ZnSe laser. It is shown that, at lasing times of at least 3 ms, the sensitivity of the laser to intracavity absorption increases. This allows one to reach an effective path length of 900 km and enables detection of weak lines with absorption coefficients down to 1 × 10{sup -9} cm{sup -1}. (laser spectroscopy)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Study of Tm : Sc{sub 2}SiO{sub 5} laser pumped into the {sup 3}H{sub 6} – {sup 3}F{sub 4} transition of Tm{sup 3+} ions

The Tm{sup 3+} : Sc{sub 2}SiO{sub 5} crystals of optical quality are grown by the Czochralski method. Lasing at a wavelength of ∼1.98 μm is obtained in an active element made of a grown crystal under pumping by an erbium Raman fiber laser at a wavelength of 1.678 μm. The slope efficiency of the laser reaches 42% at an output power up to 320 mW. (lasers)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Functional possibilities for forming different inverse population distributions in diode-side-pumped laser heads

The functional possibilities of diode-side-pumped laser heads of solid-state lasers for forming inverse population distributions of different types are analysed. The invariants determining the relationship between the laser head parameters upon scaling are found. The results of comparative experimental studies are presented. (lasers)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Influence of pump wavelength and core size on stimulated Brillouin scattering spectra of acoustically antiguiding optical fibres

Optical fibres having an acoustically antiguiding structure produced by alumina doping of their core have been fabricated and investigated. The stimulated Brillouin scattering (SBS) spectra of the fibres have been measured and calculated theoretically. The results demonstrate that the shape of the SBS spectrum of the acoustically antiguiding fibres strongly depends on the pump wavelength, core size and dopant profile across the fibre. A considerable broadening of the SBS gain spectrum is only possible at certain guidance parameters of the fibre and a fixed operating wavelength. (fibre and integrated-optical structures)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Investigation of diode-pump absorption efficiency and thermo-optical effects in a high-power Yb:KGW laser

Diode-pump absorption is experimentally studied in a high-power Yb:KGd(WO{sub 4}){sub 2} (Yb:KGW) laser in the presence and absence of lasing. The maximum absorption efficiency in the cw regime exceeds 77% which is by a factor of 1.4 greater than the maximum absorption efficiency in the absence of lasing. The powers of thermo-optical lenses induced in laser crystals during lasing are measured. A strong dependence of the lens power and aberrations on the orientation of laser crystals relative to the propagation direction and polarisation is confirmed. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

High-power compact laser with segmented longitudinal pumping of coupled laser channels

The characteristics of a compact Nd:YAG/Cr:YAG laser with segmented end pumping using a bundle of seven optical fibres are presented. In the regime of optical coupling of thus formed seven laser channels, 3-ns pulses with an energy up to 20 mJ, as well as their trains, are obtained. The used method makes it possible to scale the energy and power of lasers of this type with controlled spatial beam profile. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Formation of the active medium in high-power repetitively pulsed gas lasers pumped by an electron-beam-controlled discharge

A high-power repetitively pulsed e-beam-controlled discharge CO{sub 2} laser is simulated numerically; the simulation results are compared with experimental data. Optimal sizes and design of electrodes and configuration of the external magnetic field are found, which allow one to introduce no less than 90% electric pump energy into a specified volume of the active medium, including the active volume of a laser with an aperture of 110 × 110 cm. The results obtained can also be used to design other types of highpower gas lasers. (lasers)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Optimisation of thulium fibre laser parameters with generation of pulses by pump modulation

The formation of relaxation pulses of a thulium fibre laser (λ = 1.9 μm) by modulating the power of a pump erbium fibre laser (λ = 1.55 μm) is studied. A theoretical model is developed to find the dependences of pulse duration and peak power on different cavity parameters. The optimal cavity parameters for achieving the minimal pulse duration are determined. The results are confirmed by experimental development of a laser emitting pulses with a duration shorter than 10 ns, a peak power of 1.8 kW and a repetition rate of 50 kHz. (control of radiation parameters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Pulsed electron-beam-pumped laser based on AlGaN/InGaN/GaN quantum-well heterostructure

The parameters of pulsed blue-violet (λ ≈ 430 nm at T = 300 K) lasers based on an AlGaN/InGaN/GaN structure with five InGaN quantum wells and transverse electron-beam pumping are studied. At room temperature of the active element, the minimum electron energy was 9 keV and the minimum threshold electron beam current density was 8 A cm{sup -2} at an electron energy of 18 keV. (lasers)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

A dual-end-pumped Ho:YAG laser with a high energy output

We report a high energy output from a Ho:YAG oscillator resonantly double-end pumped by Tm:YLF lasers at room temperature. The maximum pulse energy of 52.5 mJ was achieved at a pulse repetition rate of 100Hz and a pulse duration of 35.2 ns, corresponding to a peak power of approximately 1.5 MW. The output wavelength was 2090.7 nm with beam quality factor M{sup 2} ∼ 1.2. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

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