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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Spectral narrowing and broadening of Cr:ZnS/Se laser oscillation due to mode competition and spatial hole burning in the gain element

In this paper, we demonstrate the laser characterization of Cr:ZnS/Se polycrystalline gain media in non-selective unpolarized, linearly polarized, and twisted mode cavities. Lasers were based on post-growth diffusion-doped, commercially available antireflective-coated Cr:ZnSe and Cr:ZnS polycrystals with a length of 9 mm. The spectral output of lasers based on these gain elements in non-selective unpolarized and linearly polarized cavities was measured to be broadened to ∼20-50 nm due to the spatial hole burning (SHB) effect. SHB alleviation in the same crystals was realized in the “twisted mode” cavity, with linewidth narrowing to ∼80-90 pm. Both broadened and narrow-line oscillations were captured by adjusting the orientation of intracavity waveplates with respect to facilitated polarization.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Fourier-method beam analysis for coherent vertical cavity surface emitting laser arrays

Effective engineering and exploitation of coherently coupled vertical cavity surface emitting laser arrays will benefit from simple and fast characterization of the optical coupling and coherence. We propose a Fourier method of analyzing beam profiles as an alternative to the prior beam visibility analysis and show that the mode suppression ratio and phase between a pair of supermodes can be extracted. Our analysis enables fast quantitative determination of the array coherence and supermode characteristics.

Strzebonski, Pawel (ORCID:0000000156286296)↗
DOE OSTI2024

Linewidth narrowing in self-injection locked lasers: Effects of quantum confinement

This paper explores the impact of gain medium on linewidth narrowing in integrated self-injection locked III–V/SiN lasers, theoretically and experimentally. We focus on the effects of carrier densities of states in zero- and two-dimensional structures due to quantum-dot and quantum-well confinement. The theoretical approach includes (a) multimode laser interaction to treat mode competition and wave mixing, (b) quantum-optical contributions from spontaneous emission, and (c) composite laser/free-space eigenmodes to describe outcoupling and coupling among components within an extended cavity. For single-cavity lasers, such as distributed feedback lasers, the model reproduces the experimentally observed better linewidth performance of quantum-dot active regions over quantum-well ones. When applied to integrated III–V/SiN lasers, our analysis indicates Hz-level linewidth performance for both quantum-dot and quantum-well gain media due to overcoming the difference in carrier-induced refractive index by incorporating a high-Q SiN passive resonator. Trade-offs are also explored between linewidth, output power, and threshold current.

Cavity quantum electrodynamics↗
DOE OSTI2025

High-luminosity meV-resolution single-shot hard X-ray spectrograph for cavity-based X-ray free-electron lasers

Cavity-based X-ray free-electron lasers (CBXFELs) represent a possible realization of fully coherent hard X-ray sources having high spectral brilliance along with a narrow spectral bandwidth of ∼1–50 meV, a high repetition pulse rate of ∼1 MHz, and good stability. A diagnostic tool is required to measure CBXFEL spectra with meV resolution and high luminosity on a shot-to-shot basis. We have designed a high-luminosity single-shot hard X-ray spectrograph that images 9.831 keV X-rays in a ∼200 meV spectral window with a spectral resolution of a few meV. The spectrograph is designed around angular dispersion of X-rays in Bragg diffraction from crystals. It operates close to design specifications, exhibiting a linear dispersion rate of ∼1.4 µm meV −1 and a ∼200 meV window of high-fidelity spectral imaging. The experimentally demonstrated spectral resolution is ∼20 meV; this resolution is twice as low as expected from theory primarily because the spectrograph is highly sensitive to crystal angular instabilities. The experiment was performed at the bending magnet X-ray optics testing beamline 1-BM at the Advanced Photon Source.

Bragg diffraction↗
DOE OSTI2022

Colliding Pulse Mode Locking and Nonequilibrium Carrier Dynamics within Vertical External-Cavity Surface-Emitting Lasers

The complex nonlinear dynamics of colliding counterpropagating ultrashort laser pulses circulating in a vertical external-cavity surface-emitting ring laser cavity are captured by a first-principles quantum-mechanical microscopic model coupled to an intracavity beam propagator. Furthermore, our numerical simulations establish that overall mode locking stability is sensitive to relative phases and delays of the pulses impinging on the semiconductor saturable absorber mirror. Delay offsets of the counterpropagating pulses lead to asymmetric carrier recovery and instability, often leading in turn to single unidirectional circulating pulses. Although computationally challenging, we also include transverse effects and show that the influence of interference patterns from spatial gratings written by the counterpropagating pulses is significant in stabilizing the modelocked pulses.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Anomalous Purcell decay of strongly driven inhomogeneous emitters coupled to a cavity

We perform resonant fluorescence lifetime measurements on a nanocavity-coupled erbium ensemble as a function of cavity-laser detuning and pump power. Our measurements reveal an anomalous three-fold suppression of the ensemble Purcell factor at zero cavity detuning and high pump fluence. We capture qualitative aspects of this decay rate suppression using a Tavis–Cummings model of non-interacting spins coupled to a common cavity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Integrated dispersion compensated mode-locked quantum dot laser

Quantum dot lasers are excellent on-chip light sources, offering high defect tolerance, low threshold, low temperature variation, and high feedback insensitivity. Yet a monolithic integration technique combining epitaxial quantum dot lasers with passive waveguides has not been demonstrated and is needed for complex photonic integrated circuits. We present here, for the first time to our knowledge, a monolithc offset quantum dot integration platform that permits formation of a laser cavity utilizing both the robust quantum dot active region and the versatility of passive GaAs waveguide structures. This platform is substrate agnostic and therefore compatible with the quantum dot lasers directly grown on Si. As an illustration of the potential of this platform, we designed and fabricated a 20 GHz mode-locked laser with a dispersion-engineered on-chip waveguide mirror. Due to the dispersion compensation effect of the waveguide mirror, the pulse width of the mode-locked laser is reduced by a factor of 2.8.

Zhang, Zeyu (ORCID:0000000271576272)↗
DOE OSTI2021

High energy (0.8 J) mechanically Q-switched 2.94 μm Er:YAG laser

We report a flashlamp pumped mechanically Q-switched (MQS) 2.94 μm Er:YAG laser based on a spinning mirror with a highest output energy of 805 mJ at a pulse duration of 61 ns and 13 MW of peak power at 1 Hz repetition rate. This record output energy was achieved with the use of 300 mm long MQS Er:YAG laser cavity consisting of a 70% output coupler, 7 × 120 mm AR coated Er(50%):YAG crystal, and 4200 rad/s angular speed of the spinning mirror. The pulse jitter was also measured by using optical triggering and was smaller than 10 ns for 150 ns Q-switched pulses, which could be applicable to many laser applications where precise synchronization of pulses is required.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Low-threshold, single-transverse-mode, 940-nm vertical-cavity surface-emitting laser with a mode filter and half-wavelength cavity

We demonstrate a structure for a vertical-cavity surface-emitting laser (VCSEL) with a mode filter and half-wavelength (λ/2) cavity. The effects of λ/2- and λ-cavities on the threshold current are studied. The thickness and etched diameter of the mode filter are optimised to achieve single-transverse-mode output. The results show that when changing from λ-cavity to λ/2-cavity, the threshold current of the VCSEL decreases by 30.7% (from 0.85 mA to 0.65 mA). In addition, for the mode-filter thickness of 80 nm, and the etched diameter of 2.5 μm, the side mode suppression ratio reaches 90 dB, which meets the requirement of single-transverse-mode output. The VCSELs with the optimised design can overcome many difficulties and have great potential in 3D face recognition. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Identification of Brillouin Zones by In-Plane Lasing from Light-Cone Surface Lattice Resonances

Periodic optical structures can control the flow of light, which has facilitated applications in optical fibers, laser cavities, and biochemical sensors. The first Brillouin zone (BZ) in reciprocal space can describe all the electromagnetic fields localized inside a photonic lattice. However, photonic lattices also exhibit radiative losses from light scattering, but the radiated fields are not captured by the first BZ. In a two-dimensional lattice, the in-plane wavevectors of photonic modes are limited by the so-called light cone, which depicts free-photon dispersion relations in the surrounding medium. Here we show that projection of the light cone on extended BZs provides a geometric method to observe radiated electromagnetic fields of photonic lattice modes. We developed a coupled dipole radiation theory to reveal how lattice geometry and dipole orientation affect the angular distributions of the radiated fields. Using dye molecules as local dipole emitters to excite and probe the optical modes, we experimentally identified high-order BZ edges through directional, in-plane lasing emission.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

On quantum-dot lasing at gain peak with linewidth enhancement factor $α$ H = 0

This paper describes an investigation of the linewidth enhancement factor α H in a semiconductor quantum-dot laser. Results are presented for active region parameters and laser configurations important for minimizing α H . In particular, the feasibility of lasing at the gain peak with α H = 0 is explored. The study uses a many-body theory with dephasing effects from carrier scattering treated at the level of quantum-kinetic equations. InAs quantum-dot lasers with different p-modulation doping densities are fabricated and measured to verify the calculated criteria on laser cavity design and epitaxial growth conditions.

42 ENGINEERING↗
DOE OSTI2022

Measurement of amplification and absorption of a THz quantum-cascade metasurface free-space amplifier

An active amplifying metasurface based on a quantum-cascade gain material at 2.7 THz is studied. The metasurface is first evaluated as the active component of an external cavity laser with excellent beam quality and frequency tunability from 2.55–2.8 THz. Amplification and absorption of the metasurface alone are then separately measured at a single frequency using a probe signal from a CO 2 -pumped gas laser operating at 2.743 THz. The metasurface reflectance vs bias is measured and compared with expectations from non-equilibrium Green’s function simulations of the quantum-cascade gain material and FEM simulations of the metasurface reflectance. A peak amplification on the order of 0.3 dB is measured. Design strategies are discussed for increasing single-reflection amplification (upward of 10 dB) and reducing power dissipation. Further increased amplification could be achieved by cascading multiple metasurfaces.

Curwen, Christopher A.↗
DOE OSTI2025

Ink-sprayed transparent ceramic multilayer planar waveguides for ribbon lasers

Multilayer transparent ceramic planar waveguides were fabricated using a newly developed particle-loaded ink spraying method, characterized, and lased. Waveguides with five Yb:YAG gain regions and four Lu:YAG index-matched regions were produced for application as a “ribbon laser,” as well as a homogeneous Yb:YAG waveguide. Elemental mapping revealed that the waveguide thicknesses varied from 40 to 69 μm, comprised of layers of less than 10 µm. The Yb concentration profiles were fit to a diffusion profile. The homogeneous and multilayer waveguides were tested in a laser cavity and produced similar slope efficiencies, with a maximum of 31% achieved. In conclusion, their beam profiles provided evidence of the ribbon structure affecting the preferred mode.

Osborne, Ross [Lawrence Livermore National Laborat↗
DOE OSTI2021

Spectroscopy of GR1 centers in synthetic diamonds

We report on the spectroscopic characterization, absorption saturation, and excited-state dynamics of GR1 centers in synthetic diamonds. The non-linear optical measurements reveal an efficient bleaching of the GR1 center’s ground level under ns-pulsed 633 nm excitation. The maxima of absorption and emission cross sections were estimated to be 4.5 × 10 −17 cm 2 and 9 × 10 −17 cm 2 at 630 nm and 780 nm, respectively. The radiative lifetime of the excited level was estimated to be 8.5 ns. The 658 nm probe kinetics uncovered relaxation of 1 T 2 excited level going predominantly to a metastable state with a lifetime of 220 μs. An induced absorption detected with the use of a highly concentrated diamond sample could be due to up-conversion and photoionization processes in additional impurity-vacancy center with absorption at the short-wavelength tail of GR1. The results presented here indicate that synthetic diamonds with GR1 centers could serve as near infrared gain media or passive Q-switchers for laser cavities over the 633–750 nm spectral range. Optimization of the center concentration and the crystal parameters are required to minimize the induced absorption at the lasing wavelengths.

36 MATERIALS SCIENCE↗
DOE OSTI2021

System and method for laser system having non-planar thin disc gain media

The present disclosure relates to a laser system. The laser system may have at least non-flat gain media disc. At least one pump source may be configured to generate a beam that pumps the non-flat gain media disc. A laser cavity may be formed by the pump source and the non-flat gain media disc. An output coupler may be included for receiving and directing the output beam toward an external component.

Dawson, Jay W.↗
DOE OSTI2021

Demonstration of a 20‐W membrane‐external‐cavity surface‐emitting laser for sodium guide star applications

Abstract We present a record 20‐W continuous‐wave output power membrane‐external‐cavity surface‐emitting laser (MECSEL) double‐bonded to silicon carbide (SiC) heat spreaders emitting around 1178 nm. We achieved a maximum slope efficiency of 27.7% and an optical‐to‐optical efficiency of 26.7%. By utilising an intracavity birefringent filtre, the wavelength was tuned over 75 nm and maximum output power of 12.7 W was recorded at 1178 nm. This study shows the potential of MECSELs to achieve high‐performance and cost‐effective optically pumped semiconductor disk lasers targeting applications in sodium guide stars.

Priante, D.↗