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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Vector measurements using a pulsed, optically pumped atomic magnetometer

An atomic magnetometer, and a method for using same is disclosed. The method for measuring an ambient magnetic field uses an atomic magnetometer that has a probe light beam with a probe axis that probes a polarization vector of an atomic population confined within a vapor cell. The method employs one or more measurement cycles. In each measurement cycle, the polarization vector is prepared in an initial state via an optical pumping pulse. The vapor cell is then subjected to the ambient magnetic field, which results in rotation of the polarization vector by Larmor precession. Within the measurement cycle, at a point in time after the polarization vector has been prepared in the initial state, the ambient magnetic field rotates the direction of the polarization vector, and at least one measurement is made of a projection of the Larmor-rotated polarization vector onto the probe axis during or after application of a magnetic waveform.

Schwindt, Peter↗
DOE OSTI2022

Nonlinear quantum behavior of ultrashort-pulse optical parametric oscillators

The quantum features of ultrashort-pulse optical parametric oscillators (OPOs) are investigated theoretically in the nonlinear regime near and above threshold. Viewing the pulsed OPO as a multimode open quantum system, we rigorously derive a general input-output model that features nonlinear coupling among many cavity (i.e., system) signal modes and a broadband single-pass (i.e., reservoir) pump field. Under appropriate assumptions, our model produces a Lindblad master equation with multimode nonlinear Lindblad operators describing two-photon dissipation and a multimode four-wave-mixing Hamiltonian describing a broadband, dispersive optical cascade, which we show is required to preserve causality. To simplify the multimode complexity of the model, we employ a supermode decomposition to perform numerical simulations in the regime where the pulsed supermodes experience strong single-photon nonlinearity. We find that the quantum nonlinear dynamics induces pump depletion as well as corrections to the below-threshold squeezing spectrum predicted by linearized models. We also observe the formation of non-Gaussian states with Wigner-function negativity and show that the multimode interactions with the pump, both dissipative and dispersive, can act as effective decoherence channels. Finally, we briefly discuss some experimental considerations for potentially observing such quantum nonlinear phenomena with ultrashort-pulse OPOs on nonlinear nanophotonic platforms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Temporal reflection of an optical pulse from a short soliton: impact of Raman scattering

We study temporal reflection of an optical pulse from the refractive-index barrier created by a short pump soliton inside a nonlinear dispersive medium such as an optical fiber. One feature is that the soliton’s speed changes continuously as its spectrum redshifts because of intrapulse Raman scattering. We use the generalized nonlinear Schrödinger equation to find the shape and spectrum of the reflected pulse. Both are affected considerably by the soliton’s trajectory. The reflected pulse can become considerably narrower compared to the incident pulse under conditions that involve a type of temporal focusing. This phenomenon is explained through space–time duality by showing that the temporal situation is analogous to an optical beam incident obliquely on a parabolic mirror. We obtain an approximate analytic expression for the reflected pulse’s spectrum and use it to derive the temporal version of the transformation law for the

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Absorption properties of graphene quantum dots under ultrashort optical pulses

Here, we study the interaction of graphene quantum dots (GQDs) with ultrashort and strong optical pulses theoretically. An important characteristic of such interaction is the energy accumulated by GQDs after the pulse. We show that the GQD absorbance has a highly nonlinear dependence on the field amplitude. At small-field amplitudes, the absorbance strongly depends on the frequency of the pulse and the band gap of a QD, i.e., its size. At large-field amplitudes, ~1 V/Å, the absorbance has a weak nonmonotonic dependence on the size of the dot with its maximum value of ≈ 4.5 % realized for GQD consisting of ≈ 60 atoms. As a function of the field amplitude, the absorbance also has a maximum, the position of which depends on the size of the dot.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Single-shot cross-correlation of counter-propagating, short optical pulses using random quasi-phase-matching

The single-shot cross-correlation of the short optical pulses generated by two laser facilities is acquired using random quasi-phase-matching of the counter-propagating beams in a disordered ferroelectric crystal. Transverse sum–frequency generation of the two counter-propagating pulses at different central wavelengths yields their time-dependent background-free cross-correlation after spectral filtering. Their relative delay is directly determined on every shot from the measured cross-correlation, making it a simple diagnostic for jitter studies and temporal characterization.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Transition metal dichalcogenide monolayers in an ultrashort optical pulse: Femtosecond currents and anisotropic electron dynamics

We theoretically study the interaction of an ultrafast intense linearly polarized optical pulse with monolayers of transition metal dichalcogenides (TMDCs). Such a strong pulse redistributes electrons between the bands and generates femtosecond currents during the pulse. Due to the large bandwidth of the incident pulse, this process is completely an off-resonant. While in TMDCs, the time-reversal symmetry is conserved, the inversion symmetry is broken, and these monolayers have axial symmetry along the armchair direction but not along with the zigzag one. The pulse, polarized along with asymmetric directions of TMDC monolayer, generates both longitudinal, i.e., along the direction of polarization, and transverse, i.e., in the perpendicular direction, currents. Such currents result in charge transfer through the system. Finally, we study different TMDC materials and show how the femtosecond transport in TMDC monolayers depend on their parameters, such as lattice constant and bandgap.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Universal structure of propagation-invariant optical pulses

Space–time structuring of light—where spatial and temporal degrees of freedom are deliberately coupled and controlled—is an emerging area of optics that enables novel configurations of electromagnetic fields. Of particular importance for applications are optical pulses whose peak intensity travels at an arbitrary, tunable velocity while maintaining its spatiotemporal profile. Space–time wave packets (STWPs) and the ideal flying focus (FF) are two prominent realizations of these pulses. Here, we show that these realizations share an identical spatiotemporal field structure and that this structure represents a universal solution for constant-velocity, propagation-invariant pulses.

Almeida, R. (ORCID:0000000288435855)↗
DOE OSTI2022

Method and system for arbitrary optical pulse generation

A system, method, and apparatus for continuous seed laser pulses supplied to a CW pumped pre-amplifier and/or power-amplifier chain comprises an optical modulator configured to impress pulse signals on an optical signal, a waveform generator configured to establish a structure of the optical signal, and a keep-alive circuit that generates a continuous electrical pulse pattern provided to the optical modulator, wherein the system provides a continuous seed laser pulse structure.

Johnson, David↗
DOE OSTI2024

Striated composite layers of silica and hafnia offering advantageous properties for short-pulse optical coatings

Monolayers containing subnanometer striations of silica and hafnia to form composite materials at varying ratios are explored as a method to develop high-index dielectric layers with increased laser-induced–damage thresholds (LIDTs). These layers can then be used in multilayer dielectric coatings for short-pulse, high-peak-power laser applications, particularly in regions of the highest electric-field intensity. Fabrication is achieved by means of exposure to two different evaporant vapor plumes, where local exposure to each plume is controlled via shielding to prevent simultaneous exposure. The LIDT of the resulting layers has been evaluated at 1053 nm with 600-fs pulses. The results indicate that such hafnia/silica layers exhibit LIDTs similar to silica for a refractive index of ≤1.65. These results suggest that the use of these layers in locations subjected to high electric-field intensity within multilayer dielectric coatings may significantly improve the LIDT, with this deposition process providing particular benefit for scaling to large-aperture, high-fluence components.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Control of valley polarization in gapped graphene by linearly polarized ultrashort optical pulse

We present a versatile model of gapped graphene to manipulate valley polarization by using ultrafast linearly polarized pulses of zero areas. First, a circularly polarized pulse of a single oscillation produces a valley-selective population of the conduction band by means of topological resonance. Then we apply a linearly polarized femtosecond-long pulse that changes the valley polarization. The magnitude of such a change depends on the amplitude and the direction of polarization of the pulse. In conclusion, our protocol provides a favorable platform for applications in valleytronics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Selective bond formation triggered by short optical pulses: quantum dynamics of a four-center ring closure

Here we report bond formation induced by an ultrashort UV pulse. The photochemical process is described by quantum dynamics as coherent electronic and nuclear motions during the ultrashort pulse induced ring closure of norbornadiene to quadricyclane. Norbornadiene consists of two ethylene moieties connected by a rigid (CH 2 ) 3 bridge. Upon photoexcitation, two new sigma bonds are formed, resulting in the closure of a four-atom ring. As a medium-sized polyatomic molecule, norbornadiene exhibits a high density of strongly coupled electronic states from about 6 eV above the ground state. We report on inducing the formation of the new bonds using a short femtosecond UV pulse to pump a non-equilibrium electronic density in the open form that evolves towards the closed ring form. As the coherent electronic-nuclear coupled dynamics unfold, the excited states change character through non-adiabatic interactions and become valence states for the two new C–C bonds of quadricyclane. Our three-dimensional fully quantum dynamical grid simulations during the first 200 fs show that short UV pulses of different polarization initiate markedly different initial non-equilibrium electronic densities that follow different dynamical paths to the S 0 /S 1 conical intersection. They lead to different initial relative yields of quadricyclane, thereby opening the way to controlling bond-making with attopulses.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Method and apparatus for measuring optical pulses

A pulse analysis system or method includes a frequency filter that receives an ultrafast pulse under test and disperses the pulse under test over a frequency range. The frequency filter separates the pulse under test into component frequency slices and provides the frequency slices to a detector coupled to a digitizer, which processes the digitized signal and collects a sonogram characteristic of the pulse under test. The frequency slices are arranged to overlap. Ptychography is performed on the sonogram to obtain characteristics of the pulse under test.

Kane, Daniel J.↗
DOE OSTI2023

Method and apparatus for measuring optical pulses

A pulse analysis system or method includes a frequency filter that receives an ultrafast pulse under test and disperses the pulse under test over a frequency range. The frequency filter separates the pulse under test into component frequency slices and provides the frequency slices to a detector coupled to a digitizer, which processes the digitized signal and collects a sonogram characteristic of the pulse under test. The frequency slices are arranged to overlap. Ptychography is performed on the sonogram to obtain characteristics of the pulse under test.

Kane, Daniel J.↗
DOE OSTI2022

System and method for plasmonic control of short pulses in optical fibers

The present disclosure relates to an optical waveguide system. The system has a first waveguide having a core-guide and a cladding material portion surrounding and encasing the core-guide to form a substantially D-shaped cross sectional profile with an exposed flat section running along a length thereof. The core-guide enables a core-guide mode for an optical pulse signal having a first characteristic, travelling through the core-guide. A material layer of non-linear material is used which forms a second waveguide. The material layer is disposed on the exposed flat section of the cladding material portion. The material layer forms a plasmonic device to achieve a desired coupling with the core-guide to couple optical energy travelling through the core-guide into the material layer to modify the optical energy travelling through the core-guide such that the optical energy travelling through the core-guide has a second characteristic different from the first characteristic.

Feigenbaum, Eyal↗
DOE OSTI2023

Achieving 100 GW idler pulses from an existing petawatt optical parametric chirped pulse amplifier

Optical parametric chirped-pulse-amplification produces two broadband pulses, a signal and an idler, that can both provide peak powers >100 GW. In most cases the signal is used, but compressing the longer-wavelength idler opens up opportunities for experiments where the driving laser wavelength is a key parameter. This paper will describe several subsystems that were added to a petawatt class, Multi-Terawatt optical parametric amplifier line (MTW-OPAL) at the Laboratory for Laser Energetics to address two long-standing issues introduced by the use of the idler, angular dispersion, and spectral phase reversal. To the best of our knowledge, this is the first time that compensation of angular dispersion and phase reversal has been achieved in a single system and results in a 100 GW, 120-fs duration, pulse at 1170 nm.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Optical pulse-induced ultrafast antiferrodistortive transition in SrTiO 3

The ultrafast dynamics of the antiferrodistortive phase transition in perovskite SrTiO 3 is monitored via time-domain Brillouin scattering. Using femtosecond optical pulses, we initiate a thermally driven tetragonal-to-cubic structural transformation and detect the crystal phase through changes in the frequency of Brillouin oscillations (BO) induced by propagating acoustic phonons. Coupling the measured BO frequency with a spatiotemporal heat diffusion model, we demonstrate that, for a sample kept in the tetragonal phase, deposition of sufficient thermal energy induces a rapid transformation of the heat-affected region to the cubic phase. The initial phase change is followed by a slower reverse cubic-to-tetragonal phase transformation occurring on a timescale of hundreds of picoseconds. Here, we attribute this ultrafast phase transformation in the perovskite to a structural resemblance between atomic displacements of the R-point soft optic mode of the cubic phase and the tetragonal phase, both characterized by anti-phase rotation of oxygen octahedra. The structural relaxation time exhibits a strong temperature dependence consistent with the prediction of the equation of motion describing collective oxygen octahedra rotation based on the energy landscape of the phenomenological Landau theory of phase transitions. Evidence of such a fast structural transition in perovskites can open up new avenues in information processing and energy storage sectors.

36 MATERIALS SCIENCE↗