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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 OSTI2024

Broadband laser output by application of stimulated rotational Raman scattering during high-intensity propagation of laser pulses with modified spectral profiles

Research at the Naval Research Laboratory pursues advanced laser technologies that can mitigate laser plasma instabilities (LPI) in applications such as inertial confinement fusion. Increased laser bandwidth is currently being developed as a strategy to suppress LPI. In particular, stimulated rotational Raman scattering (SRRS) has been demonstrated using the Nike krypton fluoride (KrF) laser facility as a viable method for enhancing bandwidth. The technique is applicable to other large laser facilities. Through a combination of high-intensity propagation and optimization of the laser spectrum in the low-energy stages of the laser, the output spectrum of Nike has been broadened with SRRS from its standard operating value of 1 THz full width at half-maximum (FWHM) bandwidth to span a range greater than 4.5 THz. This amount of bandwidth has been shown in simulations to be effective for mitigation of slow-growth laser plasma instabilities, such as cross-beam energy transport (CBET).

Optics↗
DOE OSTI2022

Downhole laser system with an improved laser output production and data collection

One or more embodiments relates to a method of growing ultrasmooth and high quantum efficiency CsTe photocathodes. The method includes exposing a substrate of Cs using an alkali source such as an effusion cell; and controlling co-evaporating growth and co-deposition forming a CsTe growth. The method further includes monitoring a stoichiometry of the CsTe growth.

Mcintyre, Dustin↗
DOE OSTI2024

Downhole laser system with an improved laser output production and data collection

One or more embodiments relates to a method of growing ultrasmooth and high quantum efficiency CsTe photocathodes. The method includes exposing a substrate of Cs using an alkali source such as an effusion cell; and controlling co-evaporating growth and co-deposition forming a CsTe growth. The method further includes monitoring a stoichiometry of the CsTe growth.

McIntyre, Dustin↗
DOE OSTI2023

Compact laser source with frequency modulators generating multiple lines

A compact laser source and a single sideband modulator used therein is disclosed. The compact laser source includes a seed laser and one or more channels, with each channel generating one or more output laser beams having corresponding different wavelengths. The compact laser source can be formed in whole or in part on a single optical motherboard to thereby minimize space and power requirements. By employing the disclosed single sideband modulator, harmonics in the generated output laser beams can be minimized. The compact laser source finds application in an atom interferometer (AI) system, which may be used to measure gravity, acceleration, or rotation of the AI system.

Lentine, Anthony L.↗
DOE OSTI2022

High power picosecond green and deep ultraviolet generations with an all-fiberized MOPA

We demonstrate high power picosecond green and deep ultraviolet (DUV) lasers based on an all-fiberized master oscillator power amplifier (MOPA). The main power amplifier is fabricated with a highly Yb-doped large mode area (LMA) silicate glass fiber. It delivers 75.2-W laser output at 1029 nm with a pulse repetition rate of 10 MHz and a pulse duration of 70 ps. With a lithium triborate (LBO) crystal, a 43.0-W green output at 514.5 nm has been achieved with a pulse duration of 55 ps. With a caesium lithium borate (CLBO) crystal, a 14.5-W picosecond DUV output at 257 nm has been generated, which is the highest power for the all-fiber based DUV laser, to the best of our knowledge.

Pan, Lei (ORCID:0000000288896117)↗
DOE OSTI2022

Method for controlling fiber growth in a laser heated pedestal growth system by controlling a laser power output, a pedestal feedstock rate of motion, and a draw rate

One or more embodiments relate to a method for controlling fiber growth and fiber diameter in a laser heated pedestal growth (LHPG) system so as to provide long, continuous single-crystal optical fibers of uniform diameter. The method generally provides three independent parameter feedback controls to control the molten zone height, laser power, and fiber drawing rates simultaneously in order to reduce the mismatch between instantaneous diameter changes and current diameter. The method permits the growth of fibers with non-uniform diameters along the fiber's length. The method also provides the capability to stop the LHPG system, remove the exhausted pedestal feedstock with a second pedestal feedstock, and restart the LHPG system to provide a continuous fiber.

Buric, Michael P.↗
DOE OSTI2023

High precision control of laser energy for laser–matter interaction studies

Precise, highly reproducible control of the laser energy is required for high confidence laser–matter interaction research such as in dynamic compression science and high energy density physics. The energy must be adjustable without affecting the pulse shape (time varying intensity) or beam smoothness. We have developed a convenient two-stage energy tuning method for a nominal 100 J, 351 nm (UV) laser. The energy is adjusted in 10 J (10%) increments by operating the laser at full energy and inserting a beam splitter in the laser output. As the splitter is located after the final frequency tripling optics, the UV pulse shape is unchanged. The energy is varied by substituting a splitter of different reflectivity. For finer 3 J (3%) increments, the infrared pulse is attenuated inside the laser before the final amplifier. This requires modest tuning to preserve the pulse shape. The demonstrated variation in shot-to-shot reproducibility is less than +/–2.5 J (5% of the full energy), irrespective of the laser output energy. These approaches can be adapted to most ~100 J class lasers. We describe these techniques and show two examples where they have elucidated the underlying physics in laser shock compression experiments. One used only the beam splitters to establish the pressure for melting in iron. The other combined both techniques to finely increment the peak stress (~2 GPa steps) in germanium to precisely determine the onset and completion of melting—including the melting kinetics. Furthermore, these unambiguous results would not be possible without the developments described here.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Influence of defects on the femtosecond laser damage resistance of multilayer dielectric gratings

Multilayer dielectric (MLD) gratings with high diffraction efficiency and a high laser-induced damage (LID) threshold for pulse compressors are key to scaling the peak and average power of chirped pulse amplification lasers. However, surface defects introduced by manufacturing, storage, and handling processes can reduce the LID resistance of MLD gratings and impact the laser output. The underlying mechanisms of such defect-initiated LID remain unclear, especially in the femtosecond regime. In this Letter, we model dynamic processes in interactions of a 20-fs near-infrared (NIR) laser pulse and a MLD grating design in the presence of cylindrically symmetrical nodules and particle contaminants and cracks at the surface. Utilizing a dynamic model based on a 2D finite difference in time domain (FDTD) field solver coupled with photoionization, electron collision, and refractive index modification, we study the simulation results for the damage site distribution initiated by defects of various types and sizes and its impact on the LID threshold of the grating design.

Zhang, Simin (ORCID:0000000174948230)↗
DOE OSTI2023

Spectral shaping of an ultrafast ytterbium fiber laser via a passive intracavity optical filter: a simple and reliable route to sub-45 fs pulses

We investigate the use of passive intracavity optical filters for controlling the laser output spectrum of a polarization-mode-locked, ultrafast ytterbium fiber laser. The overall lasing bandwidth is increased or extended by strategic choice of the filter cutoff frequency. Overall laser performance, including pulse compression and intensity noise, is investigated for both shortpass and longpass filters with a range of cutoff frequencies. The intracavity filter not only shapes the output spectra, but also provides a route for overall broader bandwidths and shorter pulses in ytterbium fiber lasers. These results demonstrate that spectral shaping with a passive filter is a useful tool to routinely achieve sub-45 fs pulse durations in ytterbium fiber lasers.

Cooper, Nicholas D.↗
DOE OSTI2019

Role of spontaneous emission in the formation of the steady-state optical spectrum of a diode laser

Based on Maxwell’s equations, we derive a van der Pol-type equation for self-oscillations in the cavity of a diode laser. Its solution is self-oscillations (lasing) even in the absence of spontaneous emission. This solution differs fundamentally from solutions obtained using rate equations containing an additional term in the form of spontaneous emission intensity. Taking into account spontaneous emission in the van der Pol model makes calculation results more realistic and allows one to find parameters characterising diode laser output coherence, including the spectral densities of laser light amplitude and phase fluctuations. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Optimization and active stabilization of a far-infrared laser for NSTX-U high poloidal wavenumber scattering diagnostics

The far-infrared (FIR) laser output beam power and profile are important parameters in the laser-aided diagnostics, directly influencing the spatial resolution and signal-to-noise ratio of measurements. Here, this work focuses on developing a systematic control method to enhance FIR laser beam quality through optimized mirror alignment and real-time feedback-based precision cavity length tuning. A 150 W CO 2 laser, aligned with the waveguide axis using a HeNe reference laser, serves as the pump source. The sensitivity of FIR beam intensity to pump gas pressure and thermal expansion is investigated, revealing that even a 1 µm cavity expansion can significantly degrade output power stability to about two-thirds of its original value. To address this, a feedback control module has been designed and implemented for active cavity length adjustment, stabilizing the output power at ∼30 mW. In addition, maintaining a high formic acid gas pressure ($>$190 mTorr) within the cavity ensures reliable operation. The optimized FIR laser will be deployed on the National Spherical Torus eXperiment-U high poloidal wavenumber scattering system for studying electron-scale turbulence in tokamak plasmas.

Xu, Xinhang [Univ. of California, Davis, CA (Unite↗
DOE OSTI2019

Numerical simulation of amplification of frequency-modulated radiation in a gas amplifier THL-100 laser system

Numerical simulation methods have been used to study the effect of frequency modulation of input laser radiation with a pulse duration of 250 ps on the gain characteristics in a gas XeF (C – A) amplifier of the hybrid THL-100 laser system at a pump energy of 270 – 400 J. Using the Wigner distribution function, local radiation spectra are calculated at various points of the input laser beam with positive and negative chirps. The effect of the pump energy of the amplifier on the energy, intensity, and duration of the output laser radiation pulses is investigated. It is shown that with an insignificant change in energy, the pulse duration of the output radiation turns out to be longer with a negative chirp of the input radiation. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Pulsed laser module based on a high-power semiconductor laser for the spectral range 1500 – 1600 nm

A laser source for bleaching passive Q-switches of erbium-ytterbium lasers is developed and studied. The developed and studied compact pulsed module (peak power exceeding 10 W in a pulse with a duration of 1 μs at a wavelength around 1550 nm) is made on the basis of a semiconductor lasers with an ultra-narrow waveguide integrated with a pulsed pump card. To optimise the output laser characteristics, a series resistance was used in the laser pump circuit. The powers of the free-space and fibre-coupled modules at a temperature of 25 °C are 15 and 12 W, respectively, at a pulse shape close to rectangular. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Heat transfer in water under laser heating through fibres for endovenous laser coagulation

We report the results of studying heat transfer in water heated by a cw laser with wavelengths of 1.55 and 1.94 μm through optical fibres with end-face and radial outputs. It is shown that, depending on the power and wavelength of the radiation, heat transfer is implemented via convection, bubble boiling, or explosive boiling and occurs asymmetrically, mainly in the forward − upward direction for the fibre with the end-face output and upward for the radial output. (laser medicine)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Output power saturation effect in Yb – Er fibre lasers

The output power saturation effect in Yb – Er fibre lasers is experimentally observed. A formula for estimating the saturation power is derived. A method is proposed for measuring the {sup 4}I{sub 11/2} level lifetime or the concentration of Er ions based on the measurements of the saturation power. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Multiwavelength erbium-doped fiber laser based on a polarization-dependent in-line Mach–Zehnder interferometer

A multiwavelength erbium-doped fiber laser based on a polarization-dependent in-line Mach–Zehnder Interferometer (in-line MZI) is proposed and experimental demonstrated. The polarization-dependent in-line MZI demonstrated is constructed by sandwiching a length of polarization maintaining fiber (PMF) between two abrupt fiber tapers fabricated in SMF. The proposed in-line MZI can work as a cost-effective all-fiber-based polarizer. In combination with the nonlinear polarization rotation technique, stable multiwavelength laser comb with uniform wavelength spacing is achieved at room temperature. The wavelength spacing is 0.8 nm. By properly tuning the PCs, the output laser combs with double and triple channel spacing can be also obtained.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Laser particles with omnidirectional emission for cell tracking

The ability to track individual cells in space over time is crucial to analyzing heterogeneous cell populations. Recently, microlaser particles have emerged as unique optical probes for massively multiplexed single-cell tagging. However, the microlaser far-field emission is inherently direction-dependent, which causes strong intensity fluctuations when the orientation of the particle varies randomly inside cells. Here, we demonstrate a general solution based on the incorporation of nanoscale light scatterers into microlasers. Two schemes are developed by introducing either boundary defects or a scattering layer into microdisk lasers. The resulting laser output is omnidirectional, with the minimum-to-maximum ratio of the angle-dependent intensity improving from 0.007 (-24 dB) to > 0.23 (-6 dB). After transfer into live cells in vitro, the omnidirectional laser particles within moving cells could be tracked continuously with high signal-to-noise ratios for 2 h, while conventional microlasers exhibited frequent signal loss causing tracking failure.

59 BASIC BIOLOGICAL SCIENCES↗