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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Beyond nonlinear saturation of backward Raman amplifiers

Backward Raman amplification is limited by relativistic nonlinear dephasing resulting in saturation of the leading spike of the amplified pulse. We employed pump detuning in order to mitigate the relativistic phase mismatch and to overcome the associated saturation. In an amplified pulse can then be reshaped into a monospike pulse with little precursory power ahead of it, with the maximum intensity increasing by a factor of two. Finally, this detuning can be employed advantageously both in regimes where the group velocity dispersion is unimportant and where the dispersion is important but small.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Enhancement and control of laser wakefields via a backward Raman amplifier

The Backward Raman Amplifier (BRA) is proposed as a possible scheme for improving laser driven plasma wakefields. One- and two-dimensional particle-in-cell code simulations and a 3-Wave coupling model are presented and compared to demonstrate how the BRA can be applied to the laser wakefield accelerator (LWFA) in the non-relativistic regime to counteract limitations such as pump depletion and diffraction. This article provides a discussion on optimal parameters for the combination of BRA and LWFA and a prescription for a BRA pump frequency chirp to ensure coupling beyond the particle dephasing limit. Simulation results demonstrate a reduction or alleviation of the effects of diffraction and an increase in wake amplitude and sustainability and provide direct insights into new methods of controlling plasma wakes in LWFA and other applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Saturation of the leading spike growth in backward Raman amplifiers

Backward Raman amplification of laser pulses in plasmas can produce nearly relativistic unfocused output intensities and multi-exawatt powers in compact devices. The largest achievable intensity depends on which of major competitive processes set this limit. It is shown here that the relativistic electron nonlinearity can cause saturation of the leading amplified spike intensity before filamentation instabilities develop. A simple analytical model for the saturation, which supports numerical simulations, is suggested. The upper limit for the leading output spike unfocused intensity is calculated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Multifrequency Raman amplifiers

In its usual implementation, the Raman amplifier features only one pump carrier frequency. However, pulses with well-separated frequencies can also be Raman amplified while compressed in time. Amplification with frequency-separated pumps is shown to hold even in the highly nonlinear, pump-depletion regime, as derived through a fluid model, and demonstrated via particle-in-cell (PIC) simulations. The resulting efficiency is similar to single-frequency amplifiers, but, due to the beat-wave waveform of both the pump lasers and the amplified seed pulses, these amplifiers feature higher seed intensities with a shorter spike duration. Advantageously, these amplifiers also suffer less noise backscattering, because the total fluence is split between the different spectral components.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Compact Ultraintense Femtosecond Laser via Raman Amplifier and Compressor in Plasma

The main objective of this project was to conduct experimental and theoretical research to find conditions leading to higher, than previously obtained efficiency η of transfer the pump energy into the short seed beam in plasma of Stimulated Raman Back-Scattering (SRBS). We have demonstrated very large amplification and compression in our earlier SRBS plasma. However, the efficiency η was much too low to reach very high intensity of the output beam in the focal spot. Recently, by solving a very difficult technical SRBS’ problem, namely, the creation of very reproducible and much larger diameter plasma channels than in our earlier research, we propose a new approach to obtain higher efficiency η. The crucial new result was a very reproducible, low noise amplified seed in the larger diameter of the plasma channel leading to the higher efficiency. Using this new setup and very encouraging results about increase efficiency continuing this approach in the future the efficiency is expect to reach the range of η ≈15 - 20 % required to develop practical SRBS plasma laser. Intellectual Merit: The model for the present project was created by our earlier SRBS experiments. The main objective of those experiments was to amplify and compress the seed pulses in a plasma . The experiments demonstrated an unprecedented large pulse intensity amplification of 20,000 in system of 2-passes in ~2mm long plasma, and the seed pulse compression from 550fsec down to ~50fsec. The pump and seed beams in the present project have diameters of ~0.2–0.25mm each, propagating in ~0.35 - 0.45mm diameter and ~2-2.5mm long plasma channels (optimal length for our SRBS experiment) with input pump and seed intensities of 2x1014 and 3x1013 W/cm2, respectively. Such an SRBS system design was “prescribed” by computer simulations, which predict elimination of the SRBS “ saturation” for a such relatively short plasma channel. Plasma channels has been created by combining shorter (200psec) and longer (5nsec) laser pulses using an axicon lens for shorter pulse and spherical lens for longer pulse, a unique procedure we have developed for SRBS experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Flying focus and its application to plasma-based laser amplifiers

Combining a chirped laser pulse with a chromatic lens yields a flying focus—a laser focus that moves dynamically in time. This provides control over the propagation of the peak laser intensity within an extended focal region that can be many times larger than the system’s Rayleigh length. Any velocity is achievable, including backward relative to the laser propagation direction. Previous simulation results have shown that a laser beam with a flying focus can create a counter-propagating ionization wave and subsequently pump a frequency-downshifted laser via the stimulated Raman scattering instability. Compared to a conventional Raman amplification scheme, several advantages were highlighted, including improved temperature control, plasma uniformity, and precursor growth mitigation. Here, we extend those results to demonstrate additional benefits: (1) the flying focus makes it possible for an unseeded Raman amplifier to produce a short, high-intensity beam; and (2) the flying focus minimizes collisional absorption of the pump, facilitating amplifier operation at higher plasma densities. Preliminary experiments have laid the groundwork for a high-performance plasma-based laser amplifier. The focal spot dynamics were initially confirmed at low intensity. It was subsequently demonstrated that ionization waves of arbitrary velocity can be produced at higher intensity. Here, we show a counter-propagating ionization front moving at approximately the speed of light—the optimal result for a Raman amplifier.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Experimental investigation of nonlinear operation mode of a DP-QPSK 100G link with co-propagating-pump Raman amplification

The nonlinear interference noise in a coherent single-span fibre-optic communication link (FOCL) with co-propagating Raman amplification is investigated at different levels of input Raman pump and channel powers and dispersion. A simple phenomenological expression for calculating the nonlinear noise power at the output of a single-channel FOCL is presented. The merit of using a distributed Raman amplifier with co-propagating pump up to 1 W in a single-span single-channel FOCL is experimentally investigated. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Laser–plasma amplification of an ultrabroadband laser pulse to 0.3 TW

Producing on-target laser intensities much greater than 10 23 W cm −2 with current laser technologies is a roadblock to accessing new regimes of physics such as strong-field quantum electrodynamics. Laser–plasma amplifiers show promise to realize these intensities by augmenting the final amplifier and compressor in traditional chirped-pulse-amplification architectures with a plasma-based amplification and compression stage that operates at a much higher damage threshold. Here we demonstrate amplification of an ultrabroadband (>60 nm) pulse in a laser–plasma Raman amplifier. We directly amplified seed intensities up to 3.7 × 10 15 W cm −2 and measured efficiencies up to 8.7%. Single-shot SPIDER measurements show a factor-of-2 reduction in the amplified pulse duration with final powers up to 0.3 TW, a 10× improvement over previous results. Final pulse durations of 64 fs are measured. Energy transfers greater than 220 mJ from the picosecond pump into the seed result in a 30× energy amplification of a 7.6 mJ seed. These results set the stage for a compact plasma afterburner based on Raman amplification that could extend the scientific capability of existing petawatt-class laser facilities to enable experiments at the intensity frontier.

Shaw, J. L. [Univ. of Rochester, NY (United States↗
DOE OSTI2014

Backward Raman amplification in the Langmuir wavebreaking regime

In plasma-based backward Raman amplifiers, the output pulse intensity increases with the input pump pulse intensity, as long as the Langmuir wave mediating energy transfer from the pump to the seed pulse remains intact. However, at high pump intensity, the Langmuir wave breaks, at which point the amplification efficiency may no longer increase with the pump intensity. Numerical simulations presented here, employing a one-dimensional Vlasov-Maxwell code, show that, although the amplification efficiency remains high when the pump only mildly exceeds the wavebreaking threshold, the efficiency drops precipitously at larger pump intensities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Optimisation of frequency-modulated characteristics of output radiation in a lidar with Raman amplification

The reported study is aimed at increasing the power in the transmission path of a lidar with Raman amplification for longpath sensing of methane by optimising the frequency-modulated characteristics of the output radiation. The pump current of the used distributed-feedback master laser was modulated by a linearfrequency signal with simultaneous application of a non-synchronous high-frequency signal. For such a modulation regime, the Raman amplifier provided the mean output power of 2.5 W at a wavelength of 1650 nm. The spectral broadening did not significantly decrease the lidar sensitivity at long paths. (lidars)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

An ultra-high gain and efficient amplifier based on Raman amplification in plasma

Raman amplification arising from the excitation of a density echelon in plasma could lead to amplifiers that significantly exceed current power limits of conventional laser media. Here we show that 1–100 J pump pulses can amplify picojoule seed pulses to nearly joule level. The extremely high gain also leads to significant amplification of backscattered radiation from “noise”, arising from stochastic plasma fluctuations that competes with externally injected seed pulses, which are amplified to similar levels at the highest pump energies. The pump energy is scattered into the seed at an oblique angle with 14 J sr -1 , and net gains of more than eight orders of magnitude. The maximum gain coefficient, of 180 cm -1 , exceeds high-power solid-state amplifying media by orders of magnitude. The observation of a minimum of 640 J sr -1 directly backscattered from noise, corresponding to ≈10% of the pump energy in the observation solid angle, implies potential overall efficiencies greater than 10%.

42 ENGINEERING↗
DOE OSTI2019

Flat gain C + L band using optical amplifiers for 200 × 14 Gbps DWDM system

This paper has shown the analysis of 200 channels dense wavelength division multiplexing (DWDM) system with the data rate of 14 Gbps for attaining the flat gain for the channel spectrum from 1520 to 1640 nm. Analysis has also extended with the power amplification of erbium–ytterbium co-doped optical amplifier (EYBCDOWA) and Raman optical amplifier for the transmission distance of 120 km to mitigate the effect of crosstalk and bit error rate (BER). Final analysis has also recommended that this proposed system is capable to deliver the flat gain of 19.5 dB with minor variation of 0.95 dB to maintain the acceptable dense communication for long distance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Integrated silicon optical amplifier with reduced residual pump

An optical amplifier device employing a Mach-Zehnder Interferometer (MZI) that reduces the amount of residual pump power in the optical output of the amplifier is disclosed. The MZI amplifier employs two geometrically linear optical amplifier arms or two multi-spatial-mode racetrack optical amplifiers to amplify a signal with a pumping beam, with the signal output port having extremely low levels of residual pump power. The MZI optical amplifier is a silicon photonic integrated circuit, with all optical amplifiers, couplers, phase shifters, and optical attenuators formed of silicon photonic integrated circuit elements. The MZI optical amplifier may include one, two, or three MZI stages, and multiple MZI optical amplifiers may be used in parallel or sequentially to achieve higher overall signal gain or power. The MZI optical amplifier may employ Brillouin-scattering-based amplifiers, Raman-based integrated waveguide optical amplifiers, or Erbium-doped integrated waveguide optical amplifiers.

Lentine, Anthony L.↗