scholarly journals Resonant dual-pulse laser ignition technique based on oxygen REMPI pre-ionization

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ciprian Dumitrache ◽  
Carter Butte ◽  
Azer Yalin
Keyword(s):  
Near Infrared ◽  
Multiphoton Ionization ◽  
Single Pulse ◽  
Combustion Efficiency ◽  
Laser Ignition ◽  
Plasma Parameters ◽  
Laser Plasmas ◽  
Measurement Results ◽  
Gas Ionization ◽  
Inverse Bremsstrahlung Absorption

AbstractThis contribution investigates a novel laser ignition method based on a dual-pulse resonant pre-ionization scheme. The first laser pulse efficiently creates initial gas ionization (seed electrons) through a 2 + 1 resonantly-enhanced multiphoton ionization (REMPI) scheme targeting molecular oxygen (λ ~ 287.6 nm). This pulse is followed by a second non-resonant near-infrared pulse (λ = 1064 nm) for energy addition into the gas via inverse bremsstrahlung absorption. The sequence of two pulses creates a laser induced plasma that exhibits high peak electron number density and temperature (ne ~ 8 × 1017 cm-3 at t = 100 ns and T ~ 8000 K at t = 10 μs, respectively). These plasma parameters are similar to those attained for typical single-pulse near-infrared laser plasmas but with the advantage of substantially lower pulse energy (by factor of ~ 2.5) in the dual-pulse REMPI case. A combustion study focusing on ignition of propane/air mixtures shows that the dual-pulse REMPI method leads to an extension of the lean flammability limit, and an increase in combustion efficiency near the lean limit, as compared to laser ignition with a single NIR pulse. The measurement results and observed gas dynamics are discussed in the context of their impact on combustion applications.

Chain-Length-Dependent Termination in Acrylate Radical Polymerization Studied via Pulsed-Laser-Initiated RAFT Polymerization

2007 ◽  
Vol 60 (10) ◽  
pp. 779 ◽  
Author(s):  
Michael Buback ◽  
Pascal Hesse ◽  
Thomas Junkers ◽  
Thomas Theis ◽  
Philipp Vana
Keyword(s):  
Radical Polymerization ◽  
Chain Length ◽  
Near Infrared ◽  
Pulsed Laser ◽  
Monomer Concentration ◽  
Nir Spectroscopy ◽  
Single Pulse ◽  
Rate Coefficients ◽  
Radical Chain ◽  
Chain Flexibility

The chain-length dependence of the termination rate coefficient, kt, in methyl acrylate (MA) and dodecyl acrylate (DA) radical polymerization has been determined via the single pulse pulsed-laser polymerization near-infrared reversible addition–fragmentation chain transfer (SP-PLP-NIR-RAFT) technique. Polymerization is induced by a laser SP and the resulting decay in monomer concentration, cM, is monitored via NIR spectroscopy with a time resolution of microseconds. A RAFT agent ensures the correlation of radical chain length and monomer-to-polymer conversion. The obtained rate coefficients for termination of two radicals of approximately the same chain length, i, are represented by power-law expressions, kt(i,i) ∝ i–α. For both monomers, composite model behaviour of kt(i,i) showing two distinct chain length regimes is observed. The exponent αs referring to short chain lengths is close to unity, whereas the exponent αl, which characterizes the chain-length dependency of large radicals, is slightly above the theoretical value for coiled chain-end radicals. The crossover chain length, ic, which separates the two regions, decreases from MA (ic = 30) to DA (ic = 20). The results for MA and DA are consistent with earlier data reported for butyl acrylate. There appears to be a correlation of αs and ic with chain flexibility.

scholarly journals Influence of Polyisobutylene Kerosene Additive on Combustion Efficiency in a Liquid Propellant Rocket Engine

Aerospace ◽  
2019 ◽  
Vol 6 (12) ◽  
pp. 129 ◽  
Author(s):  
Igor Borovik ◽  
Evgeniy Strokach ◽  
Alexander Kozlov ◽  
Valeriy Gaponov ◽  
Vladimir Chvanov ◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Film Cooling ◽  
Rocket Engine ◽  
Combustion Efficiency ◽  
Liquid Propellant ◽  
Gaseous Oxygen ◽  
Wall Film ◽  
Measurement Results ◽  
Liquid Propellant Rocket Engine ◽  
Propellant Rocket

The combustion of kerosene with the polymer additive polyisobutylene (PIB) was experimentally investigated. The aim of the study was to measure the effect of PIB kerosene on the efficiency of combustion chamber cooling and the combustion efficiency of the liquid propellant for a rocket engine operating on kerosene and gaseous oxygen (GOX). The study was conducted on an experimental rocket engine using kerosene wall film cooling in the combustion chamber. Fire tests showed that the addition of polyisobutylene to kerosene had no significant effect on the combustion efficiency. However, analysis of the wall temperature measurement results showed that the use of PIB kerosene is more effective for film cooling than pure kerosene, which can increase the efficiency of combustion chamber cooling and subsequently increase its reliability and reusability. Thus, the findings of this study are expected to be of use in further investigations of wall film cooling efficiency.

Multiphoton Ionization of Liquid-to-Supercritical Methanol. Ultrafast Dynamics of Electron Localization and Geminate Recombination

2015 ◽  
Vol 229 (10-12) ◽  
Author(s):  
Annika Gehrmann ◽  
Peter Vöhringer
Keyword(s):  
Near Infrared ◽  
Transient Absorption ◽  
Multiphoton Ionization ◽  
Ultrafast Dynamics ◽  
Electron Localization ◽  
Geminate Recombination ◽  
Supercritical Methanol ◽  
Solvated Electrons

AbstractSolvated electrons have been generated by 150 fs, 266 nm multiphoton ionization of methanol and their primary dynamics have been recorded through near-infrared transient absorption over a wide temperature (294 K ≤ 

scholarly journals Optical ionization and heating of gases by intense picosecond KrF laser radiation

1995 ◽  
Vol 13 (1) ◽  
pp. 19-31 ◽  
Author(s):  
A.A. Offenberger ◽  
W. Blyth ◽  
S.G. Preston ◽  
J.S. Wark ◽  
M.H. Key ◽  
...  
Keyword(s):  
Laser Radiation ◽  
Electron Temperature ◽  
Short Wavelength ◽  
Stimulated Raman Scattering ◽  
Multiphoton Ionization ◽  
Thomson Scattering ◽  
Uv Laser ◽  
X Ray ◽  
Above Threshold Ionization ◽  
Inverse Bremsstrahlung Absorption

We report on multiphoton ionization experiments using picosecond (ps) and sub-ps UV-laser radiation at focused intensities up to 1018 W/cm2. The experiments are concerned with determining the electron temperature of optically ionized gases produced by intense KrF lasers. Thomson scattering, stimulated Raman scattering (SRS), and X-ray emission measurements have been made and compared with modeling calculations of heating. A particular objective is to identify the respective roles of above-threshold ionization, nonlinear inverse bremsstrahlung absorption, and SRS in determining the temperature of the electrons. Results for 350-fs pulses are compared with previous measurements for 12-ps pulses (for which strikingly different behavior is observed). The importance of using subps, short-wavelength lasers to minimize electron temperature is confirmed.

Comparison of coronal plasma parameters in IR and UV laser plasmas

1983 ◽  
Author(s):  
W. Seka ◽  
L. M. Goldman ◽  
R. L. Keck ◽  
S. LetzrIng ◽  
Martin C. Richardson ◽  
...  
Keyword(s):  
Coronal Plasma ◽  
Uv Laser ◽  
Plasma Parameters ◽  
Laser Plasmas

scholarly journals Laser generated plasmas as a source for real time studies in X-ray crystal research: Part II: In search of an optimum choice of laser plasma coupling conditions

1984 ◽  
Vol 2 (2) ◽  
pp. 187-199 ◽  
Author(s):  
K. Schäfer ◽  
W. D. Zimmer
Keyword(s):  
Real Time ◽  
Laser Plasma ◽  
Electron Spectrum ◽  
Line Emission ◽  
Simplified Model ◽  
Hot Electron ◽  
Plasma Parameters ◽  
X Ray ◽  
Laser Plasmas ◽  
Plasma Coupling

For real-time diffraction experiments in X-ray crystal research a simplified model is chosen to describe laser-generated plasmas. This enables a rough estimate of the optimum laser plasma parameters necessary to maximize the line emission of highly ionized species. Furthermore, the use of the hot electron spectrum of laser plasmas to generate ultrashort Kα-emission is discussed.

scholarly journals Comparison between mirror Langmuir probe and gas-puff imaging measurements of intermittent fluctuations in the Alcator C-Mod scrape-off layer

2020 ◽  
Vol 86 (5) ◽  
Author(s):  
R. Kube ◽  
A. Theodorsen ◽  
O. E. Garcia ◽  
D. Brunner ◽  
B. LaBombard ◽  
...  
Keyword(s):  
Time Series ◽  
Langmuir Probe ◽  
Time Series Data ◽  
Line Emission ◽  
Single Pulse ◽  
Statistical Properties ◽  
Series Data ◽  
Plasma Parameters ◽  
Order Unity ◽  
Plasma Fluctuations

Statistical properties of the scrape-off layer plasma fluctuations are studied in ohmically heated plasmas in the Alcator C-Mod tokamak. For the first time, plasma fluctuations as well as parameters that describe the fluctuations are compared across measurements from a mirror Langmuir probe (MLP) and from gas-puff imaging (GPI) that sample the same plasma discharge. This comparison is complemented by an analysis of line emission time-series data, synthesized from the MLP electron density and temperature measurements. The fluctuations observed by the MLP and GPI typically display relative fluctuation amplitudes of order unity together with positively skewed and flattened probability density functions. Such data time series are well described by an established stochastic framework that models the data as a superposition of uncorrelated, two-sided exponential pulses. The most important parameter of the process is the intermittency parameter, $\gamma = {\tau _{d}} / {\tau _{w}}$ , where ${\tau _{d}}$ denotes the duration time of a single pulse and ${\tau _{w}}$ gives the average waiting time between consecutive pulses. Here we show, using a new deconvolution method, that these parameters can be consistently estimated from different statistics of the data. We also show that the statistical properties of the data sampled by the MLP and GPI diagnostic are very similar. Finally, a synthetic GPI signal using only plasma parameters sampled by the MLP shows qualitatively different fluctuation statistics from the measured GPI signal.

scholarly journals Studying the small-scale structure of a polarization jet during the April 20, 2018 geomagnetic storm

2021 ◽  
Vol 7 (1) ◽  
pp. 21-33
Author(s):  
Aleksandr Sinevich ◽  
Aleksandr Chernyshov ◽  
Dmitriy Chugunin ◽  
W. Miloch ◽  
Michael Mogilevsky
Keyword(s):  
Geomagnetic Storm ◽  
Sampling Rate ◽  
Scale Structure ◽  
Small Scale ◽  
Langmuir Probes ◽  
Plasma Parameters ◽  
Small Scale Structure ◽  
Measurement Results ◽  
Spatial Dimensions ◽  
Density Inhomogeneities

In this work, we study the small-scale structure of a polarization jet in the subauroral region during the April 20, 2018 geomagnetic storm. We report measurement results of plasma parameters inside the polarization jet with a maximum sampling rate of up to 1 kHz, obtained with Langmuir probes installed on the NorSat-1 microsatellite. The study establishes the presence of temperature and electron density inhomogeneities inside the polarization jet with spatial dimensions of tens to hundreds of meters. The previously known features of the polarization jet evolution have been confirmed. We have also found that the distribution of the electron temperature inside the jet forms two separate peaks as the geomagnetic activity develops during the storm.

scholarly journals Passively Q-Switched Yb:CALGO Laser Based on Mo:BiVO4 Absorber

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2364
Author(s):  
Lina Zhao ◽  
Ye Yuan ◽  
Luyang Tong ◽  
Wenyu Zhang ◽  
Zhongshuai Zhang ◽  
...  
Keyword(s):  
Repetition Rate ◽  
Peak Power ◽  
Near Infrared ◽  
Maximum Output Power ◽  
Single Pulse ◽  
Infrared Region ◽  
Maximum Output ◽  
Linear Absorption ◽  
Central Wavelength ◽  
Transmission Electron

A stable, passively Q-switched Yb:CaGdAlO4 laser based on Mo:BiVO4 saturable absorber was demonstrated. Close observations of the structure and morphology of the nanoparticles by using transmission electron microscope, Raman spectrum and linear absorption were measured. The nonlinear transmission of Mo:BiVO4 was characterized by a 30 ps laser with a central wavelength of 1064 nm and a repetition rate of 10 Hz. The experimental maximum output power of the pulsed laser was 510 mW with a repetition rate of 87 kHz and pulse width of 3.18 μs, corresponding to a peak power of 1.84 W and a single pulse energy of 5.8 μJ. The experimental results indicate that Mo:BiVO4-SA is a great candidate for passively Q-switched lasers in the near infrared region.

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