scholarly journals Observation of repetitive bursts in emission of fast ions and neutrons in sub-nanosecond laser-solid experiments

2013 ◽  
Vol 31 (3) ◽  
pp. 395-401 ◽  
Author(s):  
J. Krása ◽  
D. Klír ◽  
A. Velyhan ◽  
D. Margarone ◽  
E. Krouský ◽  
...  
Keyword(s):  
Laser System ◽  
Target Surface ◽  
Current Mode ◽  
Energy Spectra ◽  
Nanosecond Laser ◽  
Fast Ions ◽  
Peak Energy ◽  
Fusion Neutrons ◽  
Deuterated Polyethylene ◽  
Broad Energy

AbstractA massive deuterated polyethylene target was exposed to laser intensities of about 3 × 1016 W/cm2 employing the 3-TW Prague Asterix Laser System (PALS). We achieved a yield of 2 × 108 neutrons per laser shot. Average time-of-flight signals of scintillation detectors operated in current mode reveal broad energy spectra of fusion neutrons with dominating energy of about 2.45 MeV. The energy dependence of the neutron yield shows a consistency in results of nanosecond, picosecond and sub-picosecond experiments. Here we also show that ions emitted in the backward direction from the front target surface have a multi-peak energy spectrum, which is caused by burst emission mechanisms.

scholarly journals Experimental studies of generation of ~100 MeV Au-ions from the laser-produced plasma

2009 ◽  
Vol 27 (1) ◽  
pp. 137-147 ◽  
Author(s):  
L. Láska ◽  
J. Krása ◽  
A. Velyhan ◽  
K. Jungwirth ◽  
E. Krouský ◽  
...  
Keyword(s):  
Laser System ◽  
Experimental Studies ◽  
Target Surface ◽  
Laser Frequency ◽  
Target Thickness ◽  
Focus Position ◽  
Experimental Conditions ◽  
Irradiation Detection ◽  
Fast Ions ◽  
Burn Through

AbstractUsing the PALS iodine laser system, Au ions with the charge state up to 58+ and with the kinetic energy as high as ~300 MeV were generated. The production of these ions was tested in dependence on the laser frequency (1ω, 3ω), on the irradiation/detection angles (0°, 30°), on the focus position with regard to the target surface, and on the target thickness (500 µm, 200 µm, 80 µm). A larger amount of the fastest ions was produced with 1ω than with 3ω, the most of the fast ions were recorded in the direction ~10°from the target normal, the optimum focus position is in front of the target and should be set on with a precision of 50 µm. The forward emission is weaker than the backward one for both of the thinner targets (which burn through) at our experimental conditions.

Impact of the lasr wavelength and fluence on the ablation rate of aluminium

Open Physics ◽  
2008 ◽  
Vol 6 (2) ◽  
Author(s):  
Mihai Stafe ◽  
Ionut Vladoiu ◽  
Ion Popescu
Keyword(s):  
Plasma Plume ◽  
Second Harmonic ◽  
Laser System ◽  
Target Surface ◽  
Threshold Value ◽  
Laser Pulses ◽  
Ablation Rate ◽  
Nanosecond Laser ◽  
Nanosecond Laser Pulses ◽  
532 Nm

AbstractThe dependence of the ablation rate of aluminium on the fluence of nanosecond laser pulses with wavelengths of 532 nm and respectively 1064 nm is investigated in atmospheric air. The fluence of the pulses is varied by changing the diameter of the irradiated area at the target surface, and the wavelength is varied by using the fundamental and the second harmonic of a Q-switched Nd-YAG laser system. The results indicate an approximately logarithmic increase of the ablation rate with the fluence for ablation rates smaller than ∼6 μm/pulse at 532 nm, and 0.3 μm/pulse at 1064 nm wavelength. The significantly smaller ablation rate at 1064 nm is due to the small optical absorptivity, the strong oxidation of the aluminium target, and to the strong attenuation of the pulses into the plasma plume at this wavelength. A jump of the ablation rate is observed at the fluence threshold value, which is ∼50 J/cm2 for the second harmonic, and ∼15 J/cm2 for the fundamental pulses. Further increasing the fluence leads to a steep increase of the ablation rate at both wavelengths, the increase of the ablation rate being approximately exponential in the case of visible pulses. The jump of the ablation rate at the threshold fluence value is due to the transition from a normal vaporization regime to a phase explosion regime, and to the change of the dimensionality of the hydrodynamics of the plasma-plume.

scholarly journals Discrimination of ablation, shielding, and interface layer effects on the steady-state formation of persistent bubbles under liquid flow conditions during laser synthesis of colloids

2021 ◽  
Author(s):  
Mark-Robert Kalus ◽  
Riskyanti Lanyumba ◽  
Stephan Barcikowski ◽  
Bilal Gökce
Keyword(s):  
Steady State ◽  
Laser Ablation ◽  
Liquid Flow ◽  
Production Efficiency ◽  
Synthesis Method ◽  
Target Surface ◽  
Interface Layer ◽  
Nanosecond Laser ◽  
Viscous Liquids ◽  
Shielding Effects

AbstractOver the past decade, laser ablation in liquids (LAL) was established as an innovative nanoparticle synthesis method obeying the principles of green chemistry. While one of the main advantages of this method is the absence of stabilizers leading to nanoparticles with “clean” ligand-free surfaces, its main disadvantage is the comparably low nanoparticle production efficiency dampening the sustainability of the method and preventing the use of laser-synthesized nanoparticles in applications that require high amounts of material. In this study, the effects of productivity-dampening entities that become particularly relevant for LAL with high repetition rate lasers, i.e., persistent bubbles or colloidal nanoparticles (NPs), on the synthesis of colloidal gold nanoparticles in different solvents are studied. Especially under batch ablation conditions in highly viscous liquids with prolonged ablation times both shielding entities are closely interconnected and need to be disentangled. By performing liquid flow-assisted nanosecond laser ablation of gold in liquids with different viscosity and nanoparticle or bubble diffusivity, it is shown that a steady-state is reached after a few seconds with fixed individual contributions of bubble- and colloid-induced shielding effects. By analyzing dimensionless numbers (i.e., Axial Peclet, Reynolds, and Schmidt) it is demonstrated how these shielding effects strongly depend on the liquid’s transport properties and the flow-induced formation of an interface layer along the target surface. In highly viscous liquids, the transport of NPs and persistent bubbles within this interface layer is strongly diffusion-controlled. This diffusion-limitation not only affects the agglomeration of the NPs but also leads to high local densities of NPs and bubbles near the target surface, shielding up to 80% of the laser power. Hence, the ablation rate does not only depend on the total amount of shielding matter in the flow channel, but also on the location of the persistent bubbles and NPs. By comparing LAL in different liquids, it is demonstrated that 30 times more gas is produced per ablated amount of substance in acetone and ethylene glycol compared to ablation in water. This finding confirms that chemical effects contribute to the liquid’s decomposition and the ablation yield as well. Furthermore, it is shown that the highest ablation efficiencies and monodisperse qualities are achieved in liquids with the lowest viscosities and gas formation rates at the highest volumetric flow rates.

Compact nanosecond laser system for the ignition of aeronautic combustion engines

2016 ◽  
Vol 120 (23) ◽  
pp. 233102 ◽  
Author(s):  
G. Amiard-Hudebine ◽  
G. Tison ◽  
E. Freysz
Keyword(s):  
Laser System ◽  
Nanosecond Laser ◽  
Combustion Engines

Self-modulated wakefield acceleration in a centimetre self-guiding channel

2012 ◽  
Vol 78 (4) ◽  
pp. 433-440 ◽  
Author(s):  
C. KAMPERIDIS ◽  
C. BELLEI ◽  
N. BOURGEOIS ◽  
M. C. KALUZA ◽  
K. KRUSHELNICK ◽  
...  
Keyword(s):  
Focal Spot ◽  
Spot Size ◽  
High Energy ◽  
Energy Spectra ◽  
Focal Spot Size ◽  
Electron Bunches ◽  
Gas Jets ◽  
Wakefield Acceleration ◽  
Helium Gas ◽  
Broad Energy

AbstractSelf-modulated wakefield acceleration was investigated at densities down to ~4 × 1018 cm−3 by propagating the 50 TW 300 fs LULI laser in helium gas jets at lengths up to 1 cm. Long interaction lengths were achieved by closer matching of the initial focal spot size to the matched spot size for these densities. Electrons with energies extending to 180 MeV were observed in broad energy spectra which show some evidence for non-Maxwellian features at high energy. Two-dimensional PIC simulations indicate that the intial laser pulse breaks up into small pulselets that are eventually compressed and focused inside the first few plasma periods, leading to a ‘bubble-like’ acceleration of electron bunches.

Third-order nonlinear optical properties of carboxyl group dominant carbon nanodots

2016 ◽  
Vol 4 (36) ◽  
pp. 8490-8495 ◽  
Author(s):  
Liang Bai ◽  
Shi Qiao ◽  
Yu Fang ◽  
Jianguo Tian ◽  
J. Mcleod ◽  
...  
Keyword(s):  
Optical Properties ◽  
Nonlinear Optical ◽  
Laser System ◽  
Carbon Nanodots ◽  
Nanosecond Laser ◽  
Carboxyl Group ◽  
Third Order ◽  
Nlo Property ◽  
System P ◽  
532 Nm

We quantitatively investigate the nonlinear optical (NLO) property of carbon nanodots (CNDs, less than 10 nm) by the Z-scan technique using a tunable 532 nm nanosecond laser system.

scholarly journals First measurement of the 2.4 MeV and 2.9 MeV 6He three-cluster resonant states via the 3H(4He, pα)2n four-body reaction

2014 ◽  
Vol 29 (19) ◽  
pp. 1450105 ◽  
Author(s):  
Giuseppe Mandaglio ◽  
Orest Povoroznyk ◽  
Olga K. Gorpinich ◽  
Olexiy O. Jachmenjov ◽  
Antonio Anastasi ◽  
...  
Keyword(s):  
Excited States ◽  
Beam Energy ◽  
Threshold Energy ◽  
Theoretical Models ◽  
Light Nuclei ◽  
Energy Spectra ◽  
Excitation Energies ◽  
Resonant States ◽  
Peak Energy ◽  
Coincidence Spectra

Two new low-lying 6 He levels at excitation energies of about 2.4 MeV and 2.9 MeV were observed in the experimental investigation of the p-α coincidence spectra obtained by the 3 H (4 He , p α)2 n four-body reaction at E4 He beam energy of 27.2 MeV. The relevant E* peak energy and Γ energy width spectroscopic parameters for such 6 He * excited states decaying into the α+ n+n channel were obtained by analyzing the bidimensional (E p , Eα) energy spectra. The present new result of two low-lying 6 He * excited states above the 4 He +2 n threshold energy of 0.974 MeV is important for the investigation of the nuclear structure of neutron-rich light nuclei and also as a basic test for theoretical models in the study of the three-cluster resonance feature of 6 He .

scholarly journals Studies of ablated plasma and shocks produced in a planar target by a sub-nanosecond laser pulse of intensity relevant to shock ignition

2015 ◽  
Vol 33 (3) ◽  
pp. 561-575 ◽  
Author(s):  
J. Badziak ◽  
L. Antonelli ◽  
F. Baffigi ◽  
D. Batani ◽  
T. Chodukowski ◽  
...  
Keyword(s):  
Laser Pulse ◽  
Laser Intensity ◽  
Laser System ◽  
Energy Conversion Efficiency ◽  
Hot Electrons ◽  
Plastic Layer ◽  
Maximum Pressure ◽  
Nanosecond Laser Pulse ◽  
Nanosecond Laser ◽  
Planar Target

AbstractThe effect of laser intensity on characteristics of the plasma ablated from a low-Z (CH) planar target irradiated by a 250 ps, 0.438 µm laser pulse with the intensity of up to 1016 W/cm2 as well as on parameters of the laser-driven shock generated in the target for various scale-lengths of preformed plasma was investigated at the kilojoule Prague Asterix Laser System (PALS) laser facility. Characteristics of the plasma were measured with the use of 3-frame interferometry, ion diagnostics, an X-ray spectrometer, and Kα imaging. Parameters of the shock generated in a Cl doped CH target by the intense 3ω laser pulse were inferred by numerical hydrodynamic simulations from the measurements of craters produced by the shock in the massive Cu target behind the CH layer. It was found that the pressure of the shock generated in the plastic layer is relatively weakly influenced by the preplasma (the pressure drop due to the preplasma presence is ~10–20%) and at the pulse intensity of ~1016 W/cm2 the maximum pressure reaches ~80–90 Mbar. However, an increase in pressure of the shock with the laser intensity is slower than predicted by theory for a planar shock and the maximum pressure achieved in the experiment is by a factor of ~2 lower than predicted by the theory. Both at the preplasma absence and presence, the laser-to-hot electrons energy conversion efficiency is small, ~1% or below, and the influence of hot electrons on the generated shock is expected to be weak.

scholarly journals Micro-grooving of brittle materials using textured diamond grinding wheels shaped by an integrated nanosecond laser system

2021 ◽  
Author(s):  
Zongchao Geng ◽  
Zhen Tong ◽  
Wenbin Zhong ◽  
Guoqin Huang ◽  
Changcai Cui ◽  
...  
Keyword(s):  
Laser System ◽  
Brittle Materials ◽  
Research Progress ◽  
Nanosecond Laser ◽  
Grinding Wheels ◽  
Diamond Grinding ◽  
Hard And Brittle Materials ◽  
Micro Grooving ◽  
Offset Compensation ◽  
High Flexibility

Abstract The freeform surfaces including both the aspherical and prismatic concave/convex have been widely utilized in optical, electronical, and biomedical areas. Most recently, it is reported that grinding with structured wheels provides new possibility to generate patterns on hard and brittle materials. This paper reports the latest research progress on micro-grooving glass ceramic using laser structured bronze bond diamond grinding wheels. A nanosecond pulse laser is firstly integrated into an ultra-precision machine tool and used for the in-line conditioning of super abrasive grinding wheels, i.e. truing, dressing, and profiling/texturing. Meanwhile, an offset compensation method, considering the shifting depth of focus (DoF) at different laser irradiation position, is proposed to accurately generate various profiles on the periphery of the grinding wheels. Three types of patterns (riblets, grooves, and pillars) are successfully fabricated on the ceramic substrate using the laser textured grinding wheels. The results indicate that the integrated laser system offers high flexibility and accuracy in shaping super abrasive grinding wheels, and the grinding using textured grinding wheels provide a promising solution to generate functional structures on hard and brittle materials.

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