scholarly journals Динамика спинорной экситон-поляритонной системы в латерально сжатых GaAs микрорезонаторах при резонансном фотовозбуждении

2018 ◽  
Vol 60 (8) ◽  
pp. 1567
Author(s):  
А.А. Деменев ◽  
Н.А. Гиппиус ◽  
В.Д. Кулаковский
Keyword(s):  
Laser Pulse ◽  
Spatial Coherence ◽  
Picosecond Laser ◽  
Threshold Value ◽  
Laser Pulses ◽  
Josephson Effects ◽  
High Q ◽  
Wide Range ◽  
Linearly Polarized ◽  
Polariton Branch

AbstractThe evolution of the spatial coherence and the polarization has been studied in a freely decaying polariton condensate that is resonantly excited by linearly polarized picosecond laser pulses at the lower and upper sublevels of the lower polariton branch in a high-Q GaAs-based microcavity with a reduced lateral symmetry without excitation of the exciton reservoir. It is found that the condensate inherits the coherence of the exciting laser pulse at both sublevels in a wide range of excitation densities and retains it for several dozen picoseconds. The linear polarization of the photoexcited condensate is retained only in the condensate at the lower sublevel. The linearly polarized condensate excited at the upper sublevel loses its stability at the excitation densities higher a threshold value: it enters a regime of internal Josephson oscillations with strongly oscillating circular and diagonal linear degrees of polarization. The polariton–polariton interaction leads to the nonlinear Josephson effects at high condensate densities. All the effects are well described in terms of the spinor Gross–Pitaevskii equations. The cause of the polarization instability of the condensate is shown to be the spin anisotropy of the polariton–polariton interaction.

scholarly journals Cylindrically and non-cylindrically symmetric expansion dynamics of tin microdroplets after ultrashort laser pulse impact

2021 ◽  
Vol 127 (2) ◽  
Author(s):  
Tiago de Faria Pinto ◽  
Jan Mathijssen ◽  
Randy Meijer ◽  
Hao Zhang ◽  
Alex Bayerle ◽  
...  
Keyword(s):  
Laser Pulse ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Droplet Deformation ◽  
Cylindrically Symmetric ◽  
Linearly Polarized ◽  
Particle Hydrodynamics ◽  
Deformation Dynamics ◽  
Smoothed Particle ◽  
Asymmetric Shock

AbstractIn this work, the expansion dynamics of liquid tin micro-droplets irradiated by femtosecond laser pulses were investigated. The effects of laser pulse duration, energy, and polarization on ablation, cavitation, and spallation dynamics were studied using laser pulse durations ranging from 220 fs to 10 ps, with energies ranging from 1 to 5 mJ, for micro-droplets with an initial radius of 15 and 23 $$\upmu$$ μ m. Using linearly polarized laser pulses, cylindrically asymmetric shock waves were produced, leading to novel non-symmetric target shapes, the asymmetry of which was studied as a function of laser pulse parameters and droplet size. A good qualitative agreement was obtained between smoothed-particle hydrodynamics simulations and high-resolution stroboscopic experimental data of the droplet deformation dynamics.

Residual heat generated during laser processing of CFRP with picosecond laser pulses

2018 ◽  
Vol 7 (3) ◽  
pp. 157-163
Author(s):  
Christian Freitag ◽  
Leon Pauly ◽  
Daniel J. Förster ◽  
Margit Wiedenmann ◽  
Rudolf Weber ◽  
...  
Keyword(s):  
Laser Pulse ◽  
Heat Affected Zone ◽  
Laser Processing ◽  
Picosecond Laser ◽  
Theoretical Models ◽  
Laser Pulses ◽  
Groove Depth ◽  
Interaction Zone ◽  
Heat Accumulation ◽  
Residual Heat

Abstract One of the major reasons for the formation of a heat-affected zone during laser processing of carbon fiber-reinforced plastics (CFRP) with repetitive picosecond (ps) laser pulses is heat accumulation. A fraction of every laser pulse is left as what we termed residual heat in the material also after the completed ablation process and leads to a gradual temperature increase in the processed workpiece. If the time between two consecutive pulses is too short to allow for a sufficient cooling of the material in the interaction zone, the resulting temperature can finally exceed a critical temperature and lead to the formation of a heat-affected zone. This accumulation effect depends on the amount of energy per laser pulse that is left in the material as residual heat. Which fraction of the incident pulse energy is left as residual heat in the workpiece depends on the laser and process parameters, the material properties, and the geometry of the interaction zone, but the influence of the individual quantities at the present state of knowledge is not known precisely due to the lack of comprehensive theoretical models. With the present study, we, therefore, experimentally determined the amount of residual heat by means of calorimetry. We investigated the dependence of the residual heat on the fluence, the pulse overlap, and the depth of laser-generated grooves in CRFP. As expected, the residual heat was found to increase with increasing groove depth. This increase occurs due to an indirect heating of the kerf walls by the ablation plasma and the change in the absorbed laser fluence caused by the altered geometry of the generated structures.

Transverse spatial coherence of a transient nickellike silver soft-x-ray laser pumped by a single picosecond laser pulse

2004 ◽  
Vol 29 (8) ◽  
pp. 881 ◽  
Author(s):  
A. Lucianetti ◽  
K. A. Janulewicz ◽  
R. Kroemer ◽  
G. Priebe ◽  
J. Tümmler ◽  
...  
Keyword(s):  
Laser Pulse ◽  
Spatial Coherence ◽  
Picosecond Laser ◽  
Picosecond Laser Pulse ◽  
X Ray

scholarly journals 3D Titania Nanofiber-Like Webs Induced by Plasma Ionization: A New Direction for Bioreactivity and Osteoinductivity Enhancement of Biomaterials

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Mohammad-Hossein Beigi ◽  
Naghmeh Safaie ◽  
Mohammad-Hossein Nasr-Esfahani ◽  
Amirkianoosh Kiani
Keyword(s):  
Colorimetric Method ◽  
Three Dimensional ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Ambient Air ◽  
Analytical Form ◽  
Ion Release ◽  
Characterization Methods ◽  
Wide Range

AbstractIn this study, we describe the formation method of web-like three-dimensional (3-D) titania nanofibrous structures coated on transparent substrate via a high intensity laser induced reverse transfer (HILIRT) process. First, we demonstrate the mechanism of ablation and deposition of Ti on the glass substrates using multiple picosecond laser pulses at ambient air in an explicit analytical form and compare the theoretical results with the experimental results of generated nanofibers. We then examine the performance of the developed glass samples coated by titania nanofibrous structures at varied laser pulse durations by electron microscopy and characterization methods. We follow this by exploring the response of human bone-derived mesenchymal stem cells (BMSCs) with the specimens, using a wide range of in-vitro analyses including MTS assay (colorimetric method for assessing cell metabolic activity), immunocytochemistry, mineralization, ion release examination, gene expression analysis, and protein adsorption and absorption analysis. Our results from the quantitative and qualitative analyses show a significant biocompatibility improvement in the laser treated samples compared to untreated substrates. By decreasing the pulse duration, more titania nanofibers with denser structures can be generated during the HILIRT technique. The findings also suggest that the density of nanostructures and concentration of coated nanofibers play critical roles in the bioreactivity properties of the treated samples, which results in early osteogenic differentiation of BMSCs.

Self-Guided Intense Laser Pulse Propagation in Air

2001 ◽  
Vol 6 (1) ◽  
pp. 21-26
Author(s):  
R. Danielius ◽  
D. Mikalauskas ◽  
A. Dubietis ◽  
A. Piskarskas
Keyword(s):  
Laser Pulse ◽  
Laser Beam ◽  
Phase Modulation ◽  
Large Scale ◽  
Pulse Propagation ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Intense Laser ◽  
Intense Laser Pulse ◽  
Self Phase Modulation

We report on observation of self-guiding of picosecond laser pulses in air that produces large-scale self-phase modulation. The converging picosecond laser beam produced a confined filament over 3 m of propagation with the whitelight spectrum.

scholarly journals Wakefield generation and electron acceleration by intense super-Gaussian laser pulses propagating in plasma

2013 ◽  
Vol 31 (4) ◽  
pp. 583-588 ◽  
Author(s):  
Pallavi Jha ◽  
Akanksha Saroch ◽  
Rohit Kumar Mishra
Keyword(s):  
Laser Pulse ◽  
Laser Pulses ◽  
Gaussian Pulse ◽  
Simulation Studies ◽  
One Dimensional ◽  
Particle In Cell ◽  
Peak Energy ◽  
Test Electron ◽  
Linearly Polarized ◽  
Relativistic Regime

AbstractEvolution of longitudinal electrostatic wakefields, due to the propagation of a linearly polarized super-Gaussian laser pulse through homogeneous plasma has been presented via two-dimensional particle-in-cell simulations. The wakes generated are compared with those generated by a Gaussian laser pulse in the relativistic regime. Further, one-dimensional numerical model has been used to validate the generated wakefields via simulation studies. Separatrix curves are plotted to study the trapping and energy gain of an externally injected test electron, due to the generated electrostatic wakefields. An enhancement in the peak energy of an externally injected electron accelerated by wakes generated by super-Gaussian pulse as compared to Gaussian pulse case has been observed.

scholarly journals Spin effects in nonlinear Compton scattering in ultrashort linearly-polarized laser pulses

2013 ◽  
Vol 31 (3) ◽  
pp. 503-513 ◽  
Author(s):  
K. Krajewska ◽  
J. Z. Kamiński
Keyword(s):  
Laser Pulse ◽  
Compton Scattering ◽  
Laser Pulses ◽  
Energy Spectra ◽  
Scattered Electron ◽  
Spin Effects ◽  
Spin Flip ◽  
Driving Pulse ◽  
Linearly Polarized ◽  
Quantum Behavior

AbstractThe nonlinear Compton scattering by a linearly polarized laser pulse of finite duration is analyzed, with a focus on the spin effects of target electrons. We show that, although the Compton scattering accompanied by the electron no-spin flip is dominant, for some energy regions of Compton photons their emission is dominated by the process leading to the electron spin flip. This feature is observed for different pulse durations, and can be treated as a signature of quantum behavior. Similar conclusions are reached when analyzing the scattered electron energy spectra. This time, the sensitivity of spin effects to the carrier-envelope phase of the driving pulse is demonstrated. The possibility of electron acceleration by means of Compton scattering is also discussed.

scholarly journals Extending Single Cell Bioprinting from Femtosecond to Picosecond Laser Pulse Durations

Micromachines ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1172
Author(s):  
Jun Zhang ◽  
Yasemin Geiger ◽  
Florian Sotier ◽  
Sasa Djordjevic ◽  
Denitsa Docheva ◽  
...  
Keyword(s):  
Laser Pulse ◽  
Single Cell ◽  
Pulse Duration ◽  
Cavitation Bubble ◽  
Mammalian Cells ◽  
Single Cells ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Cost Efficient

Femtosecond laser pulses have been successfully used for film-free single-cell bioprinting, enabling precise and efficient selection and positioning of individual mammalian cells from a complex cell mixture (based on morphology or fluorescence) onto a 2D target substrate or a 3D pre-processed scaffold. In order to evaluate the effects of higher pulse durations on the bioprinting process, we investigated cavitation bubble and jet dynamics in the femto- and picosecond regime. By increasing the laser pulse duration from 600 fs to 14.1 ps, less energy is deposited in the hydrogel for the cavitation bubble expansion, resulting in less kinetic energy for the jet propagation with a slower jet velocity. Under appropriate conditions, single cells can be reliably transferred with a cell survival rate after transfer above 95% through the entire pulse duration range. More cost efficient and compact laser sources with pulse durations in the picosecond range could be used for film-free bioprinting and single-cell transfer.

Optical Properties of Picosecond Laser Irradiated Graphite

1988 ◽  
Vol 100 ◽  
Author(s):  
A. M. Malvezzi ◽  
G. Reverberi ◽  
N. Bloembergen
Keyword(s):  
Optical Properties ◽  
Direct Evidence ◽  
Picosecond Laser ◽  
Threshold Value ◽  
Laser Pulses ◽  
Index Of Refraction ◽  
Transient Complex ◽  
Irradiated Graphite ◽  
Pump And Probe ◽  
Complex Index Of Refraction

ABSTRACTWe have employed pump-and-probe techniques coupled to ellipsometry to measure the transient complex index of refraction at 1.064 μm of higly oriented pyrolitic graphite (HOPG) interacting with 20 ps, .532 μm laser pulses. When the laser pump fluence exceeds the threshold value for melting, measurements indicate a substantial decrease of both real and imaginary parts of the index of refraction, thus confirming that molten graphite becomes less metallic. Measurements provide also direct evidence of the insensitivity of our picosecond results to evaporation from the irradiated surface.

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