scholarly journals Optimized Computation of Tight Focusing of Short Pulses Using Mapping to Periodic Space

2021 ◽  
Vol 11 (3) ◽  
pp. 956
Author(s):  
Elena Panova ◽  
Valentin Volokitin ◽  
Evgeny Efimenko ◽  
Julien Ferri ◽  
Thomas Blackburn ◽  
...  
Keyword(s):  
Near Field ◽  
Finite Difference Methods ◽  
Laser Pulses ◽  
Numerical Dispersion ◽  
Far Field ◽  
Single Node ◽  
Short Pulses ◽  
Tight Focusing ◽  
The Stability ◽  
Periodic Space

When a pulsed, few-cycle electromagnetic wave is focused by optics with f-number smaller than two, the frequency components it contains are focused to different regions of space, building up a complex electromagnetic field structure. Accurate numerical computation of this structure is essential for many applications such as the analysis, diagnostics, and control of high-intensity laser-matter interactions. However, straightforward use of finite-difference methods can impose unacceptably high demands on computational resources, owing to the necessity of resolving far-field and near-field zones at sufficiently high resolution to overcome numerical dispersion effects. Here, we present a procedure for fast computation of tight focusing by mapping a spherically curved far-field region to periodic space, where the field can be advanced by a dispersion-free spectral solver. In many cases of interest, the mapping reduces both run time and memory requirements by a factor of order 10, making it possible to carry out simulations on a desktop machine or a single node of a supercomputer. We provide an open-source C++ implementation with Python bindings and demonstrate its use for a desktop machine, where the routine provides the opportunity to use the resolution sufficient for handling the pulses with spectra spanning over several octaves. The described approach can facilitate the stability analysis of theoretical proposals, the studies based on statistical inferences, as well as the overall development and analysis of experiments with tightly-focused short laser pulses.

Far-field and near-field material processing with. femtosecond laser pulses

1999 ◽  
Vol 69 (7) ◽  
pp. S7-S11 ◽  
Author(s):  
F. Korte ◽  
S. Nolte ◽  
B.N. Chichkov ◽  
T. Bauer ◽  
G. Kamlage ◽  
...  
Keyword(s):  
Material Processing ◽  
Femtosecond Laser ◽  
Near Field ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Far Field

Stability and mixing of a vertical plane buoyant jet in confined depth

1979 ◽  
Vol 94 (2) ◽  
pp. 275-304 ◽  
Author(s):  
Gerhard H. Jirka ◽  
Donald R. F. Harleman
Keyword(s):  
Hydraulic Jump ◽  
Near Field ◽  
Vertical Plane ◽  
Convective Transport ◽  
Relative Depth ◽  
Far Field ◽  
Buoyant Jet ◽  
Densimetric Froude Number ◽  
Mixing Characteristics ◽  
The Stability

A plane turbulent buoyant jet discharging vertically into a two-dimensional channel of confined depth is considered. The channel opens at both ends into a large outside reservoir, thus defining a steady symmetrical flow field within the channel. The analysis is aimed at two aspects, the stability and the bulk mixing characteristics of the discharge. A stable discharge configuration is defined as one in which a buoyant surface layer is formed which spreads horizontally and does not communicate with the initial buoyant jet region. On the other hand, the discharge configuration is unstable when a recirculating cell exists on both sides of the jet efflux.It is shown that discharge stability is only dependent on the dynamic interaction of three near-field regions, a buoyant jet region, a surface impingement region and an internal hydraulic jump region. The buoyant jet region is analysed with the assumption of a variable entrainment coefficient in a form corresponding to an approximately constant jet-spreading angle as confirmed by different experimental sources. The properties of surface impingement and internal jump regions are determined on the basis of control volume analyses. Under the Boussinesq approximation, only two dimensionless parameters govern the near-field interaction; these are a discharge densimetric Froude number and a relative depth. For certain parameter combinations, namely those implying low buoyancy and shallow depth, there is no solution to the conjugate downstream condition in the hydraulic jump which would satisfy both momentum and energy conservation principles. Arguments are given which interpret this condition as one which leads to the establishment of a near-field recirculation cell and, thus, discharge instability.The far-field boundary conditions, while having no influence on discharge stability, determine the bulk mixing characteristics of the jet discharge. The governing equations for the two-layered counterflow system in the far field are solved. The strength of the convective transport, and hence the related dilution ratio, is governed by another non-dimensional parameter, the product of the relative channel length and the boundary friction coefficient.Experiments in a laboratory flume, covering a range of the governing parameters, are in excellent agreement with the theoretical predictions, both the stability criterion and the bulk mixing characteristics.

Far-field and near-field material processing with. femtosecond laser pulses

1999 ◽  
Vol 69 (S1) ◽  
pp. S7-S11 ◽  
Author(s):  
F. Korte ◽  
S. Nolte ◽  
B.N. Chichkov ◽  
T. Bauer ◽  
G. Kamlage ◽  
...  
Keyword(s):  
Material Processing ◽  
Femtosecond Laser ◽  
Near Field ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Far Field

Modelling of pollutant mixing in the St. Lawrence River

1995 ◽  
Vol 22 (5) ◽  
pp. 1041-1045 ◽  
Author(s):  
Siping Zhou ◽  
J. A. McCorquodale ◽  
J. Biberhofer
Keyword(s):  
Field Model ◽  
Near Field ◽  
Numerical Dispersion ◽  
Far Field ◽  
Mixing Processes ◽  
Numerical Diffusion ◽  
Contaminant Loads ◽  
Highly Nonlinear ◽  
Upwind Method ◽  
St Lawrence River

Many of Canada's large rivers, such as the connecting channels of the Great Lakes, receive contaminant loads from industrial, municipal, and tributary sources. These contaminants experience two general types of mixing, outlet-dominated mixing processes (near field) and river-dominated mixing processes (far field). This note is concerned with the numerical modelling of the far field processes by a fully elliptic form of the two-dimensional depth-averaged river model proposed by Rodi et al. Many of the popular hydrodynamics codes experience numerical diffusion which far exceeds the real turbulent diffusion; a new method known as the semi-implicit skewed upwind method is introduced to minimize the numerical dispersion for rivers with highly nonlinear alignment. The new model is verified by comparison with the field data obtained from a dye study in the St. Lawrence River. Key words: pollutant transport, river mixing, far field model, numerical diffusion.

Magnetic Tag Antenna for UHF Near-field and Far-Field RFID Applications

2015 ◽  
Vol 5 (2) ◽  
pp. 119
Author(s):  
Mondher Dhaouadi ◽  
M. Mabrouk ◽  
T. Vuong ◽  
A. Ghazel
Keyword(s):  
Near Field ◽  
Far Field ◽  
Rfid Applications

Far field modeling of the Mamala Bay outfalls

1998 ◽  
Vol 38 (10) ◽  
pp. 323-330
Author(s):  
Philip J. W. Roberts
Keyword(s):  
Field Model ◽  
Near Field ◽  
Far Field ◽  
Field Modeling ◽  
Visitation Frequency ◽  
Statistical Variation ◽  
Long Time ◽  
Harmonic Average ◽  
Ocean Outfall ◽  
Acoustic Doppler Current Profilers

The results of far field modeling of the wastefield formed by the Sand Island, Honolulu, ocean outfall are presented. A far field model, FRFIELD, was coupled to a near field model, NRFIELD. The input data for the models were long time series of oceanographic observations over the whole water column including currents measured by Acoustic Doppler Current Profilers and density stratification measured by thermistor strings. Thousands of simulations were made to predict the statistical variation of wastefield properties around the diffuser. It was shown that the visitation frequency of the wastefield decreases rapidly with distance from the diffuser. The spatial variation of minimum and harmonic average dilutions was also predicted. Average dilution increases rapidly with distance. It is concluded that any impact of the discharge will be confined to a relatively small area around the diffuser and beach impacts are not likely to be significant.

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