8,554 research outputs found
Dynamics of ripple formation on silicon surfaces by ultrashort laser pulses in sub-ablation conditions
An investigation of ultrashort pulsed laser induced surface modification due
to conditions that result in a superheated melted liquid layer and material
evaporation are considered. To describe the surface modification occurring
after cooling and resolidification of the melted layer and understand the
underlying physical fundamental mechanisms, a unified model is presented to
account for crater and subwavelength ripple formation based on a synergy of
electron excitation and capillary waves solidification. The proposed
theoretical framework aims to address the laser-material interaction in
sub-ablation conditions and thus minimal mass removal in combination with a
hydrodynamics-based scenario of the crater creation and ripple formation
following surface irradiation with single and multiple pulses, respectively.
The development of the periodic structures is attributed to the interference of
the incident wave with a surface plasmon wave. Details of the surface
morphology attained are elaborated as a function of the imposed conditions and
results are tested against experimental data
A Dirichlet-to-Neumann approach for the exact computation of guided modes in photonic crystal waveguides
This works deals with one dimensional infinite perturbation - namely line
defects - in periodic media. In optics, such defects are created to construct
an (open) waveguide that concentrates light. The existence and the computation
of the eigenmodes is a crucial issue. This is related to a self-adjoint
eigenvalue problem associated to a PDE in an unbounded domain (in the
directions orthogonal to the line defect), which makes both the analysis and
the computations more complex. Using a Dirichlet-to-Neumann (DtN) approach, we
show that this problem is equivalent to one set on a small neighborhood of the
defect. On contrary to existing methods, this one is exact but there is a price
to be paid : the reduction of the problem leads to a nonlinear eigenvalue
problem of a fixed point nature
Reduced basis method for source mask optimization
Image modeling and simulation are critical to extending the limits of leading
edge lithography technologies used for IC making. Simultaneous source mask
optimization (SMO) has become an important objective in the field of
computational lithography. SMO is considered essential to extending immersion
lithography beyond the 45nm node. However, SMO is computationally extremely
challenging and time-consuming. The key challenges are due to run time vs.
accuracy tradeoffs of the imaging models used for the computational
lithography. We present a new technique to be incorporated in the SMO flow.
This new approach is based on the reduced basis method (RBM) applied to the
simulation of light transmission through the lithography masks. It provides a
rigorous approximation to the exact lithographical problem, based on fully
vectorial Maxwell's equations. Using the reduced basis method, the optimization
process is divided into an offline and an online steps. In the offline step, a
RBM model with variable geometrical parameters is built self-adaptively and
using a Finite Element (FEM) based solver. In the online step, the RBM model
can be solved very fast for arbitrary illumination and geometrical parameters,
such as dimensions of OPC features, line widths, etc. This approach
dramatically reduces computational costs of the optimization procedure while
providing accuracy superior to the approaches involving simplified mask models.
RBM furthermore provides rigorous error estimators, which assure the quality
and reliability of the reduced basis solutions. We apply the reduced basis
method to a 3D SMO example. We quantify performance, computational costs and
accuracy of our method.Comment: BACUS Photomask Technology 201
Real-World Repetition Estimation by Div, Grad and Curl
We consider the problem of estimating repetition in video, such as performing
push-ups, cutting a melon or playing violin. Existing work shows good results
under the assumption of static and stationary periodicity. As realistic video
is rarely perfectly static and stationary, the often preferred Fourier-based
measurements is inapt. Instead, we adopt the wavelet transform to better handle
non-static and non-stationary video dynamics. From the flow field and its
differentials, we derive three fundamental motion types and three motion
continuities of intrinsic periodicity in 3D. On top of this, the 2D perception
of 3D periodicity considers two extreme viewpoints. What follows are 18
fundamental cases of recurrent perception in 2D. In practice, to deal with the
variety of repetitive appearance, our theory implies measuring time-varying
flow and its differentials (gradient, divergence and curl) over segmented
foreground motion. For experiments, we introduce the new QUVA Repetition
dataset, reflecting reality by including non-static and non-stationary videos.
On the task of counting repetitions in video, we obtain favorable results
compared to a deep learning alternative
Finite-Difference Time-Domain Study of Guided Modes in Nano-plasmonic Waveguides
A conformal dispersive finite-difference time-domain (FDTD) method is
developed for the study of one-dimensional (1-D) plasmonic waveguides formed by
an array of periodic infinite-long silver cylinders at optical frequencies. The
curved surfaces of circular and elliptical inclusions are modelled in
orthogonal FDTD grid using effective permittivities (EPs) and the material
frequency dispersion is taken into account using an auxiliary differential
equation (ADE) method. The proposed FDTD method does not introduce numerical
instability but it requires a fourth-order discretisation procedure. To the
authors' knowledge, it is the first time that the modelling of curved
structures using a conformal scheme is combined with the dispersive FDTD
method. The dispersion diagrams obtained using EPs and staircase approximations
are compared with those from the frequency domain embedding method. It is shown
that the dispersion diagram can be modified by adding additional elements or
changing geometry of inclusions. Numerical simulations of plasmonic waveguides
formed by seven elements show that row(s) of silver nanoscale cylinders can
guide the propagation of light due to the coupling of surface plasmons.Comment: 6 pages, 10 figures, accepted for publication, IEEE Trans. Antennas
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