67 research outputs found
Strong-field approximation for harmonic generation in diatomic molecules
The generation of high-order harmonics in diatomic molecules is investigated
within the framework of the strong-field approximation. We show that the
conventional saddle-point approximation is not suitable for large internuclear
distances. An adapted saddle-point method that takes into account the molecular
structure is presented. We analyze the predictions for the harmonic-generation
spectra in both the velocity and the length gauge. At large internuclear
separations, we compare the resulting cutoffs with the predictions of the
simple-man's model. Good agreement is obtained only by using the adapted
saddle-point method combined with the velocity gauge.Comment: 24 pages, 7 figure
The effect of dressing on high-order harmonic generation in vibrating H molecules
We develop the strong-field approximation for high-order harmonic generation
in hydrogen molecules, including the vibrational motion and the laser-induced
coupling of the lowest two Born-Oppenheimer states in the molecular ion that is
created by the initial ionization of the molecule. We show that the field
dressing becomes important at long laser wavelengths (m),
leading to an overall reduction of harmonic generation and modifying the ratio
of harmonic signals from different isotopes.Comment: 23 pages, 11 figures, submitted to PR
Control of recollision wave packets for molecular orbital tomography using short laser pulses
The tomographic imaging of arbitrary molecular orbitals via high-order
harmonic generation requires that electrons recollide from one direction only.
Within a semi-classical model, we show that extremely short phase-stabilized
laser pulses offer control over the momentum distribution of the returning
electrons. By adjusting the carrier-envelope phase, recollisions can be forced
to occur from mainly one side, while retaining a broad energy spectrum. The
signatures of the semi-classical distributions are observed in harmonic spectra
obtained by numerical solution of the time-dependent Schr\"{o}dinger equation.Comment: 8 pages, 4 figures; v2: Added some extra clarifications; v3: minor
grammatical change
Molecular Orbital Tomography using Short Laser Pulses
Recently, a method to image molecular electronic wave functions using high
harmonic generation (HHG) was introduced by Itatani \textit{et al.\} [Nature
{\textbf{432}}, 876 (2004)]. We show that, while the tomographic reconstruction
of general orbitals with arbitrary symmetry cannot be performed with long laser
pulses, this becomes possible when extremely short pulses are used. An
alternative reconstruction equation based on momentum matrix elements, rather
than on dipole matrix elements, is proposed. We present simulations of the
procedure for 2D model systems based on numerical solutions of the
time-dependent Schr\"{o}dinger equation, and present results from further
post-processing of the reconstructed orbitals.Comment: 5 pages, 2 figure
Восстановление стабильности плечевого сустава по модернизированной методике Бристов-Латаржет при привычном вывихе плеча
Modification of Bristow-Latarjet
procedure using whole scapular
coracoid process on muscle stem
placed and fi xed apical at the anterior - inferior edge of the glena, as a
continuation of it, allowed in all 26
cases to re-stabilisation of humeral
head in joint, without repeated dislocations with functional reabilitation
in the most of cases (n=23).Модификация методики Бристов-Латаржет, с использованием
всего клювовидного отростка
лопатки на мышечной ножке у
его верхушке, установленного у
передне-нижнего края суставной
впадины лопатки и фиксированного 1-2 винтами (иногда дополненные и спицами) обеспечивали
во всех 26 случаях восстановление
стабильности плечевого сустава
и полную функциональную реабилитацию (n = 23)
27-летний опыт проведения эндопротезирования тазобедренного сустава во II-й клинике Клинической Больницы Травматологии и Ортопедии
Our experience of 619 hip arthroplasties (monopolar = 44,4%, bipolar = 25,5%, total = 30,1%) which
were performed in femoral neck and
trochanteric fractures, and in other
orthopedical pathologies of hip joint,
also good results in 95% of cases, afford authors to reccomend using this
surgical intervention wider.Клинический опыт проведения 619
протезирований тазобедренного
сустава (монополярные – 44,4%,
биполярные – 25,5% и тотальные
– 30,1%), выполненых при переломах шейки бедра, вертельной
области при различных ортопедических патологиях тазобедренного сустава, а также достигнутые
положительные результаты в
95% случаях позволяют авторам
рекомендовать эти хирургические
вмешательства к более широкому
применению
One and two-center processes in high-order harmonic generation in diatomic molecules: influence of the internuclear separation
We analyze the influence of different recombination scenarios, involving one
or two centers, on high-order harmonic generation (HHG) in diatomic molecules,
for different values of the internuclear separation. We work within the
strong-field approximation, and employ modified saddle-point equations, in
which the structure of the molecule is incorporated. We find that the
two-center interference patterns, attributed to high-order harmonic emission at
spatially separated centers, are formed by the quantum interference of the
orbits starting at a center and finishing at a different center in the molecule with those starting and ending at a same center
Within our framework, we also show that contributions starting at different
centers exhibit different orders of magnitude, due to the influence of
additional potential-energy shifts. This holds even for small internuclear
distances. Similar results can also be obtained by considering single-atom
saddle-point equations and an adequate choice of molecular prefactors.Comment: 8 pages, 5 figure
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