641 research outputs found
Theory of high harmonic generation in relativistic laser interaction with overdense plasma
High harmonic generation due to the interaction of a short ultra relativistic
laser pulse with overdense plasma is studied analytically and numerically. On
the basis of the ultra relativistic similarity theory we show that the high
harmonic spectrum is universal, i.e. it does not depend on the interaction
details. The spectrum includes the power law part for
, followed by exponential decay. Here
is the largest relativistic -factor of the plasma
surface and is the second derivative of the surface velocity at this
moment. The high harmonic cutoff at is parametrically
larger than the predicted by the ``oscillating mirror''
model based on the Doppler effect. The cornerstone of our theory is the new
physical phenomenon: spikes in the relativistic -factor of the plasma
surface. These spikes define the high harmonic spectrum and lead to attosecond
pulses in the reflected radiation.Comment: 12 pages, 9 figure
The direct evaluation of attosecond chirp from a streaking measurement
We derive an analytical expression, from classical electron trajectories in a
laser field, that relates the breadth of a streaked photoelectron spectrum to
the group-delay dispersion of an isolated attosecond pulse. Based on this
analytical expression, we introduce a simple, efficient and robust procedure to
instantly extract the attosecond pulse's chirp from the streaking measurement.Comment: 4 figure
Ultrasmall divergence of laser-driven ion beams from nanometer thick foils
We report on experimental studies of divergence of proton beams from
nanometer thick diamond-like carbon (DLC) foils irradiated by an intense laser
with high contrast. Proton beams with extremely small divergence (half angle)
of 2 degree are observed in addition with a remarkably well-collimated feature
over the whole energy range, showing one order of magnitude reduction of the
divergence angle in comparison to the results from micrometer thick targets. We
demonstrate that this reduction arises from a steep longitudinal electron
density gradient and an exponentially decaying transverse profile at the rear
side of the ultrathin foils. Agreements are found both in an analytical model
and in particle-in-cell simulations. Those novel features make nm foils an
attractive alternative for high flux experiments relevant for fundamental
research in nuclear and warm dense matter physics.Comment: 11 pages, 5 figure
Giant half-cycle attosecond pulses
Half-cycle picosecond pulses have been produced from thin photo-conductors,
when applying an electric field across the surface and switching on conduction
by a short laser pulse. Then the transverse current in the wafer plane emits
half-cycle pulses in normal direction, and pulses of 500 fs duration and 1e6
V/m peak electric field have been observed. Here we show that single half-cycle
pulses of 50 as duration and up to 1e13 V/m can be produced when irradiating a
double foil target by intense few-cycle laser pulses. Focused onto an
ultra-thin foil, all electrons are blown out, forming a uniform sheet of
relativistic electrons. A second layer, placed at some distance behind,
reflects the drive beam, but lets electrons pass straight. Under oblique
incidence, beam reflection provides the transverse current, which emits intense
half-cycle pulses. Such a pulse may completely ionize even heavier atoms. New
types of attosecond pump-probe experiments will become possible.Comment: 5 pages, 4 figures, to be presented at LEI2011-Light at Extreme
Intensities and China-Germany Symposium on Laser Acceleratio
TSPY1 copy number variation influences spermatogenesis and shows differences among Y lineages.
CONTEXT: TSPY1 is a tandemly-repeated gene on the human Y chromosome forming an array of approximately 21–35 copies. The testicular expression pattern and the inferred function of the TSPY1 protein suggest possible involvement in spermatogenesis. However, data are scarce on TSPY1 copy number variation in different Y lineages and its role in spermatogenesis. OBJECTIVES: We sought to define: 1) the extent of TSPY1 copy number variation within and among Y chromosome haplogroups; and 2) the role of TSPY1 dosage in spermatogenic efficiency. MATERIALS AND METHODS: A total of 154 idiopathic infertile men and 130 normozoospermic controls from Central Italy were analyzed. We used a quantitative PCR assay to measure TSPY1 copy number and also defined Y haplogroups in all subjects. RESULTS: We provide evidence that TSPY1 copy number shows substantial variation among Y haplogroups and thus that population stratification does represent a potential bias in case-control association studies. We also found: 1) a significant positive correlation between TSPY1 copy number and sperm count (P < 0.001); 2) a significant difference in mean TSPY1 copy number between patients and controls (28.4 ± 8.3 vs. 33.9 ± 10.7; P < 0.001); and 3) a 1.5-fold increased risk of abnormal sperm parameters in men with less than 33 copies (P < 0.001). CONCLUSIONS: TSPY copy number variation significantly influences spermatogenic efficiency. Low TSPY1 copy number is a new risk factor for male infertility with potential clinical consequences
Subcycle controlled charge-directed reactivity with few-cycle midinfrared pulses
The steering of electron motion in molecules is accessible with waveform-
controlled few-cycle laser light and may control the outcome of light-induced
chemical reactions. An optical cycle of light, however, is much shorter than
the duration of the fastest dissociation reactions, severely limiting the
degree of control that can be achieved. To overcome this limitation, we
extended the control metrology to the midinfrared studying the prototypical
dissociative ionization of D2 at 2.1 μm. Pronounced subcycle control of the
directional D+ ion emission from the fragmentation of D+2 is observed,
demonstrating unprecedented charge-directed reactivity. Two reaction pathways,
showing directional ion emission, could be observed and controlled
simultaneously for the first time. Quantum-dynamical calculations elucidate
the dissociation channels, their observed phase relation, and the control
mechanisms
One-Pot Silver Nanoring Synthesis
Silver colloidal nanorings have been synthesized by reducing silver ions with NaBH4 in trisodium citrate buffers. pH increase, by addition of NaOH, was used to speed up reduction reaction. The UV–vis absorption spectra of resulting silver nanorings showed two peaks accounting for transverse and longitudinal surface plasmon resonance, at ≈400 nm, and between 600 and 700 nm, respectively. The shapes of these silver nanoparticles (nanorings) depended on AgNO3/NaBH4 ratio, pH and reaction temperature. Particles were analysed by transmission electron microscopy, scanning electron microscopy and X-ray diffraction. A reaction pathway is proposed to explain silver nanoring formation
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