238 research outputs found
Thermoelastic study of nanolayered structures using time-resolved x-ray diffraction at high repetition rate
We investigate the thermoelastic response of a nanolayered sample composed of
a metallic SrRuO3 (SRO) electrode sandwiched between a ferroelectric
Pb(Zr0.2Ti0.8)O3 (PZT) film with negative thermal expansion and a SrTiO3
substrate. SRO is rapidly heated by fs-laser pulses with 208 kHz repetition
rate. Diffraction of x-ray pulses derived from a synchrotron measures the
transient out-of-plane lattice constant c of all three materials simultaneously
from 120 ps to 5 mus with a relative accuracy up to Delta c/c = 10^-6. The
in-plane propagation of sound is essential for understanding the delayed out of
plane expansion.Comment: 5 pages, 3 figure
Recent progress of GaAsP HPD development for the MAGIC telescope project
Today the Hybrid Photon Detector (HPD) is one of the few low light level
(LLL) sensors that can provide an excellent single and multiple photoelectron
(ph.e.) amplitude resolution. The recently developed HPDs for the MAGIC
telescope project with a GaAsP photocathode, namely the R9792U-40, provide a
peak quantum efficiency (QE) of more than 50% and a pulse width of ~2 nsec. In
addition, the afterpulsing rate of these tubes is very low compared to that of
conventional photomultiplier tubes (PMTs), i.e. the value is ~300 times lower.
Photocathode aging measurements showed life time of more than 10 years under
standard operating conditions of the Cherenkov Telescopes. Here we want to
report on the recent progress with the above mentioned HPDs.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of
the MAGIC Collaboratio
Study of the performance and capability of the new ultra-fast 2 GSample/s FADC data acquisition system of the MAGIC telescope
In February 2007 the MAGIC Air Cherenkov Telescope for gamma-ray astronomy
was fully upgraded with an ultra fast 2 GSamples/s digitization system. Since
the Cherenkov light flashes are very short, a fast readout can minimize the
influence of the background from the light of the night sky. Also, the time
structure of the event is an additional parameter to reduce the background from
unwanted hadronic showers. An overview of the performance of the new system and
its impact on the sensitivity of the MAGIC instrument will be presented.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of
the MAGIC Collaboratio
Picosecond strain dynamics in GeSbTe monitored by time-resolved x-ray diffraction
Coherent phonons (CP) generated by laser pulses on the femtosecond scale have
been proposed as a means to achieve ultrafast, non-thermal switching in
phase-change materials such as GeSbTe(GST). Here we use
ultrafast optical pump pulses to induce coherent acoustic phonons and
stroboscopically measure the corresponding lattice distortions in GST using 100
ps x-ray pulses from the ESRF storage ring. A linear-chain model provides a
good description of the observed changes in the diffraction signal, however,
the magnitudes of the measured shifts are too large to be explained by thermal
effects alone implying the presence of transient non-equilibrium electron
heating in addition to temperature driven expansion. The information on the
movement of atoms during the excitation process can lead to greater insight
into the possibilities of using CP-induced phase-transitions in GST.Comment: 7 pages, 4 figures, Phys. Rev. B, in pres
- …