Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed ...frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent ...acoustic phonons were excited in the crystals by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm. The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated, monochromatic pulses of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the unperturbed rocking-curve peak.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Several thin foils have been heated by X-ray radiation emitted by a small gold cavity irradiated with the LULI facility Nd glass laser. The foils were heated to moderate temperatures (10–25 eV) in ...conditions near local thermodynamic equilibrium. Measurements of the absorption of K
α transitions of aluminum, of the K-shell transitions of boron, and of the
n=2–3 and 4 transitions of nickel are reported. A 5000 l/mm transmission grating spectrograph recorded the boron data, and a flat thallium hydrogen phthalate (TlAP) crystal was used for aluminum and nickel absorption measurements. The nickel and aluminum spectra indicate a higher temperature (22–25 eV) than the boron case (14 eV), explained by a difference in the absorption spectra of these elements. In the Ni case the measured 2p-3d spin–orbit–split absorption structures compared well with theoretical spectra obtained with the SCO superconfiguration code using the spin orbit split transition arrays formalism (SOSA). The heating of the foils as calculated with radiative hydrodynamic simulations is very similar to the experimental data.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Ultrafast X-ray diffraction of laser-irradiated crystals Heimann, P.A.; Lindenberg, A.M.; Kang, I. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2001, Volume:
467
Journal Article
Peer reviewed
Open access
Coherent acoustic phonons have been observed in the X-ray diffraction of a laser-excited InSb crystal. Modeling based on time-dependent dynamical diffraction theory has allowed the extraction of ...fundamental constants, such as the electron-acoustic phonon coupling time. A dedicated beamline for time-resolved studies has been developed at the Advanced Light Source with special considerations toward high transmission, low scattering and a wide photon energy range. The facility combines a bend magnet beamline, time-resolved detectors and a femtosecond laser system.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Three 5000 lines/mm gold transmission gratings have been tested with the radiation from the Super-ACO synchrotron in the range 250 eV<
E<850 eV. Typical results for the spectral dependence of the ...grating efficiency at different diffraction orders are presented. This grating theoretically built to have no second order exhibits second order as high as 15–20% of first order. The very thin 5000 L/mm gratings are supported by a larger grid which perturbs the recorded data by separating each order in three peaks. Fraunhofer diffraction of the support grid has been modelled and can explain this effect. The high resolution gratings were used to measure the harmonics of the beamline monochromator grating (550 L/mm) and to measure the emission and absorption of laser-produced plasmas in the XUV range.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Pump-probe time-resolved x-ray diffraction of allowed and nearly forbidden reflections in InSb is used to follow the propagation of a coherent acoustic pulse generated by ultrafast laser excitation. ...The surface and bulk components of the strain could be simultaneously measured due to the large x-ray penetration depth. Comparison of the experimental data with dynamical diffraction simulations suggests that the conventional model for impulsively generated strain underestimates the partitioning of energy into coherent modes.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The Nova laser facility has been used to produce matter in extreme conditions in the laboratory. The plasmas are produced by imploding spherical capsules filled with deuterium and trace amounts of ...Ar. A spectroscopic study of these indirectly driven, inertially confined plasmas provides measurements of the plasma parameters as a function of time. Multiple diagnostics measure peak n{sub e}{approx}1x10{sup 24} cm{sup -3} and T{sub e}{approx}1000 eV. A series of experiments have demonstrated that the results are reliable and reproducible. These experiments are designed to produce laboratory implosions that can serve as a ''testbed'' for high energy density matter. Measuring temperature gradients are the next step so that they can become sources suitable for studying physics such as high-density plasma effects or radiative cooling. (c) 2000 The American Astronomical Society.
Resonance lines of hydrogenlike aluminum ions emitted from a high-power laser-produced plasma have been recorded using a novel ultrahigh-resolution double-crystal x-ray spectrometer. The resolution ...provided by this instrument allows, for the first time, well resolved emitted line profiles and positions to be measured as a function of observation angle. Interpretation of the measured line shapes, positions, and intensities require simulations which include the transfer of radiation in a plasma with a large velocity gradient.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
PDF
