Professor Justin Wark

Abstract:

In direct drive inertial confinement fusion, the residual speckle pattern remaining after beam smoothing plays an important role in the seeding of instabilities at the ablation front. An x-ray laser is used as an extreme ultraviolet backlighter to characterize the imprinted modulation in thin foils for smoothing by random phase plate and by spectral dispersion for both 0.35 and 0.53 mu m irradiation, and by induced spatial incoherence for 0.53 mu m irradiation. Measurements of the imprinted modulation due to a single optical mode generated by two beam interference, and modification of the imprint with a superposed smooth irradiation to study time dependence of the imprinting process are demonstrated. (C) 1997 American Institute of Physics.

Abstract:

In recent experiments the capacity has been developed to generate plasmas at high densities. Standard methods used to diagnose plasmas are difficult to apply at these conditions, since it is necessary to calculate the entire spectrum as there is significant overlap of spectral lines. However, for most elements, the number of individual spectral line profiles calculated using the semiclassical method is very small. We present a method to use an approximate line width formula, coupled with an accurate database to generate a large number of line profiles. We evaluate the accuracy and utility of such an approach by comparison with semiclassical calculations. © 1997 The American Physical Society.

Abstract:

A switch based on ultrashort pulse laser heating of diffraction crystals provide insights about x-ray diffraction that forms a synchrotron with sub-picosecond time resolution. A change is diffracted intensity results from thermal expansion of the crystal over an x-ray absorption depth. The reduction in diffracted intensity is limited by the laser fluence to about 15%. It also asserts that experiments using an ultrashort pulse Ti:Sapphire laser synchronized to the ring and a laser pump/x-ray probe are possible. With regards to temporal resolution, a higher level of it can be obtained by using an ultrafast streak camera synchronized to the laser.

Abstract:

The system of a synchrotron radiation utilizing X-ray streak camera for ultrafast experiments is discussed. The X-ray streak camera includes a short-pulse laser and an ultrafast subpicosecond X-ray detector that are accurately synchronized to the synchrotron. The camera's detector is considered to be the fastest, having a 0.54 ps single shot temporal resolution. The camera also has a pair of meander-type deflection plates found before a magnetic focusing lens which obtains very high sweep speeds on the exit phosphor. The duration of the X-ray beam from the synchrotron source was also measured to be at 5 kev.