Streaking and splashing: design of a grazing incidence x-ray streak camera and time-resolved measurements of the structure of water

摘要

The performance of cesium iodide photocathodes has been characterized for use with grazing incidence soft x-rays. The total electron yield and pulsed quantum efficiency has been measured in a reflection geometry as a function of photon energy (100 eV to 1 keV), angle of incidence, and the electric field between the anode and photocathode. The total electron yield and pulsed quantum efficiency increase as the x-ray penetration depth approaches the secondary electron escape depth Unit quantum efficiency in a grazing incidence geometry is demonstrated. A weak electnc-field dependence is observed for the total yield measurements, while no significant dependence is found for the pulsed quantum efficiency. The effect of the pulse height distribution on the detective quantum efficiency is discussed Theoretical predictions agree accurately with expenment.ududDemonstrated unit quantum efficiency in a reflection geometry motivated the development of a grazing incidence x-ray streak camera for the Ultrafast X-ray Science beamline, under construction at the Advanced Light Source, Lawrence Berkeley National Laboratory, USA Design considerations particular to synchrotron radiation sources are discussed. An analytical model and particle simulation for a camera incorporating magnetostatic imaging and meander sweep plates is presented. The camera is characterised with the third harmonic from a titanium-sapphire based laser system, 70 ps intrinsic and 150 fs “sliced” x-ray photon pulses from a synchrotron bend magnet source. A grazing incidence x-ray streak camera with an instrument temporal response of 6 ps is demonstrated.ududDynamical changes in the structure factor of liquid water are measured using time-resolved x-ray diffraction techniques with 100 ps resolution. On short time scales, before the system has had time to expand following femtosecond optical excitation, temperatureinduced changes associated with rearrangements of the hydrogen-bonded structure at constant volume are observed. Transient changes in the pair correlation function associated with isochonc heating effects are extracted and interpreted in terms of a decrease in the local tetrahedral ordering in the liquid.