Pump-probe and other timing experiments in synchrotron radiation

Abstract

There are many transient, kinetic, intermediate-state and other time-dependent scientific phenomena that remain poorly understood. Intense undulator radiation (UR) from insertion devices in third-generation synchrotron radiation sources creates new possibilities for high energy pump-probe-timing research. We propose a VUV/SXR dual beam, two-color facility for (1) pump-probe-type experiments with continuously variable pump-pulse-to-probe-pulse interval, (2) harmonic phase-shift experiments that should achieve a time resolution of better than 1 ps [1], and (3) Michelson-type interferometric experiments, such as Fourier-transform stimulated-emission spectroscopy [2] for wavelengths shorter than 1000 Å. As conceived for the Advanced Light Source (ALS). Lawrence Berkeley Laboratory, the proposed beamline utilizes a pump beam of high-intensity UR from a 61-period undulator with 8-cm periods, and a probe beam of monochromatized synchrotron radiation (SR) from the following bending magnet. A unique optical variable delay unit (which also greatly reduces the higher-order content of the SR) is used to delay the arrival of the SR pulse at the crossing point of the two beams. The SR pulse may be delayed to arrive between 0.1 and 2.5 ns after the UR pulse. Because the UR pulse from the next electron bucket of the ALS is emitted 2.0 ns later, delay of the SR pulse by 2.0 ns allows superposition of two pulses, and utilization of the coherence properties of UR.