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Apparatus for the measurement of the electronic excited‐state structure of single crystals using X‐ray diffraction
Author(s) -
White M. A.,
Pressprich M. R.,
Coppens P.,
Coppens D. D.
Publication year - 1994
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889894002724
Subject(s) - chopper , diffractometer , excited state , diffraction , laser , cryostat , optics , single crystal , materials science , instrumentation (computer programming) , atomic physics , crystal (programming language) , synchrotron radiation , chemistry , physics , crystallography , condensed matter physics , programming language , superconductivity , quantum mechanics , voltage , computer science , operating system , scanning electron microscope
Instrumentation for measuring the X‐ray diffraction pattern of optically excited crystals is described. The experiment uses a high‐power (~1 W) laser and a single‐crystal diffractometer equipped with a helium cryostat ( T < 70 K). The laser beam is modulated by a mechanical chopper and the diffraction signal gated in synchronization with the chopper phase. The modulation method is capable of observing small changes (down to about 0.01%) in the structure factors upon excitation of a fraction of the molecules in the crystal, given adequate counting statistics. The technique can be used for relatively long lived electronic excited states ( τ ≃ 0.1–10 ms). The optical system is also suitable for time‐resolved measurements using the time structure of synchrotron radiation.