The Review of Laser Engineering
Online ISSN : 1349-6603
Print ISSN : 0387-0200
ISSN-L : 0387-0200
Laser Review
Time-Frequency Two-Dimensional Imaging Spectroscopy Using a Reflective Echelon Mirror
Jun TAKEDAYasuo MINAMIIkufumi KATAYAMA
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2015 Volume 43 Issue 4 Pages 208-

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Abstract
We proposed broadband single-shot femtosecond spectroscopy in a time-frequency space using a reflective echelon mirror that makes a spatially encoded time-delay for a white-light continuum probe pulse. It produces a temporal step of 66 fs and an overall time-delay of 33 ps. With this technique, we observed an ultrafast crystalline-to-amorphous phase-change in chalcogenide alloys: Ge2Sb2Te5 (GST) and GeTe thin films. We even measured the absorbance change that accompanied the ultrafast amorphization for laser fluences above the critical value, where a permanent recording mark was formed. The observed rise time to reach amorphization was 130~200 fs both in GST and GeTe thin films, suggesting that ultrafast amorphization can be attributed to the rearrangement of Ge atoms from an octahedral to a tetrahedral structure.
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© 2015 by The Laser Society of Japan
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