This work was supported by the National Research Foundation of Korea (grant no.: 20090078897 and 20110020033) to MC and a KBSI grant (E33300) to HR. The experimental data presented here were measured using the UV-visible femtosecond laser system in KBSI. HR is grateful to Dr Deok-Soo Kim for his help in drawing a figure. JCH was supported by Army Research Office Grants no. W911 NF-12-1-0263 and no. W911-NF-09-0-01417. JSC was supported by an NSF IGERT Fellowship.
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