Ultrafast free-carrier generation in optically transparent materials

Recently, few-femtosecond pulses have become available at hard X-ray free electron lasers. Coupled with available sub-10 fs optical pulses, investigations into few-femtosecond dynamics are not far off. However, sufficient synchronization between optical lasers and X-ray pulses continues to be challenging.

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In this paper a ''measure-and-sort'' approach has been proposed, which achieves sub-10 fs rms error measurement at hard X-ray FELs, far beyond the 100-200 fs rms jitter limitations. This timing diagnostic, now routinely available at the Linac Coherent Light Source (LCLS), is based on ultrafast free-carrier generation in optically transparent materials. Theoretical modeling of the ultrafast free-carrier generation with a dedicated Monte Carlo code has enabled accurate understanding of the experimental measurements on a microscopic level. Correlation between two independent measurements gives unambiguous demonstration of 10 fs rms error in reporting the optical/X-ray delay, with single shot error suggesting the possibility of reaching few-femtosecond resolution.

Nature Photonics 7 (2013) 215
http://www.nature.com/nphoton/journal/v7/n3/full/nphoton.2013.11.html