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Beam Physics Seminar

Friday, October 29, 9:30 AM
ARC Bldg. Room 231/233

Ultrafast Demagnetization Of Ferromagnetic Iron Films Studied By Terahertz Time-domain Spectroscopy

David Hilton
Los Alamos National Lab

Broadband, ultrashort terahertz pulses are commonly used to characterize picosecond changes to the optical conductivity of semiconductors and the vibrational and rotational dynamics in solids and gasses. In this talk, I will discuss mechanisms for generating broadband, picosecond terahertz (THz) pulses from optical femtosecond laser sources, including optical rectification in a nonlinear single crystal, carrier acceleration in photoconductive switches, the pondermotive acceleration of electrons in plasma, and via ultrafast demagnetization in ferromagnetic samples. In a photoconductive switch, an above band gap femtosecond laser pulse is injected into a semiconductor which produces photoexcited carriers that are accelerated by an applied electrical bias to emit a THz pulse. In contrast to a photoconductive switch, which relies on an ultrafast injection and acceleration of electronic charges in the semiconductor, we have recently demonstrated THz emission due to ultrafast changes to a single crystal iron sample's magnetization after excitation by an intense femtosecond pump pulse (Optics Letters, vol. 29, pg. 1805). I will show that the emitted THz pulse is a direct measure of the time-changing magnetic field inside the sample, in contrast to earlier all-optical studies of ultrafast demagnetization which demonstrate ambiguous results due to well known experimental artifacts. Finally, I will present the recent results of our terahertz time domain spectroscopy of iron and compare these results both to the terahertz emission spectroscopy study and to a variety of other materials.

Talk Slides: (slides)

For more information, please contact Dr. Alex Bogacz, Chair of CASA Seminar Committee

Updated May 11, 2016
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