Terahertz-frequency electrical conductivity measurements of ultrashort laser-ablated plasmas

K. Y. Kim; B. Yellampelle; J. H. Glownia; A. J. Taylor; G. Rodriguez

doi:10.1117/12.668945

7 June 2006 Terahertz-frequency electrical conductivity measurements of ultrashort laser-ablated plasmas

K. Y. Kim, B. Yellampelle, J. H. Glownia, A. J. Taylor, G. Rodriguez

Proceedings Volume 6261, High-Power Laser Ablation VI; 62612Q (2006) https://doi.org/10.1117/12.668945
Event: High-Power Laser Ablation 2006, 2006, Taos, NM, United States

Abstract

We investigate the phase transitions of intense ultrashort laser-heated solids, from the cold solid to the hot dense plasma state, by measuring the complex electrical conductivity (or refractive index) transients at terahertz (1 THz = 10¹² Hz) frequencies. Using optical-pump, terahertz-probe spectroscopy, we measured the phase shifts and absorption of terahertz probe pulses that were reflected from the warm dense plasma. To characterize the THz field, we developed and used a single-shot, high-temporal-resolution THz diagnostic capable of measuring free-space electromagnetic pulse fields in time and space. Due to relatively large focal spot sizes of the THz probe (~mm), mainly limited by the diffraction properties of THz radiation, the optical pump pulse was weakly focused onto the target in order to overfill the THz probe spot size with a peak intensity of ~10¹³ W/cm². In contrast to the previous measurements of conductivities at optical frequencies, our THz non-contact probe method can directly measure quasi-DC electrical conductivities, providing insight into the transport nature of warm dense matter and any present discrepancies with the Drude model. In case of warm dense aluminum, we observe a noticeable deviation from the Drude model even in the ~10¹³ W/cm² laser intensity regime. In addition, we observe strong coherent THz emission produced by a current surge in the laser-produced plasma.

Citation Download Citation

K. Y. Kim, B. Yellampelle, J. H. Glownia, A. J. Taylor, and G. Rodriguez "Terahertz-frequency electrical conductivity measurements of ultrashort laser-ablated plasmas", Proc. SPIE 6261, High-Power Laser Ablation VI, 62612Q (7 June 2006); https://doi.org/10.1117/12.668945

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