1. Presented by Emily Sprague PULSE Institute, Aaron Lindenberg, Dan Daranciang, & Haidan Wen

2.  Background ▪ Plasma Filamentation ▪ THz generation  Experimental Setup  Results  Conclusions  Future Work Courtesy of http://en.wikipedia.org/wiki/Plasma_%28physics%29

3.  Created by mode-locked oscillators ▪ Ti:sapphire oscillators ▪ wavelengths of 680 nm to 1130 nm  Optimization ▪ Minimal chirp ▪ Large bandwidth  Used to generate plasma

4.  Photons from an external source are absorbed by a gas, emitting electrons  Because of abundance of charge carriers, interacts with itself and surrounding EM fields  Used in THz generation Courtesy of http://www.isibrno.cz/omitec/index.php?action=libs.html

5.  Could potentially replace x-rays as a form of non- ionizing radiation  Applications in medical imaging, material science studies, and atomic spectroscopy  5 types of plasma-based generation methods Courtesy of http://www.stanford.edu/group/lindenberg/research.html

6.  Superposition of fundamental and second-harmonic pulse fields  Optimization ▪ Relative phase shift ▪ Exact temporal overlap ▪ Polarization Courtesy of M.D. Thomson, M. Kreß, T. Loffler, and H.G. Roskos. Laser & Photon. Rev. 1, No. 4, 349–368 (2007)

7.  Ti:sapphire laser ▪ 50 fs 800 nm pulse  Mirrors  Lenses ▪ f=100 mm (beam 2) ▪ f=200 mm (beam 1)  Beam splitter ▪ Controls polarization  beam 1: p-polarized  beam 2: s-polarized  Delay Stage ▪ Controls path length and relative delay between arrival of plasmas

8.  s-p polarized ▪ Beam 2 vertically polarized ▪ Beam 1 horizontally polarized  s-s polarized ▪ Beam 1 and beam 2 vertically polarized  p-p polarized ▪ Beam 1 and beam 2 horizontally polarized

9.  Before time-zero: no plasma interaction  Time zero: both plasmas arrive and interfere  After time-zero: secondary fluorescence

10. Time Zero: two plasmas arrive simultaneously Before time zero After time zero

14.  Peak intensity and point of decay consistently occured at the same time values  Decay time was constant across all polarizations (~50 steps)  All power levels and polarization sets experienced a full decay back to the starting intensities  No valuable data was obtained below a power of 250 mW  Peak intensity was always strongest for s-p polarizations and weakest for p-p polarizations

15.  Slope of the decay decreased with decreasing power in stationary arm  Peak and decay ratios increased with decreasing power in the stationary arm  Results are reproducible  Spike at time zero is dramatic and still not understood by scientific community

16.  Time dependent spectral studies of plasma ▪ Analysis of wavelengths of plasma fluorescence ▪ Resolve between scatter or enhanced tunneling ionzation  Better camera resolution Courtesy of http://opticsclub.engineering.ucdavis.edu/

18. Thank you!