Laser Filamentation of a Femtosecond Pulse in Air at 400nm Page: 1 of 4
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Laser filamentation of a femtosecond
pulse in air at 400nm
T.R. Nelson, T.S. Luk, A.C. Bernstein and S. Cameron
Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185
(505) 284-3393, email@example.com
Abstract: Quantitative measurements of the properties of laser filaments at 400nm are presented. Included
are measurements of the conical emission spectra, as well as the filament conductivity. Comparisons are made
for these phenomena with 800nm filaments.
2000 Optical Society of America
OCIS codes: (010.1300) Atmospheric propagation, 190.3270 Kerr effect
Nonlinear propagation of ultrashort laser pulses in air has been a subject of great interest in recent years, with a large
amount of work being done at 800nm due to the availability of broadband IR laser materials. Recent studies have
begun to examine the nonlinear propagation of laser pulses at wavelengths other than 800nm [1,2]. In this paper we
present what to the best of our knowledge is the first rigorous measurements of the characteristics of laser filaments
2. Experimental Setup
The laser system used for the measurements was a Ti:Sapphire 5TW custom design built for Sandia National
Laboratories by Continuum Corporation. The laser was run at 800nm with a compressed energy of -20mJ, in a
pulsewidth of 5Ofs. The frequency conversion to 400nm was performed with a 1mm thick BBO crystal, and the
residual 800nm light was removed by taking multiple reflections off of dielectric mirrors coated to be high reflectors
for 400nm. The conversion efficiency was -30%, resulting in a beam energy of 6mJ at 400nm. The beam was then
allowed to propagate freely over a range of 15m, without the use of any focusing or beam shaping optics.
3.1 Basic Properties
With 6mJ of energy in the blue, a cluster of 2-3 filaments formed within the first 5m from the BBO crystal, and the
cluster propagated for 3-5m on average. Using the filament to ablate a gold substrate demonstrated a filament
diameter of 150 m. Energy measurements yielded 400 - 450pJ present in two filaments, suggesting an average of
-200pJ per filament. However visual inspection of burn patterns produced by the filaments on paper indicates that
one filament was much stronger than the other one.
3.2 Conical Emission Properties
The divergence angle of the conical emission from the 400nm filament was measured to be 3.5mrad (full angle).
The spectral content of the conical emission shows significant broadening from the linear propagation case, as is
shown in Figure la. Figure lb shows the spectral content of the conical emission from a filament generated by the
red seed beam from the same laser before the BBO crystal. As can be seen, the red conical emission is biased
towards the blue side of the spectrum, while the blue emission is biased towards the red,
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NELSON,THOMAS R.; LUK,TING S.; BERNSTEIN,AARON C. & CAMERON,STEWART M. Laser Filamentation of a Femtosecond Pulse in Air at 400nm, article, October 27, 2000; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc723089/m1/1/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.