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DIRECTED
ENERGY
PROFESSIONAL
SOCIETY
Abstract: 24-Symp-184
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UNCLASSIFIED, PUBLIC RELEASE
Ionization of Air by Intense Long Wave Infrared Two-Color Laser Pulses
Mapping the wavelength dependence of plasma generation in air by intense, short laser pulses is essential for understanding and optimizing their propagation in the atmosphere. However, there are few laser sources capable of sufficient peak intensity to experimentally study the wavelength dependence. Air plasmas produced using near-infrared (NIR) femtosecond lasers are studied frequently, and arise from multiphoton ionization with a modest degree of inverse bremsstrahlung and ponderomotive excitation providing energy to the electron population. How this picture changes at longer wavelengths has not been thoroughly investigated, however we expect tunneling ionization and the wavelength-squared dependence of the electron quiver energy to substantially alter the overall ionization dynamics relative to the NIR case. We present preliminary observations of air plasmas generated by tightly focusing two-color picosecond-duration long wave-infrared (LWIR) pulses in air. In a two-color pulse, the fundamental (9.2 microns) is superimposed with the second harmonic (4.6 microns). We find that in addition to strong field ionization by the fundamental, the second harmonic field mediates collisional ionization. Further, the microwave radiation resulting from the picosecond-duration LWIR laser plasma has a substantially larger amplitude than that from a femtosecond-duration NIR laser pulse of the same peak power. The early measurements show that the characteristics of air plasmas resulting from LWIR laser pulses fundamentally differ from NIR-produced plasmas. Our ongoing work seeks to quantify these differences, and identify mechanisms to explain them.
Funding Acknowledgement:
This work is supported by the U.S. Naval Research Laboratory Base Program. This material is based upon work supported by the National Science Foundation MPS-Ascend Postdoctoral Research Fellowship under Grant No. 2213242, and by the U.S. Department of Energy under contract DE-SC0012704.
UNCLASSIFIED, PUBLIC RELEASE
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