Multi-color filaments for extended range, applied to remote sensing and laser induced EMP
Abstract
A basic research program aimed at projecting high intensity or high energy over long distances is proposed. Remote manipulation of beams and pulses will lead to lasing in air, and remote creation of an electromagnetic pulse (EMP). This will be achieved by exploiting a combination of nonlinear properties of air over very different time scales, as well as intense pulses at IR and UV wavelengths. The slowest time scale involves the thermodynamic properties of air. A continuous train of heat bursts created in air along the light beam produces a cylindrical pressure distribution susceptible to guide the beam. These heat bursts are produced by a series of ionizing light pulses, each creating a shock wave that does not decay before the arrival of the next pulse (20 to 100 microseconds later). The next (shorter) time constant of importance is that of the rotational period of the molecule. The ultrashort pulses create rotational wave packets involved in an optical gain mechanism of the excited ion. Thanks to the pressure waveguide this gain can be confined to a long cylindrical volume, leading to lasing. This lasing can be directed towards the source, by exciting the medium with a sequence of properly spaced pulses. Another approach to backward lasing will be to engineer the leading edge of the pulse to create a gain moving at the speed of light towards the source. This involves the fastest nonlinearity which is the electronic third order susceptibility, responsible for four wave mixing, beam self focusing, and phase modulation. Four wave mixing will be exploited as a means to couple light beams of different wavelengths. Uv pulses of 100 mJ energy and 10 to 200 ps in duration can be an energy reservoir for intense fs IR pulses, providing through four wave mixing amplification and stretching of the ultrashort IR pulses. The goal is to have this gain and stretching process lead to avalanche and plasma created EMP. A high repetition laser (10 kHz to 50 kHz at 800 nm) will be constructed in the first part of the program, and used with various beam shaping to create a steady state waveguide in air for intense (50 mJ, 50 fs) pulses issued from the same laser system. Beam shaping in space and time will be used to postpone the starting point of waveguiding, leading to the creation of remote light filaments. The required phase modulation to be applied on UV pulses will be achieved through a new method involving cascaded nonlinearity in sum frequency generation. Lasing in air in the forward and backward directions will be investigated with different combinations of beams, using phase masks to create vortex of different order, different polarization and pulse sequencing. EMP generation by plasma will first be investigated in a chamber, where the beam parameters are more easily controlled and not affected by propagation. The plasma created by a combination of ps UV and fs IR pulses will be studied through analysis of the momentum distribution of electrons extracted from the interaction volume in a Velocity Mapping Instrument (VMI). The optimum pulse durations, relative timing and polarization of the UV and IR pulses determined by this chamber study will guide the remote generation of plasma using nested filaments produced by the high and low repetition IR pulses combined with low repetition ps energetic UV pulses. Conditions for amplification, stretching and collapse of the IR pulses leading to avalanche breakdown will be sought.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 22, 2019
- Source ID
- W911NF1910272
Entities
People
- Jean-claude Diels
Organizations
- Army Contracting Command
- United States Army
- University of New Mexico