When an ultra-short, ultra-intense laser pulse propagates through theatmospheric air, along plasma filaments may develop.Their light is confined to adiameter of about 100μm maintained over distances up to several hundred meters,and a weakly ionized plasma channel is generated along the laser beam path.Aiming to understand thoroughly this very particular kind of propagation,numerical simulations that reproduce the filament propagation in air have beenentirely implemented.The presented results, with the aid of the laboratoryexperiments, bring key elements to the understanding of remote projection of laserplasma filaments in air.　　The generated plasma through filamentation is cold plasma and thus it can besuspended in free space to serve as a transmission line "waveguide" forelectromagnetic energy.Laser plasma filaments can propagate through turbulentregions, low atmospheric pressure, a dense cloud, or rain and the filament is robustagainst obstacles.Also, laser filaments have a very low visible signature and theplasma filament is stable and reproducible.Based on all these properties, one cansay that the laser plasma filaments channel is an efficient robust waveguide.If onecan produce a sheath of filaments, it would be like an instantaneous and flyingconducting/dielectric sheath.Electromagnetic energy could thus be guided throughthe sheath overcoming its natural large divergence over a long distance whilemaintaining a high energy density.Since filaments technically could be both longand projected to long distances, a filament sheath could guide electromagneticenergy to a remote target for any civilian or military applications.　　The main goal of this thesis is the attempt to use the femtosecond plasmachannel, produced through the propagation of femtosecond laser pulse in air, as ameans of short distance point to point wireless channel of pulsed-modulatedelectromagnetic energy.A number of schemes including diverse filamentcharacteristics and geometries as well as the operating frequencies will be lookedat.The coupling of different propagation modes in both the proposed plasmawaveguides and in free-space propagation in an challenge to determine the bestconfiguration for coupling of an electromagnetic pulse to the femtosecond-plasmachannels, for maximum received power over distance will be explored.The biggestchallenge to this procedure is to determine the best configuration for coupling of anelectromagnetic pulse to the femtosecond-plasma channels.　　In the laboratory, we have shown for the first time that guiding electromagneticwaves in the microwave frequency band along a single plasma filament is possibleover distances of several centimeters corresponding to a microwave signal intensityenhancement of more than 3-fold over free space propagation.This currentpropagation distance along the femtosecond laser filament is found to be inagreement with the theoretical calculations, and limited by the relatively highresistance of the single plasma filament.Theoretical result predicts that theattenuation length of microwave can be up to hundreds of meters when using asingle transmission line consisting of a bundle of femtosecond laser plasmafilaments.In addition and based on the possibility of microwave guiding along asingle femtosecond plasma filament, we introduced a new simple, fast and nonintrusive experimental method to obtain the basic parameters of femtosecond lasergenerated plasma filament.Based on a simple physical model and by comparingthe detected microwaves that propagate along the plasma filament and a copperwire with known conductivity and spatial dimension, the basic parameters of theplasma filament are obtained.The measured electron density of～6×1016cm-3 is ingood qualitative agreement with the results of numerical simulations.By couplingthe measurements with theoretical plasma decay models, the temporal evolution ofthe electron density, electron temperature and plasma conductivity are also given.As a result of being able to channel microwave radiation along the plasma filament,we were then able to obtain the plasma density distribution along the filamentlength.　　In the theoretical work, we examined different possible configurations ofguiding electromagnetic energy using femtosecond plasma channels including,single plasma wire transmission line, double geometry plasma transmission line,and cylindrical plasma waveguide.Modeling and simulation show, under idealconditions, the possible modes of coupling and losses as a function of sourceparameters.It was shown that plasma filaments can either behave like lossyconductors or lossless dielectrics depending on both the plasma parameters(electron density, collision frequency, and distances between the plasma filaments...) and operating frequency and their behavior can be characterized by modelstreating them as such.　　The analysis presented in the thesis show that, even though the attenuation ofelectromagnetic radiation induced by the different loss mechanisms accompaniedthe femtosecond plasma transmission lines (waveguides), such as plasmaabsorption and leakage through the discontinuity of the plasma filament,femtosecond laser plasma transmission lines can provide a considerableenhancement of electromagnetic energy transmission relative to freely propagatingto several hundred meters up to few kilometers depending on plasma parametersand the initial electromagnetic radiation energy.Over longer distances, factors suchas energy levels and plasma recombination rates and lifetimes will be limitingfactors.Thus, the femtosecond plasma transmission lines may have uses fordirected energy and point to point communication.The femtosecond plasmafilaments transmission lines may be useful for transporting pulsed-modulatedelectromagnetic energy because of its wide-band property and short duration.