Penetration by a Laser-Light Induced Field and Coupling to a Monopole Attached on Axis to a Body of Revolution
In this paper is presenteda methodfor computing, andan experimental procedure for verifying, the coupling of a signal, caused by a modulatedlaser beam, to a loadimp edance terminating a coaxial waveguide whose center conductor protrudes into a an open-ended body of revolution (BOR). The excitation is the signal radiated by electrons emittedfrom the conducting surface by an impinging laser beam, modulated in such a way that the electrons escaping the surface oscillate harmonically in time causing them to radiate a coherent signal at an angular frequency Ï‰. For a vanishingly small spot of laser light on the conducting surface, the radiating source is modeled as an electric dipole normal to and located at the surface. To perform this computation directly is very difficult so we resort to an indirect methodthat allows us to realize significant savings with no loss in generality. The indirect approach adopted here takes the advantage of the reciprocity andallo ws one to determine the receivedsignal at the coax terminal load from knowledge of the field radiated by a small wire probe mounted on the symmetry axis of the BOR under the condition that the excitation results from a current generator impressedat the terminal endof the coax. This scheme necessitates the formulation andsolution of a simpler integral equation. In principle, the approach developed to solve this problem is exact and rigorous. The validity of this approach is demonstrated numerically and experimentally.