Patent Number: 048878855
Section: abstract

Arrangements are disclosed for generating a well defined traveling wave beam substantially unaffected by diffractive spreading. In different embodiments, the beam can be an electromagnetic wave, particle beam, a transverse beam, a longitudinal beam such as an acoustic beam, or any type of beam to which the Helmholtz generalized wave equation is applicable. Pursuant to the teachings herein, a beam is generated having a transverse dependence of a Bessel function, and a longitudinal dependence which is entirely in phaser form, which results in a beam having a substantial depth of field which is substantially unaffected by diffractive spreading. In first and second disclosed embodiments respectively, optical and acoustical beams are generated by placing a circular annular source of the beam in the focal plane of a focussing means, which results in the generation of a well defined beam thereby because the far field intensity pattern of an object is the Fourier transform thereof, and the Fourier transform of a Bessel function is a circular function. In a third disclosed embodiment, a microwave beam is generated by transmitting a coherent microwave beam sequentially through a phase modulator, having a periodic stop function pattern, and a spatial filter, whose transmittance is the modulus of the Bessel function, to generate a microwave beam having a transverse Bessel function profile.. More specifically, several embodiments are disclosed of an integrated optical laser cavity and an integrated microwave maser cavity for increasing the efficiency of production of the laser or maser beam. The integrated laser and maser cavities are designed to generate directly from their own gain medium a Bessel-mode diffraction-free beam.