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 focusing 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 step 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.

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.

An end assembly for a gas laser has a support flange brazed or heliarc welded to a gas reservoir at one end of a laser tube. The flange supports a cathode, a replaceable Brewster angle window, and a replaceable gas feed tube. Ceramic feedthroughs brazed or heliarc welded to holes in the flange bring wires through the flange while maintaining insulation therefrom. The helical cathode is joined to copper stubs from the feedthroughs by crimped sleeves. Brewster angle window and gas pinch-off tube are bolted with nuts onto threaded extensions on the flange. Vacuum seals are provided by compression fittings squeezed between threaded extension and gas pinch-off tube or metal extension member by the nuts. A glass-to-metal bond between metal extension member and glass tube terminating Brewster angle window is made.