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.
This patent application is a continuation-in-part application of Ser. No. 915,187, filed Oct. 3, 1986 for DIFFRACTION FREE ARRANGEMENT, which is hereby expressly incorporated by reference herein.
In order to generate a Bessel beam at a location remote from an optical arrangement, the optical arrangement includes, a first beam converging element which is illuminated by a collimated beam, a second beam converging element which is illuminated by a beam which has passed through the first beam converging element. The first and second beam converging elements ere arranged in a manner to radiate a ring beam which is parallel with an optical axis. A third beam converging element is further provided which is illuminated by the ring beam. The third beam converging element is arranged to generate a non-diffractive beam at a location which is remote therefrom. Further, an improvement of a bar code reader is disclosed, which includes a laser source for producing a laser beam. A laser beam deflecting member is provided to deflect the laser beam so as to form a scan pattern comprised of two scan lines. The two scan lines are oriented at a predetermined angle with respect to one another. A combination of photo sensor and electric circuitry is provided to detect the beginning of the scan pattern and to discriminate between the two scan lines.
A Fourier hologram with the distribution of a radial harmonic function creates, in the far field, a pseudo non-diffracting beam. The properties of this pseudo non-diffracting beam can be set by appropriate characterization of the radial harmonic function. Various operations can also be carried out to change the position of the beam relative to the focal point. The beam can be shifted in space, twisted, or tilted.
5640411 - Waveguide laser - Owned by Deutsche Forschungsanstalt fuer Luft-und Raumfahrt e.V. (Bonn,DE)
A waveguide laser comprises a laser-active medium, a pump source for the laser-active medium and a resonator with a waveguide extending in an axial direction and formed from a cylindrical, outer optical waveguide surface and a cylindrical, inner optical waveguide surface. A resonator radiation field extends substantially parallel to the axial direction between the outer and inner optical waveguide surfaces. The waveguide laser further comprises two cavity mirrors between which the resonator radiation field extends and of which at least a first mirror comprises successive maximum and minimum reflectivity values in a direction azimuthal to the axial direction. The maximum and minimum reflectivity values of the first cavity mirror, viewed in the azimuthal direction, are arranged at the location of maximum and minimum intensities of a selected azimuthally closed mode of the resonator, which mode is enclosed by the resonator radiation field. Intermediate regions, in which the reflectivity is between the maximum and minimum values, extend in the azimuthal direction between the successive maximum and minimum values.
A method and a system for generating a beam of radiation in a target plane located in a near-filed region of a radiation emitting means. A beam of radiation having a substantially plane wavefront is emitted. A normal Bessel beam, having its transverse profile substantially in the form of a Bessel function, is produced from said emitted beam of radiation. The normal Bessel beam is produced in a first medium of a refraction index n.sub.1 and is directed towards the target plane located in a second medium having a refraction index n.sub.2, such that n.sub.2 <n.sub.1. Passage of the normal Bessel beam from the first medium into the second medium results in the generation of an evanescent Bessel beam of radiation propagating in the second medium. The evanescent Bessel beam has a center lobe significantly smaller in size than the wavelength of radiation in the second medium, and basically retains its shape in the second medium.
Novel designs for an efficient coupling mechanism for the conversion of typical profile laser beams into Jo profile beams are presented. Five specific embodiments are provided which employ non-linear optical mechanisms in the conversion process.
