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Showing papers on "Bessel beam published in 1995"


Patent
Koji Ichie1
07 Sep 1995
TL;DR: A laser scanning optical system is composed of two axicon prisms which are arranged such that apexes thereof are opposed forward or backward to each other at a predetermined distance and optical axes thereof are coincident with each other and which are made of respective materials having a same refractive index and shaped with a same apical angle.
Abstract: A laser scanning optical system is so arranged to comprise an optical converting unit, an optical scanning unit, and an optical converging unit. Here, the optical converting unit is composed of two axicon prisms which are arranged such that apexes thereof are opposed forward or backward to each other at a predetermined distance and optical axes thereof are coincident with each other and which are made of respective materials having a same refractive index and shaped with a same apical angle. By this, the laser beam incident into the optical converting unit becomes a cylindrical ray bundle having an annular cross-sectional intensity perpendicular to the optical axis. Therefore, the cylindrical ray bundle is changed in the traveling direction by the optical scanning unit to be scanned and is then converged by the optical converging unit to become a Bessel beam having a high energy utilization factor, a high resolution and a long focal depth.

226 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported the application of the Bessel beam to Doppler velocity estimation in medical imaging, tissue characterization, and nondestructive evaluation of materials, and demonstrated that this beam has the advantage that velocity estimation is less subject to the depth of moving objects and its shoulders have distinct shoulders that increase the accuracy of velocity estimation.
Abstract: Limited-diffraction beams have a large depth of field and could be applied to medical imaging, tissue characterization, and nondestructive evaluation of materials. This paper reports the application of limited-diffraction beams, specifically, the Bessel beam, to Doppler velocity estimation. The Bessel beam has the advantage that velocity estimation is less subject to the depth of moving objects and the Doppler spectrum has distinct shoulders that increase the accuracy of velocity (both magnitude and Doppler angle) estimation in noisy environments. The shoulders of the Doppler spectrum might also help in solving the inverse problem, e.g., estimation of the velocity distribution in vessels. >

46 citations


Journal ArticleDOI
TL;DR: In this paper, the Bessel-beam representation for partially coherent fields is introduced as an alternative to the familiar angular spectrum representation, applied to far fields generated by partially coherent secondary sources, nondiffracting partially coherent field, and statistically homogeneous fields.
Abstract: The Bessel-beam representation for partially coherent fields is introduced as an alternative to the familiar angular spectrum representation. This alternative representation is applied to far fields generated by partially coherent secondary sources, nondiffracting partially coherent fields, and statistically homogeneous fields. A scheme for generating nondiffracting partially coherent fields is also discussed.

22 citations


Journal ArticleDOI
TL;DR: A theory of the recently discussed and demonstrated novel phenomenon of self-phase-matching is given by representing the conical beam by a Bessel beam and as a superposition of Bessel beams.
Abstract: A theory of the recently discussed and demonstrated novel phenomenon of self-phase-matching [B. Glushko, B. Kryzhanovsky, and D. Sarkisyan, Phys. Rev. Lett. 71, 243 (1993)] is given by representing the conical beam, produced in the experiments, by a Bessel beam and as a superposition of Bessel beams. The predictions of the theory with the superposition of Bessel beams are in conformity with the observed behavior.

20 citations


Book ChapterDOI
01 Jan 1995
TL;DR: In this paper, Lu and Greenleaf discovered families of limited diffraction beams with an X-like shape along the beam axis and was termed X wave, which is different from the Bessel beam because they have multiple frequencies.
Abstract: Limited diffraction beams are a class of non-spreading solutions to the isotropic/homogeneous scalar wave equation. The first limited diffraction beam, called Bessel beam, was discovered by Durnin in 1987.1 Later, Lu and Greenleaf discovered families of limited diffraction beams2,3 that include all the limited diffraction beams known previously, in addition to an infinity of new beams. One family of limited diffraction beams has an X-like shape along the beam axis and was termed X wave. X waves are different from the Bessel beam because they have multiple frequencies.2

19 citations


Journal ArticleDOI
TL;DR: It is demonstrated that when the effective wavelength of the Bessel pump beam is varied, the Bragg wavelength for DFB is altered, and as a result the output wavelength can be tuned.
Abstract: A distributed-feedback (DFB) dye laser that is pumped by a standing Bessel-beam wave is constructed. Because of the long line focus of the Bessel beam, the laser medium is pumped in only a very thin filament (a few micrometers) along the optical axis. At the same time, longitudinal-mode selection is achieved because of the DFB effect. It is demonstrated that when the effective wavelength of the Bessel pump beam is varied, the Bragg wavelength for DFB is altered, and as a result the output wavelength can be tuned.

18 citations


Journal ArticleDOI
TL;DR: In this article, the non-fracturing propagation of the ideal zero-order Bessel beam is explained in terms of geometrical imaging and the interference of spherical waves emitted from the ring source.
Abstract: The nondiffractive propagation of the ideal zero-order Bessel beam is explained in terms of both the geometrical imaging and the interference of spherical waves emitted from the ring source. The source shift with respect to the focal plane of the imaging system is simply related to the divergence of the produced beam. The intensity distribution of the ideal Bessel beam in the focal region is examined for an aberration-free lens of finite aperture. Both the resolution gain at the focal plane and the position of the axial intensity maximum are investigated in dependence on the truncation of the input Bessel beam.

14 citations


Journal ArticleDOI
TL;DR: In this paper, the Fraunhofer diffraction pattern of a Bessel beam focused by an aperture lens was studied both theoretically and experimentally, and it was shown that the pattern can be determined essentially by two parameters, namely, the Fresnel number N a and truncation parameter β.

9 citations


Journal ArticleDOI
TL;DR: The Fraunhofer diffraction pattern of a narrow annular slit is recorded holographically to generate a beam that approximates a diffraction-free Bessel beam, and this beam is amplified by two-wave mixing in a photorefractive crystal.
Abstract: The Fraunhofer diffraction pattern of a narrow annular slit is recorded holographically to generate a beam that approximates a diffraction-free Bessel beam. The experimental limitations resulting from the annular-slit parameters such as the opening width and the transmission coefficient are discussed. The reconstructed Bessel beam is amplified by two-wave mixing in a photorefractive crystal. Thus the efficient conversion of a relatively large beam with a constant (or Gaussian) intensity distribution into a nondiffracting beam is achieved entirely by direct physical interference. We show that diffraction-free beams reproduced and amplified in this way can be applied to the measurement of the velocity of small objects by the use of the laser Doppler technique. In addition, the advantages of Bessel beams, especially in measuring the velocity of solids, are discussed.

7 citations


Journal ArticleDOI
TL;DR: In this article, the spontaneous emission of an atom inside a very high finesse Fabry-Perot micro-cavity of the type employed in semiconductor microlasers was shown to generate a non-diffracting Bessel beam outside the micro-Cavity.

5 citations


Patent
21 Jul 1995
TL;DR: In this paper, the authors proposed to miniaturize a Bessel beam scanning device by converting a light beam having a circular section into Bessel beams to scan an object, separating the scanning light beam from its reflected light, and converting this reflected light into an electric signal.
Abstract: PURPOSE:To miniaturize a Bessel beam scanning device by converting a light beam having a circular section into a Bessel beam to scan an object, separating the scanning light beam from its reflected light, and converting this reflected light into an electric signal. CONSTITUTION:An axicon lens 12 converts the laser beam L emitted from a beam emitting part 11 and having a circular section into a Bessel beam. A polygon mirror 14 momentarily changes the direction of the light sent from a flat and hollow mirror 13 which reflects the Bessel beam and then scans the surface of a scanning object 1 by the beam L. A hole 17 is formed at the center part of the mirrow 13 that serves as a separating means. Thus the light reflected from the object 1 is reflected again by the mirrow 14 and led to the back of the mirrow 13 through the hole 17. Then this reflected light is condensed on the surface of a photodetector 20 by a condenser lens 18. Therefore the separating means is just required to have such a size that can process the reflected light propagating through the hollow part of the circular light beam. Thus a beam scanning device can be miniaturized.

01 Jan 1995
TL;DR: In this article, the authors reported the application of the Bessel beam to Doppler velocity estimation in medical imaging, tissue characterization, and nondestructive evaluation of materials.
Abstract: Limited-diffraction beams have a large depth of field and could be applied to medical imaging, tissue character- ization, and nondestructive evaluation of materials. This paper reports the application of limited-diffraction beams, specifically, the Bessel beam, to Doppler velocity estimation. The Bessel beam has the advantage that velocity estimation is less subject to the depth of moving objects and the Doppler spectrum has distinct shoulders that increase the accuracy of velocity (both magnitude and Doppler angle) estimation in noisy environments. The shoulders of the Doppler spectrum might also help in solving the inverse problem, e.g., estimation of the velocity distribution in vessels.

Journal Article
01 Jan 1995-Optik
TL;DR: In this article, the authors show that the optical field in the shadow of an obstacle illuminated by a spherical wave is an approximate zero-order Bessel beam, which is verified by experimental demonstrations.