The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Propagation-Invariant Waves in Acoustic, Optical, and Radio-Wave Fields

Janne Salo

Dissertation for the degree of Doctor of Technology to be presented with due permission for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 18th of January, 2003, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-6293-2)   [4288 KB]
Dissertation is also available in print (ISBN 951-22-6292-4)

Abstract

The physical phenomena considered in this thesis are associated with electromagnetic and acoustic waves that propagate in free space or in homogeneous media without diffraction. The concept of rotationally periodic wave propagation is introduced in the first journal article included in the thesis and it is subsequently used to analyse waves that avoid diffractive deterioration by repeatedly returning to their initial shape, possibly rotated around the optical axis. Such waves constitute an essential generalisation to several kinds of acoustic and optical beams, such as Bessel beams and self-imaging waves. Additionally, rotationally periodic waves also comprise pulsed wave forms that may propagate with a velocity independent of the speed of light (or sound) in the particular medium. This does not, however, lead to any violation of relativistic principles, as the pulse is continuously reformed by signals that have synchronously been transmitted from different locations. The individual articles in this dissertation mainly concentrate on the properties of pulsed waves.

Two specific issues are also treated in the dissertation: (i) Acoustic nondiffracting waves are considered in anisotropic, piezoelectric crystals. Their propagation may differ drastically from that of ordinary (plane) waves, and nondiffracting waves may also include effects such as internal diffraction, phonon focusing, and caustics. Possible transducer structures are considered for the generation of nondiffracting waves into bulk crystals. (ii) Generation of Bessel beams have also been verified with the use of radio holograms in the millimetre-wave regime. Hologram techniques developed have allowed the investigation of various other wave forms and their propagation, such as tapered plane waves and radio-wave vortices. A back-propagation algorithm has also been introduced for designing holograms that form wave fields of an arbitrary design.

This thesis consists of an overview and of the following 8 publications:

  1. J. Salo and M. M. Salomaa: Diffraction-free pulses at arbitrary speeds, Journal of Optics A, September 2001, vol. 3, no. 5, pp. 366-373. © 2001 IOP Publishing Ltd. By permission.
  2. J. Salo and M. M. Salomaa: Subsonic nondiffracting waves, Acoustics Research Letters Online, January 2001, vol. 2, issue 1, pp. 31-36.
  3. J. Salo, J. Fagerholm, A. T. Friberg, and M. M. Salomaa: Unified Description of Nondiffracting X and Y Waves, Physical Review E, September 2000, vol. 62, no. 3, pp. 4261-4275. © 2000 American Physical Society. By permission.
  4. J. Salo, A. T. Friberg, and M. M. Salomaa: Orthogonal X waves, Journal of Physics A, November 2001, vol. 34, no. 43, pp. 9319-9327. © 2001 IOP Publishing Ltd. By permission.
  5. J. Salo, J. Fagerholm, A. T. Friberg, and M. M. Salomaa: Nondiffracting Bulk-Acoustic X waves in Crystals, Physical Review Letters, August 1999, vol. 83, no. 6, pp. 1171-1174. © 1999 American Physical Society. By permission.
  6. J. Salo and M. M. Salomaa: Nondiffracting Waves in Anisotropic Media, Report TKK-F-A817, 2002, submitted for publication. © 2002 by authors and American Physical Society. By permission.
  7. J. Salo, J. Meltaus, E. Noponen, J. Westerholm, M. M. Salomaa, A. Lönnqvist, J. Säily, J. Häkli, J. Ala-Laurinaho, and A. V. Räisänen: Millimetre-wave Bessel beams using computer holograms, Electronics Letters, June 2001, vol. 37, issue 13, pp. 834-835. © 2001 IEE. By permission.
  8. J. Salo, J. Meltaus, E. Noponen, M. M. Salomaa, A. Lönnqvist, T. Koskinen, V. Viikari, J. Säily, J. Häkli, J. Ala-Laurinaho, J. Mallat and A. V. Räisänen: Holograms for shaping radio-wave fields, Journal of Optics A, September 2002, vol. 4, no. 5, pp. S161-S167. © 2002 IOP Publishing Ltd. By permission.

Keywords: nondiffracting waves, Bessel beams, X waves, bulk-acoustic waves, radio holograms

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© 2003 Helsinki University of Technology

Last update 2011-05-26