Spatiotemporal characterization of diffractive and non-diffractive light pulses
Date
2013-07-01
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Abstract
Ülilühikesed laseriimpulsid on väärtuslikud optilised tööriistad, nad on ühed lühimad sündmused, mida inimene suudab tekitada. Mitmel pool, kus neid kasutatakse – materjalide töötlemisel, andmesides, kirurgias, litograafias, mikro-osakestega manipuleerimisel, spektroskoopias, mittelineaarses optikas, jne – läheb vaja valgusimpulsse, mille intensiivsuse maksimum on fokusseeritud võimalikult väiksesse aja- ja ruumipiirkonda. Seda aga takistavad paratamatult nii difraktsioon kui ka dispersioon, mille mõju on seda tugevam, mida lühemad on impulsid. Tekitamaks sedavõrd lühikesi impulsse, mis koosnevad vaid mõnest üksikust valguse elektrivälja võnkest, on vaja, et nende valgusimpulsside spekter laiuks üle oktaavi nähtava valguse piirkonnas ja seetõttu on väga tundlikud dispersioonile. Eksisteerivad aga teatud lainevõrrandi lahendid, mille maksimum levib justkui difraktsioonist ja/või dispersioonist puutumatult. Neid lainepakette nimetataks mittedifrageeruvateks või lokaliseeritud laineteks. Lisaks tavapäraselt pikemale fookuse teravussügavusele on nendel valguskuulidel ka muid kasulikke ja mõneti intrigeerivaid omadusi. Nii võib impulsside maksimum levida valguse kiirusest erineva kiirusega – nii sub- kui ka superluminaalselt – või hoopiski kiirenduda vaakumis, ilma et talle mõjuks mõni jõud, või isetaastuda pärast takistusi. Käesolevas doktoritöös on uuritud erinevate ülilaiaribaliste mittedifrageeruvate lainete tekitamist ja levi nii teoreetiliselt kui ka eksperimentaalselt. Impulsslaineväljade mõõtmiseks on kasutatud ja täiustatud ruumilis-spektraalsel interferomeetrial põhinevat SEA TADPOLE mõõteseadet, mis võimaldab mõõta erinevaid lainevälju kujundavate optiliste süsteemide impulsskostet väga kõrge ajalise ja ruumilise lahutusega. Töös on käsitletud superluminaalselt levivaid Bessel-X impulsse, superluminaalseid kiirenduvaid kui ka aeglustuvaid Besseli impulsse, subluminaalseid Besseli lainepakette, difraktsiooni äärelaine impulsse ja kiirenduvaid Airy impulsse.
Ultrashort laser pulses are invaluable optical tools and one of the shortest events ever created by humankind. In many areas of science and technology in which they are used—(micro-)machining, communications, laser surgery, lithography, optical micro-manipulation, spectroscopy, nonlinear optics, etc.—light pulses with a intensity maximum focused into a small as possible region in space and time are required. However, the shorter the pulses the more difficult it is to achieve high localization of the pulse maximum because of the diffraction and dispersion. In order to obtain ultrashort pulses as short as a few optical cycles, a spectrum spanning over an octave in the visible region is required. Such pulses are strongly affected by the dispersion. However, there exists a certain set of solutions to the wave equation that have a maximum which propagates seemingly unaffected by the diffraction and/or dispersion. In addition to the prolonged depth of focus, those light bullets exhibit other useful and somewhat intriguing properties. For example, the pulse apex may propagate at a velocity different from the speed of light in vacuum (both subluminally and superluminally) or may even accelerate in the free space without action of any force and self-reconstruct behind obstacles. In this thesis, the formation and spatiotemporal propagation of ultrabroadband non-diffractive waves are studied both theoretically and experimentally. A variant of spatial spectral interferometry called SEA TADPOLE is used for characterization of the pulsed wavefields. This method is further developed to allow measuring the impulse responses of the optical systems with very high temporal and spatial resolutions. In this thesis, the following wavefields are studied: superluminally propagating Bessel-X pulses, superluminal accelerating and decelerating Bessel pulses, subluminal pulsed Bessel beams, boundary diffraction wave pulses, and accelerating Airy pulses.
Ultrashort laser pulses are invaluable optical tools and one of the shortest events ever created by humankind. In many areas of science and technology in which they are used—(micro-)machining, communications, laser surgery, lithography, optical micro-manipulation, spectroscopy, nonlinear optics, etc.—light pulses with a intensity maximum focused into a small as possible region in space and time are required. However, the shorter the pulses the more difficult it is to achieve high localization of the pulse maximum because of the diffraction and dispersion. In order to obtain ultrashort pulses as short as a few optical cycles, a spectrum spanning over an octave in the visible region is required. Such pulses are strongly affected by the dispersion. However, there exists a certain set of solutions to the wave equation that have a maximum which propagates seemingly unaffected by the diffraction and/or dispersion. In addition to the prolonged depth of focus, those light bullets exhibit other useful and somewhat intriguing properties. For example, the pulse apex may propagate at a velocity different from the speed of light in vacuum (both subluminally and superluminally) or may even accelerate in the free space without action of any force and self-reconstruct behind obstacles. In this thesis, the formation and spatiotemporal propagation of ultrabroadband non-diffractive waves are studied both theoretically and experimentally. A variant of spatial spectral interferometry called SEA TADPOLE is used for characterization of the pulsed wavefields. This method is further developed to allow measuring the impulse responses of the optical systems with very high temporal and spatial resolutions. In this thesis, the following wavefields are studied: superluminally propagating Bessel-X pulses, superluminal accelerating and decelerating Bessel pulses, subluminal pulsed Bessel beams, boundary diffraction wave pulses, and accelerating Airy pulses.
Description
Väitekirja elektrooniline versioon ei sisadla publikatsioone.
Keywords
valgusimpulsid, difraktsioon, lokaliseeritud lained, light pulses, diffraction, localized waves, valgusimpulsid, difraktsioon, lokaliseeritud lained, light pulses, diffraction, lokalized waves