Geometrooptical Mechanism of Wave-Front Reconstruction
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Geometrooptical Mechanism of Wave-Front Reconstruction A. M. Smolovich* Kotel’nikov Institute of Radioengineering and Electronics, Russian Academy of Sciences, Moscow, 125009 Russia *e-mail: [email protected] Received December 10, 2019; revised April 27, 2020; accepted May 4, 2020
Abstract—Mechanism of wave-front reconstruction based on geometrooptical reflection of reconstructing radiation from the surfaces of constant phase difference between the object and the reference waves used for recording an interference pattern in a recording medium is analyzed. The mechanism is compared with the holographic one. Experimental studies in a bulk recording medium and in a planar optical waveguide are carried out. Several types of achromatic optical elements are proposed. An acousto-optic focusing element capable of inducing strong local stress inside a medium in a region of special shape is discussed. The possibility of reconstruction of temporal structure of light pulses is demonstrated. Keywords: volume hologram, kinoform, ultrashort pulse, temporal pulse structure DOI: 10.1134/S0030400X20090209
INTRODUCTION The mechanism of wave-front reconstruction by a hologram is based on diffraction of reconstruction radiation from a quasi-periodic structure recorded in the hologram. It is in the local period of this structure that information on the wave-front of the object wave is contained. This mechanism works in both thin and volume holograms recorded in both converging and counterpropagating beams. According to another mechanism proposed in [1], the wave front of the object wave can be reconstructed due to geometrooptical (GO) reflection of reconstruction radiation from a single surface of the holographic-pattern maximum that works similar to a mirror of variable curvature. It is this local curvature that contains information on the object wave front. In contrast to holographic reconstruction, reconstruction radiation experiences no diffraction from a periodic interference structure under GO reconstruction. This makes the process of reconstruction achromatic, i.e., allows reconstructing an unperturbed wave front by light with a wavelength different from that used for recording [2, 3]. The GO mechanism of wave-front reconstruction was proposed for holography. However, it is substantially different from the holographic one and is of interest by itself. In the present work, the GO mechanism of wavefront reconstruction is compared with the holographic one. We explain why this mechanism does not work in ordinary holograms, including the Denisiuk-type holograms. Recording in a bulk recording medium by means of ultrashort laser pulses is used for the GO wave-front reconstruction. In another version, a twodimensional analog of the effect is obtained in a planar
optical waveguide. Several types of achromatic optical and acousto-optic elements and system are proposed. In addition, reconstruction of temporal structure of ultrashort light pulses is discussed. GO RECONSTRUCTION PRINCIPLES Let object wave AO(r)exp[ikLO(r)] and
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