1,721,001 research outputs found
Quantum electromagnetic X waves
No full textWe provide a quantum description of X waves by considering two different kinds of quantum states of the electromagnetic field whose field amplitude expectation value coincides with a propagation-invariant solution of the Maxwell equation. The difference between the two states is of pure quantum mechanical origin since they are internally entangled and disentangled and can be generated by different linear or nonlinear processes. (c) 2007 Optical Society of America
Spontaneous photonic lattices and nonlinear waves in nanodisordered ferroelectrics
Full text linkIn this Thesis we deal with nanodisordered ferroelectric perovskite crystals. These material have been demonstrated to be a good test-bed to study nonlinear optical phenomena due to their strong optical properties. In fact, their embedded disorder enhances their response at the phase transition and makes these materials suitable to sustain solitons and rogue waves also with low optical power.
We first use self-focusing at the paraelectric phase to study nonlinear wave propagation. Our experiments are conceived to investigate the evolution of structured waves in time and in space. We make three beams to interfere to optically observe the Fermi-Pasta-Ulam-Tsingou recurrence. We experimentally verify its analytic solution provided by Grinevich-Santini that allows us to predict the exact position of each recurrence. Moreover, we demonstrate that the periodic behavior is lost if the system ceases to be integrable. We study the appropriate interference pattern in the form of nondiffractive Bessel beams to investigate what happens to such waves in a self-focusing medium. We identify two regimes: a Bessel beam selftrapping and a breathing soliton. Furthermore, we demonstrate the feasibility of Bessel beam writing to build a scalable and rewritable network of waveguides inside the bulk ferroelectric medium.
We also studied the unique properties of the ferroelectric phase. The most evident outcome is the so-called super-crystal that is a spontaneous photonic 3D lattice that emerges from the interplay between material order and disorder. We study the super-crystal in different ways and we recover the periodic behavior for linear and nonlinear propagation. In detail we report a periodic pattern for birefringence and second harmonic generation. The main result is that we have observed the highest value of the refractive index reported in literature for visible light and we have connected the effect to the super-crystal. This material allows, in theory, to transmit light without any information loss, that is without diffraction and chromatic dispersion.
The physics of diffraction is also investigated with the introduction of an innovative method to achieve super-resolution. We exploit a confocal microscope and a remote knifeedge technique. This allows us to directly study the role of evanescent waves in superresolution imaging forming, i.e. they are filtered out as the super-resolved image approaches to the diffraction-limited one. Experiments here are performed with a terahertz frequency, λ ∼ 1.00 mm, to easily accede the near field and capture the information carried by the evanescent wave
Universal space-time properties of X waves
No full textExact results concerning spatiotemporal universal features of three-dimensional propagation-invariant solutions of the wave equation (X waves) are derived. In particular, relations connecting the pulse transverse extension to the longitudinal coordinate and the propagation velocity to the spatial field distribution are obtained for the whole class of X waves. (C) 2004 Optical Society of America
Approach to space-charge field description in photorefractive crystals
No full textRecent analytical results in the frame of photorefractive spatial-soliton propagation are exploited to derive a novel scheme for the investigation of space-charge field formation in photorefractive crystals. The procedure is specialized to describe a two-wave mixing configuration. To test our predictions, we have performed an experiment in a sample of BaTiO3. © 1998 Optical Society of America
Counterpropagating spatial Kerr soliton in reflection gratings
No full textWe analytically predict the existence of both spatial bright and dark counterpropagating solitons in a reflection grating in the presence of the Kerr nonlinearity. The basic trapping mechanism consists of a twofold balance where diffraction is compensated by self-focusing and reflection is altered by the nonlinear-induced interferometric grating. We find that, whenever the spectral soliton profile lies within the grating stop band, bright and dark solitons exist only if the mutual phase of the counterpropagating solitons is pi or 0, respectively. (c) 2006 Optical Society of America
Anisotropic charge displacement supporting isolated photorefractive optical needles
No full textStrong asymmetry in the charge distribution supporting a single noninteracting spatial needle soliton in a paraelectric photorefractive is directly observed by means of electroholographic readout. Whereas in trapping conditions a quasi-circular wave is supported, the underlying double-dipolar structure can be made to support two distinct propagation modes. © 2001 Optical Society of America
Transverse and soliton instabilities due to counterpropagation through a reflection grating in Kerr media
No full textTransverse instabilities are shown to accompany counterpropagation of optical beams through reflection gratings in Kerr media. The instability threshold of continuous waves is analytically derived, and it is shown that the presence of the grating broadens and narrows the stability region of plane waves in focusing and defocusing media, respectively. Furthermore, counterpropagating soliton stability is numerically investigated and compared with the transverse modulation instability analysis, revealing an underlying physical link. (c) 2006 Optical Society of America
Photorefractive solitons embedded in gratings in centrosymmetric crystals
No full textWe investigate (1 + 1D) spatial optical solitons embedded in a fixed-volume grating in centrosymmetric photorefractive crystals. We numerically identify a two-parameter soliton family and deduce both its existence surface and soliton profiles. For shallow gratings, the soliton Fourier spectrum exhibits three lobes located at the reciprocal lattice points -K, 0, and K. Soliton trapping is a consequence of both the self-induced nonlinear waveguide and the grating reflectivity, which prevents the breakaway of the lateral components. To provide a preliminary evaluation of soliton stability, we also investigate the propagation of slightly perturbed soliton profiles. (c) 2006 Optical Society of Americ
Miniaturized bending-free solitons by restoring symmetry in periodically biased photorefractives
No full textWe consider optical propagation through a centrosymmetric photorefractive crystal with the externally applied bias voltage modulated along the optical propagation direction. We analytically prove that, if the modulation scale is smaller than the optical diffraction length, the resulting effective nonlinearity has an even parity in the transverse plane for an even-symmetric intensity profile and supports bending-free solitons down to few-micrometer beam widths. Numerical integration of the full photorefractive model for light-matter interaction allows us to confirm the feasibility of these miniaturized solitons and, for longer modulation periods, to investigate the excitation of self-trapped wiggling optical beams. (c) 2008 Optical Society of Americ
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