Incoherent Light Beams Research Articles

Experimental generation of polarization entanglement from spontaneous parametric down-conversion pumped by spatiotemporally highly incoherent light

The authors experimentally demonstrate the generation of polarization entanglement through spontaneous parametric down-conversion pumped by a spatiotemporally highly incoherent light beam. However, polarization entanglement from the spatiotemporally incoherent pump is susceptible to degradation. Theoretical analysis shows that the degradation stems from the coupling between the spatiotemporal and polarization degrees of freedom, which is introduced by the birefringence and dispersion of the nonlinear crystal.

Ultrathin picoscale white light interferometer

White light interferometry is a well established technique with diverse precision applications, however, the conventional interferometers such as Michelson, Mach-Zehnder or Linnik are large in size, demand tedious alignment for obtaining white light fringes, require noise-isolation techniques to achieve sub-nanometric stability and importantly, exhibit unbalanced dispersion causing uncertainty in absolute zero delay reference. Here, we demonstrate an ultrathin white light interferometer enabling picometer resolution by exploiting the wavefront division of a broadband incoherent light beam after transmission through a pair of micrometer thin identical glass plates. Spatial overlap between the two diffracted split wavefronts readily produce high-contrast and stable white light fringes, with unambiguous reference to absolute zero path-delay position. The colored fringes evolve when one of the ultrathin plates is rotated to tune the interferometer with picometric resolution over tens of μm range. Our theoretical analysis validates formation of fringes and highlights self-calibration of the interferometer for picoscale measurements. We demonstrate measurement of coherence length of several broadband incoherent sources as small as a few micrometer with picoscale resolution. Furthermore, we propose a versatile double-pass configuration using the ultrathin interferometer enabling a sample cavity for additional applications in probing dynamical properties of matter.

Scalar and vector supermode solitons owing to competing nonlocal nonlinearities.

We investigate scalar and vector multi-hump spatial solitons resulting from competing Kerr-like nonlinear responses excited in a nonlocal medium by either one or two (mutually incoherent) light beams. Two-color vector supermode solitons are more amenable to control but exhibit an intriguing form of spontaneous symmetry breaking in propagation.

Thermal behavior analysis of interconnect structures of Si semiconductor devices using the temperature dependent reflectance of an incoherent light beam

The amount of light reflected from the light-irradiated device varies depending on the surface temperature at that location. In this paper, we show that, by using an incoherent light beam with a noninvasive wavelength, it is possible to measure the temperature change of the interconnect structure with a size of µm order Si semiconductor devices. As a method of measuring the temperature change, lock-in thermography has been reported. However, it is difficult to measure the temperature change of the fine structure. The spatial resolution of this method is about 10 µm. Here, by using a noninvasive incoherent light beam, the spatial resolution of µm order is achieved. We applied this method to a 4-µm-wide interconnect test element group (TEG) device with a passivation film to observe the temperature change of the interconnect structure.

An optochemically organized nonlinear waveguide lattice with primitive cubic symmetry

We describe the first example of a primitive cubic lattice assembled spontaneously from three mutually orthogonal and intersecting arrays of cylindrical, multimode waveguides. The lattice is generated in a single, room-temperature step with separate (mutually incoherent) incandescent light bulbs. To demonstrate its potential as a nonlinear photonic lattice, we generated a self-trapped lattice beam of incoherent white light. These two findings open entirely new experimental opportunities to study the behavior of spatially and temporally incoherent, polychromatic lattice solitons in 3-D Bravais lattices.

X-shape two-dimensional photovoltaic dark spatial solitons with fully incoherent white light

We report on the first successful experimental observation of X-shape two-dimensional photovoltaic dark spatial solitons in an anisotropic LiNbO3: Fe crystal with fully incoherent white light beams under odd or even initial conditions. This kind of solitons results from the photovoltaic self-defocusing nonlinearity, which depends on the orientation of the principal axes of the crystal.

Nonlinear interaction and reflection of incoherent light beams

The interaction dynamics between two incoherent light beams in a medium with thermal nonlin-earity is studied both experimentally and theoretically. It is shown that in the mode of a nonlinear reflection the transformation of a spatial structure of a weak signal beam can be theoretically described in the framework of a spatially distributed model for a nonlinear change in the refractive index of the medium.

An experimental study of the interactions of self-trapped white light beams in a photopolymer

Interactions of two parallel-propagating and mutually incoherent white light beams were examined in a photopolymerizable organosiloxane. The beams fused when separated by a distance corresponding to the width of each beam but at separation distances⪢beam width, formed two self-trapped beams that repelled each other. At separation distances<beam width, they suffered filamentation but ultimately fused into a single self-trapped beam.

Mathematical modeling of ceramics metallization technology

Metallization of ceramics by an incoherent light beam has been simulated. A ceramic substrate with a metal-containing paste deposited on its surface is considered as an infinite planar two-layer medium. The Stefan problem with phase transitions is formulated and solved by the quasi-stationary Leibenzon method.

Spontaneous Pattern Formation Due to Modulation Instability of Incoherent White Light in a Photopolymerizable Medium

Spontaneous pattern formation due to modulation instability was observed in a broad uniform beam of incoherent white light propagating in an optically isotropic, photopolymerizable organosiloxane. Pattern formation originates from intensity-dependent refractive index changes due to polymerization, which cause competition between the natural diffraction (broadening) and self-induced refraction of the beam. Under these nonlinear conditions, weak intensity modulations in the beam, noise, that would be negligible under linear conditions are amplified. The amplified patterns become unstable over time and spontaneously divide into individual self-trapped filaments of white light of essentially identical diameter (76 +/- 3 microm), which propagate through the medium without diffracting. In the case of noise with a weak 1-D periodic modulation, for example, the uniform beam transformed into a 1-D periodic array of self-trapped lamellae, which in turn formed a 2-D array of self-trapped cylindrical filaments. Although the rate of pattern formation varied inversely with optical power (measured from 8.4 to 59.8 mW), the uniform beam always split into discrete filaments, demonstrating that they are the most stable form of light propagation under the nonlinear conditions created by polymerization. Each filament of light retained the spectral composition and incoherence of white light, which showed that the entire polychromatic, incoherent and unpolarized wavepacket collectively participated in pattern formation. These findings are consistent with recent theoretical models of nonlinear white light propagation and with experimental observations of pattern formation in coherent and partially coherent light. Because refractive index changes due to polymerization are permanent, pattern formation imparts microstructure to the organosiloxane. Optical micrographs revealed that, after pattern formation, the initially homogeneous medium consisted entirely of a closely packed array of narrow channel waveguides induced by self-trapped filaments.

Coherence enhancement of spatially incoherent light beams through soliton interaction in logarithmically saturable nonlinear media

We investigate numerically the interaction between incoherent spatial solitons in a nonlinear medium with logarithmic saturable nonlinearity base on the coherent density approach. Numerical simulations show that both the intensity and the spatial coherence can be greatly enhanced through soliton interaction. At the same time, we show that the soliton interaction can be controlled by the total partial incoherence, which can not only suppress the coherent soliton interaction such as attractive, repulsive or exchange energy, but also induce weak attractive due to incoherent superposition of two incoherent solitons.

Two-Dimensional Photovoltaic Dark Spatial Solitons ofPartially Spatially Incoherent Light

We report a successful experimental observation of self-trappingof two-dimensional photovoltaic dark solitons in an anisotropic crystalwith partially spatially incoherent light beams. This kind of solitonsresults from the bulk photovoltaic effect, which depends on thedirection of propagation of the optical beam and on the orientation ofthe intensity gradient, with respect to the principal axes of the crystal.

Incoherent multi-gap optical solitons in nonlinear photonic lattices

We demonstrate numerically that partially incoherent light can be trapped in the spectral band gaps of a photonic lattice, creating partially incoherent multi-component spatial optical solitons in a self-defocusing nonlinear periodic medium. We find numerically such incoherent multi-gap optical solitons and discuss how to generate them in experiment by interfering incoherent light beams at the input of a nonlinear periodic medium.

Incoherent vector vortex-mode solitons in self-focusing nonlinear media

We suggest a novel type of composite spatial optical soliton created by a coherent vortex beam guiding a partially incoherent light beam in a self-focusing nonlinear medium. We show that the incoherence of the guided mode may enhance, rather than suppress, the vortex azimuthal instability, and we also demonstrate strong destabilization of dipole-mode solitons by partially incoherent light.

Interference comparative analysis of the shape of wavefronts of incoherent light beams

A technique of interference comparative analysis of the shape of wavefronts that can be applied to incoherent light beams is proposed. The difference in the shape of the wavefronts of the incoherent light beams under study is visualized by using the moire pattern appearing upon superposition in real time of the lateralshear interferograms or their photographs. The possibility of producing the interference pattern that visualizes the difference in the shape of the wavefronts of incoherent beams with an enhanced measurement sensitivity is shown. The results of experimental testing of this technique in visualization of the difference between the shapes of the wavefronts of two light beams emitted by different lasers are presented.

Coherent addition of spatially incoherent light beams

We report on efficient coherent addition of spatially incoherent multimode laser beam distributions. Such addition is demonstrated within a multi-channel laser resonator configuration, obtaining more than 90% combining efficiency while preserving the good beam quality. We explain the rather surprising physical phenomenon of coherently adding spatially incoherent light by self-phase-locking of each of the modal components within the multimode beams. Our approach could lead to significantly higher output powers concomitantly with good beam qualities than were hitherto possible in laser systems.

Experiments on partially coherent photorefractive solitons

We provide an overview of experimental studies on partially coherent spatial solitons in photorefractive materials, including the first experimental demonstration of bright and dark incoherent solitons, incoherent vortex solitons, Y-junction dark solitons and anti-dark solitons, and pixel-like incoherent soliton arrays. These solitons are created with partially spatially incoherent light beams by using the non-instantaneous photorefractive screening nonlinearity. Experimental results on waveguides induced by incoherent solitons are also presented and their potential applications for soliton-driven photonics are discussed. In particular, these experiments introduce the possibility of controlling high-power laser beams with low-power incoherent light sources in waveguide arrays as well as in planar, circular and beam-splitting waveguides optically induced in bulk photorefractive materials.

Cavity pattern formation with incoherent light.

We study the propagation dynamics of an incoherent light beam circulating in a passive cavity containing noninstantaneous nonlinear media. It is shown that patterns form in this cavity in spite of spatial incoherence of the light. We show that the pattern formation process is always associated with two consecutive thresholds. The first (instability) threshold is unaffected by the cavity boundary conditions, whereas the second threshold is induced by the feedback through the interplay of nonlinear gain and cavity loss.

Spatial soliton pixels from partially incoherent light

We report what is to our knowledge the first observation of pixellike spatial solitons from partially spatially incoherent light. We created an array of as many as 32x32 soliton pixels by launching a spatially modulated incoherent light beam into a noninstantaneous self-focusing photorefraction medium. These solitons were stable and robust, forming a steady-state two-dimensional waveguide array in which optical coupling and control of local waveguide channels could be realized.

Anamorphic, adiabatic beam shaping of diffuse light using a tapered reflective tube

A concept of anamorphic, adiabatic shaping of diffuse, spatially incoherent light beams is presented. The beam shaping is done with a long tube with reflective walls. The concept is numerically investigated and experimentally illustrated for the specific example of one-dimensional diffuse-beam collimation. Depending on the exact geometry of the tube, two cases are investigated: (1) when the one-dimensional brightness is conserved in both transverse directions; (2) when there is coupling between the two transverse directions in terms of brightness, which leads to an output beam with a much more uniform angular distribution.