1,721,043 research outputs found
Unified space–time description of pulsed twin beams
No full textThis work provides a mathematical derivation of a quasi-stationary (QS) model for multimode parametric down-conversion (PDC), which was presented in Gatti et al. (Gatti et al., Sci. Rep. 13, 16786) with heuristic arguments. Here, the model is derived from the 3D + 1 propagation equation of the quantum fields in a nonlinear crystal, and its approximations are discussed thoroughly. Thanks to its relative simplicity, and to the fact that it is valid in any gain regime, both at a quantum and classical level, it allows a unified description of disparate experimental observations conducted over the last 20 years, often described in the past by means of limited ad hoc models.This article is part of the theme issue 'The quantum theory of light'
Modeling the space-time correlation of pulsed twin beams
Full text linkEntangled twin-beams generated by parametric down-conversion are among the favorite sources for imaging-oriented applications, due their multimodal nature in space and time. However, a satisfactory theoretical description is still lacking. In this work we propose a semi-analytic model which aims to bridge the gap between time-consuming numerical simulations and the unrealistic plane-wave pump theory. The model is used to study the quantum correlation and the coherence in the angle-frequency domain of the parametric emission, and demonstrates a g1 / 2 growth of their size as the gain g increases, with a corresponding contraction of the space-time distribution. These predictions are systematically compared with the results of stochastic numerical simulations, performed in the Wigner representation, of the full model equations: an excellent agreement is shown even for parameters well outside the expected limit of validity of the model
Engineering multipartite coupling in doubly pumped parametric down-conversion processes
No full textWe investigate the quantum state generated by optical parametric down-conversion in a χ(2) medium driven by two noncollinear light modes. The analysis shows the emergence of multimode, namely, three- or four-mode, entangled states in a subset of the spatiotemporal modes generated by the process. These appear as bright spots against the background fluorescence, providing an interesting analogy with the phenomenology recently observed in two-dimensional nonlinear photonic crystals. We study two realistic setups. (1) Noncritical phase matching in a periodically poled lithium tantalate slab, characterized by a three-mode entangled state. (2) A type I setup in a beta-barium borate crystal, where the spatial walk-off between the two pumps can be exploited to make a transition to a four-mode entangled state. In both cases, we show that the properties of the state can be controlled by modulating the relative intensity of two pump waves, making the device a versatile tool for quantum state engineering
Etching and drilling of through-holes in thin glass by means of picosecond Bessel beams
No full textIn this paper, we present a laser etching and drilling technique for thin glass materials based on the use of finite-energy pulsed Bessel beams orthogonally impinging on the sample surface. Thanks to the elongated focal zone of the quasinon-diffractive beam, the laser processing can be performed without scanning the beam position along the thickness of the transparent material sample, but simply moving the sample in the plane orthogonal to the beam. We first present the results of single-shot glass microfabrication performed to identify the optimal laser parameters needed for an efficient internal material ablation. We then describe the micromachining technique used for etching the dielectric material at glass-air interfaces and for generating, without chemical etching, through-holes in thin glasses
Hot-spots and gain enhancement in a doubly pumped parametric down-conversion process
No full textWe experimentally investigate the parametric down-conversion process in a nonlinear bulk crystal, driven by two non-collinear pump modes. The experiment shows the emergence of bright hot-spots in modes shared by the two pumps, similar to the phenomenology recently observed in 2D nonlinear photonic crystals. By exploiting the spatial walk-off between the two extraordinary pump modes, we have been able to recreate a peculiar resonance condition, reported by a local enhancement of the parametric gain, which corresponds to a transition from a three-mode to a four-mode coupling. From a quantum point of view, this opens the way to the generation of multimode entangled states of light, such as tripartite or quadripartite states, in simple bulk nonlinear sources
Engineering a multimode coupling in doubly pumped parametric down-conversion: Hot-spots and gain enhancement
No full textEngineering a multimode coupling in doubly pumped parametric down-conversion: hot-spots and gain enhancement
No full textWe present a parametric down-conversion (PDC) process in a nonlinear ß-barium borate (BBO) crystal, driven by two non-collinear pump beams, obtained from a Mach-Zehnder type interferometer. We show the possibility to reproduce in a bulk crystal a phenomenology analogue to that previously observed in a PDC process inside a χ 2 2D nonlinear photonic crystal (NPC) [1] , [2]. Each pump mode generates a family of cones of parametric radiation collinear with its direction. The intersection zones define an ensemble of modes shared by the two pumps, indistinguishably populated by the photons generated by pump 1 or by pump 2. As in [1] , in the high-gain regime these two possibilities sum up coherently, leading to a local increase of the parametric gain. Indeed we observe an unusual far-field distribution of the down-converted light, in the form of three bright branches of hot-spots against a more diffuse background [3]
Ultrafast Laser Micromachining in Crystals Using Bessel Beams
No full textUltrafast laser micromachining in bulk diamond and sapphire has been realized using finite energy Bessel-Gauss beams. The hardness of diamond and crack formation in sapphire have been addressed and tackled using different optimization techniques
Nonlinear electromagnetic X waves
No full textLocalized wave packet (LWP) exist with normal group-velocity dispersion (GVD) in the form of nonlinear X waves (NLXWs) or X-wave solitons. To date X-shaped waves are known only in the context of linear acoutic or electromagnetic propagation, and constitute the polichromatic generalization of diffraction-free Besel beams. They are observed in both acoustical and optical experiment, both requiring input beam-shaping technique. It is found that propagation-invariant NLXWs that can be naturally regarded as the continuation of linear X waves into the nonlinear regime
Spatial Entanglement in Optical Parametric Down-Conversion
No full textSpatial quantum correlation in parametric down-conversion (PDC) are investigated with a theoretical model which takes into account the broadband character of the PDC emission. Recent experimental results on the detection of local sub-shot noise correlation in the PDC far-field are presented
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