11 research outputs found
Syntheses, crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2, 2'-bipyridine and TCNQ
From the aqueous-methanolic systems Ni(NO3)2 – LiTCNQ – 5, 5'-dmbpy and Ni(NO3)2 – LiTCNQ – 4, 4'-dmbpy three novel complexes [Ni(5, 5'-dmbpy)3](TCNQ)2 (1), [Ni(4, 4'-dmbpy)3](TCNQ)2 (2) and [Ni(4, 4'-dmbpy)3]2(TCNQ-TCNQ)(TCNQ)2·0.60H2O (3), were isolated in single crystal form. The new compounds were identified using chemical analyses and IR spectroscopy. Single crystal studies of all samples corroborated their compositions and have shown that their ionic structures contain the complex cations [Ni(5, 5'-dmbpy)]2+ (1) or [Ni(4, 4'-dmbpy)]2+ (2 and 3). The anionic parts of the respective crystal structures 1–3 are formed by TCNQ·- anion-radicals and in 3 also by a s-dimerized dianion (TCNQ-TCNQ)2- with a C-C distance of 1.663(5) Å. The supramolecular structures are governed by weak hydrogen bonding interactions. The variable-temperature (2–300 K) magnetic studies of 1 and 3 confirmed the presence of magnetically active Ni(II) atoms with S = 1 and TCNQ·- anion-radicals with S = 1/2 while the (TCNQ-TCNQ)2- dianion is magnetically silent. The magnetic behavior was described by a complex magnetic model assuming strong antiferromagnetic interactions between some TCNQ·- anion-radicals
Optimal Concentration of Light in Turbid Materials
In turbid materials it is impossible to concentrate light into a focus with
conventional optics. Recently it has been shown that the intensity on a dyed
probe inside a turbid material can be enhanced by spatially shaping the wave
front of light before it enters a turbid medium. Here we show that this
enhancement is due to concentration of light energy to a spot much smaller than
a wavelength. We focus light on a dyed probe sphere that is hidden under an
opaque layer. The light is optimally concentrated to a focus which does not
exceed the smallest focal area physically possible by more than 68%. A
comparison between the intensity enhancements of both the emission and
excitation light supports the conclusion of optimal light concentration.Comment: We corrected an ambiguous description of the focus size in our
abstract and text pointed out by an anonymous refere
Tunable beam shaping with a phased array acousto-optic modulator
We demonstrate the generation of Bessel beams using an acousto-optic array based on a liquid filled cavity surrounded by a cylindrical multi-element ultrasound transducer array. Conversion of a Gaussian laser mode into a Bessel beam with tunable order and position is shown. Also higher-order Bessel beams up to the fourth order are successfully generated with experimental results very closely matching simulations
Controlling waves in space and time for imaging and focusing in complex media
In complex media such as white paint and biological tissue, light encounters nanoscale refractive-index inhomogeneities that cause multiple scattering. Such scattering is usually seen as an impediment to focusing and imaging. However, scientists have recently used strongly scattering materials to focus, shape and compress waves by controlling the many degrees of freedom in the incident waves. This was first demonstrated in the acoustic and microwave domains using time reversal, and is now being performed in the optical realm using spatial light modulators to address the many thousands of spatial degrees of freedom of light. This approach is being used to investigate phenomena such as optical super-resolution and the time reversal of light, thus opening many new avenues for imaging and focusing in turbid medi
Propagation characteristics of Airy beams:dependence upon spatial coherence and wavelength
We generate a broadband "white light" Airy beam and characterize the dependence of the beam properties on wavelength. Experimental results are presented showing that the beam's deflection coefficient and its characteristic length are wavelength dependent. In contrast the aperture coefficient is not wavelength dependent. However, this coefficient depends on the spatial coherence of the beam. We model this behaviour theoretically by extending the Gaussian-Schell model to describe the effect of spatial coherence on the propagation of Airy beams. The experimental results are compared to the model and good agreement is observed. (C) 2009 Optical Society of America</p