Pitch tuning induced by optical torque in heliconical cholesteric liquid crystals – PHYSICAL REVIEW RESEARCH vol.1, 033215 (2019)

G. Nava, F. Ciciulla, O. S. Iadlovska , O.D. Lavrentovich F. Simoni  & L. Lucchetti

Heliconical cholesteric liquid crystals are expected to be more sensitive to torque induced by light field since their structure allows both bend and twist in molecular orientations, differently from the conventional cholesterics in which only twist deformation is involved, requiring much higher fields. We report here a demonstration of tuning the helical pitch in heliconical cholesterics induced by an optical torque. Experimental observations are in agreement with expectations of the classical theory extended to include the effect of the optical field. A dual control of the helical pitch is achieved including both the low-frequency electric field applied along the helix axis and the optical field orthogonal to it.

Optofluidic platform using liquid crystals in lithium niobite microchannel – SCIENTIFIC REPORTS vol.9, 1062 (2019)

Silvio Bonfadini, Fabrizio Ciciulla, Luigino Criante, Annamaria Zaltron, Francesco Simoni, Victor Reshetnyak  & Liana Lucchetti

We demonstrate the all optical control of the molecular orientation of nematic liquid crystals confined in microfluidic channels engraved in lithium niobate. Microchannels are obtained by a novel approach based on femtosecond pulse laser micromachining carried on in controlled atmosphere. The combined effect of photovoltaic and pyroelectric fields generated by light in lithium niobate crystals on the liquid crystal orientation, is reported for the first time. The total space charge field and its dependence on the incident light intensity can be controlled by changing the direction of pump light propagation through the microfluidic chip. The results reported in this manuscript demonstrate that liquid crystals and lithium niobate can efficiently be combined in microfluidic configuration, in order to push forward anovel class of optofluidic devices.

Light-actuated contactless macro motors exploiting Bénard–Marangoni convection – OPTICS EXPRESS vol.27, 13574 (2019)

Daniele Lucchetta, Riccardo Castagna, Francesco Simoni

Near-infrared light is commonly used to move small objects floating on water by exploiting the Bénard-Marangoni convection. This is because infrared light is absorbed well by water and the induced thermal gradients are responsible for the objects’ motion. However, visible light was recently used to move macroscopic objects on the free liquid surfaces. In this work, we show the use of visible light to rotate symmetric millimeter-sized objects. Those objects represent light-driven macro motors that are able to work in a continuous or step-bystep mode. We studied light intensity’s effects on our system’s angular velocity and estimated the entire process’s conversion efficiency.

Colossal nonlinear optical response of liquid crystals – JOURNAL OF MOLECULAR LIQUIDS vol.267, 67 (2018)

Francesco Simoni, Liana Lucchetti

We briefly review the main steps related to the discovery of the extraordinarily large nonlinear optical response nematic liquid crystals doped by Methyl Red leading to detection of n2 > 10^3 cm^2/W in 1 μm thin films, that is the strongest nonlinear response ever reported in liquid crystals. This investigation started from the researches of Professor Yuri Reznikov on light-induced anchoring effects in these materials.

An Unconventional Approach to Photomobile Composite Polymer Films-ADVANCED MATERIALS vol.29, 1604800 (2017)

R.Castagna, L.Nucara, F. Simoni, L. Greci, M. Rippa, L. Petti, D. E. Lucchetta

Here, we propose a very cheap and fast (one-step-synthesis) method to produce highly bending Pmp films and suggest a method to produce highly bending Pmp films and suggest a couple of applications: i) by coating a Pmp film with a thin gold layer (a few nanometers) making it thus conductive, we realized an optically activated electrical switch; ii) we demonstrate a an optically activated electrical switch; ii) we demonstrate a an optically activated electrical switch; ii) we demonstrate a photodriven caterpillar-miming robot.

Giant optical nonlinearity in DNA lyotropic liquid crystals – OPTICS EXPRESS vol.25, 25951 (2017)

L.Lucchetti, T. P. Fraccia, F. Ciciulla, F.Simoni, T.Bellini

We report the experimental evidence of nonlinear optical response in DNA lyotropic nematic liquid crystals. Pump-probe experiments indicate that the non-linearity is remarkably large. Quantitative assessment of the non-linear optical coefficient by transient optical grating demonstrates that the response is of the same order of the well-known Giant Optical Nonlinearity (GON) of thermotropic nematics. These results represent a further incentive to the current investigation of potential applications of DNA in biophotonics.