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Light controlled phase shifter for optofluidics


We report the light-induced control of optical phase shift
by a liquid crystal cell made with LiNbO3:Fe crystals as substrates. We show that a phase shift of few πs can be easily reached fo two orthogonal polarizations due to liquid crystal reorientation driven by the photovoltaic electric field originated in the substrates. This effect is exploited to get all-optical swithing with a contrast of about 80% , by a 2 s pump pulse.





OPTICS LETTERS
   41, 333 (2016)

J. EUR. OPT. SOC. 11, 16007 (2016)




Optical measurement of flow rate in a microfluidic channel


A way to measure flow rate inside a microchannel using a contactless optical technique is reported. The optofluidic device consists of a Bragg grating written on a soft wall, namely a Mylar stripe glued on the top of a microfluidic channel. Diffraction of a white-light probe beam is used to detect the small displacements of the grating caused by the liquid flowing inside the microchannel. A simple model of the hydraulic circuit gives theoretical expressions for the response time of the diffracted signal allowing to fit the experimental data and determine the applied flow rates.


MICROFLUID. and NANOFLUID.  20, 9 (2016)

  Optical
  nonlinearity
  in the nematic
  phase of
  bent-core

  mesogens


Nonlinear optical response of the cybotactic nematic phase of a bent-core mesogen has been investigated for the first time through self-phase modulation induced by a Gaussian beam. The material exhibits a high nonlinear response achieving a nonlinear index n2 ≈ 5 10−5 cm2∕W and an unconventional behavior characterized by two different regimes. While the high-intensity regime can be easily explained in terms of a thermal indexing effect, the low-intensity regime is metastable and characterized by an unusual dependence on the irradiation energy. It is suggested that a change of the director configuration, possibly due to a light-induced modification of surface anchoring, is responsible for the observed behavior.


OPTICS LETTERS   40, 2953 (2015)
  Controlled  
  motion of
  floating
  macro-objects
  induced by
  light


Photons energy can be conventionally converted to mechanical work through a series of energy-expensive steps such as for example delivery and storage. However, these steps can be by passed obtaining a straightforward conversion of photons energy to mechanical work. As an example, in literature, high power near infrared light is used to move small objects floating on fluid surfaces, exploiting the Marangoni effect. In this work we use a low power non-collimated visible laser-light to induce thermal surface tension gradients, resulting in the movement of objects floating on fluid surfaces. By real time tracking of the object trajectories, we evaluate the average applied driving force caused by the light irradiation. In addition we show how transparent objects can be moved by light when the supporting fluids are properly doped.

AIP ADVANCES   5, 077147 (2015)

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