Papers by Antigone Marino
Journal of the Optical Society of America A, 2022
Molecular Crystals and Liquid Crystals, 2006
Optics Express, 2006
Dielectric aperiodic Thue-Morse structures up to 128 layers have been fabricated by using porous ... more Dielectric aperiodic Thue-Morse structures up to 128 layers have been fabricated by using porous silicon technology. The photonic band gap properties of Thue-Morse multilayers have been theoretically investigated by means of the transfer matrix method and the integrated density of states. The theoretical approach has been compared and discussed with the reflectivity measurements at variable angles for both the transverse electric and transverse magnetic polarizations of light. The photonic band gap regions, wide 70 nm and 90 nm, included between 0 and 30°, have been observed for the sixth and seventh orders, respectively.
Journal of Physics: Condensed Matter, 2008
... Ilaria Rea1,2, Antigone Marino2, Mario Iodice1, Giuseppe Coppola1, Ivo Rendina1 and Luca De S... more ... Ilaria Rea1,2, Antigone Marino2, Mario Iodice1, Giuseppe Coppola1, Ivo Rendina1 and Luca De Stefano1 ... normal incidence, focused by a 40× (NA = 0.65) microscope objective (figure 1(B)). The sample was mounted on a motor-ized xy micrometric stage (Micos LS-110) and ...
Molecular Crystals and Liquid Crystals, 2003
One key point for an advantageous use of liquid crystals in optical devices for telecom applicati... more One key point for an advantageous use of liquid crystals in optical devices for telecom applications is a proper design and simulation capability. For this purpose it is mandatory to know the optical behaviour of these materials at the wavelength of interest, i.e. the transparency windows of the optical fibers in the Near-IR region. To this aim, we have applied
We have studied the dynamical response of a new polymer-liquid crystal composite, realised in a f... more We have studied the dynamical response of a new polymer-liquid crystal composite, realised in a form of a thick grating. This structure, named POLICRYPS, consists in an alternate sequence of homogeneous polymer slides and liquid crystal stripes. Optimisation of response time is an important factor to propose POLICRYPS as basic element in different photonic devices for telecom applications. We analyse the response dependence on the pulse duration and amplitude: we show that both ON and OFF switching times are depending on the applied electric field and propose a phenomenological explanation for this unexpected behaviour. Moreover we outline the possibility to get response times of the order of 100 µs by properly choosing the pulse shape. Results are very interesting for applications and induce to a deeper analysis of the microscopic interaction between liquid crystal and polymer interfaces in POLICRYPS gratings.
A nonzero pretilt angle is generally used in vertical aligned (VA) mode liquid crystal (LC) displ... more A nonzero pretilt angle is generally used in vertical aligned (VA) mode liquid crystal (LC) displays to avoid domain formation during molecular reorientation by electric field, as well as to reduce both driving voltage and response time. The pretilt effect on electro-optical properties of a VA LC cell has been investigated. Pretilt was controlled changing the angle of SiO x deposition on the substrate surfaces. The tilt angle distribution versus the applied voltage is obtained by Variable Angle Spectroscopic Ellipsometry and compared with the simulated curves. A good compromise between contrast and response time is reached in cells with different pretilt values on the two cell substrates.
Recently important efforts have been dedicated to the realization of a new kind of photonic cryst... more Recently important efforts have been dedicated to the realization of a new kind of photonic crystals, known as photonic quasicrystals, in which the lack of the translational symmetry is compensated by rotational symmetries not achievable by the conventional periodic crystals. Here we show a novel approach to their fabrication based on the use of a programmable Spatial Light Modulator encoding Computer-Generated Holograms. Using this single beam technique we fabricated Penrose-tiled structures possessing rotational symmetry up to 23-fold, and a twodimensional Thue-Morse structure, which is an aperiodic structure not achievable by multiple beam holography.
Thin Solid Films, 2004
Generalized spectroscopic ellipsometry (g-SE) has been applied to many anisotropic materials. Thi... more Generalized spectroscopic ellipsometry (g-SE) has been applied to many anisotropic materials. This measurement is based on the 2=2 Jones matrix sample representation, which is often sufficient. However, when the reflected or transmitted light becomes sufficiently depolarized, the Mueller-matrix (MM) representation may be required for anisotropic materials characterization. We report measurements of a 33.85 mm thick liquid crystal layer sandwiched between two glass substrates. In addition to the sample anisotropy, the measurement is significantly depolarized. Mueller-matrix measurements are acquired in transmission as a function of wavelength, angle of incidence, and sample orientation to characterize the liquid crystal layer. Experimental measurements allow characterization of the liquid crystal anisotropy and orientation. ᮊ
Sensors and Actuators B: Chemical, 2009
We have fabricated, and characterized a Bragg grating, having a pitch of 10 m, directly etched on... more We have fabricated, and characterized a Bragg grating, having a pitch of 10 m, directly etched on a porous silicon-based planar waveguide to be used as an optical sensor for chemical substances. The transmission spectrum of this device shows a well-defined peak in the near infrared wavelength region due to a high order resonance of the Bragg grating. On exposure to different volatile organic compounds the peak undergoes distinct shifts. The phenomenon is fast and completely reversible. Limits of detection of hundred of ppm can be estimated from the experimental data.
Physical Review E, 2005
We have studied the electro-optical and angular behavior of holographic-polymer-dispersed liquid ... more We have studied the electro-optical and angular behavior of holographic-polymer-dispersed liquid crystal gratings at different wavelengths, in the visible and in the near-infrared range. As usual in these kinds of materials, a strong polarization dependent behavior was observed. Our samples showed very high diffraction efficiency for p-polarized radiation at 1.55 microm, which is very interesting for many possible applications in the telecom field. However, we also observed a very unusual behavior for visible p-polarized light and we try to suggest some explanation for that. By analyzing the angular dependence of the diffraction efficiency, we could measure the components of the permittivity modulation tensor and infer important information about the main parameters involved in the grating structure: the degree of phase separation and the anisotropy in the liquid crystal droplet distribution. In our opinion, this simple and nondestructive methodology can be very useful for studying these kinds of materials and getting information on their morphology, in view of optimizing their properties. Finally, we discuss the role of the refractive index optical dispersion in order to describe the behavior of these materials at different wavelengths. These remarks are especially important when properties in the infrared range are extrapolated from measurements in the visible.
Optics Express, 2006
Dielectric aperiodic Thue-Morse structures up to 128 layers have been fabricated by using porous ... more Dielectric aperiodic Thue-Morse structures up to 128 layers have been fabricated by using porous silicon technology. The photonic band gap properties of Thue-Morse multilayers have been theoretically investigated by means of the transfer matrix method and the integrated density of states. The theoretical approach has been compared and discussed with the reflectivity measurements at variable angles for both the transverse electric and transverse magnetic polarizations of light. The photonic band gap regions, wide 70 nm and 90 nm, included between 0 and 30°, have been observed for the sixth and seventh orders, respectively.
Molecular Crystals and Liquid Crystals, 2006
Molecular Crystals and Liquid Crystals, 2010
We present a Monte Carlo study of a liquid crystal-polymer interface, focusing on a single cell w... more We present a Monte Carlo study of a liquid crystal-polymer interface, focusing on a single cell with boundary conditions tailored to mimic the main features of the system and we examine the effect of an external applied field. A simple lattice spin model, based on the Lebwohl-Lasher hamiltonian, has been employed to represent the nematic and the polymer molecules. The
Molecular Crystals and Liquid Crystals, 2007
Standard multiple-beam holography has been largely used to produce gratings in polymer-liquid cry... more Standard multiple-beam holography has been largely used to produce gratings in polymer-liquid crystal composites, like POLICRYPS, H-PDLC gratings and POLIPHEM . In this work we present a different approach to liquid crystalpolymeric grating production, based on the Computer-Generated Holography (CGH). The great advantage of using CGH is that interferometer-based schemes are no longer necessary, avoiding problems related to long term stability of the interference pattern and multi-beam complex optical setup. Moreover, the CGH technique allows a wider choice of pattern designs. In this preliminary work, we obtained promising results, as for instance the patterning of a square-wave refractive index modulation of a LCpolymeric composite, a pattern which is not achievable with standard two-beam holography.
Molecular Crystals and Liquid Crystals, 2003
... E-mail: [email protected] ... Furthermore, we noticed that times tON are affected b... more ... E-mail: [email protected] ... Furthermore, we noticed that times tON are affected by large errors even greater than 25%, while tOFF errors can be estimated in 5%. From the other hand, it seemed that the switching ON process is not ruled by a single time constant so that ...
Journal of Physics: Condensed Matter, 2008
... Ilaria Rea1,2, Antigone Marino2, Mario Iodice1, Giuseppe Coppola1, Ivo Rendina1 and Luca De S... more ... Ilaria Rea1,2, Antigone Marino2, Mario Iodice1, Giuseppe Coppola1, Ivo Rendina1 and Luca De Stefano1 ... normal incidence, focused by a 40× (NA = 0.65) microscope objective (figure 1(B)). The sample was mounted on a motor-ized xy micrometric stage (Micos LS-110) and ...
Journal of Applied Physics, 2010
We describe an experimental procedure for accurate measurement of anchoring energy strength of li... more We describe an experimental procedure for accurate measurement of anchoring energy strength of liquid crystal cells. This technique is based on the possibility of gathering a large amount of very precise data about the linear optical response of the cell in different experimental conditions, using spectroscopic ellipsometry. Then, a careful data analysis exploiting data inversion method, supplemented by simulations from the elastic theory, is able to provide the searched information. The technique has been applied to vertical aligned nematic cells, chosen for its widespread use in the present display market. The results obtained in this particular case together with a thorough comparison with existing alternative techniques, suggest that our technique can be an optimum candidate for the industrial implementation of such measurement. A particular example is fully worked out, giving a result with a precision of 1.5% and an accuracy of 10%.
Molecular Crystals and Liquid Crystals, 2009
In recent years there has been much interest in the physics and possible technological applicatio... more In recent years there has been much interest in the physics and possible technological applications of liquid crystal-based tuneable Bragg gratings. Such optical devices can be realised using special composite materials based on a sequence of polymeric sheets alternated by layers containing only liquid crystal, sometimes known as Policryps and Poliphem.
Uploads
Papers by Antigone Marino