Search results for "Light beam"
showing 10 items of 58 documents
Vortex beam generation and other advanced optics experiments reproduced with a twisted-nematic liquid-crystal display with limited phase modulation
2016
In this work we propose the use of twisted-nematic liquid-crystal spatial light modulators (TN-LC-SLM) as a useful tool for training students in the manipulation of light beams with phase-only masks. In particular, we focus the work on the realization of phase-only gratings and phase-only spiral phases for the generation of vortex beams, beams carrying orbital angular momentum (OAM). Despite the extensive activity in this field, its experimental implementation for educational purposes is limited because it requires the use of very expensive high-resolution liquid-crystal on silicon (LCOS) SLMs. Here, we show that a low-cost experimental implementation can be done with older TNLC technology.…
Self-trapping of speckled light beams
2008
A speckle beam of light breaks up into small fragments as it propagates in a standard self-focusing nonlinear material. Now, by exploiting the non-local thermal response of a material, it is possible to trap a speckle beam in a self-induced waveguide.
Axial resonance of periodic patterns by using a Fresnel biprism.
2013
This paper proposes a method for the generation of high-contrast localized sinusoidal fringes with spatially noncoherent illumination and relatively high light throughput. The method, somehow similar to the classical Lau effect, is based on the use of a Fresnel biprism. It has some advantages over previous methods for the noncoherent production of interference fringes. One is the flexibility of the method, which allows the control of the fringe period by means of a simple axial shift of the biprism. Second is the rapid axial fall-off in visibility around the high-contrast fringe planes. And third is the possibility of creating fringes with increasing or with constant period as the light bea…
Imperfect symmetry breaking
2018
By considering a nonlinear resonator driven by an elliptically polarized beam, we study experimentally the robustness of spontaneous symmetry breaking to controlled asymmetries. In particular, we reveal that different asymmetries can balance each other.
Application of optical tomography for measurements of aeration parameters in large water tanks
2003
The paper presents a design and application study of a prototype optical tomograph for the detection and definition of shapes of gas bubbles moving in a liquid. In the applied method of measurements, the column is exposed to a homogeneous light beam and next the ray is detected with the use of optical waveguided detectors. Spatial reconstruction of the bubble shapes is done on the basis of the signals coming from two perpendicular systems of detectors. The bubble shape is approximated by an ellipsoid with suitably determined semi-axes and with the use of genetic algorithms based on the neuron network. Influence of the structure and dynamics of the measuring path on errors in representation …
Modeling the interactions between light and crystallizing polymer during fast cooling
2004
In this work, an experimental set-up able to quench thin polymer films whilst recording the sample thermal history as well as the overall and depolarized light intensities of a laser beam emerging from the sample is described. The interactions between the light beam and the crystallizing material have been modeled accounting for absorption and scattering phenomena. The proposed model was found to be able to reproduce the ex- perimentally observed behavior of light intensities and it was validated by comparison with conventional DSC analysis. On the basis of this model, a method to obtain crystallinity evo- lution is proposed and applied to some fast cooling runs. The method was applied to q…
Giant collective incoherent shock waves in strong turbulence
2016
Contrary to conventional coherent shocks, we show theoretically and experimentally that nonlocal turbulent flows lead to the emergence of large-scale incoherent shock waves, which constitute a collective phenomenon of the incoherent field as a whole.
Optical tweezing using tunable optical lattices along a few-mode silicon waveguide
2018
International audience; Fourteen years ago, optical lattices and holographic tweezers were considered as a revolution, allowing for trapping andmanipulating multiple particles at the same time using laser light. Since then, near-field optical forces have arousedtremendous interest as they enable efficient trapping of a wide range of objects, from living cells to atoms, in integrateddevices. Yet, handling at will multiple objects using a guided light beam remains a challenging task for current on-chipoptical trapping techniques. We demonstrate here on-chip optical trapping of dielectric microbeads and bacteria usingone-dimensional optical lattices created by near-field mode beating along a f…
Optical retarder system with programmable spectral retardance.
2014
An optical system that works as a retarder waveplate with programmable spectral retardance is proposed. The system is based on a pixelated liquid crystal on silicon (LCoS) spatial light modulator (SLM). The input light beam is spectrally dispersed and different spectral components are projected onto different pixels of the LCoS-SLM. A different retardance is then addressed for each pixel, adapted to the incoming wavelength. Light reflected from the SLM is then recombined by the same setup. In this way a programmable polarization spectrum can be encoded. We illustrate the broadband characterization that is required for proper use of the system. Then several examples are shown, including spec…
Dynamical binary modulation of ultrabroadband light beams by using principal states of polarization of liquid crystal devices
2009
Dynamical modulation of ultrabroadband beams, such as those produced by femtosecond laser or incoherent sources, is not an easy task due to the dispersive nature of the devices commonly employed. Phase modulation has been performed by means of deformable micromirror arrays. These devices are expensive and do not permit amplitude modulation. For micro- and nano-structuring of materials with femtosecond lasers is common to pattern the surface with the light irradiance produced by a computer generated hologram implemented onto a liquid crystal (LC) type spatial light modulator. This enables dynamical patterning [1,2]. Reduced spectral bandwidths, of the order of tens of nanometers, have been u…