In this paper we are going to present some results regarding the optical trapping and manipulation of dielectric
microparticles immersed in fluids. The experiments will be done in Mie regime, i.e diameter of the particles is larger
than the laser wavelength. We will report optical trapping of multiple particles and their manipulation by means of
optical tweezers setup. To catch microobjects we will use a Gaussian laser beam and to manipulate them we are going to
calculate diffractive optical elements (DOEs) by iterative algorithm and spherical wave method.
Small displacements of a microparticle in an optical trap can be measured using back focal plane interferometry. The
position of the particle is evaluated by analyzing the fringes pattern obtained by interference between the light scattered
by the particle and unscaterred light in the back focal plane of the condenser. The fringes positions are detected with a
quadrant photo diode, allowing nanometric precision. In this paper we analyze theoretically some parameters that may
influence the measurements: laser power fluctuations, local fluid viscosity, condenser focal length, particle size.
Between other sensing and identification technologies that of Surface Acoustic Waves, (SAW), is a unique sensing
system. The principal advantage to most SAW systems is that they can use two or three SAW sensors and compare the
measurements between them, providing a good accuracy. We have carried out the design of both piezoelectric substrate
and interdigital transducers, (IDTs), and has tested them in a delay line mode operation. The measurement of changes in
the surface waves characteristics were materialized by applying of a radio frequency electric field to the piezoelectric
crystal by means of IDTs. The finger width of the IDTs was measured by high accuracy optical coherent method. The
results are presented in the work. The potential development of microsensors as an array of four or five miniature
sensors, sensitive to Werent chemicals may be used as mobile chemical detecting units carried by remote control
vehicles to the site chemical contamination.
A strongly focused laser beam through an objective microscope with high NA allows the trapping of dielectric particles
with micrometric sizes. The trapping force is proportional to the power of the laser, the relative refractive index (the ratio
between the refractive index of the particle and the refractive index of the medium surrounding it) and the trapping
geometry (shape of the laser beam, shape of the particle, transmission and reflection coefficients). Numerical models to
evaluate the trapping force can be developed for simple geometrical shapes of the trapped particle. For particles with
complicated shapes the trapping force should be measured experimentally. The goal of this paper is to evaluate a
measurement method based on the equilibrium between the drag force in a fluid with known viscosity and the transversal
trapping force. A particle with a known size is fist trapped in a cell filled with water. After stable trapping, the cell is
shifted with controlled velocities using piezoelectric actuators. If the velocity exceeds a certain threshold, the particle
escapes from the trap. This threshold allows to determine the trapping force. Experimental results obtained with high and
low index particles are presented and discussed.
In this work we present a numerical evaluation of the forces in an optical tweezers system, for metallic nanoparticles in the
Rayleigh regime. Initially a Gaussian beam is described in the scalar approximation, and the forces it can apply on Rayleigh
dielectric and metallic particles are computed within the point-dipole approach. The method is then extended to dielectric
and metallic Rayleigh particles in a Laguerre-Gaussian beam, i.e. a higher order beam that is increasingly used for optical
trapping experiments. We discuss the limits of the approximation for the beam intensity by comparing the numerical results
with the experimental measurements that can be found in literature.
In this paper we analyze the electromagnetic modes in photonic crystals. This is important because of the wide range of potential applications of structures which allow a complete control over light propagating in them. We focus to study the fundamental behavior of one- and two-dimensional photonic crystals, which are easier to investigate than three-dimensional structures. We will study the photonic band structure in the TM modes (E-polarization) and in the TE modes (H-polarization).
One of the most critical components of a PSK receiver is the PLL. A technique that makes possible to avoid a PLL device is based on the transmission of a reference carrier together with the modulated signal. The carrier can be extracted at the receiver end for demodulation. In this paper is made an analysis from the point of view of the performances of this kind of system and the main purpose is to minimize the error probability searching a suitable power splitting ratio at the transmitter.