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Abstract
The optical tweezers is a tool capable of capturing and manipulating particles of micrometers
order. The optical tweezers, basically, consists of a tightly focused infrared laser incident on a
particle with refractive index larger than the surrounding media index. The optical forces
actuating on the particle are of order of femto to pico Newtons. For this reason, the main
application of an optical tweezers is in the microscopic world, especially in the study of cells
that can be manipulated individually without thermal damage. In this work, we treat of
theoretical and experimental aspects related to the optical tweezers. Chapter 2 contains the
description of the set‐ups used in this thesis. Special emphasis was given to those points critical
for the understanding and to mounting an optical tweezers set up. Chapter 3 describes the use
of the high sensitivity of the optical tweezers to observe the Mie resonances in microspheres
captured and illuminated by plane waves and focalized beams. It also contains the description
of the measurements of the intensity of the optical force as a function of the distance of the laser
focus to the center of the particle. Our results show the fundamental hole of the laser
polarization for the forces of an optical tweezers. This can only be explained by a complete
electromagnetic theory. Chapter 4 shows that it is possible to add the capability of manipulation
of an optical tweezers to the ability of characterization of linear and non‐linear spectroscopic
techniques in only one integrated system. With this system, we were able to perform Raman,
Hyper Rayleigh, Hyper Raman and Two‐Photon Excited Luminescence in biological and nonbiological
samples. Chapter 5 describes an optical tweezers calibration method to measure
forces as small as 200 femto Newtons of the protozoa Leishmania amazonensis. We also used
the optical tweezers to measure the elasticity of normal, storaged, sickle and irradiated red
blood cells. Chapter 6 contains the conclusions and perspectives.
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