The deformability of erythrocytes is a critical determinant of blood flow in microcirculation. By capturing red blood cells (RBC) with optical tweezers and dragging them through a viscous fluid we were able to measure their overall elasticity. We measured, and compared, the RBC deformability of 15 homozygous patients (HbSS) including five patients taking hydroxyurea (HU) for at least 6 months (HbSS/HU), 10 subjects with sickle cell trait (HbAS) and 35 normal controls. Our results showed that the RBC deformability was significantly lower in haemoglobin S (HbS) subjects (HbSS and HbAS), except for HbSS/HU cells, whose deformability was similar to the normal controls. Our data showed that the laser optical tweezers technique is able to detect differences in HbS RBC from subjects taking HU, and to differentiate RBC from normal controls and HbAS, indicating that this is a very sensitive method and can be applied for detection of drug-response in sickle cell disease.

The frequency degenerate and nondegenerate two-photon absorption (2PA) spectra of direct band gap semiconductor quantum dots are studied. Measuring the spectra for both cases in samples of CdSe and CdTe with different quantum dot sizes and size distributions, we observe that the 2PA spectra and the 2PA coefficient are size dependent, so that smaller dots have smaller 2PA even after taking into account the volume fraction. Theory considering the mixing of the hole bands, in a k · p model, explains the data quite well except for the smallest dots. A comparison with the parabolic band approximation is also shown

We have calculated the electronic structure of spherical PbS, PbSe, and PbTe quantum dots using a fourband envelope-function formalism that accounts for band anisotropy. By comparing our results with an analytical calculation that assumes a spherical approximation of the k ជ •p ជ Hamiltonian, we show that the effects of band anisotropy are more pronounced for the excited states and increase with the confinement. We also show how the same technique can be applied to ellipsoidal quantum dots.

We report measurements of frequency degenerate and nondegenerate two-photon absorption (2PA) spectra of CdTe quantum dots, QDs, in glass matrices and compare them with 2PA in bulk CdTe. We find that the 2PA is strongly dependent on the size of the QDs becoming smaller with decreasing size, even when normalizing to the volume of the dots. We adapt a simple degenerate 2PA model, based on the effective mass approximation, to nondegenerate 2PA, and this model correctly describes the experimental data for 2-photon energies up to ~ 1.4Eg. This suggests that, once the spectrum for one size of quantum dot is known, the model can be used for predicting the degenerate and nondegenerate 2PA spectra of different sized QDs of the same semiconductor.

Raman, opticalabsorption, and transmission electron microscopy study of size effects in germanium quantum dots Appl.Excitonic optical properties in semiconductor thin quantum boxes of intermediate regime between zero and two dimensions Appl.

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Analytical solution for optical trapping force on a spherical dielectric particle for an arbitrary positioned focused beam is presented in a generalized Lorenz-Mie and vectorial diffraction theory. In this case the exact electromagnetic field is considered in the focal region. A double tweezers setup was employed to perform ultra sensitive force spectroscopy and observe the forces, demonstrating the selectively couple of the transverse electric (TE), transverse magnetic (TM) modes by means of the beam polarization and positioning, and to observe correspondent morphology-dependent resonances (MDR) as a change in the optical force. The theoretical prediction of the theory agrees well with the experimental results. The algorithm presented here can be easily extended to other beam geometries and scattering particles. G. Gouesbet, B. Maheu, G. Grehan, "Light scattering from a sphere arbitrarily located in a Gaussian beam using Bromwich formulation," J Opt Soc Am A, 5, 1427-1443 (1988