Acousto-holographic optical tweezers

Acousto-optic deflectors (AODs) allow the creation of multiple optical traps by time-sharing, that is, by rapidly cycling the laser focus between designated spatial locations. The traps thus formed are not permanent. In this Letter, we successfully demonstrate the creation of multiple and permanent traps by means of AODs driven by specially encoded radio frequency signals. The generation of complex acoustic signals allows us to treat such devices as super-fast spatial light modulators. Using this technique, it is possible to generate several static optical trap arrays and switch them at kilohertz (kHz) rates, allowing independent control of each trap group. Additionally, we discuss the compatibility of this method with precise force and position measurements, and the improvement in their frequency bandwidth compared to time-sharing optical tweezers, especially when many objects are trapped.

Artificially-induced organelles are optimal targets for optical trapping experiments in living cells

Optical trapping supplies information on the structural, kinetic or rheological properties of inner constituents of the cell. However, the application of significant forces to intracellular objects is notoriously difficult due to a combination of factors, such as the small difference between the refractive indices of the target structures and the cytoplasm. Here we discuss the possibility of artificially inducing the formation of spherical organelles in the endoplasmic reticulum, which would contain densely packed engineered proteins, to be used as optimized targets for optical trapping experiments. The high index of refraction and large size of our organelles provide a firm grip for optical trapping and thereby allow us to exert large forces easily within safe irradiation limits. This has clear advantages over alternative probes, such as subcellular organelles or internalized synthetic beads.

A method for the automatic characterization of bone architecture in 3D mice microtomographic images

We developed an automatic method to characterize mice bone architecture from three-dimensional (3D) microtomographic images. The distal metaphyses of the femur of mice were imaged using 3D synchrotron radiation microtomography at the European Synchrotron Radiation Facility (ID19) with a voxel size of 6.65 mum. Within each reconstructed volume, a region of interest was defined and trabecular and cortical bones were automatically separated. Then, 3D morphologic and topologic model-independent parameters quantifying the 3D bone architecture were computed in both regions. The technique was applied to study the response of the C57BL/6J@Ico strain of mice submitted to a model of bone loss by hind limb unloading produced by tail-suspension.

Optical correlation by use of partial phase-only modulation with VGA liquid-crystal displays

The development of liquid-crystal panels for use in commercial equipment has been aimed at improving the pixel resolution and the display efficiency. These improvements have led to a reduction in the thickness of such devices, among other outcomes, that involves a loss in phase modulation. We propose a modification of the classical phase-only filter to permit displays in VGA liquid-crystal panels with a constant amplitude modulation and less than a 2pi phase modulation. The method was tested experimentally in an optical setup.

On-axis joint transform correlation based on a four-level power spectrum

We propose a method to obtain a single centered correlation with use of a joint transform correlator. We analyze the required setup to carry out the whole process optically, and we also present experimental results.

Nonlinear filtering in object and Fourier space in a joint transform optical correlator: comparison and experimental realization

The use of different kinds of nonlinear filtering in a joint transform correlator are studied and compared. The study is divided into two parts, one corresponding to object space and the second to the Fourier domain of the joint power spectrum. In the first part, phase and inverse filters are computed; their inverse Fourier transforms are also computed, thereby becoming the reference in the object space. In the Fourier space, the binarization of the power spectrum is realized and compared with a new procedure for removing the spatial envelope. All cases are simulated and experimentally implemented by a compact joint transform correlator.