During development, the axons of neurons in the mammalian central nervous system lose their ability to regenerate after
injury. In order to study the regeneration process, we developed a system integrating an optical tweezers and a laser
dissector to manipulate the sample. A sub-nanosecond pulsed UVA laser was used to inflict a partial damage to the axon
of mouse hippocampal neurons at early days in vitro. Partial axonal transections were performed in a highly controlled
and reproducible way without affecting the regeneration process. Force spectroscopy measurements, during and after the
ablation of the axon, were performed by optical tweezers with a bead attached to the neuronal membrane. Thus, the
release of tension in the neurite could be analyzed in order to quantify the inflicted damage. After dissection, we
monitored the viscoelastic properties of the axonal membrane, the cytoskeleton reorganization, and the dynamics of the
newly formed growth cones during regeneration. In order to follow cytoskeleton dynamics in a long time window by
tracking a bead attached to the neuron, we developed a real-time control of the microscope stage position with sub-millisecond
and nanometer resolution. Axonal regeneration was documented by long-term (24-48 hours) bright-field live
imaging using an optical microscope equipped with a custom-built cell culture incubator.
Nonlinear optical microscopy is a relatively new and rapidly growing field of optical engineering, where Ti:sapphire ultrafast laser sources and technologies are finding a wide application. Diagnostic techniques addressed to this kind of application have been widely developed in the last few years. Research efforts have been focused on the evaluation and eventual correction of laser pulse duration widening due to group velocity dispersion of microscope optics, and devices have been specially designed to perform second-order autocorrelation measurements at the objective focal plane. In the present work, innovative, simple setups and procedures are reported that make the best use of all the facilities and characteristics of the microscope itself, so that only a few optical components are needed to temporal characterize the laser pulse at the specimen plane.
Photonic crystals are attractive optical materials for controlling and manipulating light. They are of great interest for both fundamental and applied research, and are expected to find commercial applications soon. In this work digital holography, white light interferometry and atomic force microscopy have been applied to the inspection and characterization of 1D and 2D nanofabricated LiN photonic crystals. Periodic pattern with periods ranging form several microns to a fraction of micron have been accurately analysed. Optical methods allow exploring relatively large areas while atomic force microscopy is well suited for high-resolution inspection of the small features.
We report on the fabrication and characterization of the first periodic sub-micron scale one- and two-dimensional surface structures in congruent 500 μm thick lithium niobate crystal samples. Structures with periods from 2 μm down to 500 nm, lateral feature sizes down to 200 nm and depths around 10 μm, largely compatible with conventional waveguide fabrication, have been obtained. Such structures are fabricated by selective wet etching of ferroelectric domain engineered samples obtained by electric field poling performed at an overpoling regime. Holographic lithography is here used to obtain sub-micron periodic insulating gratings to be used for selective ferroelectric domain reversal. The short-pitch fabricated structures are attractive in a wide range of applications, such as nonlinear short-wavelength conversion processes, backward second-harmonic generation, fabrication of novel tunable photonic crystal (PC) devices, electro-optically modulated Bragg gratings. Moreover moire beating effect is used in the photolithographic process to fabricate even more complex structures which could find applications in complicated photonic bandgap devices involving for example micro-ring resonators. In order to investigate the possibility to utilize these structures for PC applications, accurate and complete topographic characterization has been performed by using different techniques. Atomic force microscope provides high-resolution information about the lateral and depth feature size of the structures. Interferometric techniques, based on digital holography, have been used for wide field information about the homogeneity and periodicity of the structures.
Multiphoton microscopy is a relatively new and rapidly growing field of applied optics where Ti:Sapphire ultrafast laser sources and related technology find a wide application. Laser beam diagnostic techniques specially devoted to this kind of application has been widely developed in these last years. Research efforts have been addressed to the evaluation and the eventual correction of the laser pulse duration widening due to group velocity dispersion caused by the microscope optics. Temporal characterization is thus a fundamental task when operating a ultrafast laser system for multiphoton microscopy applications and it is carried out by means of autocorrelators specially designed to perform pulse width measurements at the focus of the microscope objective. In the present communication, an innovative autocorrelator set-up and a simple metrological procedure are reported.
Planar waveguides have been realized in lithium fluoride crystals by ion-beam irradiation. Ion bombardment produces color centers in the LiF crystal, increasing locally the refractive index. Confocal microscopy is applied to the characterization of the waveguides in order to assess the uniformity and distribution of color centers through the measurement of the photoluminescence emission.
Optical waveguides in lithium fluoride (LiF) crystals have been obtained by He<sup>+</sup> ion beam irradiation. The waveguides
have been characterized by several techniques. In particular, we describe here the application of confocal microscopy to their characterization and show the first results obtained. We have also carried out a preliminary evaluation of the potential of this technique for the assessment of structural and spectroscopic characteristics of the waveguides.