Digital holographic microscopy has numerous applications in biology for visualizing living cells and 3D tissues. This technique allows for the direct visualization of biological structures avoiding invasive and phototoxic procedures such as fixation and dying processing. In this study we have characterized the morphometry changes of neurons subject to osmolarity changes. For this purpose, we have measured the variations of the amplitude and the oscillation frequency of the plasmatic membrane, as well as the volume changes of the cells before the osmotic shock. There was a relation between the neural culture ageing and its behavioral changes. "Long-term" cultures that had not previously been studied were used to analyze the behavioral changes in aged cells.
In this paper we report on the use of digital holographic microscopy for 3D real time imaging of cultured neurons and neural networks, in vitro. Digital holographic microscopy is employed as an assessment tool to study the biophysical origin of neurodegenerative diseases. Our study consists in the morphological characterization of the axon, dendrites and cell bodies. The average size and thickness of the soma were 21 and 13 μm, respectively. Furthermore, the average size and diameter of some randomly selected neurites were 4.8 and 0.89 μm, respectively. In addition, the spatiotemporal growth process of cellular bodies and extensions was fitted to by a non-linear behavior of the nerve system. Remarkably, this non-linear process represents the relationship between the growth process of cellular body with respect to the axon and dendrites of the neurons.
Time-delay of transmitted pulses with respect to the incident pulse in bacteriorhodopsin films has been studied without the use of a pump beam. Based on a modified saturable absorber model, analytical expressions of the transmitted pulse have been obtained. As a result, time delay, distortion and fractional delay have been theoretically analyzed for sinusoidal pulses with a low background.
We present our first experimental results of lens irradiation obtained with ultrashort pulse lasers. The irradiation was done with the Ti:Safire laser which irradiates at 800 nm with a repetition rate of 76 MHz. The maximum average intensity used was 300mW, with pulses of 4 nJ. The holographic images obtained have given us information about the focusing process of the lens capsule as well as its rupture, thus indicating the level of penetration in the lens and capsule rupture. The results obtained in these first experiments allow us to establish protocols and techniques to break the capsule of the lenses as well as to carry out possible modifications inside the lens. As the optical system developed works in real time, it is possible to perform dosimetry measurements in the light-lens interaction processes giving quantitative information about the breakdown of the tissue structures. In future projects the possible side effects of thermal action and local modification of the capsule will be analyzed; these are important aspects in the field of noninvasive lens surgery.
Digital Holographic Microscopy (DHM) is a potentially non-invasive new technology which can be applied in many
areas from applied imaging science to biomedical optics. DHM is an interferometric technique that gives us a number of
important advantages such as the possibility to acquire holograms at high speed, to obtain complete information about
amplitude and phase and to use image processing techniques. In this sense, DHM offers rapid 3D imaging with a
theoretically higher resolution than OCT (Optical Coherent Tomography). By this technique optical path measurements
with sensitivities in the nanometer range of reflective and transparent objects can be obtained.
In this work, we use DHM to study the effect of ablation using 4.5 nJ pulses on chicken corneas. For this, a titanium
sapphire laser at 800 nm and 76 MHz frequency (Vitesse, Coherent Inc. USA) was focused to its diffraction-limited spot
size by a 10x objective of 0.3 numerical aperture. The width of the pulse (170 fs) at the sample was measured by spectral
techniques. The average beam power at the sample was 340 mW and all the system was mechanically driven by a XY
synchronization unit that controls the speed of the sample movement. The speed of the sample was varied between 1-50
μm/s.
The studied chicken corneal tissue was previously processed by Trypan dye in order to visualize the irradiated area. The
photodisrupted zone was analyzed by a HDM technique by illuminating it using a laser diode source (λ=683 nm) linearly
polarized in a modified Mach-Zehnder with an off-axis geometry configuration. The reflected object wave by the tissue
surface (specimen) interferes with the reference wave and a CCD camera records the hologram. As a result, the influence
of the speed of photodisruption in the depth of the ablated corneas was analyzed. Therefore, it is possible to analyze
thermal and photoirradiated effects on corneal tissues which allow us the possibility to optimize the interaction of
intratissue and the intratissue target region of interest.
Protein Bacteriorhodopsin (bR) is one of the most promising and widely studied biomaterials for photonic applications
like optical storage, modulation devices and photosynthetic light energy transduction. In this paper, we present the
corresponding experimental results when pH-controlled modifications of bR doped polymeric films are realized in order
to apply these systems to all-optical switching processes and technologies.
In this work, the performance of wild type bR processed in polymeric films with different pH was tested in several series
of experiments by varying the pump beam (532 nm) period of ON and OFF and analyzing the amplitude contrast and
switching time of the probe beam (633 nm). The influence of pH values on contrast ratio and switching time were also
discussed and the optimal value was found by defining a new parameter called "switching speed". As a result, the
variation of pH can be used to obtain different time of response and speed of modulation. Concretely, we find that, in
function of pH, variations of a magnitude order in contrast ratio and time response can be obtained. So, at the red region
of the probe beam, high pH values produce high transmission with flat response in the contrast ratio and a magnitude
order variation in switching time. On the other hand, at medium pH values and when high intensities are used, the
switching time and contrast ratio are better. Moreover, it is demonstrated that as a function of the wavelength of the
probe beam the transmission response curve changes. Absorption response is very important and depends on relaxation
time processes of intermediate species which are function of pH values. Therefore, these results bring the possibility for
controlling the contrast ratio and the switching time in a specific way which could be useful for different applications.
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