María Teresa Flores-Arias

Timing jitter smoothing by Talbot effect. I. Variance

A study of the stochastic description of the Talbot effect in the temporal domain under random timing jitter is presented. The relevant statistical quantity is the variance. The variance of a train of pulses, each one affected by random timing jitter, shows peaks in the edges of the pulses. When this train is Talbot-imaged, the variance becomes flattened along the unit interval corresponding to each pulse as a result of the dispersion of the individual pulses of the train. Fractional Talbot devices are also analyzed. In particular, it is shown that this smoothing effect also occurs in Talbot devices leading to N× repetition rates of the original train.

Description of gradient-index crystalline lens by a first-order optical system

This paper uses the correspondence between the canonical integral transform and the ray-transfer matrix of a first-order optical system to analyse paraxial properties of the crystalline lens of the human eye regarded as a gradient-index (GRIN) medium limited by curved surfaces. Matrix factorization is provided to evaluate cardinal elements and refractive powers of the crystalline lens.

Timing jitter smoothing by Talbot effect. II. Intensity spectrum

The power spectral density of the intensity of jittery trains after an integer temporal Talbot dispersive line is computed in the small-signal approximation. The influence in the spectrum of the optical linewidth and chirp of the Gaussian pulses of the train and also of different pulse-to-pulse timing jitter correlations is addressed. Before entering the Talbot dispersive line, timing jitter produces noise sidebands around the harmonics of the train. The temporal Talbot effect adds a multiplicative factor to the noise spectral density that depends on the characteristics of both the pulses and the dispersive line but not on the pulse-to-pulse correlation or the value of the timing jitters standard deviation. The structure of this multiplicative term is peaked, resulting in narrowband noise patterns in specific locations of the spectrum and, in particular, around the harmonics of the train. Thus the temporal Talbot effect provides a dispersive mechanism for noise filtering. The bandwidth of the dispersion-induced noise peaks is ∼1 order of magnitude below the repetition-rate frequency.

Fractional Talbot effect in a Selfoc gradient-index lens

The fractional Talbot effect is demonstrated inside a standard 0.25-pitch Selfoc gradient-index lens under uniform illumination. Comparisons with theoretical expressions of positions and magnification of fractional Talbot images are given.

Talbot effect in a tapered gradient-index medium for nonuniform and uniform illumination

A generalization of the Talbot effect to the case of a tapered gradient-index medium for nonuniform and uniform illumination is considered. Self-image positions are changed by a function depending on the taper profile, the illumination, and the periodic object. An analogy with the conventional lens-imaging formula for both types of illumination is presented.

A laser-based technology for fabricating a soda-lime glass based microfluidic device for circulating tumour cell capture

We developed a laser-based technique for fabricating microfluidic microchips on soda-lime glass substrates. The proposed methodology combines a laser direct writing, as a manufacturing tool for the fabrication of the microfluidics structures, followed by a post-thermal treatment with a CO2 laser. This treatment will allow reshaping and improving the morphological (roughness) and optical qualities (transparency) of the generated microfluidics structures. The use of lasers commonly implemented for material processing makes this technique highly competitive when compared with other glass microstructuring approaches. The manufactured chips were tested with tumour cells (Hec 1A) after being functionalized with an epithelial cell adhesion molecule (EpCAM) antibody coating. Cells were successfully arrested on the pillars after being flown through the device giving our technology a translational application in the field of cancer research.

Single-pulse laser ablation threshold of borosilicate, fused silica, sapphire, and soda-lime glass for pulse widths of 500 fs, 10 ps, 20 ns.

In this work, we report a comparative study of the laser ablation threshold of borosilicate, fused silica, sapphire, and soda-lime glass as a function of the pulse width and for IR laser wavelengths. We determine the ablation threshold for three different pulse durations: τ=500  fs, 10 ps, and 20 ns. Experiments have been performed using a single laser pulse per shot in an ambient (air) environment. The results show a significant difference, of two orders of magnitude, between the group of ablation thresholds obtained for femtosecond, picosecond, and nanosecond pulses. This difference is reduced to 1 order of magnitude in the soda-lime substrate with tin impurities, pointing out the importance of the incubation effect. The morphology of the marks generated over the different glass materials by one single pulse of different pulse durations has been analyzed using a scanning electron microscope (FESEM ULTRA Plus). Our results are important for practical purposes, providing the ablation threshold data of four commonly used substrates at three different pulse durations in the infrared regime (1030-1064 nm) and complete data for increasing the understanding of the differences in the mechanisms leading ablation in the nanosecond, picosecond, and femtosecond regimes.

Gradient parameter and axial and field rays in the gradient-index crystalline lens model

Gradient-index models of the human lens have received wide attention in optometry and vision sciences for considering how changes in the refractive index profile with age and accommodation may affect refractive power. This paper uses the continuous asymmetric bi-elliptical model to determine gradient parameter and axial and field rays of the human lens in order to study the paraxial propagation of light through the crystalline lens of the eye.

Table-top laser-based proton acceleration in nanostructured targets

The interaction of ultrashort, high intensity laser pulses with thin foil targets leads to ion acceleration on the target rear surface. To make this ion source useful for applications, it is important to optimize the transfer of energy from the laser into the accelerated ions. One of the most promising ways to achieve this consists in engineering the target front by introducing periodic nanostructures. In this paper, the effect of these structures on ion acceleration is studied analytically and with multi-dimensional particle-in-cell simulations. We assessed the role of the structure shape, size, and the angle of laser incidence for obtaining the efficient energy transfer. Local control of electron trajectories is exploited to maximize the energy delivered into the target. Based on our numerical simulations, we propose a precise range of parameters for fabrication of nanostructured targets, which can increase the energy of the accelerated ions without requiring a higher laser intensity.

Refractive index modification in glass by laser backwriting ablation of metals.

We report the use of laser ablation of metal targets onto a glass substrate as a way of producing waveguiding devices. In the geometry employed, the nanosecond pulses used for the ablation pass through the glass substrate, and are focused on the metal surface, which is located in close proximity with the substrate. We present measurements of the refractive index profile obtained with this technique, and present a discussion of the physical mechanisms that produce the profiles measured.