I. Arias

Observation of spontaneous self-channeling of light in air below the collapse threshold

We report the observation of the self-guided propagation of 120 fs, 0.56 mJ infrared radiation in air for distances greater than 1 m. In contrast with the known case of filamentation, in the present experiment the laser power is lower than the collapse threshold. Therefore the counterbalance between Kerr self-focusing and ionization induced defocusing as the stabilizing mechanism is ruled out. Instead, we find evidence of a process in which the transversal beam distribution reshapes into a form similar to a Townes soliton, with the particularity of a very high stability. We include numerical support for this conclusion.

Silver halide sensitized gelatin process effects in holographic lenses recorded on Slavich PFG-01 plates

In this work we study the feasibility of using silver halide sensitized gelatin based on PFG-01 (Slavich) emulsions to construct uniaxial compound lenses. This processing is able to introduce variations in the thickness and refractive index of the emulsion. We prove that these changes are not sufficient to provide the observed variations in Bragg conditions in the reconstruction and that a shear-type effect must exist to explain the performance of processed emulsions. We study the characteristics of a compound lens, obtaining acceptable image quality, good resolution, and the typical field limitation of volume holographic elements.

Femtosecond laser induced micromodifications in Nd:SBN crystals: Amorphization and luminescence inhibition

We report on femtosecond laser modification of Nd:SBN crystals. Basic properties such as the ablation threshold have been obtained from the analysis of the ablation depths at different laser fluences. The induced micromodifications have been investigated by optical microscopy as well as by microphotoluminescence and micro-Raman experiments. We have found that in the vicinity of the ablated volume material amorphization can be induced along different directions. Furthermore, we have found that this material amorphization is accompanied by a strong inhibition of the Nd3+ luminescence. The analysis of the spatial extension of the luminescence inhibition as a function of the laser fluence has been used to elucidate the origin of the femtosecond laser induced material amorphization.

Field improvement in a uniaxial centered lens composed of two stacked-volume holographic elements

Arrangements are described for the recording of volume holograms with two sections that, when stacked together, work as uniaxial centered lenses and allow one to solve the problem of angular selectivity in the imaging of wide objects. The performance of such systems is examined qualitatively, and suggestions aimed at improving these designs are proposed.

Anamorphic white light Fourier processor with holographic lenses

Two anamorphic and achromatic Fourier processors were designed and constructed using diffractive and refractive cylindrical lenses. The diffractive lenses are holographic lenses recorded on silver halide material. In both processors the achromatic one-dimensional Fourier transform plane was obtained with two holographic lenses and one refractive cylindrical lens. The image with the same magnification in both directions at the output plane was formed with two different combinations of lenses. The differences between the two processors are analyzed, and in both cases the chromatic aberration in the Fourier plane and in the output plane is evaluated. Even though single cylindrical refractive lenses were used to image in one direction, good results were obtained.

Fabrication and characterization of Mach-Zehnder devices in LiNbO/sub 3/ written with femtosecond laser pulses

In this work the fabrication and characterization of Mach Zehnder interferometers fabricated on lithium niobate substrates by using femtosecond laser writing is presented. The main features and guiding performance of these devices are also shown. The overall losses were determined for different bending angles, from this study 0.65/spl deg/ was obtained as the maximum angle to get appreciable output signal at the interferometers. This one step process fabrication method opens the possibility to write more complexes geometries either on the surface or inside these interesting optical crystals.

Pulse compression with volume holographic transmission gratings recorded in Slavich PFG-04 emulsion

In this work we design and construct a pulse compressor with volume transmission holographic gratings, to compensate the second order dispersion in femtosecond laser pulses emitting at 794 nm with a spectral broadband of 10 nm. The gratings (730 lines/mm) are recorded in PFG-04 dichromated gelatine emulsion with a wavelength of 532 nm, reaching enough index modulation to use the gratings illuminated with 800 nm light source with high efficiency (around 80% of efficiency in each grating). This efficiency is expected to be increased with an antireflection coating. We measure the factor of compression as a function of the grating distance using an autocorrelator, finding a good agreement with theoretical curve. A dispersed pulse (580 fs) is reduced to the bandwidth limited value of 106 fs with the grating pair separated by 27 mm.

Design of a holographic optical element for a pulse compressor

Nonlinear chirped pulse compression can be theoretically achieved to any order by using a nonplane grating with adequate groove spacing. We evaluate the holographic recording of a grating that compensates to the quadratic chirp. A suitable design is found, and the building tolerances are analyzed.

Nonlinear effects in the propagation of short laser pulses in air

Non linear propagation of ultra short pulses in air is studied. By preparing an initial field distribution by an amplitude mask we can obtain a Townes soliton[1] (self similar channel of coherent radiation) in air. Experimental observation can be described accurately by the numerical integration of the Non Linear Schroedinger Equation (NLSE) and allow us to explain the origin of the remarkable stability of this soliton as a balance between diffraction and Kerr effect. We further explore on the role of coherence by revisiting the two slit Youngs experiment but now in the non linear regime.

Observation of channels of radiation during the propagation in air of short pulses below the collapse threshold

We report the observation of self-guided propagation of 120 fs, 0.56 mJ infrared pulse in air for distances greater than a meter (more than thirty Rayleigh Lengths). The numerical simulations demonstrates the this localized structure corresponds to a Townes soliton, specially stable under these conditions.