We present an approach to generate paraxial laser beams with arbitrary spatial distribution in the femtosecond time regime. The proposed technique is based upon a pair of volume phase holographic gratings working in parallel arrangement. It exploits the spatial coherence properties of the incoming laser beam in a compact and robust setup that mitigates angular and spatial chirp. The gratings were recorded in a photopolymerizable glass with a high optical damage threshold and a large optical throughput. Setup performance is studied and experimentally demonstrated by generating Laguerre-Gaussian femtosecond pulses.

Three different holographic photomaterials belonging to the class of photopolymerizable glasses have been synthesized using sol-gel techniques, and characterized with the purpose of a comparative study. Their behavior is analyzed in terms of achieved refractive index modulation, dark diffusion mechanism, diffraction efficiency and optical quality; in order to determine their suitability for different holographic applications.

Abstract:The majority of the applications of ultrashort laser pulses require a control of its spectral bandwidth. In this paper we show the capability of volume phase holographic gratings recorded in photopolymerizable glasses for spectral pulse reshaping of ultrashort laser pulses originated in an Amplified Ti: Sapphire laser system and its second harmonic. Gratings with high laser induce damage threshold (LIDT) allowing wide spectral bandwidth operability satisfy these demands. We have performed LIDT testing in the photopolymerizable glass showing that the sample remains unaltered after more than 10 million pulses with 0,75 TW/cm 2 at 1 KHz repetition rate. Furthermore, it has been developed a theoretical model, as an extension of the Kogelnik's theory, providing key gratings design for bandwidth operability. The main features of the diffracted beams are in agreement with the model, showing that non-linear effects are negligible in this material up to the fluence threshold for laser induced damage. The high versatility of the grating design along with the excellent LIDT indicates that this material is a promising candidate for ultrashort laser pulses manipulations.

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Experimental results to the saturation and diffraction efficiency from holographic gratings are presented in this investigation. The experiments were carried out during real time holographic gratings formation. Dichromated poly(vinyl alcohol) was doped with nickel(II) chloride hexahydrate and it is used like optical material. The influence of the hologram parameters to get the maximum diffraction efficiency is studied at room conditions. This study contributes to get more information about the behavior of this material for holographic gratings recording.

Thermal poling induced second-order nonlinearity in femtosecond-laser-modified fused silica Appl. Phys. Lett. 93, 061115 (2008) A procedure to characterize the induced damage and the incubation effects in volume transmission gratings under femtosecond laser pulse train illumination is presented. It was also developed a formalism that explains the damage processes. Our proposal was employed on glass gratings to show the effectiveness of the method and its potential to design transmission gratings with enhanced laser induced damage threshold. This procedure is able to be extended to any transmission grating composed by chemically non-uniform material, opening up new perspectives to femtosecond laser pulse shaping. V C 2014 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4892010] Diffraction gratings are essential parts of femtosecond laser systems. They are used as dispersive elements in compressors and stretchers as well as for temporal, spatial, and spectral pulse shaping, to name a few. A laser induceddamage threshold (LIDT) characterization of gratings, i.e., the highest fluence value for which no damage is produced, is a main task to determine its applicability range. In the last years, LIDT in reflection multilayer dielectric gratings [1][2][3] and in mixed metal dielectric gratings 4 has been investigated by varying the material composition of the multilayer and by proving different grating profiles. The damage dynamics were established for a wide class of gratings, but only in the reflection geometry. No research on LIDT has been reported in the transmission geometry at the present time. In this Letter, we propose a procedure to characterize the induced damage and the incubation effects, i.e., permanent material changes produced by multiple pulse accumulation mechanisms, in volume transmission gratings when implemented in a femtosecond laser system. Besides, we develop a formalism to explain the damage processes. Our approach is tested on a photopolymerizable glass grating, showing the validity of the method to design transmission gratings with enhanced LIDT.The analysis is based on the photopolymerizable glass 5-9 because the transmission gratings on this type of material have been implemented to spatial 10 and spectral 11 pulse shaping in a femtosecond laser system. We start with the grating characterization. The grating is formed by a permanent spatial modulation of the refractive index, nðxÞ ¼ n b þ n 1 ðxÞ; within the bulk of the glass. Parameter n b is the background refractive index of the insulating binder (the glass) and

Abstract:We show experimentally that the metallic salt, FeCl 3 , at different concentrations, provides photosensitivity and conductivity characteristics with poly(vinyl alcohol) material. The holographic recording in this photosensitive material was made in real time.The effect of applied voltage on holographic diffraction gratings in the recording process and the changes in their diffraction efficiency, depending on their composition, are shown. In addition, we describe the photo-mechanism, physicochemical processes, and water condensations involved in changes of the formation of images due to applied voltage. The results suggest that polymers doped with metallic salts may have potential as inexpensive photosensitive materials that are easy to work under normal laboratory condition.

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