G. A. Torchia

Red, green, and blue simultaneous generation in aperiodically poled Zn-diffused LiNbO3:Er3+/Yb3+ nonlinear channel waveguides

In this work, continuous-wave broadly tunable simultaneous generation of red (650–690 nm), green (520–575 nm), and blue (425–495 nm) light in aperiodically poled Zn-diffused LiNbO3:Er3+/Yb3+ channel waveguides is reported after Ti:sapphire excitation in the 850–990 nm range. The red and green emissions arise from energy transfer and upconversion mechanisms between Yb3+ and Er3+ ions, while the blue light with a maximum efficiency of 0.04% W−1 cm−1 is produced by quasi-phase matching processes.

Continuous wave laser generation at 1064 nm in femtosecond laser inscribed Nd:YVO4 channel waveguides

We report on continuous wave 1064 nm laser generation from an ultrafast laser inscribed neodymium-doped yttrium orthovanadate channel waveguide with pumping at 808 nm. Single-mode stable laser operations have been observed with pump powers at threshold as low as 14 mW and with laser slope efficiencies as high as 38.7%.

Femtosecond laser written surface waveguides fabricated in Nd:YAG ceramics

Near surface channel waveguides have been fabricated in Neodymium doped YAG ceramics by using IR femtosecond laser irradiation at the low frequency regime. Single mode guidance has been demonstrated with propagation losses of ~1 dB/cm. Time resolved confocal micro-luminescence experiments have been used to determine the spectroscopic properties of the Nd(3+) laser ions in the channel waveguide as well as to elucidate the waveguide formation processes.

Femtosecond-laser-written, stress-induced Nd:YVO 4 waveguides preserving fluorescence and Raman gain

We report the formation of optical waveguides in the self-Raman Nd:YVO(4) laser crystal by femtosecond laser inscription. The confocal fluorescence and Raman images have revealed that the waveguide is constituted by a locally compressed area in which the original fluorescence and Raman gains of the Nd:YVO(4) system are preserved. Thus the obtained structures emerge as promising candidates for highly efficient self-Raman integrated laser sources.

Anisotropic lattice changes in femtosecond laser inscribed Nd3+:MgO:LiNbO3 optical waveguides

We report on the fabrication and microspectroscopy imaging of femtosecond laser written double-filament based Nd3+:MgO:LiNbO3 optical waveguides. The waveguiding high refractive-index regions are identified by blueshifts of the Nd3+ ion fluorescence lines with no deterioration in the fluorescence efficiency, whereas filamentary low-index regions are identified by both a Nd3+ line redshift and a fluorescence efficiency reduction. The lattice structural micromodifications at the origin of both waveguide formation and Nd3+ fluorescence changes have been investigated by means of confocal micro-Raman experiments. We have found that the direct laser written filaments are mainly constituted by a large density of defects, together with a marked axial compression perpendicular to the filaments (along the optical c-axis). Conversely, the high-index waveguiding regions are characterized by a pronounced anisotropic dilatation of the LiNbO3 lattice xy-planes.

Silver-silver oxide core-shell nanoparticles by femtosecond laser ablation: core and shell sizing by extinction spectroscopy

The generation of small silver metal nanoparticles (Nps) by ultrashort pulsed laser ablation has been an active area of research in recent years due to their interest in several fields of applied research such as biotechnology and material research, in particular those with sizes smaller than 10 nm. In general, laser ablation tends to produce environmentally clean metal Nps compared with wet chemical methods. However, since silver may be oxidized in the presence of water or ethanol, core–shell silver–silver oxide (Ag–Ag2O) Nps can be formed, whose size and thickness must be determined and characterized for functionalization related to future applications. This work analyses the size characteristics of core–shell Ag–Ag2O colloid nanostructures (smaller than 10 nm) obtained by femtosecond laser ablation of solid silver targets in different liquid media (water or ethanol) through the study of their optical extinction spectra. A fit of full experimental spectrum using Mie theory allows the determination of core size and shell thickness distributions as a function of fluence. The red-shift of the plasmon peak wavelength with respect to the bare-core peak wavelength at 400 nm, produced by the oxide shell, may be easily measured even for very small thicknesses. It was found that the dominant Ag2O effective thickness is inversely proportional to the fluence, reaching a maximum of 0.2 nm for a fluence of 60 J cm−2 and a minimum of 0.04 nm for a fluence of 1000 J cm−2.

Self-frequency-doubling of ultrafast laser inscribed neodymium doped yttrium aluminum borate waveguides

Buried channel optical waveguides, supporting orthogonal polarizations, have been fabricated in a neodymium doped yttrium aluminum borate nonlinear laser crystal by ultrafast laser inscription following the so-called “double line” approach. Confocal fluorescence and second harmonic imaging experiments have revealed that the original fluorescence and nonlinear properties have been not deteriorated by the waveguide inscription procedure. Preliminary laser experiments have shown the ability of the fabricated structures for green laser light generation under 808 nm optical pumping by self-frequency-doubling of the 1.06 μm laser line of neodymium ions.

Analysis of the main optical mechanisms responsible for fragmentation of gold nanoparticles by femtosecond laser radiation

Studies of fragmentation process of gold nanoparticles (Nps) in deionized water after generation by femtosecond laser ablation were performed. To analyze the fragmentation process, direct IR ultrafast pulses or super-continuum (SC) radiation focused in the colloidal solution were used in separate steps. IR pulses and SC generated externally in a sapphire crystal or directly inside the water were applied under low fluence regime. In the latter cases, to evaluate the effect on fragmentation of the different spectral bands present in the SC, we have determined different efficiency regions characterized by means of the product between the spectral response and the optical extinction spectrum corresponding to the initial Nps solution. From the analysis of this product function, we can conclude that the main fragmentation mechanism is due to linear absorption in the visible region. Likewise, the SC generated in water resulted more efficient than the SC obtained externally by a sapphire crystal. This fact may be...

μ-Raman spectroscopy characterization of LiNbO3 femtosecond laser written waveguides

In this paper, we present an iterative method which merges experimental μ-Raman measurements and numerical simulations to describe femtosecond written waveguides in LiNbO3 crystals. This method is based on the deformation potential theory, and uses the finite element method to analyze elastic deformations after femtosecond laser micro-explosions in x-cut Mg:LiNbO3 crystals. The resultant strain and refractive index field after laser interaction were estimated and yielded similar values to those obtained in other works. The LiNbO3 Raman deformation potential constants were also estimated in this work.

High-order harmonic generation driven by chirped laser pulses induced by linear and non linear phenomena

Abstract We present a theoretical study of high-order harmonic generation (HHG) driven by ultrashort optical pulses with different kind of chirps. The goal of the present work is to perform a detailed study to clarify the relevant parameters in the chirped pulses to achieve a noticeable cut-off extensions in HHG. These chirped pulses are generated using both linear and nonlinear dispersive media. The description of the physical mechanisms origin responsible for this extension is, however, not usually reported with enough detail in the literature. The study of the behaviour of the harmonic cut-off with this kind of pulses is carried out in the classical context, by the integration of the Newton-Lorentz equation complemented with the quantum approach, based on the integration of the time dependent Schrödinger equation in full dimensions (TDSE-3D). Graphical abstract