Javier R. Vázquez de Aldana

Femtosecond laser inscribed cladding waveguides in Nd:YAG ceramics: Fabrication, fluorescence imaging and laser performance

We report on the fabrication of depressed cladding waveguide lasers in Nd:YAG (neodymium doped yttrium aluminum garnet, Nd:Y3Al5O12) ceramics microstructured by femtosecond laser pulses. Full control over the confined light spatial distribution is demonstrated by the fabrication of high contrast waveguides with hexagonal, circular and trapezoidal configurations. The confocal fluorescence measurements of the waveguides reveal that the original luminescence features of Nd3+ ions are well-preserved in the waveguide regions. Under optical pump at 808 nm, cladding waveguides showed continuous wave efficient laser oscillation. The maximum output power obtained at 1064.5 nm is ~181 mW with a slope efficiency as high as 44%, which suggests that the fabricated Nd:YAG ceramic waveguides are promising candidates for efficient integrated laser sources.

Assessment of femtosecond laser induced periodic surface structures on polymer films

In this work we present the formation of laser induced periodic surface structures (LIPSS) on spin-coated thin films of several model aromatic polymers including poly(ethylene terephthalate), poly(trimethylene terephthalate) and poly carbonate bis-phenol A upon irradiation with femtosecond pulses of 795 and 265 nm at fluences well below the ablation threshold. LIPSS are formed with period lengths similar to the laser wavelength and parallel to the direction of the laser polarization vector. Formation of LIPSS upon IR irradiation at 795 nm, a wavelength at which the polymers absorb weakly, contrasts with the absence of LIPSS in this spectral range upon irradiation with nanosecond pulses. Real and reciprocal space characterization of LIPSS obtained by Atomic Force Microscopy (AFM) and Grazing Incidence Small Angle X-ray Scattering (GISAXS), respectively, yields well correlated morphological information. Comparison of experimental and simulated GISAXS patterns suggests that LIPSS can be suitably described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice. Fluorescence measurements, after laser irradiation, provide indirect information about dynamics and structure of the polymer at the molecular level. Our results indicate that the LIPSS are formed by interference of the incident and surface scattered waves. As a result of this process, heating of the polymer surface above its glass transition temperature takes place enabling LIPSS formation.

Ultraviolet and infrared femtosecond laser induced periodic surface structures on thin polymer films

This work demonstrates the formation of femtosecond laser induced periodic surface structures (LIPSS) by multipulse irradiation with the fundamental and 3rd harmonic of a linearly polarized Ti:sapphire laser (795 and 265 nm) on thin films of the polymers poly (ethylene terephthalate), poly (trimethylene terephthalate), and poly (carbonate bisphenol A) prepared by spin-coating. LIPSS, inspected by atomic force microscopy, are formed upon multiple pulse UV and IR irradiation with wavelength-sized period in a narrow range of fluences below the ablation threshold. Control and tunability of the size and morphology of the periodic structures become thus possible ensuring photochemical integrity of polymer films.

Channel waveguide lasers in Nd:GGG crystals fabricated by femtosecond laser inscription

Buried channel waveguides have been fabricated in Nd:GGG crystals by using the femtosecond laser inscription. The waveguides are confined between two filaments with propagation losses of 2.0 dB/cm. Stable continuous wave laser oscillation at ~1061 nm has been demonstrated at room temperature. Under 808 nm optical excitation, a pump threshold of 29 mW and a slope efficiency of 25% have been obtained.

Femtosecond laser micromachining of lithium niobate depressed cladding waveguides

We report on the fabrication and characterization of femtosecond laser micromachined depressed cladding waveguides in lithium niobate crystal. The cladding structures support two-dimensional guidance of light from the visible to the mid-infrared spectral regimes. Particularly, single-mode propagation of light at a wavelength of 4 μm has been achieved for the waveguides with diameter of 50 μm. It is also found that the thermal annealing treatment reduces the propagation loss lower than 0.5 dB/cm at 1.064 μm, exhibiting good transmission properties for photonic applications.

Monolithic crystalline cladding microstructures for efficient light guiding and beam manipulation in passive and active regimes

Miniature laser sources with on-demand beam features are desirable devices for a broad range of photonic applications. Lasing based on direct-pump of miniaturized waveguiding active structures offers a low-cost but intriguing solution for compact light-emitting devices. In this work, we demonstrate a novel family of three dimensional (3D) photonic microstructures monolithically integrated in a Nd:YAG laser crystal wafer. They are produced by the femtosecond laser writing, capable of simultaneous light waveguiding and beam manipulation. In these guiding systems, tailoring of laser modes by both passive/active beam splitting and ring-shaped transformation are achieved by an appropriate design of refractive index patterns. Integration of graphene thin-layer as saturable absorber in the 3D laser structures allows for efficient passive Q-switching of tailored laser radiations which may enable miniature waveguiding lasers for broader applications. Our results pave a way to construct complex integrated passive and active laser circuits in dielectric crystals by using femtosecond laser written monolithic photonic chips.

Efficient continuous-wave laser operation at 1064 nm in Nd:YVO 4 cladding waveguides produced by femtosecond laser inscription

Cladding waveguides have been produced in Nd:YVO4 crystals by using femtosecond laser inscription. Such structures are fabricated with circular cross sections and diameters of ~100-120 μm, supporting multi-mode guidance in the two orthogonal polarizations. At room temperature continuous wave laser oscillations at wavelength of ~1064 nm have been realized through the optical pump at 808 nm with slope efficiency as high as 65% and a maximum output power of 335 mW.

Diffractive optics for spectral control of the supercontinuum generated in sapphire with femtosecond pulses

We propose the use of kinoform diffractive lenses to focus near infrared femtosecond pulses in sapphire crystals for supercontinuum generation. It is shown that a strongly peaked structure appears in the blue region of the supercontinuum spectra. The central wavelength of this peak can be easily controlled by simply changing the lens-crystal distance. Moreover, when compared with the supercontinuum generated with a refractive lens in analogous conditions, the spectral extension of the so-generated continuum is larger. Our results were corroborated for sapphire plates with different thicknesses as well as in other transparent dielectrics such as fused silica.

Ridge waveguide lasers in Nd:GGG crystals produced by swift carbon ion irradiation and femtosecond laser ablation.

We report on the fabrication of ridge waveguide in Nd:GGG crystal by using swift C(5+) ion irradiation and femtosecond laser ablation. At room temperature continuous wave laser oscillation at wavelength of ~1063 nm has been realized through the optical pump at 808 nm with a slope efficiency of 41.8% and the pump threshold is 71.6 mW.

Continuous wave ridge waveguide lasers in femtosecond laser micromachined ion irradiated Nd:YAG single crystals

Ridge waveguides have been fabricated in Nd:YAG single crystal by using femtosecond laser micromachining in an oxygen ion irradiated planar waveguide. The microphotoluminescence features have been found well preserved in the waveguide structures. Continuous wave lasers have been realized at 1.06 µm at room temperature in the ridge waveguide system with a lasing threshold of ~39 mW and a slope efficiency of 35%, which show superior performance to the planar waveguide.