Fs-laser-written erbium-doped double tungstate waveguide laser

[EN]We report on the first erbium (Er3+) doped double tungstate waveguide laser. As a gain material, we studied a monoclinic Er3+:KLu(WO4)2 crystal. A depressed-index buried channel waveguide formed by a 60 μm-diameter circular cladding was fabricated by 3D femtosecond direct laser writing. The waveguide was characterized by confocal laser microscopy, μ-Raman and μ-luminescence mapping, confirming that the crystallinity of the core is preserved. The waveguide laser, diode pumped at 981 nm, generated 8.9 mW at 1533.6 nm with a slope efficiency of 20.9% in the continuous-wave regime. The laser polarization was linear (ENm). The laser threshold was at 93 mW of absorbed pump power

Infrared lasers based on ho3+:kre(wo4)2 crystals with tm3+or yb3+ as sensitizers

Laseres de estado sólido que operan en la región espectral de seguridad ocular alrededor de los 2 micrómetros (2µm) son de elevado interés en la actualidad debido a su potencial aplicación en los campos de la medicina, teledetección remota y como fuentes de bombeo en osciladores ópticos paramétricos (OPOs) para conversión en el infrarrojo medio. La transición láser en las 2 µm es posible en los iones de tulio (Tm) ligeramente por debajo de las 2 µm y en iones de holmio (Ho) ligeramente por encima de las 2 µm. La generación láser en iones de Tm es relativamente simple con la utilización de láseres de diodo como fuentes de bombeo, sin embargo, los láseres basados en Ho se han conseguido tradicionalmente en el pasado mediante el codopaje con Tm o mediante bombeo directo del nivel emisor del Ho. Recientemente, diodos láser que operan a 1.9 µm han aparecido en el mercado con buena eficiencia y con alto potencial para el escalado en potencia de los láseres de Ho. Los láseres de Ho son más apropiados que los láseres de Tm especialmente para aplicaciones médicas por dos razones: La longitud de onda láser ligeramente por encima de las 2 µm, donde el agua (mayor componente del cuerpo humano) presenta una ligera menor absorción que la típica longitud de onda láser del Tm, hace que el láser penetre más en el tejido humano. La segunda razón es que los láseres de Ho pueden operar en régimen pulsado generando mayores energías por pulso que los láseres de Tm debido al mayor tiempo de vida del nivel emisor 5I7 y las aplicaciones médicas requieren por lo general régimen pulsado para evitar daño térmico del tejido. Numerosos óxidos y fluoruros cristalinos han demostrado ser adecuadas matrices para Ho, sin embargo, poca atención se ha puesto en los dobles tungstatos cristalinos de fase monoclínica, de fórmula química KRE(WO4)2, brevemente KREW, donde RE = Y, Gd y Lu conocidos por ser matrices láser muy eficientes para la generación láser a potencias intermedias. Estos cristales anisotrópicos presentan una elevada sección eficaz de absorción y emisión cuando son dopados con iones lantánidos y especialmente para ciertas polarizaciones. Considerando el potencial del Ho y las buenas propiedades de KREW, nuestro trabajo se centra en la investigación de las prestaciones láser en cristales de KREW dopados con Ho utilitzando tanto Tm o Yb como iones sensibilizadores y utilizando fuentes de bombeo emitiendo a 1.9 µm que permiten la excitación directa del nivel emisor. En esta tesis, presentamos los resultados basados en el crecimiento cristalino de monocristales de Ho:KREW, codopajes (Ho,Tm) y (Ho,Yb):KLuW a diferentes concentraciones de Ho, su caracterización en términos de estructura, composición y espectroscopia y finalmente la generación láser alrededor de 2.1 µm.Eye-safe solid-state lasers that operate in the 2µm spectral range are the subject of interest in the present years because of their potential applications in the field of remote sensing, medicine and as a pump source for Optical Parametric Oscillators (OPOs). Laser transitions around 2 µm are possible in the trivalent lanthanide ions Tm3+ (Tm) (slightly below 2 µm) and Ho3+ (Ho) (slightly above 2 µm). Laser generation in Tm ions is easily achieved with comfortable diode pump sources, however, Ho lasers have usually been achieved in the past either by co-doping the active medium with Tm or by direct pumping of the Ho ions with Tm lasers. Recently, relatively cheap diodes emitting around 1.9 µm are in the market to realize Ho lasers with great potential for power scaling. Ho lasers are more suitable than Tm lasers especially for medical applications because of two reasons: The laser wavelength is slightly above 2µm, where water (main component of human tissue) shows slightly less absorption than the typical wavelength of Tm leading to a deeper penetration in human tissue. The second reason is that Ho lasers can operate in pulsed regime delivering higher energies than Tm lasers due to the longer lifetime of the emitting level 5I7 and medical applications are required to be generally in pulsed regime to avoid thermal damage of human tissue. Many oxide and fluoride crystals were shown to be suitable host for Ho, however little attention was paid to the monoclinic potassium rare earth double tungstate crystal, shortly KRE(WO4)2 or KREW, where RE= Y, Gd, Lu known to be very efficient rare earth solid state hosts for generating intermediate power levels. These anisotropic crystals exhibit very high absorption and emission cross sections when doped with lanthanide ions and especially for selected polarizations. Considering the potentialities of Ho and good properties of KREW, our work focuses in the investigation of the laser performances of a Ho doped KREW either by using Tm or Yb as sensitizers and by using in-band pump sources emitting around 1.9 µm, where the development of compact solid state infrared laser emitting at 2.1 µm for intermediate power levels is followed. Here, in this thesis, we present the results based on growth of single doped Ho:KREW, co-doped (Ho,Tm) and (Ho,Yb):KLuW crystals of several doping concentrations, their characterisation in terms of structure, composition and spectroscopy and finally dedicated for the laser generation around 2.1 µm from these materials, which was highly successful

Crystal growth, optical spectroscopy, and continuous-wave laser operation of co-doped (Ho,Tm):KLu(WO4)2 monoclinic crystals

We report on the crystal growth, optical spectroscopy, and room-temperature continuous-wave laser generation around 2 μm with co-doped (Ho,Tm):KLu(WO4)2 monoclinic crystals. Co-doped crystals at different doping levels were grown by the top-seeded solution growth slow-cooling method. We characterized the spectroscopy of Ho and Tm ions in KLuW in terms of polarized optical absorption, photoluminescence, and lifetime measurements. Continuous-wave laser operation at room-temperature at a wavelength of 2.06 μm was achieved with several crystals at different co-doping levels, establishing that the optimum doping ratio is 5.29 × 1019 at./cm3 for Ho and 3.10 × 1020 at./cm3 for Tm (0.5 at. %Ho, 5.0 at. %Tm:KLuW), reaching a maximum output power of 145 mW and a slope efficiency of 12.9%.This work was supported by the Spanish Government under project MAT2011-29255-C02 and by the Generalitat de Catalunya under project 2009SGR235. It has been partially funded by the European Commission within the Seventh Framework Programme, under projects Cleanspace and FP7-SPACE2010-1–GA-263044