12,387 research outputs found
Continuous wave and modelocked femtosecond novel bulk glass lasers operating around 2000 nm
No full textThis thesis reports on the development of glass-based femtosecond laser sources around 2 µm wavelength. In order to be able to produce 2 µm radiation the dopants used were trivalent Thulium (Tm³⁺) and trivalent Holmium (Ho³⁺) that could be optically pumped with Ti:Sapphire radiation at 0.8 µm and semiconductor disk lasers (SDL) at 1.2 µm. The samples were produced at Leeds University and polished in-house in bulk form and deployed in free space laser cavities.
Tellurite compounds doped with Tm³⁺ produced stable continuous wave 1.94 µm radiation when pumped at 800 nm with a maximum efficiency of 28.4% with respect to the absorbed power and maximum output power around 120 mW when pumped using a Ti:Sapphire operating around 0.8 µm. The radiation was broadly tunable across 130 nm. Tm³⁺-Ho³⁺ doubly doped tellurite samples lased around 2.02 µm with maximum efficiency of 25.9% and with P[subscript(OUT)]=75 mW and a smooth tunability of 125 nm.
The fluorogermanate glass doped with Tm³⁺ gave an absorbed to output power efficiency of 50%. The maximum continuous wave output powers obtained were around 190 mW and limited by the available pump power at 0.8 µm. These results together with a very low threshold of 60 mW of incident power were comparable to the crystalline counterparts to this gain medium.
The Tm3+ tellurite and the Tm³⁺-Ho³⁺ tellurite compounds were also pumped by an SDL operating at 1215 nm to obtain an indication of the viability of such a pump scheme. The results were a maximum internal slope efficiency of 22.4% with a highest output power of 60 mW. The comparison demonstrated that 1.2 µm pumping was competitive with using 0.8 µm wavelength.
The use of semiconductor saturable absorbing mirror (SESAM) technology was used for the modelocking of these lasers. The SESAM was produced in Canada and implanted with As⁺ ions in order to reduce the relaxation time.
Trains of transform-limited laser pulses at 222 MHz as short as 410 fs centred at 1.99 µm were produced for the first time with a bulk Tm³⁺:Fluorogermanate glass. The maximum average output power obtained was of 84 mW. The same SESAM deployed on the Tm³⁺-Ho³⁺ Tellurite compounds gave trains of transform-limited pulses as short as 630 fs at 2.01 µm with a repetition rate of 143 MHz and a maximum averaged output power of 43 mW. The regime of propagation obtained was soliton-like and the modelocking was self-starting. The results obtained with bulk glass were very promising and open interesting research pathways within the realm of amorphous bulk gain media
Comparison of laser performance for diode-pumped Tm:YLF of various doping concentrations
No full textSingle-end-pumped laser performance of 2, 4, and 6at.% Tm-doped YLF rods is reported. For the pumping configuration employed, crystal fracture was observed to occur for a thermal load per unit absorption length of ~13W/cm. The 2at.% Tm-doped crystal was found to have a quantum yield of ~90% of that of 4at.% Tm. However, due to a lower thermal loading density, the maximum possible incident pump power is predicted to be >60% higher, hence offering a greater output power per rod for the lower doping concentration. Power scaling considerations are discussed with reference to cross-relaxation, upconversion, and thermal loading of the host crystal
Ho-doped silica fibre laser in-band pumped by a Tm-doped fibre laser
No full textOver the last few years there has been increasing interest in power-scaling of fibre-based sources operating in the eyesafe two-micron wavelength regime driven by a range of applications. Much of this interest has focussed on Tm-doped silica fibres which offer wide spectral coverage from ~1.7 µm to ~2.1 µm [1], a range of pump wavelengths and the potential to be scaled to very high powers [2]. By contrast, far less attention has been directed towards Ho-doped silica fibres which also offer a very wide range of emission wavelengths extending well beyond 2.1 µm
Efficient fiber-laser pumped Ho:LuLiF<sub>4</sub> laser
No full textWe present results for an efficient Ho:LuLiF4 laser in-band pumped by a cladding-pumped Tm-doped silica fiber laser. The polarized, tunable Tm-doped silica fiber-laser operates at 1938 nm, ideally suited for in-band pumping the 40 mm long weakly-doped (0.25 at.%) Ho:LuLiF4 crystal. Using a simple laser resonator a maximum output power of 5.1 W was achieved at a wavelength of 2066 nm for 8.0 W of absorbed pump power, when using an output coupling mirror with 20% transmission, corresponding to a slope efficiency of 70%. At a higher cavity output coupling of 37%, the lasing wavelength shifted to a higher gain peak at 2053 nm, where a maximum output power of 5.4 W was obtained with a slope efficiency of 76%. Beam quality was measured to be M2~1.1 at the maximum output power for each resonator configuration. The spectroscopy, lifetime of the upper laser level, and the laser performance will be discussed in terms of future prospects for power scaling and further improvements in the laser efficiency
Charakterisierung von Ho- und Tm-Granat-Laserkristallen
No full textCr,Tm:YAG and Cr,Tm,Ho:YAG crystals were prepared by the Czochralski crystallization method. Spectroscopic properties and laser characteristics of the crystals were studied with special regard to the influence of dope concentration and pumping parameters on the laser efficiency and to the characterization of the starting behaviour of 2 #mu#m lasers and the time response of the pulses. Within the Cr,Tm system best slope efficiency (1.8%) was obtained with a Cr(2%), Tm(7%):YAG laser rod. A substantially improved slope efficiency (3.8%) was found with a Cr(2%), Tm (5.77%), Ho(0.36%):YAG laser rod at the optimal parameters (2123 nm, 15% mirror transmission, 650 #mu#sec pumping, 3 J power output, 130 J pumping energy). Interaction between the Tm "3H_4 - and the Ho "5J_7 levels leads to an attenuation of the oscillation of the Ho-laser. The different dynamical behaviour of TM- and Ho-lasers has to be considered for medical application. (WEN)SIGLEAvailable from TIB Hannover: F93B1394+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman
Growth and spectra properties of Tm, Ho doped and Tm, Ho co-doped CaGdAlO4 crystals
No full textGrowth of Tm, Ho doped and Tm, Ho co-doped CaGdAlO4 crystals by Czochralski method are investigated for the first time. Tm:CaGdAlO4 crystal without any crack was obtained. The segregation coefficient and XRD were detected and the results revealed that the cell parameters decreased with increasing of the doping concentration. The absorption spectra, J-O parameters, emission spectra and fluorescence lifetime of were discussed. The absorption cross sections were calculated to be 0.61 x 10(-20) cm(2) and 1.49 x 10(-20) cm(2) at 793 nm and 798 nm for a polarization and c polarization of Tm:CaGdAlO4 crystal, and the stimulated emission cross-section was calculated to be 0.36 x 10(-20) cm(2) at 1762 nm. The stimulated emission cross-section of Ho:CaGdAlO4 crystal was calculated to be 1.18 x 10(-20) cm(2) at 2002 nm. The width of Tm,Ho:CaGdAlO4 emission band is almost 600 nm. The results show that Tm:CaGdAlO4, Ho:CaGdAlO4 and Tm,Ho:CaGdAlO4 crystals were excellent potential ultrafast laser media. (C) 2014 Elsevier B.V. All rights reserved
Spectroscopy and microchip laser operation of Tm, Ho:KYW crystals with different Ho concentrations
No full text© 2018 Astro Ltd. The spectroscopic properties of Tm, Ho:KYW crystals with different Ho concentrations were investigated. The diode-pumped microchip laser operation of Tm (5 at.%), Ho (0.5 at.%):KYW and Tm (5 at.%), Ho (1 at.%):KYW was demonstrated. The highest, to our knowledge, output power of 480 mW with slope efficiency of 31% for CW Tm (5 at.%), Ho (0.5 at.%):KYW microchip laser was obtained
Spectroscopy and microchip laser operation of Tm, Ho:KYW crystals with different Ho concentrations
No full text© 2018 Astro Ltd. The spectroscopic properties of Tm, Ho:KYW crystals with different Ho concentrations were investigated. The diode-pumped microchip laser operation of Tm (5 at.%), Ho (0.5 at.%):KYW and Tm (5 at.%), Ho (1 at.%):KYW was demonstrated. The highest, to our knowledge, output power of 480 mW with slope efficiency of 31% for CW Tm (5 at.%), Ho (0.5 at.%):KYW microchip laser was obtained
OPTIMIZATION AND DYNAMICS OF 2µm Tm-AND Ho-LASERS
No full textWe have grown several Cr,Tm:YAG and Cr,Tm,Ho:YAG-crystals in order to optimize the dopant concentrations. We observered slope efficiencies of 1.8% for Cr,Tm:YAG and 4% for Cr,Tm,Ho:YAG. Output energies >3 Joules were measured for both crystals. The dynamical behaviour of Tm- and Ho-lasers is very different and is explained by a simple model. The influence of the dynamics on the Q-switch performance of Cr,Tm:YAG and Cr,Tm,Ho:YAG is analyzed
Magnetocaloric effect of Fe-RE-B-Nb (RE = Tb, Ho or Tm) bulk metallic glasses with high glass-forming ability
No full textThe magnetocaloric effect of (Fe0.71RE0.05B0.24)(96)Nb-4 (RE = Tb, Ho and Tm) bulk metallic glasses (BMGs) of diameters up to 6.5 mm were attained by 4.8 at.% RE alloying. The Curie temperature (T-c of Tm doped alloy, being the highest among these alloys, deviates from typical relationship between T-c and de Gennes factor. Its unique electronic structure has been suggested to attribute to the observed trend. Furthermore, Tm doped alloy presents the largest peak magnetic entropy change (|Delta S-M(pk)|) of 1.21 J kg(-1) K-1 for an applied field of 1.5 T, which compares favorably with those of other Nanoperm-type alloys. The phenomenological universal curve for Delta S-M demonstrates that alloys exhibit similar critical exponents at T-c. This family of heavy RE doped Fe-based BMGs is potential candidate used as bulk magnetic refrigerants with the final required shapes. (C) 2015 Elsevier B.V. All rights reserved
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