1,720,974 research outputs found
Towards an experimentally simple procedure for the determination of energy transfer parameters in gain media
No full textA promising technique is presented for characterization of rates of energy transfer within solid-state laser crystals. The technique is applied to a 6at.% Tm3+:YLF crystal pumped with a 1680nm laser diode
Temperature dependent Nd:KGW spectroscopy study
No full textWe report a high resolution spectroscopic characterisation of Nd:KGW as a function of temperature, over the range 80K - 450K. Measurements were made for the two dominant polarizations, with respect to the principal optical axes for the double tungstate crystal, namely E//Nm and E//Np for an Ng – cut crystal. Knowledge of the critical spectroscopic characteristics at various temperatures enables more accurate prediction of laser performance over a large range of possible operating conditions
Concentration dependence of energy transfer upconversion in Nd:YAG
No full textThe concentration dependence of energy transfer upconversion in Nd:YAG is investigated via the z-scan technique. The ETU coefficient is determined to increase from 35×10-18 cm3/s to 90×10-18 cm3/s when the concentration increases from 0.3 at.% to 1.1 at.%
Pulsed laser deposition of Yb:Y<sub>2</sub>O<sub>3</sub> planar waveguide lasers
No full textRare earth-doped sesquioxides, particularly yttria (Y2O3), scandia (Sc2O3) and lutetia (Lu2O3), are very promising materials for high power laser applications due to their excellent combination of thermal, optical and spectroscopic properties. These simple cubic crystals have been successfully doped with rare earth elements such as Yb, Tm and Er, but are challenging to grow as bulk crystals, due to their high melting points (~2400°C).Using pulsed laser deposition, we have grown both single and multilayer Yb-doped crystalline yttria waveguides on 1 cm2 YAG substrates. A multilayer sample with a 3 µm Y2O3 layer either side of a 6 µm Yb:Y2O3 doped region gave a maximum output power of 1.2 W at 1030 nm, for ~10.5 W of diode pump power. This waveguide design provides significantly higher gain for the fundamental waveguide mode than for higher order modes, enabling efficient multimode pumping whilst favouring diffraction limited output. The maximum observed slope efficiency was 22% (with respect to absorbed power), using a simple quasi-monolithic plane-plane resonator cavity with a 30%R output coupler. With no active cooling, even at these high pump powers, no sign of thermal effects in the waveguide have been observed, confirming the excellent thermal properties of this material.We will discuss these first results together with further experiments that will be performed with an optimised cavity length to achieve higher output power, lower threshold and greater slope efficiency
Concentration dependence of energy transfer upconversion in Nd:YAG
Full text linkWe present measurements of the concentration dependence of the energy transfer upconversion (ETU) macro-parameter in Nd:YAG obtained via the Z-scan technique. The ETU coefficient is found to increase from 27 × 10-18 cm3/s to 75 × 10-18 cm3/s when the concentration increases from 0.31 at.% to 1.07 at.%
Measurement of energy transfer upconversion in Nd:YAG via the z-scan technique
No full textNd:YAG is one of the workhorse gain materials for many industrial, medical and scientific laser systems. Despite a relatively high quantum defect the spectroscopic properties of the 1064 nm transition enable quite efficient operation, while the lower gain transition around 946 nm, which potentially could be more efficient due to a lower quantum defect, is additionally severely affected by detrimental thermal effects in the host material.One potentially significant parameter that leads to a non-radiative decay channel during laser operation is energy transfer upconversion (ETU). ETU can have a detrimental effect on the laser performance as an additional source of heat, furthermore reducing the population inversion and lowering the potential gain. Whilst there are many papers studying the influence of ETU on the quasi-four-level laser performance, both experimental and in simulation, the magnitude of the ETU coefficient reportedly ranges from the upper laser level has a significant range of reported values from 5x10-17 to 3x10-16 cm3/s [1, 2], as such its actual impact on performance can be difficult to ascertain with certainty. In this work, we investigate 1at.% Nd:YAG using the z-scan technique to obtain a very sensitive measure of the ETU coefficient, determined to be 4.2 ± 0.4 x 10-17 cm3/s with excellent agreement between simulation and experimental data.The Z-scan technique is a simple method, in which the change in transmission of the sample is measured as it is moved through the focus of a pump laser beam, and correlated to the saturation irradiance. Our experiment used a Ti:sapphire laser tuned to absorption peaks of Nd3+ and focussed to a beam waist radius of 20.6 ± 0.2 µm, providing a "uniform" beam throughout our 3.25 mm long 1at.% Nd:YAG sample (deviating <2% from the front to rear of the crystal). When the pump laser was tuned to 808 nm the peak (on axis) irradiance available was 54 kWcm-2, nominally four times the saturation irradiance for this absorption line. A simple spatially dependent steady state model, involving just the ground and upper laser level rate equations has been used to interpret the transmission variation as a function of pump beam irradiance, i.e. the sample position. While ground state bleaching increases the pump transmission with higher irradiance values, ETU has the opposite effect, reducing the amplitude of the highest transmission point at the highest pump irradiance, i.e. at focus. This process provides a surprisingly sensitive measure of the magnitude of the ETU coefficient. We will present a comparison of the value determined in our work and that reported in the literature and discuss the implications for the operation of the weaker laser transitions of Nd:YAG
Amplification of a radially polarised beam in an Yb:YAG thin-slab
Full text linkThe use of an Yb:YAG thin-slab architecture for amplification of a radially-polarised beam at 1030 nm is investigated and shown to be a promising route for power scaling. The detrimental impact of the Gouy phase shift on radial polarisation purity is considered and a simple scheme for effective phase shift management to restore polarisation purity is presented. Preliminary experiments based on a double-pass amplifier configuration yielded an output beam with a high radial polarisation extinction ratio of 15dB and no degradation in polarisation purity despite the non- axial symmetry of amplifier gain medium. At 50W of launched pump power a small-signal gain of 7.5dB was obtained for a 25mW input, whilst 4.4dB gain was obtained for a 1.45W input. The prospects for further power scaling are discussed
Energy transfer upconversion measurements for popular neodymium-doped crystals
No full textWe report our investigations on measuring the energy transfer upconversion (ETU) parameter in various neodymium-doped laser crystals (YAG, YVO4, GdVO4, KGW, and YLF) via the z-scan technique. Starting with a simple two-level macro-parameter spatially dependent rate equation model we obtain a good correlation for Nd:YAG at different concentrations and crystal temperatures, however the other crystals illustrate significant deviation between simulation and measurement. Currently we attribute this difference to additional ion-ion interactions in the respective samples, for which a more detailed model is currently being considered. Of the tested materials Nd:YAG appears to have the lowest ETU macro parameter, at around 0.35 x 10-16 cm3/s for a 0.6 at.% doping concentration, compared with nominally thrice this for 0.5 at% Nd:YLF and almost an order of magnitude higher for the 0.5 at.% vanadates (YVO4 and GdVO4). These values are significant for determining additional heat load in the respective gain media, especially when trying to increase the output power/energy from lasers employing these crystals, typically achieved by increasing the pump and cavity mode size
Crystal planar waveguides, a power scaling architecture for low-gain transitions
No full textIn this paper we present the underlying advantages that make the crystalline planar waveguide (PW) the key ingredient in power-scaling difficult or "weak" laser transitions, especially those which are extremely challenging to operate in other gain medium configurations. The planar waveguide architecture is shown to enable efficient laser operation of low-gain and/or quasi-four-level transitions that suffer reabsorption losses. Exemplar configurations are reported to make this case, for example, 1.4 W at 1.8 µm from a Nd:YAG double-clad planar waveguide laser (PWL), in addition to 0.5 W at 2.7 µm from a similar highly doped Er:YAG PWL. New laser performance levels from sesquioxide PWs fabricated by pulsed laser deposition are also presented for the first time, with >1 W obtained from a Yb:Y2O3 PWL. Current performance and future prospects are discussed for this laser architecture
1.2 W Yb:Y<sub>2</sub>O<sub>3</sub> planar waveguide laser
No full textA 12µm thick composite Yb-doped and undoped yttria layer is grown on a YAG substrate by pulsed laser deposition. For 8.5W of incident laser diode pump power the waveguide laser emits 1.2W at 1030nm
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