1,720,971 research outputs found
Multi-Watt, diode-pumped planar waveguide lasers
No full textThis thesis reports on progress towards diode-bar pumped crystal waveguide lasers with a high-power, high-quality output. It is shown that in order to accommodate the highly divergent, non-diffraction limited output from a diode-bar pump source, a waveguide with a relatively large numerical aperture (NA) is required. A selection of suitable waveguide fabrication techniques, including liquid phase epitaxy (LPE), pulsed laser deposition (PLD) and direct bonding, were investigated. A Nd:GGG on YAG waveguide fabricated by PLD was found to have a loss <0.5dB/cm, the lowest so far reported for a PLD layer. The waveguide lased on the four-level laser transition at around 1µm and, for the first time, on the quasi-three-level transition, around 940nm. However, the fluorescence spectra of the guide was significantly broadened with respect to bulk grown crystals. The fabrication technique of direct bonding was found to reliably produce good quality waveguides with losses <0.5dB/cm and in some cases as low as 0.2dB/cm. The waveguides had spectroscopic characteristics of the bulk material and the technique accommodates a wide range of material combinations. Both low and high NA structures can be fabricated and Nd:GGG/YAG (NA=0.75), Nd:YAG/YAG (NA=0.06), Nd:YAG/sapphire (NA=0.46) and Nd:YAG/glass (NA=0.82) direct bonded waveguide lasers were demonstrated. Pumping the volume of a planar waveguide with the high average power of a diode-bar can lead to a high inversion density and a high thermal load. This novel pumping regime was investigated experimentally and theoretically modelled. In parallel spectroscopic measurements by Dr. Stephan Guy at the University of Lyon, the Auger upconversion rate in Nd:YAG was measured to be 7 x 103s-1; significantly lower than had been reported previously. Modelling studies have shown how this upconversion, and the saturation of the absorption, can affect the gain available in an intensely pumped system. The model, and the value for the Auger rate, was consistent with experimental amplifier measurements. The associated heat load for such a system was also modelled to compare the performance of a planar waveguide with bulk slab and bulk rod-shaped gain media. The model showed that the planar waveguide maintains the thermal advantages of a slab geometry over that of a rod, although slightly higher temperature rises and slightly lower thermal stress fracture limits were predicted in a planar waveguide compared to an identical sized, but uniformly-pumped, bulk slab. Advances in coupling diode-bar pump lasers to planar waveguides have been made. A 20W fibre-lensed diode-bar, coupled with bulk cylindrical lenses, end-pumped an 80µm Nd:YAG planar waveguide and gave a maximum output power of 6.2W. The device had an optical-to-optical conversion efficiency of 31 % and M2 output beam quality of 3 x 140 in the guided and non-guided directions respectively. More compact, rod-lens focussing successfully coupled this pump source into sub-10-µm waveguides, and an output power of 3.7W was obtained from an 8µm Nd:YAG waveguide laser. A first demonstration of proximity coupling a diode-bar to a waveguide, with no intervening optics, gave a coupling efficiency of ~90% into an 8µm Nd:YAG/sapphire direct bonded waveguide. Techniques for improving the quality of the spatial mode output from the waveguide laser have been considered. In the guided direction, a metal overlaid coating gave a slight improvement in the laser mode quality and also led to a polarised output. A better solution was found by designing the first double-clad waveguides. Fabricated by direct bonding a five-layer, Yb:YAG/YAG/sapphire waveguide structure was proximity coupled to a 22W diode-bar pump laser. It gave a maximum output power of 2.2W in a side-pumped configuration. In the guided direction this laser had an output divergence with an M2 very close to 1, consistent with fundamental laser mode operation, Spatial mode selection occurred due to the confined nature of the gain region, and not the cladding-pumping of a single mode core. In the non-guided direction initial experiments aiming to improve M2 by using an unstable resonator design gave promising results but further work is required in this area. <br/
Double-clad structures and proximity coupling for diode-bar-pumped planar waveguide lasers
No full textWe report, for the first time, fabrication of double-clad planar waveguide structures and their use for multiwatt, diode-bar-pumped, planar waveguide lasers based on Nd3+ and Yb3+-doped YAG. The direct-bonded, five-layer structures of sapphire, YAG, and rare-earth-doped YAG have sufficient numerical aperture to capture the fast-axis divergence of a diode bar by proximity coupling with no intervening optics, leading to very simple and compact devices. The restriction of the doped region to the central core leads to diffraction-limited laser output in the guided direction. We also show that the direct-bonding fabrication process can lead to a linearly polarized output
Diode-bar-pumped planar waveguide lasers: double-clad structures and proximity coupling
No full textThe emission aperture of high-average-power diode-bars is inherently compatible with the geometry of thin-film waveguides. This, together with the power-handling capability of thin slabs, has lead to the possibility of very compact, high-power planar waveguide lasers. Here we report on novel waveguide structures and coupling techniques used to realise such devices in both Nd3+ and Yb3+ doped YAG
High-inversion densities in Nd:YAG: upconversion and bleaching
No full textWe report on the investigation of upconversion in Nd:YAG and its implications for intensely pumped devices. Analysis of lifetime measurements and the performance of a 1 at.% Nd-doped YAG amplifier give an Auger upconversion rate of 7 x 10-3 / s. This is significantly smaller than previously reported, but modeling of the performance of Nd:YAG devices with high-inversion densities shows that even this rate can still seriously degrade the small-signal gain and significantly increase the thermal load. The variation of cross-relaxation and upconversion rates with doping level is also described. Finally, it is found that the effect of bleaching of the Nd:YAG absorption can lead to a reduced spatial overlap between the signal and inversion profiles and thus can also significantly reduce the gain
A low-loss waveguide laser grown by pulsed laser deposition
No full textWe report the fabrication of a low propagation loss (<1dB/cm) Nd:GGG waveguide by pulsed laser deposition. Using a 2% output coupler a 1.06µm laser threshold of 4mW and slope efficiency of 20% was observed
Performance of a low loss pulsed laser deposited Nd:Gd<sub>3</sub>Ga<sub>5</sub>O<sub>12</sub> waveguide laser at 1.06µm and 0.94µm
No full textWe report the laser performance of a low propagation loss neodymium doped Gd3Ga5O12 (Nd:GGG) waveguide fabricated by pulsed laser deposition. An 8µm thick crystalline Nd:GGG film grown on an undoped Y3Al5O12 (YAG) substrate lases at 1.060µm and 1.062µm, when pumped by a Ti:sapphire laser operating at 740nm or 808nm. Using a 2.2% output coupler a 1060nm laser threshold of 4mW and a slope efficiency of 20% were observed. Laser action has also been achieved, we believe for the first time in Nd:GGG, on the quasi-three level 937nm transition. With a 2% output coupler at this wavelength a laser threshold of 17mW and a 20% slope efficiency were obtained. This demonstration of low propagation loss combined with the fact that these waveguides have a very high numerical aperture, make pulsed laser deposited thin films attractive for high power diode pumped devices
High numerical aperture planar waveguides
No full textRare earth doped planar crystal waveguides have the potential to yield efficient compact diode pumped lasers and amplifiers. Confinement of pump and signal to the waveguide core leads to high small-signal gains for amplifiers and, if additional propagation losses are small, low laser thresholds. The planar geometry is well matched to the asymmetric output of high average power diodes, simplifying the coupling and mode-matching requirements. The natural slab geometry is also ideal for thermal management. Coupling the highly divergent output of high power diode lasers into waveguides, either by focussing or proximity coupling, requires relatively thick waveguides (>10µm) and, especially for proximity coupling, a high numerical aperture (NA). We report two fabrication methods that can meet these requirements; pulsed laser deposition (PLD) and thermal bonding. The fabrication details and waveguide characterisation, including Ti:Sapphire pumped laser operation, will be discussed
Toward a high-power, brightness-enhanced, polarized, diode-bar pumped planar waveguide laser
No full textWe present recent results obtained in the design and construction of diode-bar pumped planar waveguide lasers. The Au coating of a Nd:Ga:Lu:Y3Al5O12 on Y3Al5O12 planar waveguide to produce a TE polarised laser with improved beam quality in the guided direction is also reported
Proximity-coupled, diode-bar-pumped, waveguide laser
No full textA simple and compact, side-pumped, waveguide laser is demonstrated by proximity coupling a 10W diode-bar to a contact-bonded, Nd:YAG waveguide
1.5W diode-pumped monolithic planar waveguide laser
No full textWe describe a compact and efficient Nd:YAG waveguide laser pumped by a diode-bar. An output of 1.5W is obtained for 6W incident power, with significant brightness enhancement
- …
