D.S. Gill

Growth of KNbO3 thin films on MgO by pulsed laser deposition

Crystalline and stoichiometric KNbO3 thin films have been grown on (100) oriented MgO substrates by pulsed laser deposition technique. Electron microprobe analysis and Rutherford backscattering spectroscopy of the films show a progressive loss of K with increasing substrate‐target distance. To compensate for this K loss the ceramic KNbO3 targets were enriched with K2CO3 powder, pressed at room temperature, and sintered at 650 °C. For a substrate‐target distance of 6 cm, targets with [K]/[Nb] molar ratio=2.85 yield stoichiometric KNbO3 films. A partial oxygen pressure of 2×10−2 mbar was optimum for growing transparent films. Films grown between 650 and 700 °C show the KNbO3 crystalline phase with its (110) axis preferentially oriented perpendicular to the surface of the substrate. At these temperatures KNbO3 diffusion into the MgO substrate is observed. Films grown from KNbO3 single crystal targets only contain a Mg4Nb2O9 crystalline layer.

Laser operation of an Nd:Gd3Ga5O12 thin‐film optical waveguide fabricated by pulsed laser deposition

We report the laser operation of a thin-film waveguide structure grown by the pulsed laser deposition technique. A 2.7-µm-thick crystalline film of neodymium doped Gd3Ga5O12 (Nd:GGG) lases at a wavelength centered at 1.06µm when pumped by a Ti:sapphire laser at 808 nm.

TI:SAPPHIRE PLANAR WAVEGUIDE LASER GROWN BY PULSED LASER DEPOSITION

We document the lasing performance of a waveguiding layer of Ti:sapphire, of ~12-mum thickness, grown by pulsed laser deposition from a 0.12-wt.% Ti(2)O(3) Ti:sapphire single-crystal target onto an undoped z-cut sapphire substrate. Lasing around 800 nm is observed when the waveguide layer is pumped by an argon-ion laser running on all-blue-green lines, with an absorbed power threshold of 0.56 W, with high-reflectivity (R>98%) mirrors. With a 5% pump duty cycle and a T=35% output coupler, a slope efficiency of 26% with respect to absorbed power is obtained, giving quasi-cw output powers in excess of 350 mW.

Performance of a low loss pulsed laser deposited Nd:Gd3Ga5O12 waveguide laser at 1.06µm and 0.94µm

We report the laser performance of a low-propagation-loss neodymium-doped Gd(3)Ga(5)O(12) (Nd:GGG) waveguide fabricated by pulsed-laser deposition. An 8- mum -thick crystalline Nd:GGG film grown upon an undoped Y(3)Al(5)O(12) substrate lases at 1.060 and 1.062 microm when pumped by a Ti:sapphire laser operating at 740 or 808nm.Using a 2.2% output coupler, we observed a 1060-nm laser threshold of 4mW and a slope efficiency of 20%. Laser action was also achieved, for what we believe is the first time in Nd:GGG, on the quasi-three-level 937-nm 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 (0.75) makes pulsed-laser-deposited thin films attractive for high-power diode-pumped devices.

Characterisation of GaLaS chalcogenide glass thin-film optical waveguides, fabricated by pulsed laser deposition

Abstract The fabrication of stoichiometric thin-film optical waveguides of GaLaS via a pulsed laser deposition technique is reported. Stoichiometric films are grown by ablating GaLaS bulk glass with a KrF excimer laser (λ = 248 nm) at an incident laser flux ⩾ 3.5 J/cm 2 . The composition of the films is determined by energy-dispersive X-ray analysis and the refractive index is measured by a dark-mode prism coupling technique. Photoinduced structural rearrangement of the as-deposited films leads to a blueshift in the visible absorption edge and a permanent refractive index change, Δ n , of −1%. On the basis of these results, grating structures have been written with both blue light, and e-beam addressing, and their suitability for integrated optical structures assessed.

Low loss (0.5 dB/cm) Nd:Gd3Ga5O12 waveguide layers grown by pulsed laser deposition

Nd:Gd3Ga5O12 planar waveguides, with significantly improved optical properties over those previously reported, have been fabricated on Y3Al5O12 substrates by pulsed laser deposition. Waveguide losses as low as 0.5 dB/cm have been obtained, determined by measuring the absorbed power lasing threshold with different output coupler reflectivities for both the 1060 nm and 937 nm lasing wavelengths. This order of magnitude improvement in waveguide loss is attributed to the much improved surface morphology and lower particulate count of the thin film samples.

Planar laser waveguides of Ti:sapphire, Nd:GGG and Nd:YAG grown by pulsed laser deposition

Highly efficient laser action is demonstrated in epitaxially grown Nd:GGG and Ti:sapphire layers. Waveguide losses as low as 0.5 dB/cm are achieved in films of low particulate content, high homogeneity and improved surface morphology obtained by optimized pulsed laser deposition (PLD) configurations. Low threshold laser emission is observed at 800 nm for Ti:sapphire, and at 1060 nm and 937 nm for Nd:GGG waveguides, with slope efficiencies of 26% and 20% respectively. These results verify the versatility of PLD schemes in the fabrication of novel optoelectronic structures.

Pulsed laser deposition of KNbO3 thin films

The laser ablation of stationary KNbO3 single crystal targets induces a Nb enrichment of the target surface. In rotated targets this effect is observed only in those areas irradiated with low laser fluence. The composition of the plasma formed close to the target surface is congruent with the target composition; however, at further distances K-deficient films are formed due to the preferential backscattering of K in the plasma. This loss may be compensated for by using K-rich ceramic targets. Best results so far have been obtained with [K]/[Nb] = 2.85 target composition, and crystalline KNbO3 films are formed when heating the substrates to 650 °C. Films formed on (100)MgO single crystals are usually single phase and oriented with the (110) film plane parallel to the (100) substrate surface. (100)NbO may coexist with KNbO3 on (100)MgO. At substrate temperatures higher than 650 °C, niobium diffuses into MgO forming Mg4Nb2O9 and NbO, leading to K evaporation from the film. Films formed on (001) alpha-Al2O3 (sapphire) show the coexistence of (111), (110), and (001) orientations of KNbO3, and the presence of NbO2 is also observed. KNbO3 films deposited on (001)LiNbO3 crystallize with the (111) plane of the film parallel to the substrate surface. For the latter two substrates the Nb diffusion into the substrate is lower than in MgO and consequently the K concentration retained in the film is comparatively larger.

Growth of crystalline Gd3Ga5O12 thin-film optical waveguides by pulsed laser deposition

Crystalline and stoichiometric thin film of Gd3Ga5O12, have been deposited onto heated Y3Al5O12, substrates by a pulsed laser deposition technique. The refractive indices of the films are in excellent agreement with the bulk crystal.

Pulsed‐laser deposition of Ga‐La‐S chalcogenide glass films for optical waveguide applications

Thin films of Ga-La-S chalcogenide glass have been ablatively deposited onto a range of substrates, including CaF2, and microscope cover slips. The resultant films are deficient in their sulphur composition by approximately 25%, when compared to the bulk targets used, but the interesting chalcogenide photostructural effects are not compromised by this deficiency. Experiments so far have established that photorefractive effects, such as photodoping, photobleaching and grating formation. all occur readily in the thin films, and gratings have been written using laser and e-beam addressing, to create diffractive structures for optical waveguide applications.