C.L. Bonner

High-inversion densities in Nd:YAG-upconversion and bleaching

We 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/spl times/10/sup 3/ s/sup -1/. 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.

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.

Double-clad structures and proximity coupling for diode-bar-pumped planar waveguide lasers

We 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 Nd/sup 3+/ and Yb/sup 3+/-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 end-pumped high-power Nd:Y 3 Al 5 O 12 planar waveguide laser

A compact high-power planar waveguide laser end pumped by a diode-bar is reported. The waveguide was fabricated by liquid-phase epitaxy and had an 80-microm-thick, 1.5-at. % Nd:Y(3)Al(5)O(12) core on a Y(3)Al(5)O(12) substrate. A maximum output power of 6.2 W was obtained at 1.064 microm when the device was pumped with a 20-W diode bar operating near 807 nm, giving an overall optical-to-optical conversion efficiency of 31%. The total device length was 5 cm.

Thermally bonded planar waveguide lasers

A new technique for fabricating active planar waveguide devices is reported. This process, based on the thermal bonding of precision finished crystal or glass components, allows waveguides to be assembled from very dissimilar materials and could be applied to a wide range of solid state laser or other optical media. The waveguide propagation losses, inferred from the laser performance, are found to be 0.7dB/cm for Nd:Y3Al5O12 bonded to Y3Al5O12, Nd:Y3Al5O12 bonded to glass, and 0.4dB/cm for Nd:Gd3Ga5O12 bonded to Y3Al5O12 devices.

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.

High-numerical-aperture, contact-bonded, planar waveguides for diode-bar-pumped lasers

We report on the design and fabrication of Nd:YAG planar waveguides suitable for in-plane, diode-bar pumping. Contact-bonded Nd:YAG on Sapphire waveguides are shown to have the high numerical aperture (0.46), low propagation loss (<0.2dB/cm), and good thermal properties necessary to make efficient diode-bar-pumped lasers and amplifiers. Coupling efficiencies of 73% and 60% have been demonstrated between a 20W diode-bar and an 8µm and a 4µm thick planar waveguide respectively, leading to 3.7W of waveguide-laser output.

Diode-bar-pumped planar waveguide lasers

Diode-bar lasers have been used with great success to pump high power solid state lasers in numerous different geometries; nevertheless it remains a challenge to use the highly asymmetric diode-bar output efficiently. We describe an approach to this problem in which the solid-state gain medium is fabricated as a planar waveguide, into which the high-aspect-ratio emission from the diode-bar can be coupled using a simple optical system. This is a geometry which should in principle handle heat dissipation well. We have investigated the performance of a planar Nd-doped YAG waveguide pumped by a 20-W 807-nm diode-bar. A high-quality, low propagation loss guide is essential for such a device; in this experiment we used a liquid-phase-epitaxy-grown structure. The 5-mm long waveguide had an 80-/spl mu/m-thick 1.5-at.% Nd:YAG core sandwiched between substrate and protective cladding layer of undoped YAG. The Nd content of the core raised its refractive index by 4.8/spl times/10/sup -4/ relative to substrate and cladding, creating an optical waveguide with a numerical aperture of 0.06. Pump radiation from the diode-bar was coupled into the waveguide using a cylindrical lens system which produced a line focus at the input face of the waveguide with measured beam radii of 10 /spl mu/m and /spl sim/1 mm along the guided and non-guided axes respectively. A monolithic laser cavity was formed by dielectric coatings applied to the plane-parallel end-faces of the waveguide.

Proximity-coupled, diode-bar-pumped, waveguide laser

Summary form only given. Recent work on high-power, planar waveguide lasers has been motivated by the fact that the planar geometry is ideal for thermal management and well-matched to that of diode-bar pump lasers, previously allowing simple cylindrical lens coupling. Here we report in-plane, proximity-coupling of a diode-bar to a planar waveguide with no intervening optics. This simple and highly-compact coupling arrangement is shown to be suitable for side-pumped lasers based on high-numerical-aperture (NA), contact-bonded, waveguides.

A low-loss waveguide laser grown by pulsed laser deposition

We 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