Alexander J. Maclean

Directly diode-laser-pumped Ti:sapphire laser

A directly diode-laser-pumped Ti:Al(2)O(3) laser is demonstrated. Using a 1 W, 452 nm GaN diode laser, 19 mW of cw output power is achieved in a potentially portable format. Pumping at this short wavelength induces a loss at the laser wavelength that is not seen for the more typical green pump wavelengths. This effect is characterized and discussed.

Thermal Management in 2.3-

Finite element analysis is used to study heat flow in a 2.3-mum semiconductor disk laser (or vertical-external-cavity surface-emitting laser) based on GalnAsSb-AlGaAsSb. An intra-cavity diamond heatspreader is shown to significantly improve thermal management-and hence power scalability-in this laser compared to the substrate thinning approach typically used in semiconductor disk lasers operating around 1 mum. The parameters affecting the performance of an intracavity heat-spreader are studied in the context of a 2.3-mum semiconductor disk laser: the thermal impedance at the interface between the semiconductor gain material and the heatspreader is found to be much more important than the mounting arrangements for the gain-heatspreader composite; power scaling with pump spot radius-increasing the pump power at constant pump intensity-is found to be intrinsically limited; and the pump wavelength is predicted to have less affect on thermal management than might be expected. Direct pumping of the quantum wells is found to significantly reduce the temperature rise per unit pump power.

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The semiconductor disk laser (SDL) is a versatile laser source offering multiwatt-level output powers and diffraction limited beams. While an approach to thermal management based on substrate removal has led to tens of watts of output power in the 1 μm region, the use of intracavity diamond heatspreaders for thermal management has enabled multiwatt performance levels to be achieved at wavelengths from the red to the mid-infrared. The modeling presented indicates that this dichotomy in approach arises from the ability of the heatspreader approach to bypass the thermal resistance of the mirror structure built into the SDL. The power scaling limitations of SDLs with heatspreaders are explored: nonaxial heat flow in the heatspreader is shown to limit the power scaling with pump spot radius. The critical roles of the pump spot size and output coupling on efficiency are experimentally investigated. An output power of 7 W in a 1060 nm SDL is achieved with the maximum output power achieved at a pump spot radius of 85 μm.

Semiconductor Disk Lasers: A Finite Element Analysis

Direct diode-laser pumping of a mode-locked Ti:Al(2)O(3) laser is reported. A single 1 W GaN-based diode laser operating at 452 nm is used as the pump laser. Pulse durations as short as 114 fs and average output powers of up to 13 mW are obtained.

Limits on efficiency and power scaling in semiconductor disk lasers with diamond heatspreaders

The birefringence of a number of commercially-available diamond platelets is assessed in the context of their use for intracavity thermal management in lasers. Although diamond is normally thought of as isotropic, significant birefringence is found to be present in some samples, with considerable variation from batch to batch, and in some cases across an individual sample. Nonetheless, low-loss operation is achieved in a laser cavity containing a Brewster element, either by rotating the sample or by using a diamond platelet with low birefringence.

Direct diode-laser pumping of a mode-locked Ti:sapphire laser

Using a wedged and antireflection-coated diamond heatspreader, a continuously tunable semiconductor disk laser with intracavity second-harmonic generation (SHG) is demonstrated. Output powers of > 600 mW tunable over 10 nm around 530 nm are obtained. Finite-element modeling shows that the use of a diamond heatspreader for thermal management - in contrast to substrate thinning approaches - permits power scaling across the 670-2300-nm range of these lasers. Using a green laser as an exemplar, this paper details the issues involved in translating this spectral coverage to the ultraviolet and visible via SHG. Polarization and wavelength selection are discussed and the adopted approaches presented. Almost 1 W of second-harmonic light at 530 nm is demonstrated, with an efficiency of 11% with respect to the incident pump power.

Intracavity diamond heatspreaders in lasers: the effects of birefringence

Finite element and analytical modelling of thermal effects in doped-dielectric and semiconductor disc lasers is used to assess advanced approaches to thermal management. The prospective utility of high thermal conductivity materials such as diamond—particularly to improve the spectral coverage in semiconductor disc lasers and to scale the output power of quasi-monolithic microchip lasers—is illustrated. The potential of materials with strong pump absorption to improve the practicality of doped-dielectric thin-disc lasers, particularly for mobile applications, is also outlined.

Continuous Tuning and Efficient Intracavity Second-Harmonic Generation in a Semiconductor Disk Laser With an Intracavity Diamond Heatspreader

We report high-performance single-frequency operation of a directly diode pumped GaSb vertical-external-cavity surface-emitting laser (VECSEL) at 2.3 mum. Tunability of >25 nm with a maximum single frequency output of 0.68 W is demonstrated.

Thermal management in disc lasers: doped-dielectric and semiconductor laser gain media in thin-disc and microchip formats

We report the operation of an optically-pumped vertical-external-cavity surface-emitting laser (OP-VECSEL) oscillating at wavelengths up to 2.2 µm and at output powers greater than 200 mW. This versatile platform provides a broad gain bandwidth, and may be tuned and/or controlled by the addition of elements into the external cavity. Moreover, the nature of the semiconductor structure permits precise engineering of the operating wavelength---not possible with traditional solid state crystalline lasers---and the thin (few microns) pump absorption region, coupled with the external cavity control, permits the mode conversion of a low brightness pump into a high quality TEM00 output.

Tunable, single-frequency, diode-pumped 2.3μm VECSEL

The design and initial demonstration of a directly diode-laser pumped Ti:Sapphire laser is reported. System design considerations and plans for future optimisation are presented.