Intracavity Diamond Research Articles

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

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.

High-power quantum-dot-based semiconductor disk laser

We demonstrate multiwatt cw output power from an optically pumped quantum-dot semiconductor disk laser. Continuous-wave output power of 4.35 W with 22% slope efficiency was demonstrated at a center wavelength of 1,032 nm. This represents an increase in power of 15 times and an increase in slope efficiency of 10 times from the previously published results using Stranski-Krastanow grown quantum dots. An intracavity diamond heat spreader was used for thermal management. The maximum output power was limited by the available pump power, and no sign of thermal rollover was observed.

Thermal Management in 2.3-$\mu{\hbox {m}}$ Semiconductor Disk Lasers: A Finite Element Analysis

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.

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

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> 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 <formula formulatype="inline"><tex>${&gt; 600}~\hbox{mW}$</tex></formula> 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. </para>

Effect of Heat Spreader Location on Lasing Properties of End-Pumped Vertical-External-Cavity Surface-Emitting Lasers

We characterize the lasing properties of two configurations of end-pumped vertical-external-cavity surface-emitting lasers: one with an intracavity diamond heat spreader, the other with an extracavity heat spreader. A pump-power-limited CW output power of 9.2 W at 1060 nm and a slope efficiency of ∼50.3% are achieved with the extracavity heat spreader. With the intracavity heat spreader, the output power and slope efficiency are 7.6 W and 42.2%, respectively. The difference in the slope efficiency can be explained by the difference in absorption efficiency, caused by different spatial distributions of the absorbed pump light.

Effect of the properties of an intracavity heat spreader on second harmonic generation in vertical-external-cavity surface-emitting laser

We investigate the effect of the properties of an intracavity diamond heat spreader on the lasing performance of vertical-external-cavity surface-emitting lasers. We compared two intracavity diamonds with different average birefringences. When a polarization selective element is inserted into the cavity, the infrared output powers are reduced by 13% and 7%, respectively, for the samples with higher and lower average birefringences. The pump-power limited maximum green output powers were changed from 3to5.2W by rotating the samples with lower average birefringence. In order to explain the variation in green output power, the additional round-trip loss caused by diamond birefringence was analyzed theoretically and experimentally. We found that the loss can be reduced when axes of the birefringence are aligned to the axes of the polarization selective element.

Highly efficient green VECSEL with intra-cavity diamond heat spreader

The effect of the birefringence of an intracavity diamond heat spreader on the lasing performance of a vertical external cavity surface emitting laser is investigated. The birefringence in the intra-cavity diamond caused considerable additional round-trip loss when a birefringent filter was inserted into the cavity. The effect of the birefringence of intra-cavity diamond can be reduced by rotation of the sample. By aligning the axes of the diamond birefringence and those of the Brewster surfaces, a pump-power limited green output power of 5.2 W was achieved – a pump to green conversion efficiency of 24%.

Intracavity diamond heatspreaders in lasers: the effects of birefringence

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.

Spectral narrowing and locking of a vertical-external-cavity surface-emitting laser using an intracavity volume Bragg grating

We report the use of a volume Bragg grating as an output coupler mirror to improve and stabilize the spectral characteristics of 1058-nm vertical-external-cavity surface-emitting laser which is thermally managed using an intracavity diamond heatspreader. Spectrally narrow and locked emission with up to 645mW of TEM0,0 output power is demonstrated

High power continuous wave operation of a GaSb‐based VECSEL emitting near 2.3 µm

We report on a GaSb-based optically pumped vertical external cavity surface-emitting laser (VECSEL) operating near 2.3 µm. The epitaxial layer structure has been analyzed by high-resolution X-Ray diffraction, as well as reflectivity and photoluminescence (PL) spectroscopy. PL recorded from the side facet of a cleaved sample is used to determine the true quantum well emission spectrum. CW laser operation is observed at room temperature for substrate-side-down mounted samples even without thinning the substrate. Laser output power is significantly increased to >300 mW when using an intra-cavity polycrystalline diamond heat spreader bonded to the semiconductor chip. The temperature-dependence of the VECSEL characteristics is explained by changes in the relative alignment of the cavity resonance and the gain spectrum. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

0.8 W optically pumped vertical external cavity surface emitting laser operating CW at 1550 nm

An InP based optically pumped vertical external cavity surface emitting laser has been designed and optimised for emission at 1550 nm. To overcome thermal limitations an intra-cavity synthetic diamond heatspreader is bonded to the gain structure. The laser produces 780 mW at -30/spl deg/C and 100 mW at 20/spl deg/C in a near Gaussian beam (M/sup 2/<1.2).