Intracavity Diamond Heat Spreader Research Articles

High-power flip-chip semiconductor disk laser in the 1.3 μm wavelength band.

We present 6.1 W of output power from a flip-chip semiconductor disk laser (SDL) emitting in the 1.3 μm wavelength region. This is the first demonstration of a flip-chip SDL in this wavelength range with output powers that are comparable to those obtained with intracavity diamond heat spreaders. The flip-chip configuration circumvents the optical distortions and losses that the intracavity diamond heat spreaders can introduce into the laser cavity. This is essential for several key applications of SDLs.

1180 nm VECSEL with output power beyond 20 W

The highest power result for an optically-pumped single-chip vertical external-cavity surface-emitting laser with emission near 1180 nm is reported. The gain mirror was grown by molecular beam epitaxy and incorporated a strain compensated GaInAs/GaAs/GaAsP active region. An intra-cavity diamond heat spreader was attached to the gain mirror for thermal management. In free-running operation, the laser emitted more than 20 W at a mount temperature of about 12 °C. The output spectrum was centred between 1165–1190 nm depending on the mount temperature and pump power. By using an intra-cavity birefringent filter, the full width at half-maximum linewidth could be narrowed to ≤1 nm and at the same time achieved approximately 14 W of output power near 1178 nm. Moreover, the lasing wavelength could be tuned over more than 40 nm.

200 GHz 1 W semiconductor disc laser emitting 800 fs pulses

Passive harmonic modelocking in a flip-chip semiconductor disc laser at a 193 GHz repetition rate with 900 mW of output power and a pulse duration of 830 fs is demonstrated. The high harmonic frequency is obtained via coupling of the laser cavity to an intracavity diamond heat spreader bonded to a semiconductor saturable absorber mirror.

High-peak-power optically pumped AlGaInAs eye-safe laser at 500-kHz repetition rate with an intracavity diamond heat spreader

We report on a compact efficient high-repetition-rate (>100 kHz) optically pumped AlGaInAs nanosecond eye-safe laser at 1525 nm. A diamond heat spreader bonded to the gain chip is employed to improve the heat removal. At a pump power of 13.3 W, the average output power at a repetition rate 200 kHz is up to 3.12 W, corresponding to a peak output power of 560 W. At a repetition rate 500 kHz, the maximum average power and peak power are found to be 2.32 W and 170 W, respectively.

Wafer-Fused Optically Pumped VECSELs Emitting in the 1310-nm and 1550-nm Wavebands

1300-nm, 1550-nm, and 1480-nm wavelength, optically pumped VECSELs based on wafer-fused InAlGaAs/InP-AlGaAs/GaAs gain mirrors with intracavity diamond heat spreaders are described. These devices demonstrate very low thermal impedance of 4 K/W. Maximum CW output of devices with 5 groups of quantum wells shows CW output power of 2.7 W from 180 μm apertures in both the 1300-nm and the 1550-nm bands. Devices with 3 groups of quantum wells emitting at 1480 nm and with the same aperture size show CW output of 4.8 W. These VECSELs emit a high-quality beam with beam parameter below 1.6 allowing reaching a coupling efficiency as high as 70% into a single-mode fiber. Maximum value of output power of 6.6 W was reached for 1300 nm wavelength devices with 290 μm aperture size. Based on these VECSELs, second harmonic emission at 650 nm wavelength with a record output of 3 W and Raman fiber lasers with 0.5 W emission at 1600 nm have been demonstrated.

Broadly tunable 1250 nm quantum dot-based semiconductor disk laser

Optically pumped semiconductor disk lasers with antiresonant design based on Stranski-Krastanow-grown quantum dots are demonstrated to extend the spectral coverage of such type of devices up to 1250 nm. A continuous wave output power up to 1.6 W was achieved using an intracavity diamond heat spreader. Intracavity birefringent filter was used to tune the wavelength of the device in 25 nm range.

High-Power 1.48-$\mu$m Wafer-Fused Optically Pumped Semiconductor Disk Laser

An output power up to 5 W at 1.48-μm wavelength is achieved from an optically pumped semiconductor disk laser. An active region composed of an AlGaInAs/InP heterostructure grown on an InP substrate was wafer fused with an AlGaAs/GaAs Bragg reflector grown on a GaAs substrate. An intracavity diamond heatspreader bonded to the gain structure surface provides efficient heat removal from the active element. The results further validate that the wafer fusion technique offers a flexible platform for high-power disk lasers in a wide wavelength range.

GaSb-Based Semiconductor Disk Laser With 130-nm Tuning Range at 2.5 $\mu$m

We demonstrate a GaSb-based semiconductor disk laser emitting 0.6 W of output power at 2.5 μm in a fundamental mode regime (M2 <; 1.6). A gain structure grown by molecular beam epitaxy and assembled with an intracavity diamond heat spreader demonstrates a promising potential for power scaling and broad wavelength tuning. A tuning range of 130 nm with output power up to 310 mW has been achieved which represents the largest spectral coverage reported to date for disk lasers at this wavelength.

11 W single gain-chip dilute nitride disk laser emitting around 1180 nm

We report power scaling experiments of a GaInNAs/GaAs-based semiconductor disk laser operating at ~1180 nm. Using a single gain chip cooled to mount temperature of ~10 °C we obtained 11 W of output power. For efficient thermal management we used a water-cooled microchannel mount and an intracavity diamond heat spreader. Laser performance was studied using different spot sizes of the pump beam on the gain chip and different output couplers. Intracavity frequency-doubling experiments led to generation of ~6.2 W of laser radiation at ~590 nm, a wavelength relevant for the development of sodium laser guide stars.

Short wavelength red-emitting AlGaInP-VECSEL exceeds 1.2 W continuous-wave output power

We present a vertical external cavity surface-emitting laser system based on a multi-quantum-well structure with 20 compressively strained GaInP quantum wells for an operation wavelength of around 665 nm with a monolithic integrated distributed Bragg reflector. With the help of an intra-cavity diamond heatspreader the laser operates in continuous-wave mode. Operation with a TEM00 Gaussian beam profile and a beam propagation factor of M2≤1.05 is shown as well as a high resolution spectrum of the laser line, which shows the etalon effect of the diamond. The laser can be operated at a maximum output power exceeding 1.2 W with a slope efficiency of ηdiff=18%. At maximum output power the wavelength of the laser resonance is at 670 nm, which is shortest reported until now at powers exceeding 1 W. By rotating a birefringent filter in an extended folded cavity arrangement a wavelength tuning of 21 nm was attained.

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