Diamond Heat Spreader Research Articles

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.

High power 1.25 μm InAs quantum dot vertical external-cavity surface-emitting laser

The authors demonstrate InAs quantum dot (QD)-based optically pumped vertical external-cavity surface-emitting lasers grown by molecular beam epitaxy. Active region designs utilizing two different resonant periodic gain (RPG) structures are compared. The first RPG structure is a more traditional design consisting of three QD layers per antinode of the E-field standing wave, repeated four times, for a total of 12 QD layers. The second RPG has a single-QD layer per antinode, repeated 12 times. The single-QD layer per antinode structure allows for both superior strain relief as well as more complete pump absorption and thus results in significantly improved device performance over the traditional multi-QD layer per antinode design. The authors were able to demonstrate over 3 W of output power at room temperature using a thermal grade polycrystalline chemical-vapor deposition diamond heat spreader mounted on the backside of a sample thinned by mechanical polishing.

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.

Multi-watt 1.25 µm quantum dot VECSEL

An InAs quantum dot (QD) vertical external cavity surface-emitting laser (VECSEL) operating at a wavelength of 1.25 µm is reported. The gain region of the laser consists of a resonant periodic gain structure using single QD layers at 12 adjacent electrical field antinodes – a design optimised to reduce strain accumulation and improve QD quality. A fibre-coupled 808 nm laser diode is used as a pump source and a spherical external mirror completes the cavity. Thermal management is accomplished by bonding the VECSEL sample to a chemical vapour deposition (CVD) diamond heat spreader. Continuous wave output powers in excess of 3 W have been achieved at room temperature. The broad emission spectrum makes this device an ideal candidate for wavelength tunable or modelocked applications.

1.3-$\mu$m Mode-Locked Disk Laser With Wafer Fused Gain and SESAM Structures

We report 1.3-μm mode-locked optically pumped semiconductor disk laser (SDL) made by wafer fusion. The gain medium and the saturable absorber, both based on an InP material system, were integrated with AlGaAs-GaAs distributed Bragg reflectors by localized wafer fusion. An intracavity wedged diamond heat spreader capillary bonded to the gain chip prevents the disruption of 6.4-ps pulse spectrum and supports 100 mW of average power. The results reveal an advantage of wafer fusion process of disparate materials over monolithically grown InP-based gain/absorber structures and demonstrate practical potential of the technique for long-wavelength SDLs.

高功率垂直外腔面发射激光器

A high power optically-pumped vertical-external-cavity surface-emitting laser with a diamond heatspreader is demonstrated. Owing to the good thermal conductivity, diamond can accelerate the dissipation of heat in the active region and increase the output power significantly. The effects of the curvature radius, the transmission of output coupler, the spot size of the pump, and the temperature of the heat sink on the output power are investigated. A maximum output power of 880 mW is obtained under the conditions of 10? temperature, 15-mm curvature radius, 3% transmission of the output coupler, and 8500-mW pump power. The slope efficiency and the optical-to-optical conversion efficiency of the laser are about 17% and 15%, respectively.

High-power vertical-cavity surface-emitting lasers bonded with efficient packaging

High-power vertical-cavity surface-emitting lasers (VCSELs) are processed using a wet thermal-selective oxidation technique. The VCSEL chips are packaged by employing three different bonding methods of silver solder, In-Sn solder, and metalized diamond heat spreader. After packaging, optical output power, wavelength shift, and thermal resistance of the devices are measured and compared in an experiment. The device packaged with a metalized diamond heat spreader shows the best operation characteristics among the three methods. The 200 \mu m-diameter device bonded with a metalized diamond heat spreader produces a continuous wave optical output power of 0.51 W and a corresponding power density of 1.6 kW/cm 2 at room temperature. The thermal resistance is as low as 10 K/W. The accelerated aging test is also carried out at high temperature under constant current mode. The device operates for more than 1000 h at 70 ?, and the total degradation is only about 10%.

InP/AlGaInP quantum dot semiconductor disk lasers for CW TEM_00 emission at 716 – 755 nm

Multiple layers of InP QDs, self-assembled during epitaxial growth, were incorporated into the active region of an (Al(x)Ga(1-x))(0.51)In(0.49)P based semiconductor disk laser with monolithic Al(x)Ga(1-x)As distributed Bragg reflector. Three gain structure samples were selected from the epitaxial wafer, bonded to single-crystal diamond heatspreaders and optically pumped at 532 nm within a high finesse external laser cavity. Laser emission with peak wavelengths at 716, 729, and 739 nm, respectively, was achieved from the three samples; the latter demonstrating tuning from 729 to 755 nm. Maximum continuous wave output power of 52 mW at 739 nm was achieved with 0.2% output coupling; the threshold and slope efficiency were 220 mW and 5.7% respectively.

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.

Power scaling of Nd:YVO_4 and Nd:GdVO_4 disk lasers using synthetic diamond as a heat spreader

A newly developed low-birefringence synthetic diamond is shown to be an effective intracavity heat spreader in Nd:YVO4 and Nd:GdVO4 disk lasers. A cw output power of 25.7 W from only one double pass of the pump is reported. The diamond heat spreader is shown to increase the pump power density at which fracture occurs.

Antimonide disk lasers achieve multiwatt power and a wide tuning range

The absorption lines of many environmentally important gases are found within the λ = 2–3μm wavelength range. Combined with the presence of an appropriate atmospheric window, these spectral lines represent useful diagnostics for gas spectroscopy,1 remote sensing, research in the life sciences, and free-space optical communications. Certain applications, such as laser-based tissue welding, require multiwatt optical sources with high beam quality, while others would benefit from light emitters generating ultrashort optical pulses (e.g., laser radar and freespace communications). Gallium antimonide (GaSb)-based semiconductor disk lasers2 (sometimes called vertical-external-cavity surface-emitting lasers or VECSELs) could offer a new, compact, and cost-effective alternative for use with the 2–3μm spectral window, which is currently covered by solid-state and fiber lasers as well as optical parametric sources. The VECSEL design combines power scalability and excellent beam quality with wavelength flexibility that is offered by the semiconductor gainmaterial. Additional optical elements can be used inside the laser resonator for spectral control, frequency conversion, and mode locking to produce ultrashort optical pulses. The gain mirror, deposited onto a GaSb substrate, consists of thin semiconductor films that make up a high-reflectivity Bragg mirror and a gain region. It is typically pumped at an angle using low-cost, poor-beam-quality laser-diode bars. We deployed a transparent diamond heat spreader to cool the gain region efficiently under intense optical pumping (see Figure 1). Our aim was to demonstrate generation of multiwatt output power, an extended tuning range, and short pulses near 2μm. All gain structures were grown monolithically by solid-state Figure 1. Schematic presentation of a semiconductor disk laser with a simple linear cavity. The smaller arrows indicate the direction of heat flow.

Diamond Heat Spreader Layer for High-Power Thin-GaN Light-Emitting Diodes

A diamond-coating layer is studied as a heat spreading layer for a thin-GaN light-emitting diode (LED) chip. Our results show that this diamond layer can effectively spread the heat and improve the temperature uniformity of a thin-GaN LED chip, which enhances the heat dissipation efficiency down to the heat sink. With the diamond heat spreading layer, the junction temperature of the thin-GaN LED was reduced by 20 C at 1-A current input and the uniformity of the temperature distribution is also greatly improved.

Thermal spreading properties of nanoscale diamond tips on diamond/Si

A diamond heat spreader made of nanoscale diamond tips on a diamond/Si substrate has been fabricated by planar microwave plasma enhanced chemical vapor deposition. The nanoscale diamond tips are in a conelike shape, which are ~ 1 µm in height and their average diameter at the bottom is ~ 200 nm. The nanoscale diamond tips act as a nanoscale “fin structure”, which provide extended surface area to dissipate heat away. A concept of “quasi thermal resistance” is developed to characterize the thermal spreading properties of the nanoscale diamond tips/diamond/Si structures at various air flow rates in a wind tunnel. Experimental results indicate that nanoscale diamond tips help to improve the thermal spreading properties, especially at zero air flow rate. The improvement is attributed to the large surface area of nanoscale diamond tips. At an air flow rate higher than zero, the improvement of thermal spreading properties diminishes.

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.

High-power, (AlGaIn)(AsSb) semiconductor disk laser at 20 μm

We report a high-power (AlGaIn)(AsSb) semiconductor disk laser emitting around 2 microm. With a diamond heat spreader used for thermal management, a maximum output power of just over 5 W and slope efficiencies of over 25% were demonstrated. The output wavelength was tunable over an 80 nm range centered at 1.98 microm. The beam propagation parameter (M2) was measured to be in the range of 1.1 to 1.4 for output powers up to 3 W.

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>