Liquid metal heat sink for high-power laser diodes (original) (raw)

Testing of active heat sink for advanced high-power laser diodes

2011

We report on the development of a novel active heat sink for high-power laser diodes offering unparalleled capacity in high-heat flux handling and temperature control. The heat sink employs convective heat transfer by a liquid metal flowing at high speed inside a miniature sealed flow loop. Liquid metal flow in the loop is maintained electromagnetically without any moving parts. Thermal conductance of the heat sink is electronically adjustable, allowing for precise control of diode temperature and the laser light wavelength. This paper presents the principles and challenges of liquid metal cooling, and data from testing at high heat flux and high heat loads.

Quasi-passive heat sink for high-power laser diodes

2009

We report on a novel heat sink for high-power laser diodes offering unparalleled capacity in high-heat flux handling and temperature control. The heat sink uses a liquid coolant flowing at high speed in a miniature closed and sealed loop. Diode waste heat is received at high flux and transferred to environment, coolant fluid, heat pipe, or structure at a reduced flux. When pumping solid-state or alkali vapor lasers, diode wavelength can be electronically tuned to the absorption features of the laser gain medium. This paper presents the heat sink physics, engineering design, performance modeling, and configurations.

Electronically controlled heat sink for high-power laser diodes

2009

We report on a novel electronically controlled active heat sink for high-power laser diodes offering unparalleled capacity in high-heat flux handling and temperature control. The heat sink receives diode waste heat at high flux and transfers it at reduced flux to environment, coolant fluid, heat pipe, or structure. Thermal conductance of the heat sink is electronically adjustable, allowing for precise control of diode temperature and the diode light wavelength. When pumping solid-state or alkaline vapor lasers, diode wavelength can be precisely temperature-tuned to the gain medium absorption features. This paper presents the heat sink physics, engineering design, and performance modeling.

Progress in the development of active heat sink for high-power laser diodes

2010

We report on the development of a novel active heat sink for high-power laser diodes offering unparalleled capacity in high-heat flux handling and temperature control. The heat sink receives diode waste heat at high flux and transfers it at reduced flux to environment, coolant fluid, heat pipe, or structure. Thermal conductance of the heat sink is electronically adjustable, allowing for precise control of diode temperature and the output light wavelength. When pumping solid-state lasers, diode wavelength can be precisely tuned to the absorption features of the laser gain medium. This paper presents the AHS concept, scaling laws, model predictions, and data from initial testing.

Liquid Metal Cooling for High-Power and High Heat Flux Applications

We report on the development of a novel, ultra-low thermal resistance active heat sink (AHS) for thermal management of high-power density electronic and photonic components. AHS uses a liquid metal coolant flowing at high speed in a miniature closed and sealed loop. The liquid metal coolant receives waste heat from a component at high flux and transfers it at much reduced flux to environment, primary coolant fluid, heat pipe, or structure. Liquid metal flow is maintained electromagnetically without any moving parts. Temperature of the heat load can be controlled electronically, thus allowing photonic components to operate at a stable temperature over a broad range of ambient conditions. Cooling with liquid metal is shown to require much less pumping power than comparable cooling with conventional liquids.

Next Generation Heat Sinks for High-power Diode Laser Bars

Twenty-Third Annual IEEE Semiconductor Thermal Measurement and Management Symposium, 2007

As for other electronic or optoelectronic devices, the package of a high-power laser bar has to provide the following basic features: • Mechanical stability for mounting and handling • Electrical contacting of the n-side and the p-side of the device • Cooling to remove the waste heat generated by the diode laser Given the large power turnover and comparably small size of a diode laser bar, the cooling capabilities of the package are of great importance. With a typical efficiency of 60 percent, a laser bar producing an optical output power of up to 100 W simultaneously generates 80 W of waste heat. Taking into consideration a typical size of 10 x 1.2 mm 2 to 10 x 1.5 mm 2 , this results in an extremely high heat-flux density of about 500-600 W/cm 2. To maintain its high efficiency and a long lifetime, the operating temperature of the laser bar should be kept as low as possible, typically below 60°C/140°F. This requires very effective cooling, resulting in the fact that the cooling aspect dominates the package design and material choice. Therefore, the standard heat sink material in nearly all commercially available diode laser packages is copper owing to its excellent thermal conductivity (390-400 W/mK), its good mechanical machining properties, and its comparably low price. As a consequence of the increasing output power, heat sinks with a higher thermal conductivity are desired as well. Therefore in parallel new high performance materials like diamond composites will be integrated in the heat sinks. Next generation heat sinks made out of diamond composite materials combined with copper in a sandwich structure have been designed at Fraunhofer ILT. As a first step heat sinks without water-cooling, so-called conductive cooled heat sinks, are fabricated and compared with available standard copper heat sinks. The second step is that composite materials will also be used for water-cooled heat sinks to realize higher output power of the diode laser bar. In parallel erosion and corrosion effects will be minimized. Particle image velocimetry and CFD simulation are helpful tools to locate critical areas in the cooling structure like turbulences or dead water areas. Together with expansion matching these steps will help to increase the lifetime of high power diode laser bars. Keywords High-power diode lasers, expansion matching, microchannel heat sink, macro-channel heat sink, conductively cooled heat sinks, particle image velocimetry,

Modelling of a micro-channel heat sink for cooling of high-power laser diode arrays

Micro-channel heat sinks are used in a wide variety of applications, including microelectronic devices, computers and high-energy-laser mirrors. Due to the high power density that is encountered in these devices (the density of delivered electrical power up to a few kW/cm 2) they require efficient cooling as their temperatures must generally not exceed 100 • C. In the paper a new design for micro-channel heat sink (MCHS) to be used for cooling laser diode arrays (LDA) is considered. It is made from copper and consisting of 37 micro-channels with length of 9.78 mm, width of 190 µm and depth of 180 µm with the deionized water as a cooling medium. Mathematical and numerical models of the proposed design of the heat sink were developed. A series of thermofluid numerical simulations were performed for various volumetric flow rates of the cooling medium, its inlet temperature and different thermal power released in the laser diode. The results show that the LDA temperature could be decreased from 14 to 17% in comparison with earlier proposed design of the heat sink with the further drop in temperature obtained by applying indium instead of gallium arsenide as the soldering material between the LDA and MCHS interface. Moreover, it was found that the maximum temperature, and therefore the thermal resistance of the considered heat sink, could be decreased by increasing the coolant flow rate.

Cooling approaches for high power diode laser bars

2008 58th Electronic Components and Technology Conference, 2008

The field of applications for diode laser bars is growing continuously. The reasons for this are the increasing width of available wavelengths and optical output power. In parallel to this the packaging requirements for the high power diode laser bars are enlarging and becoming more manifold. Expansion matched, non corrosive, non erosive, low thermal resistance and high thermal conductivity are some of the keywords for the packaging in the near future. Depending on the thermal power density, two different types of heat sinks are used: active water cooled and conductively cooled heat sinks. For applications with less than 60 W thermally dissipated power per laser bar conductively cooled heat sinks are preferred. Pure copper heat sinks with their high thermal conductivity achieve a good thermal performance, but the CTE mismatch between the heat sink and the laser bar and the hence required soft solder technology lead to lifetime limitations. A higher optical output power and a longer lifetime can be realized with AuSn hard solder mounted laser bars on expansion matched heat sinks. The conventional expansion-matched solution uses WCu or AlN submounts requiring an additional mounting step and degrading the thermal performance. In contrast, Fraunhofer ILT has developed conductively cooled heat sinks with integrated expansion matching. In this paper the standard packaging will be compared with the new development at Fraunhofer ILT. The main focus will be on the thermal resistance and corrosive behavior.

Micro thermal management of high-power diode laser bars

IEEE Transactions on Industrial Electronics, 2001

Lifetime and reliability of high-power diode laser bars are sensitively related to operating temperature, mounting stress, and solder electromigration. These three factors have been taken into account for the development of a new packaging technology for 1 cm laser bars of gallium arsenide. We examine the use of chemical-vapor-deposited (CVD) diamond as heatspreaders in order to reduce thermal resistance of a microchannel cooler for liquid cooling. We show that it is possible to perform hard soldering on a CVD-diamond with a new technique. Additionally, we present a controlled water cooling system fit to the flow characteristics of the cooler. It permits one to adjust the emission wavelength of the diode lasers by changing the water flux

Heat dissipation in high-power semiconductor lasers with heat pipe cooling system

Journal of Mechanical Science and Technology, 2017

This study focuses on the application of heat pipes in thermal management for high-power semiconductor lasers. The heat pipe cooling systems are used for heat dissipation in high-power semiconductor lasers. These systems are used instead of water cooling machines to realize a compact and lightweight laser module. The n-shaped heat pipe cooling system, which consists of eight 6 mm copper heat pipes with sintered powder wicks, can easily handle a heat load of up to 73 W from a single-laser unit. The fabricated U-shaped heat pipe cooling system, which consists of ten 12 mm copper heat pipes with sintered powder wicks, can easily handle a heat load of up to 300 W from five laser units. The optical power of the multi-laser module cooled by the U-shaped heat pipe cooling system reaches 210 W. These results indicate that high-power semiconductor lasers can be cooled using heat pipe cooling systems instead of water cooling machines.