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Design Difficulties

Difficulties

Laser diodes are found in high-output pulsed and continuous mode lasers.  Heat is generated as side-effect of the optical production.  With arrays of up to 25 individual diodes mounted on a single bar, bars can currently output up to 100W thermal power.  With the size of diode bars on the order of millimeters, this thermal generation results in heat fluxes up to 10⁷ W/m². 

Additionally, the optical efficiency of the diode is extremely temperature dependent, with optimum performances near room temperatures.

Considering the high flux and relatively low temperature requirements, conventional heat sink cooling systems have proved inadequate.  Advanced cooling systems incorporate liquid cooling and cryogenic systems.  These systems are often large and bulky, and can easily break down due to a large number of moving parts.  Additionally, low working temperatures and liquid environments can easily introduce moisture into the system or neighboring components which lead to detrimental thermal or electrical conditions.

To put the scope of the problem in perspective, consider the current cooling solution for computer chips.  A 3 GHz Pentium IV computer chip generates 70-100 Watts of heat over a 35mm X 35mm footprint, requiring dissipation of about 8X10⁴ W/m².  The specifications for this cooling package require dissipation of 6X10⁶ W/m², or nearly 100 times the flux found in today’s computer heat sinks.

In this project, a steady-steady state laser diode cooling package is characterized numerically and validated experimentally.  The package is designed to dissipate the heat generated by a 100 Watt diode bar which produces 60 Watts of heat.  The cooler is a multistage device which makes use of advanced low resistance materials, a thermoelectric cooler and a heat sink.