LDs need cooling to extend their life and maintain stable laser-beam characteristics during operation. For low-power LDs, passive heatsinks are usually sufficient. Medium- and high-power LD systems require forced cooling. High-power lasers use a circulating liquid for cooling; however, liquid cooling systems are beyond the scope of this book.
For mid-power LDs, thermoelectric coolers (TECs) offer a simple and reliable solution. They are a kind of semiconductor diode that operates based on the Peltier effect: the direct current flows through a p-n junction, which forces one side of the junction to cool down and the other side heat up. The cold side is used to cool designated objects, while the heat from other side is removed with the help of heatsink.
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