With their emitting areas arranged in line to make a linear array, LD bar modules achieve high performance, high output power and high reliability when coupled with cooling devices. When stacked, the output power can be as high as a few kilowatts. There are primarily three cooling methods: the compact and simple Peltier-type Open Heatsink(OHS), the more efficient Water cooling, and Hamamatsu's original Funryu cooling (highest cooling efficiency). The appropriate cooling method should be selected in accordance with the required output power, driving conditions, and application.