We investigated the properties of fluorinated refrigerants for high-power laser diode bars mounted on a funryu heat sink.
The thermal conductivity of fluorinated refrigerants is about ten times lower than that of water, but they are less
corrosive to funryu heat sinks. Using 3M's "Fluorinet" FC77 and "Novec" HFE-7300 and comparing them with water as
refrigerants, we developed a new fluorinated refrigerant cooling device that is suitable for removing heat from highpower
LDs and LD modules. This device achieved CW light-output power from a 1-cm LD bar equivalent to that for a cooling device using ion-exchange water. With HFE-7300 as the refrigerant, we achieved over 100 W of output power at a drive current of CW 120 A and over 1.5 kW for a stacked-LD module operated at a constant current of 55 A in continuous-wave (CW) mode. High-power LD bars subjected to lifetime testing under these conditions have been successfully running for over 15,000 consecutive hours.
In general, an electrical to optical power conversion efficiency for a high power LD ranges from 40 to 50%. Therefore, 50 to 60% of the input electricity is transformed into heat. The generated heat degrades the LD's optical characteristics and their lifetimes dramatically. We must not only suppress the heat generation but also remove the heat effectively from the LDs. Several years ago we proposed "FUNRYU", a water cooled heat sink. The sink has great advantages, due to its simpler structure than a micro channel cooler, in terms of cost, productivity, and water pressure.