High Power Laser Diode (LD) modules are widely used as high-brightness light sources for pumping solid-state lasers
and for direct diode laser processing utilizing a compact feature. The LD bars installed in modules are required with
higher output power, efficiency and beam quality. We have optimized the LD bar structure for high output power and
efficient operation. The water-cooled heat sink has been designed for excellent thermal performance as well as long-term
stable cooling performance. We have also developed the thermal expansion controlled assembly technique to suppress
the "smile". As a result, we have achieved an output power of over 200 W and a conversion efficiency of 58% from 940
nm LD bars under continuous wave (CW) operation with very low smile of 0.8 μm.
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.