Direct Refrigerant Cooling of Lasers

Large, stand-alone, chiller systems using a recirculating coolant loop are typical of laser cooling systems.  The coolant loop in these units are subject to failure, the coolant lines can leak, and the coolant needs to be replaced on a regular basis.  In addition, shipping these systems can be problematic due to the size and weight and the potential of coolant freezing especially where water without an antifreeze additive are used.  The coolant pumps in these systems are known to fail at a rate of 4-5 times that of a refrigeration compressor, causing costly downtime and warranty expenses for the laser provided.  Our customer came to us with a request to provide a cooling system that does not need a pump, secondary coolant loop, or a reservoir and asked for a compact cooling system that could be integrated with the laser electronics inside the customer’s chassis.  Their vision was a maintenance free, integrated, high efficiency, compact cooling system that would be sold as part of the laser system.

Aspen engineers went to work to develop a direct refrigerant cooling (DRC) system that met the requirements while maintaining a constant temperature at the laser diode under varying load conditions.  With direct refrigerant cooling, the refrigerant is directly passed through the cold plate where it extracts heat from the laser diode and associated power electronics.  By eliminating the secondary coolant loop, a smaller, more efficient, near zero maintenance system with an expected Mean Time Between Failure (MTBF) of 90,000 hours was developed.  This MTBF is at least 4 times greater than the MTBF of competing chiller systems.  Special fittings were employed to eliminate all potential vibration being transmitted from the compressor.  With phase change heat transfer in the cold plate of the system, there is excellent heat transfer observed between the diode and the refrigerant and a constant temperature is maintained across the entire cold plate.  The desired temperature is maintained at the cold plate through a controller that varies the speed of the compressor to meet changing loads or changing temperature requirements.

The Direct Refrigerant Cooling (DRC) approach used to cool this laser system is a significant upgrade from the standard chiller approach.  Typically, when a laser company sells a system, a chiller requirement is provided that defines the cooling load, temperature, flow rate, and coolant type.  It is left to their customer to assure that the cooling requirements are met.  Often these chiller systems are purchased with price as the primary criteria.  This can leave an expensive laser exposed to possible failure when the chiller is improperly maintained.  By including an efficient, high quality, maintenance free cooling system with the laser, our customers are finding that these potential issues are avoided and their customer can be assured that the cooling system will last as long as the life expectancy of the laser itself.