It is widely known that all lasers require cooling.  This is because the efficiency of these devices is often well below 50%.  This means that in a best-case scenario, a laser putting out 500 watts of light power will need to dissipate at least 500 watts of waste heat, likely more.  The incoming power to this system would be 1 kW, with 500 Watts going to the laser light and the remaining 500 Watts dissipating as heat. All lasers, regardless of size or efficiency need some form of cooling.  The question we are examining here is do I need a compressor-based cooling system for lasers?

First, let’s take a look at some basics of heat transfer.  All heat flows from hot to cold.  In most systems, the heat from the laser is dissipated to ambient air. In systems cooled by free convection (air-no fans) or force convection (fans), the heat is dissipated from a heat sink, where the laser diode is attached, to ambient air.  In all direct air cooling scenarios, the diode gets hotter until the heat being shed into the air is equal to the waste heat being generated, as shown in the figure below.  If the laser is low power, not sensitive to overheating, or the ambient air is cool enough, a fan or free convection approach works well.  This technique is inexpensive, easy to implement, and robust.  

For applications with higher power, high ambient temperature, or the laser is temperature sensitive, a pumped loop, with or without phase change, can be used to lower the temperature in the laser.  Using liquid is more efficient at removing heat from the laser, and will be more efficient at dissipating heat to the ambient air, but the diode will always be hotter than the ambient air.  

The choice to go with a passive cooling approach, such as fans or pumped loop, will always depend on the laser temperature sensitivity, heat output, and ambient air temperature.

If passive cooling approaches fail to maintain the required temperatures, then an active cooling approach using a compressor-based cooling system can be used to regulate the laser temperature.  With an active cooling system, power is consumed to maintain the appropriate temperature of the laser.   The benefit, as illustrated in the figure below, is that the required temperature can be maintained independently of the ambient air temperature.  The system can also be controlled to maintain the required temperature as the power output of the laser rises and falls. The typical laser cooling system is a chiller that maintains a constant temperature in the coolant stream of a closed loop system.    

The bottom line is that all lasers need cooling of some type to function.  At the beginning of the design process, the important question is, “What type of cooling is required for the application?”  These decisions are best made at the beginning of the design process so that the space and power claim can be considered as the assembly is conceived and arranged.  Aspen Systems has cooling modules in every environment imaginable.  From medical to laboratory to military vehicles, our active cooling, compressor-based systems are overcoming cooling challenges. Laser cooling applications range from military spec cooling systems operating in 55°C ambient air to industrial manufacturing equipment designed to run 24/7 on the factory floor.  Other applications include cooling laser diodes in laboratory equipment, cooling the skin in laser medical aesthetics applications, and cooling LiDAR systems in outdoor environments.  The cold side temperature on these systems can range from 55°C down to -40°C, depending on requirements. Talk to us about your cooling requirements today. We are looking forward to working with you on your next project.

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