Overview
Solid-state lasers generate a large amount of heat during operation. If this heat is not removed promptly, it will severely affect the service life and performance of the equipment, and in extreme cases may cause serious damage. Selecting an appropriate water-cooling system can greatly extend the lifetime of the laser and allow the device to operate at its designed performance limits.
Key design considerations for the cooling system
1. System heat-dissipation capacity
The required heat-dissipation capacity of the cooling system should be chosen based on the flashlamp pump power of the laser and must take into account heat-exchange efficiency and continuous operating time. Do not rely solely on the manufacturer’s rated cooling capacity, because different suppliers may use different standards to define cooling capacity. Actual test conditions should be used to determine the required cooling power in order to avoid insufficient heat dissipation in practice.
2. Cooling system flow rate and pressure
The laser cavity (active core) contains fine internal structures that require a certain minimum flow rate to remove generated heat in time. At the same time, there are sealing rings inside the cavity; to maintain seal integrity, excessive water pressure must be avoided. Therefore, the cooling system should be designed to ensure the required flow rate while not exceeding the maximum allowable working pressure.
3. Materials for the coolant circuit
For the coolant circuit, use stainless steel or PTFE (polytetrafluoroethylene). Avoid copper components and other materials that are prone to oxidation or corrosion. If such components oxidize, corrosion products—such as basic copper carbonate (Cu₂(OH)₂CO₃), aluminum oxide (Al₂O₃), or iron(III) oxide (Fe₂O₃)—may precipitate into the water circuit and contaminate the optical concentrator chamber, causing a reduction in laser output energy.
For flashlamp-pumped lasers used in medical aesthetic applications, we recommend a water-recirculation system combined with a heat exchanger for heat removal. If compressor-based refrigeration is used, special attention must be paid to dew-point control. As shown in the figure below:
Common Issues in Cooling Systems
Failure to regularly replace distilled water and filters
It is important to regularly check the coolant water level and maintain it at the proper level, as well as to replace the cooling water and filters periodically. Preventing the growth of algae, bacteria, and microorganisms in the water is critical. The water circuit of a laser cooling system is not fully sealed; over time, exposure to the external environment allows dust, debris, and bacteria to enter the water. This can cause water quality deterioration, resulting in insoluble substances that adhere to the inner walls of the laser water circuit, which blocks water flow, reduces circulation, and diminishes cooling efficiency.
Regular replacement of the cooling water is therefore essential. As shown in the figure below, the distilled water in the pipeline can deteriorate over time. It is recommended to replace the internal water every three months. Filters should be replaced every 3–6 months depending on usage. Additionally, the laser and water circuit should be cleaned regularly. A recommended procedure is: “add water → run the machine for a short time → drain water,” repeated 2–3 times to ensure thorough cleaning.
Failure to Drain Distilled Water During Long Periods of Inactivity
If the equipment is not going to be used for an extended period—such as during the Lunar New Year shutdown or before transporting the laser—it is essential to drain the cooling water from the chiller. Compressed air should be used to blow out any residual water from both the laser and the chiller to prevent internal freezing or leaks that could damage components. Although xenon lamps emit UV light, which has some sterilizing effect, prolonged inactivity allows microorganisms and algae in the cooling water to multiply rapidly, leading to water deterioration.
Using Coolants Other Than Distilled Water
It is strongly recommended to use only distilled water as the coolant (do not use deionized water, and no algaecide additives are necessary). Deionized water can corrode internal components of the cooling system, and long-term use of algaecides may reduce the service life of internal parts. Therefore, distilled water is the preferred and safest option.
Improper Use and Storage of Chillers in Winter
During winter, the indoor and outdoor temperature difference can be significant. After receiving the laser, it should be placed upright for at least 12 hours before powering on. If a chiller is shipped together with the laser, it must also be placed upright for at least 12 hours before use. When the ambient temperature is below 0°C and the equipment will remain unused for a long time, draining the water is necessary to prevent freezing damage.
If the water is not drained during storage or transport in subzero conditions, the water inside the laser may freeze and expand. This can lead to blocked water channels, cracks in the laser cavity, and in severe cases, complete failure of the laser, resulting in irreparable damage and significant losses. The use of antifreeze is not recommended due to its mild corrosive effects.
If the laser must be operated in environments below 0°C, a 1:1 mixture of ethylene glycol and distilled water may be used as a temporary coolant. However, long-term use of this mixture can reduce the laser’s efficiency. After such use, the coolant must be completely flushed with distilled water, filters replaced, and distilled water restored as the standard cooling medium.
A well-designed cooling system allows the laser to maintain high performance over the long term. If you have any questions regarding the design or maintenance of your water-cooling system, Beamtech is happy to assist you at any time.
