Dew Point and Condensation

What the dew point is

Fiber laser machines are water-cooled and very sensitive to too-low ambient temperatures, condensation, and overheating. Therefore, when operating fiber laser equipment in environments with too-high or too-low temperatures or excessive humidity, several important rules must be observed.

Dew point is the temperature at which water vapor begins to condense and form droplets on a surface: moisture from the air condenses and a visible film appears on surfaces.

As soon as the coolant temperature drops below the dew point, moisture appears on electrical and optical modules.

The dew-point limits for fiber lasers depend on several factors: ambient temperature, relative humidity, pressure, and the quality of the optical surfaces.

Operating conditions

• Laser systems must operate at an ambient temperature of not less than +15 °C and not more than +25 °C.
• If the temperature may rise above +35 °C, install the machine in an air-conditioned room.
• Relative humidity should preferably not exceed 50 %.
• For laser sources with power above 2000 W, the laser source must be located in an air-conditioned room.

High humidity can cause issues such as degradation of optical properties or corrosion. Condensation can seriously damage the focusing lenses.

Consequences of condensation

1. A coolant temperature below the ambient dew point causes condensate to form on the inside wall of the cutting head and on the optical lenses.
2. Using assist gas at a temperature below the ambient dew point causes rapid condensation on the optical lenses.
3. The dew point can also be reached on the surface of the optical fiber or inside its cladding. Condensate (dew) negatively affects laser operation and reduces both efficiency and service life.

Measures to prevent condensation

To prevent condensation and protect the laser from the negative effects of the dew point, apply the following measures:

1. Install the laser in a controlled environment with low relative humidity.
2. Isolate the laser from the outdoor environment.
3. Use only original lenses with an anti-condensation coating.
4. Air-condition the electrical cabinet.
5. Use cooling systems to maintain the optimal internal temperature of the laser.
6. Regularly service and clean the optical surfaces to prevent dust and other contaminants that promote dew-point formation.
7. Tune optimal process parameters (laser power and pulse frequency) to minimize heat generation. For further advice, contact the laser manufacturer or an optics specialist.
8. Keep relative humidity in the laser's working zone at 40–60 %.
9. Install heating elements on the laser or its optical path, or use dedicated heaters — this maintains a temperature high enough to prevent dew-point formation.
10. Minimize the temperature difference between the laser and the surrounding environment: keep the laser inside its enclosure or control the environment around it.
11. Continuously monitor the cooling system — it must operate correctly to prevent overheating or condensation.
12. If needed, install additional filters and humidification/dehumidification equipment to control humidity.

Measurement and target values

The dew point can be calculated using various formulas and methods. For accurate values, use dedicated instruments — hygrometers or dew-point sensors.

Controlling the dew point in fiber laser machines is essential for stable operation and high system performance. Dew-point values vary by process and material requirements; the recommended range is typically −10 °C to +5 °C.

Calculation example

If fiber laser machines are commissioned at the wrong temperature or humidity, condensate can form on the (relatively cold) coolant pipes. This can cause direct and irreversible damage to the laser source and/or cutting head.

The coolant temperature must remain well above the dew point to prevent condensation. Never place the chiller too close to other equipment, and make sure the ambient air is properly conditioned.

Example: at +29 °C and 60 % relative humidity, the dew point is about +21 °C. The coolant temperature must therefore stay well above +21 °C (in practice +23…+25 °C) to prevent condensation.

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