Laser power and intensity – Elena

Lasers are usually described in terms of power, e.g. 1,000 watts or 6kW. Laser power is the total energy emitt in the form of laser light per second. The intensity of a laser beam is equal to its power divid by the area over which the power is concentrat.

For example, focusing a 1kW laser beam over a diameter of 0.1mm (0.004 in) will result in a power density of approx. 125kW per mm2 .

The high intensity causes the material to heat up rapidly so that little time is available for heat to dissipate into the surrounding material. This produces high cutting rates and an excellent quality of cut.

A laser’s intensity also determines the thickness.

The thicker the material to cut, the higher the intensity need. Higher intensities can reache by increasing laser power or by using a focusing lens with a shorter focal length. However, focusing the beam on to a smaller spot also reduces the depth of focus and is therefore unsuitable for cutting thick materials.

We can archieve high intensity can both in pulsed and continuous beams. Accordingly, either the peak pulse power in pulsed cutting or the average power in continuous cutting determines the penetration.

Cutting speed, though, is determined by the average power level. The higher the average power, the higher the cutting speed (Fig. 2). The intensity of CO2 and fibre lasers can be very high, allowing continuous vaporisation cutting of thin materials. We can cut metals of thickness 1-1.5mm at speeds in excess of 10m/min. We use cutting gas to remove metal vapour and protect the focusing optics. As the reaction time is very short, the kind of gas is not important and so compress air is suffi cient.

Fibre lasers provide excellent focus ability even over long distances. Cutting-on-the-fly where we use scanner optics to quickly move laser beam across the material to cut. We not use cutting gas as it cannot applie over long distances and the material is evaporating spontaneously.