Laser materials processing

• Coating of the workpiece surface with good-absorbing layers, e.g. graphite-sprays.
• Treat the workpiece with an etched surface (german: gebeizt)
• Allow it to build oxide-layers during heated-up (allow contact to air-oxygen during processing, if workpiece can sustain oxides).

• Systems, which work with a hollow, insidemirrored copper-needle. The copper-needle guides entering laser beam power to a photoelectric detector located in the rotation-axis. Withsoftware then a 2-dim. pattern of the beampowers is calculated, showing the positions of the measures and the measured beam-powers there.
• Imaging-technology, using a CCD-Photo-Chip. For this purpose here, of course it is heavily necessary to add largely damping glasses set in the optical path before the chip in order not to overheat it.

Advantages of CCD-camera-type systems:

• pulsed-laser beams
• extreme narrow focus-diameters of down to ca. 10 µm
• more variety of wavelengths (using appropri. CCDs).
   

The diameter enclosing 86% of all measured beam-power is defined as the focus-diameter.

Thus, the measuring of the intensity-distribution of a beam also delivers the diameter of the beam.
 

The smallest measured diameter in the whole measured caustic of the focussed beam is df.
 

The shape of the caustic (in german: Kaustik) of a focussed beam is developed through the correct vertically positioned of multiple diameter-measurements, see fig. right. The focus-plane is localized along the caustic there, where df had been detected.

They have absorbing surfaces for the laser beam. Through the heating of the absorber the incident laser beam power can be calculated. Of course, these systems have to be calibrated by the manufacturer prior to the use.

• high laser-power PL
• high beam-intensity I (= high PL and narrow df)
   

For tolerances in the normal direction to the workpiece-surface:

• high ZRf

For tolerances in the lateral direction, perpendicular to the feed-direction:

• high df , or a scanned laser beam (scanned in lateral direction)

• Narrow df (allowing a feast feed-rate and thus little time for heating up)
• Pulsed beam-operating-mode (allowing cooling time between two high power pulses)
• Wavelength-selective absorption (appropriate beam-wavelength, or appropriate absorption-behaviour of the treated material, or both)