In coaxial observation setups, light from the processed object passes the scan lens, the scan system and a beam splitter to be imaged with a telephoto lens on a sensor. Thus, a small field of view is moved simultaneously with the laser beam. Thereby, the resolution is limited by the aperture of the scanner. Aberrations that are caused by the scanning system and by the wavelength difference between laser and observation wavelength, can only be decreased, but not eliminated, by using multispectral F-theta lenses and a time-consuming calibration.
Another possibility for observing a laser process is the installation of a lens with oblique orientation to the processing field. Caused by the oblique view, a difference in optical path occurs that depends on the tilt angle, working distance and field of view. The resulting blur at the field edges can be solved by using a lens that considers the Scheimpflug principle. It describes that the blur on an image caused by a tilted object plane can be compensated by tilting the sensor plane by a defined angle too. To realize this, Sill Optics offers a custom specific adaptor that is sensor-sided integrated into the lens. Distortion that is caused by the tilted view can be improved significantly by telecentric or bi-telecentric lenses.
For transparent workpieces there is also the opportunity of observing the working process through the material from below. Beside the observation wavelength the laser wavelength passes the imaging too. Because of that, the lens design has to fulfil additional criteria e.g. prevention of absorption peaks and design for the laser energy.
We are pleased to support you regarding the appropriate method for process observation of your system.