A flat-top beam (otherwise known as a top-hat) is used in various applications where a controlled profile is desired (i.e. a uniform density across the irradiated surface). Passing a Gaussian beam through special optics will create the flat-top beam and is the most common way of generating a flat-top beam. Uniform excimer beams are used in many material processing applications (e.g. creating integrated circuits). Industries such as welding, drilling, and medicine also make extensive use of flat-top beams. Although a rough estimate of a flat-top beam’s uniformity can be gauged visually using the image of the beam profile taken with a CCD or CMOS camera, a more accurate method is needed. The DataRay software (versions LCMvD23 and later) reports the plateau uniformity value, which gives the full width half maximum (FWHM) width of the beam’s power density histogram. The plateau uniformity of the flat-top beam is a value between zero and one used to quantify the uniformity of the flat-top beam. Zero represents a perfect flat-top beam. As the flat-top beam deviates from the theoretical flat-top, the value moves towards one. DataRay adheres to the ISO 13694 procedure for calculating the plateau uniformity. The plateau uniformity has the advantage of providing a single metric to characterize the beam uniformity across the entirety of the beam profile, rather than looking at individual slices of the beam.
Posted by Lucas Hofer on 2/26/2016 to App Notes