Top-hat
Describes a beam with flat, uniform intensity across its width and steep edges, instead of a Gaussian peak.
Lab and process talk for a flat-top intensity profile, named after the hat's cross-section. Refractive or diffractive beam shapers, homogenizers and imaging of a uniformly filled aperture produce it. Top-hat beams give even exposure for ablation, annealing and pumping, but the flat region only holds near the shaper's design plane and reverts toward Gaussian far from it.
Use the top-hat shaper for the annealing run, with the Gaussian you overcook the middle and underdo the edges.
Also heard as
- flat-top
- top hat profile
- tophat
Related terms
Gaussian beam
A beam whose intensity falls off from the center as a bell curve, the shape of an ideal single-mode laser.
Fluence
Pulse energy per unit area, usually in J/cm squared, the quantity that sets ablation and optical damage.
Beam profiler
An instrument, usually a camera or scanning slit, that measures a laser beam's intensity distribution and width.
Hot spot
A small region of a beam with much higher intensity than the rest, a common cause of optic damage.