Chem trails + lasers?
A method of laser sintering, comprising the steps of:
directing a sintering laser beam onto a surface of a powder at a sintering location; and
directing at least one heating-up laser beam onto a heating-up region near said sintering location, said heating-up laser beam being a defocussed laser beam or a laser beam focused more broadly than the sintering laser beam such that a temperature gradient between said sintering location and the surrounding powder is reduced to a predetermined value at which curl of the sintered part of the powder is greatly reduced.
https://patents.google.com/patent/EP0724494B1