Abstract: This invention provides an improved method and apparatus for non-contact quantum mechanical heating of thermoplastic fibers by resonant energy absorption of laser energy by the fiber. In one embodied form, the unique method for continuous heating of thermoplastic fibers comprises the steps of: a) preparing a thermoplastic synthetic fiber for heat treatment; b) illuminating the fiber with a beam of radiation from a carbon monoxide continuous wave laser beam of resonant frequency for the prescribed fiber being treated; c) traversing the fiber to be treated across the path of the laser beam in a direction perpendicular to the beam of radiation from the laser source; d) adjusting the rate of traversement of the fiber to maintain the temperature of the thermoplastic fiber within a temperature range of about five percent below the melting point of the thermoplastic fiber to continuously heat the fiber by resonant energy absorption of the laser beam.