US Patent 7661387 Dual laser coating apparatus and process

An apparatus for applying and fusing a powder coating to substrates of various composition uses two lasers to accurately heat the coating to the optimum temperature. A second laser has less power and heats a smaller area than the first laser. Temperature control is enhanced by the ability to superheterodyne two lasers at separate frequencies. This allows for better absorption of certain materials being fused by the laser. Another common problem associated with laser processing occurs as the polymer heats up. During the heating process the spectral lines are Doppler broadened and slightly shifted. This can affect the absorption of a laser of a fixed wavelength. With the present invention, the optimum laser frequency can be turned to a more optimum frequency for absorption still with sufficient power for fast efficient thermal processing.