Solid state lasers for stereolithography

Stereolithography (SL) is a Rapid Prototyping & Manufacturing (RP&M) technique which can be used to produce 3 dimensional plastic parts directly out computer files generated by CAD. Stereolithography systems use ultraviolet lasers to solidify liquid resin into the desired form as defined by the CAD file.

Commercially available photopolymer initiators achieve optimum absorption at certain specific wavelengths. Laser beams at wavelengths shorter than 300 nm are not usually suitable for SL because photons at that energy are absorbed by all molecules of the resin, not only by the photoinitiator molecules. In the wavelength range 310 - 355 nm the pool of efficient initiator molecules is largest.

In recent years, solid state laser technology has reached the point where it can be applied to stereolithography. Frequency tripling of the powerful lines of diode pumped Nd/YAG, Nd/YVO4, and Nd/YLF lasers results in wavelengths of 355 nm (YAG, YVO4), 351 nm (YLF), and 349 nm(YLF). All these lines are applicable for SL. Commercial diode pumped lasers with tens or even hundreds milliwatts in the ultraviolet are already available. Efficient frequency tripling of the Nd/YAG, Nd/YVO4, or Nd/YLF lasers requires pulsed operation. The pulse repetition rates at maximum average power are typically between 1 and 20 kHz. This paper describes the issues relating to the applications of pulsed all solid state lasers in SL.