A laser illuminator and illumination method for use in an inspection system, such as a semiconductor wafer inspection system or photomask inspection system is provided. The design comprises generating fundamental frequency laser energy at different fundamental wavelengths, such as 998 nm, converting a portion of the fundamental frequency laser energy to 2.sup.nd harmonic frequency laser energy, further converting the 2.sup.nd harmonic frequency laser energy to 4.sup.th harmonic frequency laser energy, and mixing the 4.sup.th harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce laser energy at a sum frequency. Mixing is accomplished by non-critical phase matching in a crystal of Cesium Lithium Borate (CLBO). Alternately, the design may employ shifting a portion of the fundamental frequency laser energy to laser energy at a Raman line and/or mixing the 2.sup.nd harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce 3.sup.rd harmonic frequency laser energy.