REFLECTED OPTICAL HARMONICS FROM DIELECTRIC MIRRORS

Optical second and third harmonics were generated in reflection from c ommercially available laser dielectric mirrors. Although most dielectr ic coatings on laser mirrors are centrosymmetric, the inversion symmet ry is broken at the dielectric-air interface. When intense femtosecond laser pulses are reflected off the dielectric mirrors, a second-order dipole contribution to surface second-harmonic generation can exist a nd is detected. More dramatically, at a laser fluence of similar to 10 GW/cm(2) the normally much weaker electric-dipole-allowed third-harmo nic generation that originated in the bulk accentuates the second-harm onic generation. These reflected harmonics are, in some cases, nonnegl igible in many sensitive experiments.