Scattered second harmonic generation on ultrashort laser pulse processed zinc coatings

We report on an easy way to achieve scattered second harmonic generation (SHG) on zinc-coated glass substrates by focusing femtosecond laser light with a pulse energy of around 50 mu J on the sample in ambient air. Contrary to irradiation in other gases, in ambient air the generated plasmas oxidized the sample surface in the focal point. The formed crater was covered with arbitrarily arranged small needle-like ZnO crystals, leading to scattered SHG. Aside from pure ZnO itself, which is well known for its SHG, several other zinc containing samples had to be laser processed before showing SHG. Comparing those samples, the strongest second harmonic (SH) signal emerged from zinc-coated glass substrates, easily prepared with ordinary zinc spray. Its SHG was comparable to that of pressed ZnO powder. For lower pulse energies, an increased SH signal emerged when moving the spot a few 10 mu m away from the crater center.