From three-photon to tunnel ionization pumped ZnO nanolasers

We report on experimental investigation of stimulated near ultraviolet (NUV) emission from a disordered array of nanowires pumped in a very broad range of pumping wavelengths ranging from near to mid-IR. The nanowires (NWs) are made of ZnO, which is a well-known wide-bandgap (3.3 eV) semiconductor material and one of a few, efficient NUV laser materials directly driven by UV pumping sources [1, 2]. In addition, two-photon pumped lasing has been demonstrated for thin films of nanocrystalline ZnO [3] as well as three-photon pumped lasing for nanowires [4]. Here, we report on stimulated emission in the 390 nm range from disordered ZnO nanowire arrays pumped via three-photon absorption of intense femtosecond laser pulses centred at 0.8 μm wavelength (near-IR) and in the tunnel ionization regime when the nanowires are excited by a mid-IR source operating at 3.9 μm central wavelength.