Enhanced absorption and cavity effects of three-photon pumped ZnO nanowires

Abstract

Semiconductor nanowire (NW) lasers attract a lot of attention as potential elements of nanophotonic circuits and lab-on-a chip devices. Here, we report on the experimental investigation of stimulated near ultraviolet (NUV) emission, pumped by three-photon absorption from near infrared femtosecond laser pulses, from ZnO NW arrays of different morphologies and compare it to the bulk. The spectrally and temporally resolved measurements of the NUV emission show both strong enhancements in the absorption and emission properties of the nanowire arrays compared to bulk samples. Thus, we determine a many times higher three-photon absorption in the nanostructure morphology compared to the bulk material. Furthermore, the threshold pumping intensity for stimulated emission in a vertically oriented nanowire array is twice lower and the emission onset time is shorter than in randomly oriented arrays, revealing strong influence of the macroscopic nanowire arrangement.

Single nanowire defined emission properties of ZnO nanowire arrays

“…This spectral narrowing manifests the transition from spontaneous emission to stimulated emission [25]. This transition is further confirmed by an increasing slope in the log-log scale dependence of the emission yield on the pumping intensity at the threshold value (figure 2(c)) and by time-resolved measurements, as found in [11].…”

“…Stimulated emission from single semiconductor NWs on a low refractive index substrate has been demonstrated upon optical pumping in the single or multiphoton absorption regime at room temperature [8,9]. Furthermore, arrays of NWs, in which individual wires are either aligned vertically [10][11][12][13] or randomly oriented [11,14,15] also showed lasing. It has been theoretically predicted that inter-wire coupling might play an important role for lasing in arrays [16][17][18].…”

“…For low pump intensities, the broadband spontaneous emission centered at ~385 nm originates from combined action of exciton and free electron recombination [26]. Previous investigations of spectral dynamics in NW array pumped via three-photon absorption suggest that, for pump intensities around the lasing threshold, the density of the excited carriers well exceeds the Mott density at room temperature, such that the emission then originates from electron-hole plasma (EHP) recombination [11,27]. In short wires the gain is not enough to compensate the cavity losses.…”

Polarization Dependent Excitation and High Harmonic Generation from Intense Mid-IR Laser Pulses in ZnO

“…The nonlinear optical properties of zinc oxide (ZnO) crystals and nanostructures have been extensively studied over the last few decades. Light conversion processes such as second (SHG) and third harmonic generation (THG) as well as multiphoton absorption have been demonstrated in a wide variety of morphologies, such as micro- and nanowires, thin films, nanoribbons or nanoparticles [ 1 , 2 , 3 , 4 ]. A common feature of all these experiments is that the observed processes can be understood in the frame of perturbative nonlinear optics.…”

Self-induced ultrafast electron-hole plasma temperature oscillations in nanowire lasers

“…To further their development, a detailed understanding of their lasing dynamics is essential. Previous studies laid the groundwork by investigating several aspects of carrier relaxation, gain dynamics, plasmonic phenomena and the role of lattice defects in a number of different material systems [16][17][18][19][20][21] . Moreover, evidence for ultrafast intensity oscillations was observed in NW lasers, for which coherent effects have been suggested as a possible explanation 22 .…”