Zhi-Wei Dong

Femtosecond pulse excited two-photon photoluminescence and second harmonic generation in ZnO nanowires

With femtosecond pulse excitation at the wavelength near 800nm, we observed three upconverted emission peaks from ZnO nanowires. The ultraviolet peak at about 385nm and the green emission band centered at about 515nm were attributed to the near band edge emission and defect level emission, respectively, while the intermediate peak was assigned to the second harmonic generation. From the quadratic dependence of the emission intensity on the excitation pulse energy, it is confirmed that the 385nm photoluminescence was mainly generated via two-photon absorption in ZnO nanowires under very intense light-matter interaction.

Multiphoton route to ZnO nanowire lasers

With intense femtosecond laser excitation, multiphoton absorption-induced stimulated emission and laser emission in ZnO bulk crystal and nanowires have been demonstrated at room temperature. UV-stimulated emission peaks appeared in both bulk crystal and nanowires when the excitation exceeded certain thresholds, and a sharp lasing peak with a linewidth of ~0.5 nm was observed from ZnO nanowires. The emission properties were attributed to the band-edge emission of the recombination of carriers excited by two- and three-photon absorption processes in the wide-bandgap semiconductor.

Observation of two-photon-induced photoluminescence in ZnO microtubes

The micrometer-sized ZnO tubes were fabricated by a hydrothermal method and characterized by scanning electron microscopy, high resolution transmission microscopy and micro-Raman spectroscopy. Photoluminescence (PL) emission from ZnO microtubes excited by light in the ultraviolet range from xenon lamp was measured. By using nanosecond laser beam at 527nm to excite ZnO microtube, we observed two-photon induced PL emission with an intense peak at 3.15eV and a weak peak at 2.65eV, which was confirmed by the quadratic dependence of the emission intensity on the excitation power.

Multiphoton absorption pumped ultraviolet stimulated emission from ZnO microtubes

We report observation of stimulated emission from ZnO microtubes pumped by multiphoton absorption using intense femtosecond pulses at wavelength around 800nm. Band edge emission, together with second harmonic generation, was observed and several stimulated emission peaks with linewidths of 0.5–0.7nm appeared at high excitation fluence. The stimulated emission from the microtubes were attributed to the excitonic effect at intermediate fluence (50–100mJ∕cm2) and electron-hole plasma at high fluence (>100mJ∕cm2), respectively. Possible Fabry-Perot cavity effects were also discussed.

Multi-photon excitation UV emission by femtosecond pulses and nonlinearity in ZnO single crystal

Optical nonlinearities and multi-photon ultraviolet (UV) excitation in ZnO single crystal were investigated by the z-scan method utilizing an intense femtosecond (fs) laser at different wavelengths. Based on the analysis of the experimental results at different excitation wavelengths near 800 nm, nonlinear optical effects that may emerge under an intense field are attributed to be responsible for the efficient two-photon absorption process under detuned excitation.

Heat treatment effect on the ultrafast dynamics and nonlinear optical properties of Ag : Si3N4 nanocermets

Ag : Si3N4 nanocermets were fabricated by the magnetron cosputtering method and were thermally treated at different temperatures. The off-resonant third-order nonlinear susceptibilities were determined to be of the order of 10−10 esu at 800 nm by the optical Kerr effect experiment. Further time-resolved pump–probe researches prove that heat treatment is a feasible way to improve the performance of ultrafast response for this material. The research results demonstrate that in addition to the common use in microelectronics, the Si3N4 nanocermets are promising in future applications in optical communication and photoelectric fields.

Multi-photon excitation in ZnO material by femtosecond pulses

Multi-photon excitation in ZnO material by femtosecond (fs) laser pulses around 800 nm was clearly observed. Under the intense field generated by fs pulses, two-photon absorption process was found very efficient in the excitation of the band edge emission from ZnO material under detuning condition. Nonlinear optical effects, such as Stark effect and Rabi effect, that may emerge under intense field are suggested to be responsible for this efficient excitation via two-photon absorption process. We consider that this NLO route to generate photoluminescence in ZnO material is meaningful in the research of blue-violet semiconductor laser field.

Two-photon absorption induced photoluminescence and the ultrafast dynamics of para-sexiphenyl nano-needles

Two-photon absorption induced photoluminescence of para-sexiphenyl nano-needles with high polarization and directional property was observed. The time-resolved measurement shows a very fast photoresponse and the absorption polarization selectivity of ground state.

Multi-photon route to ultraviolet nanowire lasers

Multi-photon absorption pumped ultraviolet ZnO nanolasers were demonstrated with femtosecond pulses at room temperature. Time resolved photoluminescence revealed that the exciton collision effect played an important role in the nonlinear lasing mechanisms.

Two-photon induced ultraviolet semiconductor laser assisted by the Rabi flopping

Ultraviolet lasing emission was observed from the wide band semiconductor ZnO excited by the fs pulses with photon energy less than the half of the bandgap via the Rabi flopping assisted Two-photon process.