Yong-Li Yan

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.

The Observation of Ultrafast Excited-state Dynamical Evolution In B800- Partially or Completely Released LH2 of Rhodobacter sphaeroides 601 at Room Temperature

Abstract Photodynamics of two kinds of peripheral antenna complexes (LU2 of Rhodobacter sphaeroides, native LH2 (RS601) and B800-released LH2 where B800-BChls were partially or completely removed with different pH treatments), were studied using femtosecond pump-probe technique at different laser wavelengths. The obtained results for these samples with different B800/B850 ratios demonstrated that under the excitation around B800 nm, the photoabsorption and photobleaching dynamics were caused by the direct excitation of upper excitonic levels of B850 and excited state of B800 pigments, respectively. Furthermore, the removal of B800 pigments had little effect on the energy transfer processes of B850 interband/intraband transfer.