Jishi Fu

Large third-order optical nonlinearity in Au:SiO2 composite films near the percolation threshold

Very large third-order optical nonlinearity, χ(3)∼2.5×10−6 esu, measured by a degenerate four wave mixing method using a short pulse (70 picosecond) laser, has been found in the rapid-thermal annealed Au:SiO2 composite films at concentrations below the Au percolation threshold. The dependence of the χ(3) on Au concentration, p, follows a cubic power law. The maximum figure of merit, χ(3)/α (with α being the absorption coefficient) is about 10−11 esu cm. We explain this result as due to local field enhancement arising from the Mie resonance of the Au nanoclusters, with strong interaction between the nanoclusters further promoting the effect.

Origin of third-order optical nonlinearity in Au:SiO 2 composite films on femtosecond and picosecond time scales

Three sorts of probe laser, which have pulse durations of 200 fs, 35 ps, and 70 ps, were employed in the measurement of the third-order nonlinear optical susceptibility x((3)) in Au:SiO(2) composite films in a degenerate four-wave mixing scheme. We found that the composite films at their absorption peak (~550 nm) had a maximum x((3)) , which depends strongly on the pulse width of the probe laser. The value of x((3)) measured with a 70-ps laser was ~30 times larger than that measured with a 200-fs laser. The time-resolved measurements revealed that the optical nonlinearity on the femtosecond time scale is attributable mainly to contributions from the interband electric-dipole transition (especially at low concentrations) and partly to those from hot electrons rather than being dominated by hot-electron excitation in the picosecond regime.

Second harmonic generation in periodically domain-inverted Sr0.6Ba0.4Nb2O6 crystal plate

Quasiphase-matched second harmonic generation (SHG) has been realized in periodically domain-inverted strontium barium niobate (Sr0.6Ba0.4Nb2O6, so-called SBN) crystal plate induced by an external electric field. Both the coercive field and Curie temperature have been determined through in situ observation of the second harmonic signals. The measured SHG conversion efficiency is about 10% at a fundamental wavelength of 977.8 nm.

The third-order non-linear optical response of the endohedral metallofullerene Dy@C82

Abstract Dy@C 82 has been prepared by an efficient solvent extraction procedure and characterized by negative-ion desorption chemical ionization mass spectrometry and UV-VIS–near-IR absorption. Degenerate four-wave-mixing measurements on the CS 2 solution of Dy@C 82 were performed using 70 ps laser pulses at 0.532 μm. The magnitude of the second hyperpolarizability γ 1111 of the Dy@C 82 molecule was (3.0±0.5)×10 −30 esu at 0.532 μm. The resonant enhancement and the electron transfer from the trapped dysprosium to the C 82 cage are suggested to bring about its larger non-linear optical response relative to the empty fullerene. The experimental results are in good agreement with our calculations based on an extended Su–Schrieffer–Heeger model and the sum-over-state method.

Third harmonic generation through coupled second-order nonlinear optical parametric processes in quasiperiodically domain-inverted Sr0.6Ba0.4Nb2O6 optical superlattices

A one-dimensional quasiperiodically domain-inverted optical superlattice has been designed and fabricated in a strontium barium niobate (Sr0.6Ba0.4Nb2O6) single-crystal plate. A third harmonic output generated through coupled second-order nonlinear parametric processes with a conversion efficiency of about 1.6% was obtained when both the second harmonic and the third harmonic were simultaneously quasiphase matched in the crystal.

Nonlinear optical response of the higher fullerene C90- a comparison with C60

Abstract Degenerate four-wave-mixing measurements on C 90 in CS 2 with different concentrations were performed using 70 ps laser pulses at 0.532 μm. The dependence of the conjugate signal intensity on the incident laser power and the concentration of C 90 were investigated. By optimizing experimental parameters, the second hyperpolarizability γ 1111 of C 90 was determined to be (1.8 ± 0.6) × 10 −30 esu, which is approximately eight times that of the C 60 molecule measured under identical conditions. Our results are in accord with the theoretical prediction that higher fullerenes should show larger nonlinear optical responses.

Second- and third-harmonic generation in quasi-periodically domain-inverted Sr/sub 0.6/Ba/sub 0.4/Nb/sub 2/O/sub 6/ single crystal plate

We have studied the quasi phase matched (QPM) SHG and THG in a quasi-periodically domain inverted SrBaNb/sub 2/O/sub 6/ (SBN) single crystal plate. The conversion efficiency for the SHG and THG is about 10% and 1.6%, respectively.