Bagher Tabibi

Optical nonlinearities of Au nanoparticles and Au/Ag coreshells

Au nanoparticles exhibited both negative and positive nonlinear absorptions with ground-state plasmon bleaching and free-carrier absorption that could be origins of the saturable and reverse-saturable optical properties. Au/Ag coreshells displayed only positive nonlinear absorption and reverse-saturable optical properties as a function of excitation intensity at the edge of surface-plasmon resonance, which implies no ground-state plasmon bleaching and the existence of two-photon absorption.

Large pure refractive nonlinearity of nanostructure silica aerogel

The nonlinear refraction coefficient of silica aerogel was estimated to be ∼−1.5×10−15 m2/W (∼−3.67×10−9 esu) with a signal-beam z-scan spectroscopy. The third-order nonlinear refraction coefficient of nanostructure silica aerogel was almost five orders larger than the nonlinear refraction (χ3) of bulk material. The large nonlinear refraction with high nonlinear figure of merit is an ideal optical property for nonlinear optical applications.

Time-resolved and temperature-dependent photoluminescence of ternary and quaternary nanocrystals of CuInS2 with ZnS capping and cation exchange

Time-resolved and temperature-dependent photoluminescence (PL) spectroscopy of ternary compound copper indium disulfide (CuInS2, or CIS) core materials, CIS/ZnS coreshells, and quaternary compound ZnCuInS2 (ZnCIS) revealed their optical properties with spectral, temporal, and thermal characteristics, which were closely linked to surface-related recombination, and shallow or deep defect-related donor-acceptor transitions. The PL peaks of semiconductor nanocrystals (SNCs) with sizes near Bohr radius displayed at ∼775 nm for CIS, ∼605 nm for CIS/ZnS, and ∼611 nm for ZnCIS. The spectral blue shift and spectral narrowing with CIS/ZnS and ZnCIS are assigned to the increased spatial confinement and surface regularity with the etching of core materials. Both the shorter lifetime at surface-trapped states or interface states and the longer lifetime at intrinsic defect-related states of CIS, CIS/ZnS, and ZnCIS SNCs were widely distributed across the entire PL spectral region. The surface or interface-trapped electr...

Large Resonant Third-order Optical Nonlinearity of CdSe Nanocrystal Quantum Dots

Resonant third-order nonlinear optical susceptibility and hyperpolarizability of CdSe nanocrystal quantum dots were revealed to be ~2.6×10 -20 - 2.7×10 -19 m 2 /V 2 and ~2.2×10 -40 m 5 /V 2 by using nanosecond degenerate four-wave mixing at 532 nm. The large nonlinearity of the CdSe nanocrystals is attributed to the resonant excitation and multiple nonlinear optical processes.

Third-order Optical Nonlinearities of Singlewall Carbon Nanotubes for Nonlinear Transmission Limiting Application

Third-order nonlinear susceptibility of single wall carbon nanotubes thin film was measured to be ~1.4u10 -16 m 2 /V 2 . The nonlinear transmission limiting threshold of carbon SWNT was ~20 MW/cm 2 with visible and nanosecond laser excitation.

Hybrid optical materials of plasmon-coupled CdSe/ZnS coreshells for photonic applications

A hybrid optical nanostructure of plasmon-coupled SQDs was developed for photonic applications. The coupling distances between the mono-layers of Au nanoparticles with a surface concentration of ~9.18 × 10-4 nm-2 and CdSe/ZnS SQDs with that of ~3.7 × 10-3 nm-2 were controlled by PMMA plasma etching. Time-resolved spectroscopy of plasmon-coupled SQDs revealed a strong shortening of the longest lifetime and ~9-fold PL enhancement. Polarization-resolved PL spectroscopy displayed linear polarization and depolarization at near- and far-field plasmon-coupling, respectively. The physical origin of PL enhancement could be attributable to both the large local field enhancement and the fast resonant energy transfer.

Z-scan and four-wave mixing characterization of semiconductor cadmium chalcogenide nanomaterials

The possible physical origin of third-order nonlinearity of cadmium chalcogenide (Te, Se, and S) semiconductor nanocrystals were discussed based on the results of both Z-scan and degenerate four-wave mixing spectroscopies at 532, 775, 800, and 1064 nm in nanosecond, picosecond, and femtosecond time scale for nonlinear photonic applications.

A model for a continuous-wave iodine laser

A model for a continuous‐wave (CW) iodine laser has been developed and compared with the experimental results obtained from a solar‐simulator‐pumped CW iodine laser. The agreement between the calculated laser power output and the experimental results is generally good for various laser parameters even when the model includes only prominent rate coefficients. The flow velocity dependence of the output power shows that the CW iodine laser cannot be achieved with a flow velocity below 1 m/s for the present solar‐simulator‐pumped CW iodine laser system.

Ultrafast Time-Resolved DFWM of CdTe Quantum Dots in Toluene

Ultrafast third-order nonlinear dynamics in CdTe quantum dots at room temperature have been investigated using a degenerate four-wave mixing at ~775 nm. The effective third-order nonlinear optical susceptibility and the intrinsic dephasing time in CdTe QDs were estimated to be ~4.39×10-22 m2/V2 and ~675 fs, respectively.

Defect-mediated spontaneous emission enhancement of plasmon-coupled CuInS 2 and CuInS 2 /ZnS

The studies of plasmon-coupled excitons at the surface-/interface-, shallow-, and deep-trapped states of copper-indium-disulfide (CIS) with/without zinc-sulfide (ZnS) shell revealed the defect-mediated spontaneous emission enhancement. The PL enhancement with spectral blue-shift of plasmon-coupled excitons in CIS quantum dots (QDs) indicates the large reduction of nonradiative decay at the surface- and shallow-trapped states with strong spectral overlapping. The PL enhancement with spectral red-shift of plasmon-coupled excitons in CIS/ZnS QDs is accredited to the defect-mediated PL enhancement by the higher fractional amplitude at the interface-trapped state around the longer spectral region. The spontaneous emission enhancement of plasmon-coupled CIS QDs were ~2.1, ~2.2, and ~2.8-folds compared to the decay rates of CIS, and those of plasmon-coupled CIS/ZnS QDs were ~24.1, ~32.8, and ~24.9-folds compared to the decay rates of CIS/ZnS at shorter, intermediate, and longer spectral regions due to relatively stable charge carriers and close to the surface plasmon resonance. The PL enhancements of plasmon-coupled CIS at room temperature and 6 K were two-fold and three-fold compared to the integrated CIS PLs, and the PL enhancements of plasmon-coupled CIS/ZnS at room temperature and 6 K were five-fold and eight-fold compared to the integrated CIS/ZnS PLs. The large PL enhancement is attributable to the plasmon-exciton coupling through Coulomb interaction and the local field enhancement. The larger PL enhancement of plasmon-coupled CIS/ZnS compared to that of plasmon-coupled CIS is accredited to the larger spontaneous emission enhancement.