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Random-distributed gold nanorod arrays (R-GNRAs) deposited on glass substrates have been systematically investigated through Z-scan, second harmonic generation (SHG), and dichromatic pump–probe mea...

Size and operating energy are two key parameters that constrain the integration capability of a nonlinear optical device. Here, we report a 60 nm thin film made of randomly distributed gold nanorod...

Femtosecond transient reflection spectroscopy was employed to study the carrier dynamics in few-layered MoS2 crystals prepared by either a chemical vapor deposition (CVD) technique or a mechanical exfoliation method. Three decay processes were observed in samples prepared by both methods. The faster processes were approximately 300–500 fs and could be attributed to defect-assisted scattering. The slower processes varied from 1 to 250 ps and were related to carrier–carrier and carrier–phonon scattering. Comparative studies between the CVD and exfoliated samples with different thicknesses demonstrated that faster decay processes occurred in thinner samples, in which the interface and defects had stronger effects. Wavelength-dependent transient reflection spectra demonstrated that a change in the sign of the signal occurred around the exciton absorption peaks, which could be attributed to competition of the stimulated emission and excited-state absorption processes around the exciton absorption peaks. Our re...

The third-order optical nonlinearities and the hot electron relaxation time (τ) of random-distributed gold nanorods arrays on glass (R-GNRA) have been investigated by using Z-scan and optical Kerr effect (OKE) techniques. Large third-order optical susceptibility (χ(3)) with the value of 2.5 × 10-6 esu has been obtained around the plamsonic resonance peak under the excitation power intensity of 0.1 GW/cm2. Further decrease of the excitation power intensity down to 0.3 MW/cm2 will lead to the significant increase of χ(3) up to 6.4 × 10-4 esu. The OKE results show that the relaxation time of R-GNRA around the plasmonic peak is 13.9 ± 0.4 ps, which is more than 4 times longer than those of the individual gold nanostructures distributed in water solutions. The Finite-difference time domain simulations demonstrate that this large enhancement of χ(3) and slow down of τ are caused by the gap-induced large local field enhancement of GNRs dimers in R-GNRA. These significant results offer great opportunities for plasmonic nanostructures in applications of photonic and photocatalytic devices.

We demonstrate broadband photoluminescence (PL) from a Au nanorod–alumina–Al substrate (Au–Al2O3–Al) sandwich structure under a peak excitation power intensity of 1.45–2.61 GW cm−2. The emission wavelength is in the range of 450–1050 nm and the lifetime is on the sub-nanosecond timescale. Comparative studies of the PL from Au–Al2O3–Al with different Au rod lengths and Au–Al2O3 without an Al coupling layer, together with finite difference time domain (FDTD) calculations, show that the PL from Au–Al2O3–Al originates from the surface plasmon enhanced supercontinuum (SC) generation in the Al2O3 membrane. This observation indicates that a SC could be realized in nanoscale plasmonic structures, which has promising applications in the minimization and integration of light sources in photonic devices.

Plasmonic nanostructures with sub-10 nm gaps possess intense electric field enhancements, leading to their high reputation for exploring various functional applications at nanoscale. Till now, although large amounts of efforts have been devoted into investigation of such structures, few works were emphased on the nonlinear optical properties in near-ultraviolet (UV) region. Here, by combining sputtering technique and an optimized anodic aluminum oxide (AAO) template growing method, we obtain aluminum (Al) nanorod array film (NRAF) with average rod diameter and gap size of 50 and 7 nm, respectively. The Al-NRAF exhibits large third-order optical nonlinear susceptibility (χ(3)) and high figure of merit (χ(3)/α) over a broad wavelength range from 360 to 900 nm, and reaches their maximums at the shortest measured wavelength. In addition, comparisons with Au-NRAF and Ag-NRAF samples further confirm that Al-NRAF has better nonlinear optical properties in the blue and near-UV wavelength regions. These results indicate that Al nanostructures are promising candidates for nonlinear plasmonic applications at blue and near-UV wavelengths.

BiFeO3, a typical multiferroic compound, owns complicated interactions among its charge, lattice, and spin degrees, while largely remaining a mystery. In this work, the BiFeO3 single crystal has been investigated in pulsed high magnetic fields up to 50 T. The lattice, spin, and charge orderings are found to couple with each other strongly. High magnetic field could drive the spin cycloid phase to a canted antiferromagnetic phase while accompanied by a clear magnetostriction response and weakening of ferroelectric polarization. The critical magnetic field for the magnetic phase transition was shifted to the lower magnetic field region by an external electric field over a broad temperature range, which indicates the complex interaction among magnetization, electrical polarization, and crystal lattice. This work has provided a clear picture to show the synergetic response of multiple ordering parameters during the magnetic phase transition in BiFeO3, which could benefit the design of BiFeO3 based spintronic devices and novel multiferroic materials with strong magnetoelectric coupling.BiFeO3, a typical multiferroic compound, owns complicated interactions among its charge, lattice, and spin degrees, while largely remaining a mystery. In this work, the BiFeO3 single crystal has been investigated in pulsed high magnetic fields up to 50 T. The lattice, spin, and charge orderings are found to couple with each other strongly. High magnetic field could drive the spin cycloid phase to a canted antiferromagnetic phase while accompanied by a clear magnetostriction response and weakening of ferroelectric polarization. The critical magnetic field for the magnetic phase transition was shifted to the lower magnetic field region by an external electric field over a broad temperature range, which indicates the complex interaction among magnetization, electrical polarization, and crystal lattice. This work has provided a clear picture to show the synergetic response of multiple ordering parameters during the magnetic phase transition in BiFeO3, which could benefit the design of BiFeO3 based spintronic ...

A low-cost, broadband white-light source based on Au nanorod-aluminum oxide (Au-AAO) nanostructures was obtained and used for micro-spectroscopy measurement. When an Au-AAO sample was excited by using a continuous-wave or a pulsed laser, smooth and broadband strong photoluminescence from 550 nm to 1560 nm could be achieved. A high-quality transmission spectrum was obtained from few-layer MoS2 flakes using Au-AAO as the illuminating source, demonstrating the suitability of the Au-AAO nanostructure as a light source for spectroscopy. This accomplishment is significant and provides a potential new white-light source for applications in bio-sensing and spectroscopy on the microscale.

A broadband all-optical switch based on the thermal lens effect of InP/ZnS quantum dots (QDs) has been demonstrated. Using a pump laser at 600 nm, whose photon energy is larger than the bandgap, thermal effects induce a large nonlinear optical refraction that modulates the beam path of a probe light to form an all-optical switch. By adjusting the sizes of the QDs, the position of the bandgap can be tuned over a wide wavelength range. Thus, both the pump and the probe wavelengths can be designed for specific applications. The on/off tests of the all-optical switches demonstrate that they work well with switching rates of hundreds of Hertz. Our result demonstrates that InP/ZnS quantum dots are a good candidate material for the application of all-optical switching.A broadband all-optical switch based on the thermal lens effect of InP/ZnS quantum dots (QDs) has been demonstrated. Using a pump laser at 600 nm, whose photon energy is larger than the bandgap, thermal effects induce a large nonlinear optical refraction that modulates the beam path of a probe light to form an all-optical switch. By adjusting the sizes of the QDs, the position of the bandgap can be tuned over a wide wavelength range. Thus, both the pump and the probe wavelengths can be designed for specific applications. The on/off tests of the all-optical switches demonstrate that they work well with switching rates of hundreds of Hertz. Our result demonstrates that InP/ZnS quantum dots are a good candidate material for the application of all-optical switching.

Surface plasmonic systems provide extremely efficient ways to modulate light-matter interaction in photon emission, light harvesting, energy conversion and transferring, etc. Various surface plasmon enhanced luminescent behaviors have been observed and investigated in these systems. But the origin of an avalanche-like photoluminescence, which was firstly reported in 2007 from Au and subsequently from Ag nanowire arrays/monomers, is still not clear. Here we show, based on systematic investigations including the excitation power/time related photoluminescent measurements as well as calculations, that this avalanche-like photoluminescence is in fact a result of surface plasmon assisted thermal radiation. Nearly all of the related observations could be perfectly interpreted with this concept. Our finding is crucial for understanding the surface plasmon mediated thermal and photoemission behaviors in plasmonic structures, which is of great importance in designing functional plasmonic devices.

Au–Ag core–shell nanorods with surface plasmon resonance wavelengths of 760–840 nm were prepared. Wavelength-dependent nonlinear absorption coefficients (β) and nonlinear refractive indices (γ) of the nanorods were measured by using Z-scan techniques. The corresponding one-photon and two-photon figures of merit (W and T) were calculated from β and γ. The results show that the requirements of W > 1 and T < 1 for the application of all-optical switching could be achieved for all the samples over a broad wavelength range. These observations make the Au–Ag core–shell nanorods a good candidate for all-optical switching devices.