Haihua Fan

Magnetic Fano resonance of heterodimer nanostructure by azimuthally polarized excitation

The optical properties of a Si-Au heterodimer nanostructure, which is composed of an Au split nanoring surrounded by a Si nanoring with a larger diameter, are investigated both theoretically and numerically. It is found that a pure magnetic plasmon Fano resonance can be achieved in the Si-Au heterodimer nanostructure when it is excited by an azimuthally polarized beam. It is revealed that the pure magnetic Fano resonance is generated by the destructive interference between the magnetic dipole resonance of the Si nanoring and the magnetic dipole resonance of the Au split nanoring. A coupled oscillator model is employed to analyze the Fano resonance of the Si-Au heterodimer nanostructure. The pure magnetic response of the Si-Au heterodimer nanostructure is verified by the current density distributions and the scattering powers of the electric and magnetic multipoles. The Fano resonance in the Si-Au heterodimer nanostructure exhibits potential applications of low-loss magnetic plasmon resonance in the construction of artificial magnetic metamaterials.

Upconversion luminescence from aluminoborate glasses doped with Tb 3+ , Eu 3+ and Dy 3+ under the excitation of 2.6-μm femtosecond laser pulses

We investigated the upconversion luminescence of three aluminoborate glasses doped with Tb(3+), Eu(3+), and Dy(3+) under the excitation of 2.6-μm femtosecond (fs) laser pulses. Efficient upconversion luminescence appearing in the visible light spectral region was observed in all three glasses and the emission spectra are quite similar to those obtained under single photon excitation. From the dependence of the luminescence intensity on the excitation intensity in the low excitation intensity regime, it was revealed that a four-photon process is involved in the generation of the upconversion luminescence in the Tb(3+)- and Eu(3+)-doped glasses while a mixed two- and three-photon process is involved in the Dy(3+)-doped glass. In the high excitation intensity regime, a reduction of the slope to about 1.0 was observed for all glasses. A physical mechanism based on the super saturation of the intermediate states of the rare-earth ions was employed to interpret the upconversion luminescence under the excitation of long-wavelength fs laser pulses. Significantly broadened luminescence spectra were observed in thick glasses under high excitation intensities and it can be attributed to the self-focusing of the laser beam in the thick glasses.

Controlling the Two-Photon-Induced Photon Cascade Emission in a Gd(3+)/Tb(3+)-Codoped Glass for Multicolor Display.

We reported the first observation of the two-photon-induced quantum cutting phenomenon in a Gd3+/Tb3+-codoped glass in which two photons at ~400 nm are simultaneously absorbed, leading to the cascade emission of three photons in the visible spectral region. The two-photon absorption induced by femtosecond laser pulses allows the excitation of the energy states in Gd3+ which are inactive for single-photon excitation and enables the observation of many new electric transitions which are invisible in the single-photon-induced luminescence. The competition between the two-photon-induced photon cascade emission and the single-photon-induced emission was manipulated to control the luminescence color of the glass. We demonstrated the change of the luminescence color from red to yellow and eventually to green by varying either the excitation wavelength or the excitation power density.

Photothermal therapy of single cancer cells mediated by naturally created gold nanorod clusters

Gold nanorods (GNRs) are generally considered to be nontoxic to normal and cancer cells. They are usually accumulated at lysosomes after entering into cells, forming GNR clusters in which strong plasmonic coupling between GNRs is expected. We investigated the photothermal therapy of single cancer cells by exploiting the significantly enhanced two-photon-induced absorption of GNR clusters naturally created in the lysosomes of cancer cells. It was revealed numerically that the plasmonic coupling between GNRs in GNR clusters can effectively enhance the photothermal conversion efficiency. As a result, the thermal damage of single cancer cells can be induced by using pulse energy as low as ~70 pJ. In experiments, the locations of GNR clusters can be accurately determined through the detection of the two-photon-induced luminescence, which is also significantly enhanced, by using a confocal laser scanning microscope. The photothermal therapy was conducted by focusing femtosecond laser light on the targeted GNR clusters, generating bubbles and deforming cell membranes. The photothermal therapy proposed in this work can lead to the rapid and acute injury of single cancer cells. The dependence of the apoptosis time on the pulse energy of femtosecond laser light was also examined. Our findings suggest a novel strategy for the photothermal therapy of single cancer cells with ultralow energy.

Efficient blue light emission from In 0.16 Ga 0.84 N/GaN multiple quantum wells excited by 2.48-μm femtosecond laser pulses

We report on the efficient blue light emission from In0.16Ga0.84N/GaN multiple quantum wells excited by femtosecond laser pulses with long wavelengths ranging from 1.24 to 2.48 μm. It is found that the trap states in GaN barrier layers lead to an efficient cascade multiphoton absorption in which the carriers are generated through simultaneous absorption of n (n=1 and 2) photons to the trap states, followed by simultaneous absorption of m (m=3, 4, and 5) photons to the conduction band. The dependence of the upconversion luminescence on excitation intensity exhibits a slope between n and n+m, which is in good agreement with the prediction based on the rate equation model.

A Novel Fast Photothermal Therapy Using Hot Spots of Gold Nanorods for Malignant Melanoma Cells

In this paper, the plasmon resonance effects of gold nanorods was used to achieve rapid photothermal therapy for malignant melanoma cells (A375 cells). After incubation with A375 cells for 24 h, gold nanorods were taken up by the cells and gold nanorod clusters were formed naturally in the organelles of A375 cells. After analyzing the angle and space between the nanorods in clusters, a series of numerical simulations were performed and the results show that the plasmon resonance coupling between the gold nanorods can lead to a field enhancement of up to 60 times. Such high energy localization causes the temperature around the nanorods to rise rapidly and induce cell death. In this treatment, a laser as low as 9.3 mW was used to irradiate a single cell for 20 s and the cell died two h later. The cell death time can also be controlled by changing the power of laser which is focused on the cells. The advantage of this therapy is low laser treatment power, short treatment time, and small treatment range. As a result, the damage of the normal tissue by the photothermal effect can be greatly avoided.

Modifying the mechanical properties of gold nanorods by copper doping and triggering their cytotoxicity with ultrasonic wave

We proposed the use of copper (Cu) doping to modify the mechanical properties of gold nanorods (AuNRs) and demonstrated the triggering of the cytotoxicity of Cu-doped AuNRs with ultrasonic wave. The mechanical properties of Cu-doped AuNRs were analyzed theoretically by using the density-function calculation and it was found that Cu-Au bond is much weaker than Au-Au bond. In experiments, AuNRs without and with Cu doping were synthesized and they were found to be low cytotoxic to both human liver hepatocellular carcinoma (HepG2) cells and normal liver cells (L02). It was found that Cu-doped AuNRs can be broken into small gold nanoparticles (<5 nm) under high-power ultrasonic wave while undoped AuNRs were quite stable, although the amount of Cu doped into AuNRs was quite small (0.2%). The small gold nanoparticles are found to be with high toxicity to HepG2 cells. The cellular viability of the HepG2 cells dropped to nearly zero after being incubated with Cu-doped AuNRs (50 nM), which had been treated with a 300-W ultrasonic wave. Our findings suggest a novel method for modifying the mechanical properties of AuNRs and especially for triggering their cytotoxicity which is quite useful for in vitro therapy of cancer cells.