Tunable optical limiting optofluidic device filled with graphene oxide dispersion in ethanol

An optofluidic device with tunable optical limiting property is proposed and demonstrated. The optofluidic device is designed for adjusting the concentration of graphene oxide (GO) in the ethanol solution and fabricated by photolithography technique. By controlling the flow rate ratio of the injection, the concentration of GO can be precisely adjusted so that the optical nonlinearity can be changed. The nonlinear optical properties and dynamic excitation relaxation of the GO/ethanol solution are investigated by using Z-scan and pump-probe measurements in the femtosecond regime within the 1.5 μm telecom band. The GO/ethanol solution presents ultrafast recovery time. Besides, the optical limiting property is in proportion to the concentration of the solution. Thus, the threshold power and the saturated power of the optical limiting property can be simply and efficiently manipulated by controlling the flow rate ratio of the injection. Furthermore, the amplitude regeneration is demonstrated by employing the proposed optofluidic device. The signal quality of intensity-impaired femtosecond pulse is significantly improved. The optofluidic device is compact and has long interaction length of optical field and nonlinear material. Heat can be dissipated in the solution and nonlinear material is isolated from other optical components, efficiently avoiding thermal damage and mechanical damage

Stroboscopic Surface Thermal Lensing for Fast Detection of Thermal Defects in Large-Scaled Coating Films

A stroboscopic surface thermal lensing (SSTL) system for the fast detection of thermal-induced defects in large-scaled optical coating films was constructed. The SSTL signal was generated by a set of double-modulators and captured by a high speed matrix camera, respectively. The spot size of both pump laser and probe laser expanded for larger detection area was finished in a single step. Based on the STL technique, both the mapping of amplitude and the phase of SSTL signal on the whole area of the coatings can be achieved simultaneously

Fabrication of Au/graphene oxide/Ag sandwich structure thin film and its tunable energetics and tailorable optical properties

Au/graphene oxide/Ag sandwich structure thin film was fabricated. The effects of graphene oxide (GO) and bimetal on the structure and optical properties of metal silver films were investigated by X-ray diffraction (XRD), optical absorption, and Raman intensity measurements, respectively. Compared to silver thin film, Au/graphene oxide/Ag sandwich structure composite thin films were observed with wider optical absorption peak and enhanced absorption intensity. The Raman signal for Rhodamine B molecules based on the Au/graphene oxide/Ag sandwich nanostructure substrate were obviously enhanced due to the bimetal layer and GO layer with tunable absorption intensity and fluorescence quenching effects.Published versio

Fiber-optic temperature sensor based on temperature-dependent refractive index of Germanium-silica coating stack

We report on a novel fiber-optic temperature sensor based on the temperature-dependent refractive index of a germanium-silica (Ge-SiO2) coating stack. The relationship between the reflectivity and the temperature-dependent refractive index of the Ge-SiO2 coating stack at 1550 nm is theoretically investigated. A reflection-type fiber-optic probe with high sensitivity and wide response range is designed and fabricated by physical vapor deposition. Experimental results show that the reflectivity is linearly dependent on temperature in the range of -30 to 130 oC, and the sensor exhibits high sensitivity and structural stability in the range of 50 to 500 K.Published versio

Broadband absorption tailoring of SiO2/Cu/ITO arrays based on hybrid coupled resonance mode

Sub-wavelength artificial photonic structures can be introduced to tailor and modulate the spectrum of materials, thus expanding the optical applications of these materials. On the basis of SiO2/Cu/ITO arrays, a hybrid coupled resonance (HCR) mechanism, including the epsilon-near-zero (ENZ) mode of ITO, local surface plasmon resonance (LSPR) mode and the microstructural gap resonance (GR) mode, was proposed and researched by systematically regulating the array period and layer thickness. The optical absorptions of the arrays were simulated under different conditions by the finite-difference time-domain (FDTD) method. ITO films were prepared and characterized to verify the existence of ENZ mode and Mie theory was used to describe the LSPR mode. The cross-sectional electric field distribution was analyzed while SiO2/Cu/ITO multilayers were also fabricated, of which absorption was measured and calculated by Macleod simulation to prove the existence of GR and LSPR mode. Finally, the broad-band tailoring of optical absorption peaks from 673 nm to 1873 nm with the intensities from 1.8 to 0.41 was realized, which expands the applications of ITO-based plasmonic metamaterials in the near infrared (NIR) region.Published versio

Monolayer-Graphene-Based Tunable Absorber in the Near-Infrared

In this paper, a tunable absorber composed of asymmetric grating based on a graphene-dielectric-metal structure is proposed. The absorption of the absorber can be modified from 99.99% to 61.73% in the near-infrared by varying the Fermi energy of graphene, and the absorption wavelength can be tuned by varying the grating period. Furthermore, the influence of other geometrical parameters, the incident angle, and polarization are analyzed in detail by a finite-difference time-domain simulation. The graphene absorbers proposed in this paper have potential applications in the fields of stealth, sense, and photoelectric conversion. When the absorber that we propose is used as a gas sensor, the sensitivity of 200 nm/RIU with FOM can reach up to 159 RIU−1

Defect-Induced Tunable Permittivity of Epsilon-Near-Zero in Indium Tin Oxide Thin Films

Defect-induced tunable permittivity of Epsilon-Near-Zero (ENZ) in indium tin oxide (ITO) thin films via annealing at different temperatures with mixed gases (98% Ar, 2% O2) was reported. Red-shift of λENZ (Epsilon-Near-Zero wavelength) from 1422 nm to 1995 nm in wavelength was observed. The modulation of permittivity is dominated by the transformation of plasma oscillation frequency and carrier concentration depending on Drude model, which was produced by the formation of structural defects and the reduction of oxygen vacancy defects during annealing. The evolution of defects can be inferred by means of X-ray diffraction (XRD), atomic force microscopy (AFM), and Raman spectroscopy. The optical bandgaps (Eg) were investigated to explain the existence of defect states. And the formation of structure defects and the electric field enhancement were further verified by finite-difference time domain (FDTD) simulation

Monolayer-Graphene-Based Tunable Absorber in the Near-Infrared

In this paper, a tunable absorber composed of asymmetric grating based on a graphene-dielectric-metal structure is proposed. The absorption of the absorber can be modified from 99.99% to 61.73% in the near-infrared by varying the Fermi energy of graphene, and the absorption wavelength can be tuned by varying the grating period. Furthermore, the influence of other geometrical parameters, the incident angle, and polarization are analyzed in detail by a finite-difference time-domain simulation. The graphene absorbers proposed in this paper have potential applications in the fields of stealth, sense, and photoelectric conversion. When the absorber that we propose is used as a gas sensor, the sensitivity of 200 nm/RIU with FOM can reach up to 159 RIU−1

Laser induced photocatalytic activity enhancement of TiO_2 thin films

In this paper, the photocatalytic activity enhancement of TiO2 thin films was realized by laser irradiation. The H2 yield of the as-irradiated film is 79 μmol/(h*m2), which is 33% more than that of the as-deposited TiO2 film. Spectrophotometer, X-ray diffraction and Raman system were employed to characterize the samples. The results showed that both the scanning rate and line spacing of the laser modification have effects on photocatalytic activity. It suggests that a phase junction is formed between the amorphous and rutile phases. The increment of H2 generation could be attributed to the alignment of Fermi levels in the phase junction.Published versio