Jimmy Yao

Surface enhanced Raman spectroscopy by interfered femtosecond laser created nanostructures

A type of surface enhanced Raman spectroscopy (SERS) by interfered femtosecond laser created nanostructures on Cu metal is presented. It is found out that finer and more uniform nanostructures (with an average feature size 100 nm or smaller) can be created on Cu metal by interfered femtosecond illumination with a phase mask. Significantly enhanced Raman signal (with an enhancement factor around 863) can be realized by using the nanostructured Cu substrate created by the interfered femtosecond laser illumination. The experimentally measured enhancement factor agrees relatively well with the theoretical analyses. Since the nanostructures can be inscribed in real time and at remote locations by the femtosecond laser inscription, the proposed SERS can be particularly useful for the standoff detection of chemicals.

Field induced dynamic waveguides based on potassium tantalate niobate crystals

In this paper, a new type of optical waveguide based on potassium tantalate niobate (KTN) electro-optic crystal is presented. The guiding property of the optical waveguide can be quickly (on the order of nanosecond) tuned and controlled by the applied external electric field, which can be useful for many applications such as broadband ultrafast optical modulators, variable optical attenuators, and dynamic gain equalizers.

Single chip super broadband InGaN/GaN LED enabled by nanostructured substrate

A new type of LED, single chip super broadband InGaN/GaN LED is presented in this paper. The LED is composed of an InGaN/GaN quantum well layer deposited on the nanostructured sapphire substrate, inscribed by femtosecond laser ablation. The super broadband emission is enabled due to the large variation of indium composition in a small local area so that different wavelengths can be emitted over a small area and the summation of these different emission wavelengths forms super broadband emission, which covers the entire visible spectral range. The result of this paper represents a major technological advance in white light LED lighting because it enables single chip white LED lighting without the need of phosphor down converter that can significantly improve the efficiency without the Stokes loss and reduce the cost.

Design and implementation of super broadband high speed waveguide switches

In this paper, based on the theory of dynamic waveguiding effect in nanodisordered KTN crystals, a detailed design and implementation of a super broadband 1x2 high speed waveguide switch is presented. The important waveguide parameters, including the dimension, the refractive index distribution, and the electric field distribution within the waveguide are quantitatively simulated and analyzed. An experimental verification of switching effect based on the design is also conducted, which confirmed the design. The broadband and high speed nature of such kind of switch can play a key role in data center networks and cloud computing, which needs low power consumption and high speed switches.

Density-controlled ZnO/TiO2 nanocomposite photoanode for improving dye-sensitized solar cells performance

Dye-sensitized solar cells (DSSCs) via ZnO/TiO2 nanocomposite photoanode with density-controlled abilities are presented in this paper. This nanocomposite photoanode is composed of TiO2 nanoparticles dispersed into densitycontrolled vertically aligned ZnO-TiO2 core-shell nanorod arrays. The density-controlled ZnO-TiO2 core-shell nanorod arrays were synthesized directly onto fluorine-doped tin oxide (FTO) substrates using an innovative two-step wet chemical route. First, the density-controlled ZnO nanorod arrays were formed by applying a ZnO hydrothermal process from a TiO2 nanocrystals template. Second, the ZnO-TiO2 core-shell nanorod arrays were formed by depositing a TiO2 shell layer from a sol-gel process. The major advantages of a density-controlled ZnO/TiO2 nanocomposite photoanode include (1) providing a better diffusion path from ZnO nanorod arrays and (2) reducing the recombination loss by introducing an energy barrier layer TiO2 conformal shell coating. To validate the advantages of a density-controlled ZnO/TiO2 nanocomposite photoanode, DSSCs based on a ZnO/TiO2 nanocomposite photoanode were fabricated, in which N719 dye was used. The average dimensions of the ZnO nanorod arrays were 20 μm and 650 nm for the length and the diameter, respectively, while the designated spacing between each nanorod was around 5 μm. The performance of the solar cell was tested by using a standard AM 1.5 solar simulator from Newport Corporation. The experimental results confirmed that an open-circuit voltage, 0.93 V, was achieved, which was much higher than the conventional TiO2 nanoparticles thin film structure for the same thickness. Thus, density-controlled ZnO/TiO2 nanocomposite photoanodes could improve the performance of DSSCs by offering a better electron diffusion path.

High open-circuit voltage dye-sensitized solar cells based on a nanocomposite photoelectrode

Abstract. A high open-circuit voltage dye-sensitized solar cell (DSSC), based on a ZnO/TiO2 nanocomposite (NC) photoelectrode, was presented. This NC photoelectrode was composed of density-controlled ZnO-TiO2 core-shell nanorod arrays and dispersed TiO2 nanoparticles. The electrochemical impedance spectroscopy results confirmed that a reduced recombination loss was achieved by applying the proposed composite nanostructure. Thus, a higher open-circuit voltage of up to 0.93 V was achieved.

High efficiency IR supercontinuum generation and applications: a review

In this paper, we have reviewed our recent works on IR supercontinuum generation (SCG) and its applications. First, we provide a brief review on the physical mechanism of the supercontinuum generation and our previous works in this field. Second, the transmission characteristics of a new type of IR fibers is presented. Furthermore, the SCG generation in this new type of optical fiber is experimentally demonstrated. Finally, the suggestion for the future effort is discussed.

Recent advances on multiple channel unequally spaced optical phased array for ultrafast LADAR

In this paper, we experimentally verify that previously proposed idea of unequally spaced optical phased array can greatly reduce grating-lobes. As the verification purpose of our previous numerical design, a laser beam is passed through unequally-spaced slits, whose spacings are the same as the previous design. Interference patterns formed after both 4- and 8-channel slits clearly show that the grating-lobes can be greatly minimized. To realize the beam steering possible, optical waveguides array, which has unequally spaced design at the output ends is fabricated. The phase of each beam can be varied using fibers array wound around PZT tubes before each beam is coupled into the waveguides array. Interference patterns formed after the outputs of both 4- and 8-channel waveguides array show that the gratinglobes can be greatly reduced using unequally spaced optical phased array technique.

Nanosecond speed pre-injected space charge controlled KTN beam deflector

In this paper, a nanosecond speed KTN beam deflector is presented. The beam deflector is based on the combination of pre-injected space charge field and high speed (nanosecond) switching field. A beam deflection speed on the order of nanosecond was demonstrated, which was fastest beam deflection speed reported so far. The experimentally results confirmed that the speed limitation of KTN beam deflector was not limited by the electro-optic (EO) effect itself but the driving electric source and circuit. With a faster speed driving source and circuit, it is possible to develop GHz frequency beam deflector.

Investigation of radiation-induced air fluorescence

In this paper, the radiation induced air fluorescence is investigated for several different types of radiation sources, including high brightness laser sources, X-ray radiation sources, and alpha radiation sources. First, the air fluorescence spectrum with three spectral bandpass filters induced by the high intensity laser was analyzed from spectrometer detector. Second, the air fluorescence intensity induced by different types of radiation are measured from photomultiplier tube detector and followed by discussion. Finally, the potential application of radiation induced air fluorescence for the radiation detection is addressed.