Xiaodong Jiang

Effects of γ-ray irradiation on optical absorption and laser damage performance of KDP crystals containing arsenic impurities

The effects of γ-irradiation on potassium dihydrogen phosphate crystals containing arsenic impurities are investigated with different optical diagnostics, including UV-VIS absorption spectroscopy, photo-thermal common-path interferometer and photoluminescence spectroscopy. The optical absorption spectra indicate that a new broad absorption band near 260 nm appears after γ-irradiation. It is found that the intensity of absorption band increases with the increasing irradiation dose and arsenic impurity concentration. The simulation of radiation defects show that this absorption is assigned to the formation of AsO₄⁴⁻ centers due to arsenic ions substituting for phosphorus ions. Laser-induced damage threshold test is conducted by using 355 nm nanosecond laser pulses. The correlations between arsenic impurity concentration and laser induced damage threshold are presented. The results indicate that the damage performance of the material decreases with the increasing arsenic impurity concentration. Possible mechanisms of the irradiation-induced defects formation under γ-irradiation of KDP crystals are discussed.

Nanoparticle attachment on Ag nanorings and nanoantenna for large increases of surface-enhanced Raman scattering

A simple and inexpensive approach based on the heat-treatment of Ag+/PVA/PVP composite film on quartz glass has been developed for fabricating large-area Ag nanorings attached small nanoparticles. The explosive decomposition of AgNO3, PVA and PVP by calcination could explain their formation. A maximum enhancement factor of 1.9 × 1010 can be obtained with the self-organized Ag nanorings attached small nanoparticles. Moreover, using the three-dimensional finite-difference time-domain (3D-FDTD) simulations, we stipulate that the EF can be obviously improved via some small Ag particle attachment on these nanorings because of the strong coupling between the discrete plasmon states of the small nanoparticles and the term of propagating plasmons of the Ag nanorings. Understanding and realization of the enhancing mechanism of nanostructured surface attachment small nanoparticles could have potential to effectively improve the SERS property of the SERS substrates.

Self-Organized Ag Nanorings Antenna Substrates for Surface-Enhanced Raman Spectroscopy

We investigate the surface-enhanced Raman spectroscopy of Ag nanorings antenna in both experiment and simulation. Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. The three-dimensional finite-difference time-domain simulation calculations indicate that the electric field enhancement of Ag nanoring antenna is strongly dependent on the gap distance. A very strong surface plasmon coupling in the gap region of Ag nanoring antenna is observed, whose field intensity is enhanced four times compared to that for Ag nanodomes antenna with the same gap distance. Surface-enhanced Raman scattering (SERS) measurements have shown that the SERS intensity acquired from the Ag nanoring antenna is about 16 times stronger than that obtained from Ag nanodomes antenna. These results pave the way to design plasmonic nanostructures for practical applications that require coupled metallic nanoparticles with enhanced electric fields.

Influence of subsurface defects on damage performance of fused silica in ultraviolet laser

Abstract. In ultraviolet pulse laser, damage performance of fused silica optics is directly dependent on the absorptive impurities and scratches in subsurface, which are induced by mechanical polishing. In the research about influence of subsurface defects on damage performance, a series of fused silica surfaces with various impurity concentrations and scratch structures were created by hydrofluoric (HF) acid solution etching. Time of Flight secondary ion mass spectrometry and scanning probe microprobe revealed that with increasing etching depth, impurity concentrations in subsurface layers are decreased, the scratch structures become smoother and the diameter:depth ratio is increased. Damage performance test with 355-nm pulse laser showed that when 600 nm subsurface thickness is removed by HF acid etching, laser-induced damage threshold of fused silica is raised by 40 percent and damage density is decreased by over one order of magnitude. Laser weak absorption was tested to explain the cause of impurity elements impacting damage performance, field enhancement caused by change of scratch structures was calculated by finite difference time domain simulation, and the calculated results are in accord with the damage test results.

High resolution characterization of modifications in fused silica after exposure to low fluence 355 nm laser at different repetition frequencies.

We report on the characterization of modifications in fused silica after exposure to low fluence (2 J/cm2) 355 nm laser at repetition frequencies of 1 Hz, 5 Hz and 10 Hz. Synchrotron based XRF spectroscopy is employed to study concentration variation of metal inclusions in the surface layer. Positron annihilation lifetime spectroscopy is used to probe atomic size defects variation in bulk silica. FT-IR is used to characterize changes of bond length and angle of Si-O-Si covalent bond of irradiated silica. Compared to the basic frequency, the big loss of cerium and iron concentration, the size enlargement of vacancy cluster and the decrease of Si-O-Si covalent bond length after 10 Hz laser irradiation are illustrated by our data. These tiny modifications provide important data to investigate laser damage mechanism.

Study of strong dipole and quadrupole plasmon resonance in Ag nanorings antenna

Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. By using absorption measurements and three-dimensional finite-difference time-domain (3D-FDTD) calculations, the dipole and quadrupole plasmon resonances of Ag nanorings antenna were investigated experimentally and theoretically. Calculations have shown that large electric fields are confined at the quadrupole of the Ag nanoring, leading to quadrupole plasmon resonances. Compared the electric enhancement factor of the exterior surfaces of Ag nanoring, the electric enhancement factor of the interior surface is about six times excited by an incident light with 514.5 nm wavelength. Furthermore, the highest electric-field intensity of Ag nanorings is around four times larger than that for Ag nanodome with the same condition. These results pave the way to design plasmonic nanostructures for practical applications that require metallic nanoparticles with enhanced electric fields.

Theory of absorption rate of carriers in fused silica under intense laser irradiation

A nonperturbative quantum theory for phonon-assisted photon absorption of conduction band electron in intense laser was developed. By carrying out the calculation in fused silica at wavelengths from ultraviolet to infrared in terawatt intensity laser, we show that the nonperturbation approach can make a uniform description of energy absorption rate at both short wavelengths and long wavelengths on terawatt per centimeter square intensity laser.

Experimental and simulative study on surface enhanced Raman scattering of rhodamine 6G adsorbed on big bulk-nanocrystalline metal substrates

Big bulk-nanocrystalline metal materials of silver (Ag) and aluminum (Al) for surface-enhanced Raman scattering (SERS) spectroscopy have been synthesized in a mold under different pressures using vacuum-warm-compaction technology. It was discovered that pressure could control the SERS activity of the bulk-nanocrystalline material. SERS properties of the bulk-nanocrystalline material in the presence of adsorbed rhodamine (R6G) could be obtained through selecting a proper pressure. Compared with the Ag nanoparticles (Al nanoparticles), the SERS peak intensity of R6G adsorbed on the bulk-nanocrystalline material is about 1000 times (100 times) stronger. The electric field enhancement of the bulk-nanocrystalline material has been described to be a systematic investigation by using three-dimensional finite-difference time-domain (3D-FDTD) simulation. The FDTD calculations have shown that the electric field enhancement of the bulk-nanocrystalline material is strongly dependent on the gap distance. In summary, SERS active bulk-nanocrystalline materials have been synthesized simply, greenly and cost effectively by the method reported here, and this method is expected to be utilized in the development of SERS-based analytical devices.

Nonlinear optical characteristics of an ADP crystal grown in a defined direction

Samples in the crystal directions of Z, X(ab) and the non-critical phase matching angle (θ = 90°,φ = 45°) were gained from high-quality ammonium dihydrogen phosphate (NH4H2PO4, ADP) crystals grown in the Z direction and in defined crystallographic direction (θ = 90°, φ = 45°) via the rapid growth method. Z-scan measurements with pico-second pulse laser irradiation at λ = 355nm were implemented to systematically investigate their nonlinear characters, such as the nonlinear absorption coefficient β, nonlinear refractive index n2 and the third order nonlinear susceptibility χ(3). The results displayed the nonlinear absorption and nonlinear refraction, and the ADP crystals exhibit the reverse saturable absorption and self-focusing effect (n2>0). The nonlinear absorption and refraction were anisotropic in the crystal directions of Z, X, and the non-critical phase matching angle (θ = 90°, φ = 45°) sorted as: [110] < X < Z. The remarkable NLA behaviors at 355 nm are identified to the co-existence of 2PA and 3PA, while 2PA is dominant and the occurrence probability of 3PA is rather low. The anisotropy of the NLA of ADP crystals is closely bound up with the damage anisotropy in our experiments.

Effect of porosity on the laser induced damage threshold of sol-gel SiO 2 and ZrO 2 single layer films

In this paper, we investigated the effect of porosity on the laser induced damage threshold (LIDT) of sol-gel SiO2 and ZnO2 single layer films. Sol-gel SiO2 films were prepared with the dip-coating method from acid and base catalyzed SiO2 sols, respectively. Some of the SiO2 base films were subsequently treated in saturated ammonia gas for 20 hours. ZnO2 sol-gel and physical vapor deposition (PVD) films were prepared by spin method and electron beam evaporation method, respectively. The films were irradiated by a pulsed Nd:YAG laser to obtain the LIDT of each film. In order to study the damage mechanism of films under laser irradiation, four types of tests were used. Thermal absorption of films was detected via Stanford photo-thermal solutions (SPTS). The porous ratio was derived via refractive index measured by ellipsometer. The surface morphologies of films were imaged by atomic force microscopy (AFM) before laser irradiation. Optical microscopy was used to characterize the defects and impurities of films before laser irradiation and damage morphology after laser irradiation. The experimental results [1–3] showed that porous ratio is an essential factor to decide the LIDT for sol-gel films, which benefits the pressure exerted on the film or substrate by the moving particle to dissipate. The films with lower thermal absorption and higher porous ratio have higher LIDT.