Third-order nonlinear optical response of Cu/Ag nanoclusters by ion implantation under 1064 nm laser excitation

The evolution of nanoclusters in sequentially ion-implanted Cu/Ag into silica glasses has been studied. The doses for implantation (×10¹⁶ ions/cm²) were 5Cu/5Ag, 5Cu/10Ag and 5Cu/15Ag, respectively. The microstructural properties of the nanoclusters are characterized by optical absorption spectra and transmission electron microscopy (TEM). Fast nonlinear optical refraction and nonlinear optical absorption coefficients were measured at 1064 nm of wavelength using Z-scan technique. Results in this project indicate that different optical nonlinearities could be selectively obtained at the near-infrared region of 1064 nm of wavelength by changing the metal ingredient percentage in silica.     

Structure and properties of molybdenum implanted with high-flux carbon ion

High purity molybdenum was implanted by C ion in a metal vapour vacuum arc (MEVVA) implanter. The influence of implantation parameters was studied by varying ion fluence and ion current density. The samples were implanted by 45 keV C ion with fluences from 1×10¹⁵ to 1×10¹⁸ ions/cm², respectively. The as-implanted samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and nanoindenter. Different morphologies were observed on the surfaces of the as-implanted samples due to irradiation damage, and clearly related to implantation parameters. XRD spectra confirm formation of β-Mo₂C with ion fluences equal to or larger than 1×10¹⁶ ions/cm², and formation of -Mo₂C with ion fluence of 1×10¹⁸ ions/cm². The maximum nanohardness and maximum modulus of the as-implanted samples increased gradually with increasing ion fluence, and reached the corresponding maximum values with ion fluence of 1×10¹⁸ ions/cm². The experimental results suggest that the structure and properties of the as-implanted Mo samples exhibited strong dependence on implantation parameters.     

Domain wall pinning in polycrystalline perovskite La0.7Sr0.3MnO3

Reversible and irreversible domain wall (DW) motions have been investigated in La_0.7Sr_0.3MnO₃ ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10⁵ A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10⁴ A/m. The Rayleigh constant η increases from 5.45×10⁻² to 1.54×10⁻¹ (A/m)⁻¹ as the temperature rises from 293 to 343 K, and η decreases from 5.58×10⁻² to 3.67×10⁻² (A/m)⁻¹ with increasing DC field from 1.99×10³ to 4.22×10⁴ A/m.     

Characterization of optical and nonlinear optical properties of silver nanoparticles prepared by laser ablation in various liquids

The optical, structural, and nonlinear optical properties of silver nanoparticles prepared by laser ablation in various liquids were investigated at 397.5, 532, and 795 nm. The TEM and spectral measurements have shown temporal dynamics of size distribution of Ag nanoparticles in solutions. The thermal-induced self-defocusing dominated in the case of high pulse repetition rate as well as in the case of nanosecond pulses. In the case of low pulse repetition rate, the self-focusing (γ = 3 × 10⁻¹³ cm² W⁻¹) and saturated absorption (β = −1.5 × 10⁻⁹ cm W⁻¹) of picosecond and femtosecond radiation were observed in these colloidal solutions. The nonlinear susceptibility of Ag nanoparticles ablated in water was measured to be 5 × 10⁻⁸ esu (at λ = 397.5 nm).     

MBE grown type-II MWIR and LWIR superlattice photodiodes

We report on the status of GaSb/InAs type-II superlattice diodes grown and fabricated at the Jet Propulsion Laboratory designed for infrared absorption 2–5 μm and 8–12 μm bands. Recent LWIR devices have produced detectivities as high as 8 × 10¹⁰ Jones with a differential resistance–area product greater than 6 Ohm cm² at 80 K with a long wavelength cutoff of approximately 12 μm. The measured internal quantum efficiency of these front-side illuminated devices is close to 30% in the 10–11 μm range. MWIR devices have produced detectivities as high as 8 × 10¹³ Jones with a differential resistance–area product greater than 3 × 10⁷ Ohm cm² at 80 K with a long wavelength cutoff of approximately 3.7 μm. The measured internal quantum efficiency of these front-side illuminated MWIR devices is close to 40% in the 2–3 μm range at low temperature and increases to over 60% near room temperature.     

Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO2 layers

Silicon nanocrystals have been synthesized in SiO₂ matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×10¹⁵, 3×10¹⁶, and 1×10¹⁷ cm⁻². Implanted samples were subsequently annealed in an N₂ ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10¹⁷ cm⁻² at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO₂ sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×10¹⁵ cm⁻². It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.     

The BCC to FCC/HCP phase transformation of the Co70Fe30 alloy produced by ion irradiation of Co70Fe30/Cu discontinuous multilayers

We report on the BCC to FCC/HCP structural transformation of Co₇₀Fe₃₀ alloy produced by room temperature ion irradiation of Co₇₀Fe₃₀/Cu discontinuous multilayers. The structural changes were analyzed by X-ray diffraction and X-ray absorption spectroscopy. For this study, two different samples were examined, one irradiated with 50 keV He⁺ and another with 600 keV Kr⁺ with doses of 1×10¹⁷ and 3×10¹⁵ ions/cm², respectively. No substantial change is observed after He⁺ irradiation, while after Kr⁺ irradiation an unexpected structural transition from BCC to FCC/HCP closed packed of the Co₇₀Fe₃₀ alloy was found.     

Picosecond nonlinear optical response of Ba0.5Sr0.5TiO3 thin films fabricated by pulsed laser deposition

Well-crystallized Ba_0.5Sr_0.5TiO₃ thin films with good surface morphology were prepared on MgO(1 0 0) substrates by pulsed laser deposition technique at a deposition temperature of 800 °C under the oxygen pressure of 2 × 10⁻³ Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (0 0 2) Ba_0.5Sr_0.5TiO₃ rocking curve and the root-mean-square surface roughness within the 5 μm × 5 μm area were 0.542° and 0.555 nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that Ba_0.5Sr_0.5TiO₃ thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂ = 5.04 × 10⁻⁶ cm²/kW and β = 3.59 × 10⁻⁶ (m/W), respectively.     

Z-scan determination of the third-order optical nonlinearity of a triphenylmethane dye using 633 nm He–Ne laser

The third-order nonlinear optical response of a triphenylmethane dye (Acid blue 7) was studied using the Z-scan technique with a continuous-wave He–Ne laser radiation at 633 nm. The magnitude and sign of the third-order nonlinear refractive index n₂ of aqueous solution of Acid blue 7 dye were determined; the negative sign indicates a self-defocusing optical nonlinearity in the sample studied. The negative nonlinear refractive index n₂ and nonlinear absorption coefficient β were estimated to be −1.88 × 10⁻⁷ cm²/W and −3.08 × 10⁻³ cm/W, respectively, corresponding to Re(χ⁽³⁾) = −8.35 × 10⁻⁶ esu, and Im(χ⁽³⁾) = −6.88 × 10⁻⁷ esu. The experimental results show that Acid blue 7 dye have potential applications in nonlinear optics.     

Effect of boron ion implantation on the structural, optical and electrical properties of ZnSe thin films

Zinc Selenide (ZnSe) thin films were deposited onto well cleaned glass substrates using vacuum evaporation technique under a vacuum of 3×10⁻⁵ mbar. The prepared ZnSe samples were implanted with mass analyzed 75 keV B⁺ ions at different doses ranging from 10¹² to 10¹⁶ ions cm⁻². The composition, thickness, microstructures, surface roughness and optical band gap of the as-deposited and boron-implanted films were studied by Rutherford backscattering (RBS), grazing incidence X-ray diffraction, Atomic force microscopy, Raman scattering and transmittance measurements. The RBS analysis indicates that the composition of the as-deposited and boron-implanted films is nearly stoichiometric. The thickness of the as-deposited film is calculated as 230 nm. The structure of the as-deposited and boron-implanted thin films is cubic. It is found that the surface roughness increases on increasing the dose of boron ions. In the optical studies, the optical band gap value decreases with an increase of boron concentration. In the electrical studies, the prepared device gave a very good response in the blue wavelength region.     

Correlation between electrical, optical properties and Ag centers of ZnO:Ag thin films

ZnO:Ag films have been fabricated on a n-Si (1 1 1) substrate and then annealed in situ in an O₂ ambient, using Ag₂O as a silver dopant by pulsed laser deposition. Hall measurements reveal that the films prepared at 400 and 450 °C show p-type behavior with a hole concentration of 6.3×10¹⁶–1.2×10¹⁷ cm^–3 and a mobility of 2.48–3.30 cm²/V s. By combining Hall measurements, electron paramagnetic resonance (EPR) signals, and photoluminescence (PL) spectra, a correlation is observed between the free hole carriers, the Ag²⁺ centers, and the neutral acceptor bound excitons. Additionally, the p-ZnO:Ag/n-Si heterojunction shows a diode-like I–V characteristic.     

EPR study of erbium-impurity complexes in silicon

Electron paramagnetic resonance (EPR) measurements have been used to characterise Er complexes formed in FZ silicon by the implantation of erbium together with either oxygen or fluorine. The samples have a 2 μm thick layer containing 10¹⁹ Er/cm³ alone or in addition 3×10¹⁹ O/cm³, 10²⁰ O/cm³ or 10²⁰ F/cm³. Various post-implantation anneals were carried out. Several different erbium centres, which have either C_1h monoclinic or trigonal symmetry, are observed and the way in which the type of centre depends on the implantation and annealing conditions is reported.     

Shadow photography of laser-driven shock waves in air

The interaction of a pulsed TE-CO₂-laser (10.6 μm wavelength, 7 μs pulse length, 0.7 J pulse energy, 10⁷ W/cm² power density, 100 kW mean power) with metals in air was investigated. Laser-supported absorption phenomena and material ablation processes are compared to those of conventional pulsed TEA-CO ₂-lasers. Of interest were the time-dependent plasma formation and the evolution of the shock waves. To achieve a time resolution better than 10 ns, a pulsed dye laser was used as a light source for the shadow photography     

Density, viscosity and ultrasonic velocity studies of aqueous solutions of sodium acetate at different temperatures

The densities and viscosities of aqueous solutions of sodium acetate have been measured at 298.15, 303.15, 308.15 and 313.15 K and at atmospheric pressure. The molality range has been studied between 6.09 × 10^− 2 to 7.314 × 10^− 1 mol kg^− 1. The experimental values of density have been used to calculate apparent molar volume, partial molar volume, solute–solute interaction parameter, and Hepler's constant. The viscosity data have been analyzed with Jone–Dole equation. Furthermore, ultrasonic velocity measurements of aqueous solutions of sodium acetate have been made at 298.15 and 308.15 K and at atmospheric pressure. From experimental values of ultrasonic velocity, apparent molar isentropic compressibility and limiting apparent molar isentropic compressibility have been calculated. All the parameters calculated from density, viscosity, and ultrasonic velocity indicate that the sodium acetate is water structure maker.     

Field emission from quantum size GaN structures

Whisker structures and quantum dots fabricated by photoelectrochemical (PEC) etching of undoped and doped metalorganic chemical vapor deposition (MOCVD)-grown GaN (2×10¹⁷ or 3×10¹⁸ cm⁻³) are investigated in relation with their field-emission characteristics. Different surface morphologies, corresponding to different etching time and photocurrent, results in different field-emission characteristics with low turn-on voltage down to 4 V/μm and the appearance of quantum-size effect in the I–V curves.     

Z-scan study of third-order optical nonlinearities in bismuth-based glasses

The third-order optical nonlinearity was measured in bismuth-based glasses by Z-scan technique using femto-second laser pulses. Re(χ⁽³⁾) = 4.9 × 10⁻¹¹ esu at 748 nm was obtained in the glass containing 65.5 mol% of Bi₂O₃. Although, the wavelength dependence of Re(χ⁽³⁾) shows resonant effect significantly, relatively small nonlinear absorption coefficient β = 0.8 cm/GW at 769 nm was estimated. Bismuth-based glass exhibits the largest third-order optical nonlinearity in oxide glasses, indicating they are promising materials used for nonlinear optical devices.     

Si doped GaAs/AlGaAs terahertz detector and phonon effect on the responsivity

Terahertz detection capability of an n-type heterojunction interfacial work function internal photoemission (HEIWIP) detector is demonstrated. Threshold frequency, f₀, of 3.2 THz (93 μm) was obtained by using n-type GaAs emitter doped to 1 × 10¹⁸ cm⁻³ and Al_0.04Ga_0.96As single barrier structure. The detector shows a broad spectral response from 30 to 3.2 THz (10–93 μm) with peak responsivity of 6.5 A/W at 7.1 THz under a forward bias field of 0.7 kV/cm at 6 K. The peak quantum efficiency and peak detectivity are 19% and 5.5 × 10⁸ Jones, respectively under a bias field of 0.7 kV/cm at 6 K. In addition, the detector can be operated up to 25 K.     

Electronic conduction properties of Au/C60/p-Si and C60/Au/p-Si sandwich structures: I–V and transducer characteristics

Gold-fullerite [C₆₀]-silicon (p-type) sandwich structures have been fabricated in order to investigate intrinsic cross-sectional and planar electronic conductive properties, in particular the C₆₀/p-Si p–n heterojunction. The turn-on voltage of this p–n heterojunction lies in the range 0.25–0.27 V. The I–V characteristics of the Au/C₆₀/p-Si structure are mostly defined by the bulk specific resistance of the fullerite crystal film itself (6×10⁷ Ω cm). I–V curves in the C₆₀/Au/p-Si structure are shown to be ohmic. Au/C₆₀/p-Si sandwiches irradiated with swift (300 MeV) heavy ions, (⁸⁴Kr¹⁴⁺) to a total fluence 10¹⁰ ion/cm² yield structures which are sensitive to ambient air pressure, specifically in the case of a transverse contact configuration, and if one of the contacts is located on the irradiated part of the fullerite film. The sandwich-structure sensitivity to pressure is 5×10⁻⁶ Pa⁻¹. This exceeds the sensitivity of conventional silicon pressure transducers by almost three orders of magnitude.     

Nonlinear refractive index measurements in antimony–sulfide glass films using a single beam nonlinear image technique

The nonlinear refractive index, n₂, of films based on the new glass system Sb₂O₃–Sb₂S₃ was measured at 1064 nm with laser pulses of 15 ps, using a single-beam nonlinear image technique in presence of a phase object. The films were prepared from bulk glasses by RF-sputtering. A large value of n₂ = 3 × 10⁻¹⁵ m²/W, which is three orders of magnitude larger than for CS₂, was determined. The result shows the strong potential of antimony–sulfide glass films for integrated nonlinear optics.     

Rapid nucleation of diamond films by pulsed laser chemical vapor deposition

The nucleation of diamond films could be greatly enhanced on mirror-polished Si substrate by a pulsed Nd:YAG laser beam without any thermal- and plasma-assisted processes during a very short time. The nucleation density increased with decreasing laser power density from 1.38×10¹⁰ to 1.17×10⁹ W/cm² and deposition pressure from 1013 to 4 mbar. The pulsed laser beam made no contribution to enhance nucleation at substrate temperature as low as 650°C. X-ray diffraction measurements showed the (1 1 1) diffraction peak of diamond for the samples obtained using only pulsed laser during 40 min. The enhanced nucleation and growth of diamond crystallites were attributed to effective excitation of reactive gases and etching of non-diamond carbon phases by the pulsed laser beam.