DUAL-FREQUENCY LASER USING ANISOTROPIC BIREFLECTANCE FILM(1.2-6.0 MHz)AND ITS POLARIZATION CHARACTER

The appropriate bireflectance film series are selected to get thebeat-frequency of dual-frequency laser using anisotropic bireflectance film (DLABF) from 1.2 MHz to6 MHz. The maximum measurement velocity of the interferometer utilizing DLABF can be up to 1.8 m/s.Generally the outputs of the DLABF in a transverse magnetic field are two orthogonalmicro-elliptical polarized components when DLABF can emit dual-frequency laser. When the laser tubeis spun in the magnetic field, the ellipticities of these two components are also changed. In somecertain relative angles, the outputs the DLABF are two almost ideally orthogonal linear polarizedcomponents. The frequency stabilization of DLABF is also discussed. The maximum variation of thebeat-frequency of the stabilized DLABF can be 0.15 kHz within 46 h. As no quarter wave plate (QWP)needed, DLABFs have better thermal stability than longitudinal Zeeman lasers.

A novel absorptive thin film for laser welding in optoelectronic device capsulation

A kind of absorptive thin film was designed and used in laser welding of SiO2, Si and LiNbO3. This absorptive thin film of three-layer metal-dielectric-metal structure is designed for further reducing the high reflectance of the Nd:YAG laser beam on the surface of the tin layer that is utilized as solder between the transparent parent materials. The actual absorption of laser energy in experiment exceeds 99%. This combination of absorber and solder transformed the laser energy into heat efficiently and decreased the minimum necessary incident laser power transmitting through the transparent parent materials. As a result, the damage of the parent materials, which is suffered from laser transmission, was avoided; On the other hand, mechanical stability of the welded materials had been improved. Experiment had been made to show the difference between welding with and without the absorptive thin film.

The Effect of Laser Irradiation on Surface Enhanced Raman Scattering for Silver Film

The laser irradiation effect on the SERS intensity for Ag film is discussed using crystal violet (CV) as a probe. The thickness of silver film,the etching time of the glass slide by gaseous hydrogen fluoride, and the laser irradiation time for different amounts of CV on silver films were investigated. The laser burn out model was proposed to explain the dependence of the SERS intensity of CV on the laser irradiation time.

Laser Protection with VO_2 Film

This paper presents the principle,properties,advantage and disadvantage,associated problems and trend of laser protection with VO 2 film for infrared detectors in the range of 3～5μm and 8～12μm regions and suggests VO 2 film is a potential protection material for infrared detectors.

Structural and electrical characterization of Bi2VO5.5 / Bi4Ti3O12 bilayer thin films deposited by pulsed laser ablation technique

The pulsed laser ablation technique has been employed to fabricate bilayer thin films con-sisting of layered structure ferroelectric bismuth vanadate (Bi2VO5.5) and bismuth titanate (Bi4Ti3O12) on platinized silicon substrate. The phase formation of these films was confirmed by X-ray diffraction (XRD) studies and the crystallites in these bilayers were randomly oriented as indicated by diffraction pattern consisting of the peaks corresponding to both the materials. The homogeneous distribution of grains (~300 nm) in these films was confirmed by atomic force microscopy. The cross-sectional scanning electron microscopy indicated the thickness of these films to be around 350 nm. The film exhi-bited P-E hysteresis loops with Pr ~ 11 ?C/cm2 and Ec ~ 115 kV/cm at room temperature. The dielectric constant of the bilayer was ~ 225 at 100 kHz which was higher than that of homogeneous Bi2VO5.5 film.

Microstructure and 355 nm Laser-Induced Damage Characteristics of Al₂O₃Films Irradiated with Oxygen Plasma under Different Energy

Al2O3 films were prepared using electron beam evaporation at room temperature. The samples were irradiated with oxygen plasma under different energy. The variations in average surface defect density and root mean square (RMS) surface roughness were characterized using an optical microscope and an atomic force microscope. Surface average defect density increased after plasma treatment. The RMS surface roughness of the samples decreased from 1.92 nm to 1.26 nm because of surface atom restructuring after oxygen plasma conditioning. A 355 nm laser-induced damage experiment indicated that the as-grown sample with the lowest defect density exhibited a higher laser-induced damage threshold (1.12 J/cm2) than the other treated samples. Laser-induced damage images revealed that defect is one of the key factors that affect laser-induced damage on Al2O3 films.

Numerical Analysis of Nd:YAG Pulsed Laser Polishing CVD Self-standing Diamond Film

Chemical vapor deposited （CVD） diamond film has broad application foreground in high-tech fields. But polycrystalline CVD self-standing diamond thick film has rough surface and non-uniform thickness that adversely affect its extensive applications. Laser polishing is a useful method to smooth self-standing diamond film. At present, attentions have been focused on experimental research on laser polishing, but the revealing of theoretical model and the forecast of polishing process are vacant. The paper presents a finite element model to simulate and analyze the mechanism of laser polishing diamond based on laser thermal conduction theory. The experimental investigation is also carried out on Nd：YAG pulsed laser smoothing diamond thick film. The simulation results have good accordance with the results of experimental results. The temperature and thermal stress fields are investigated at different incidence angles and parameters of Nd：YAG pulsed laser. The pyramidal-like roughness of diamond thick film leads to the non-homogeneous temperature fields. The temperature at the peak of diamond film is much higher than that in the valley, which leads to the smoothing of diamond thick film. The effect of laser parameters on the surface roughness and thickness of graphite transition layer is also carried out. The results show that high power density laser makes the diamond surface rapid heating, evaporation and sublimation after its graphitization. It is also found that the good polish quality of diamond thick film can be obtained by a combination of large incident angle, moderate laser pulsed energy, large repetition rate and moderate laser pulse width. The results obtained here provide the theoretical basis for laser polishing diamond film with high efficiency and high quality.

Optimization of Laser Ablation Technology for PDPhSM Matrix Nanocomposite Thin Film by Artificial Neural Networks-particle Swarm Algorithm

A new thermal ring-opening polymerization technique for 1, 1, 3, 3-tetra-ph enyl-1, 3-disilacyclobutane （TPDC） based on the use of metal nanoparticles produced by pulsed laser ablation was investigated. This method facilitates the synthesis of polydiphenysilylenemethyle （PDPhSM） thin film, which is difficult to make by conventional methods because of its insolubility and high melting point. TPDC was first evaporated on silicon substrates and then exposed to metal nanoparticles deposition by pulsed laser ablation prior to heat treatment.The TPDC films with metal nanoparticles were heated in an electric furnace in air atmosphere to induce ring-opening polymerization of TPDC. The film thicknesses before and after polymerization were measured by a stylus profilometer. Since the polymerization process competes with re-evaporation of TPDC during the heating, the thickness ratio of the polymer to the monomer was defined as the polymerization efficiency, which depends greatly on the technology conditions. Therefore, a well trained radial base function neural network model was constructed to approach the complex nonlinear relationship. Moreover, a particle swarm algorithm was firstly introduced to search for an optimum technology directly from RBF neural network model. This ensures that the fabrication of thin film with appropriate properties using pulsed laser ablation requires no in-depth understanding of the entire behavior of the technology conditions.

Laser-induced voltage effects in Ca_3Co_4O_9 thin films on tilted LaAlO_3(001) substrates grown by chemical solution deposition

Laser-induced voltage effects in c-axis oriented Ca3Co4O9 thin films have been studied with samples fabricated on 10°tilted LaAIO3 （001） substrates by a simple chemical solution deposition method. An open-circuit voltage with a rise time of about 10 ns and full width at half maximum of about 28 ns is detected when the film surface is irradiated by a 308-nm laser pulse with a duration of 25 ns. Besides, opemcircuit voltage signals are also observed when the film surface is irradiated separately by the laser pulses of 532 nm and 1064 nm. The results indicate that Ca3Co4O9 thin films have a great potential application in the wide range photodetctor from the ultraviolet to near infrared regions.

Temperature dependences of optical properties,chemical composition,structure,and laser damage in Ta_2O_5 films

Ta2O5 films are prepared by e-beam evaporation with varied deposition temperatures, annealing temperatures, and annealing times. The effects of temperature on the optical properties, chemical composition, structure, and laser- induced damage threshold （LIDT） are systematically investigated. The results show that the increase of deposition temperature decreases the film transmittance slightly, yet annealing below 923 K is beneficial for the transmittance. The XRD analysis reveals that the film is in the amorphous phase when annealed below 873 K and in thehexagonal phase when annealed at 1073 K. While an interesting near-crystalline phase is found when annealed at 923 K. The LIDT increases with the deposition temperature increasing, whereas it increases firstly and then decreases as the annealing temperature increases. In addition, the increase of the annealing time from 4 h to 12 h is favourable to improving the LIDT, which is mainly due to the improvement of the O/Ta ratio. The highest LIDT film is obtained when annealed at 923 K, owing to the lowest density of defect.

Fabrication of large-scale ripples on fluorine-doped tin oxide films by femtosecond laser irradiation

The large-scale uniform self-organized ripples are fabricated on fluorine-doped tin oxide （FTO） coated glass by femtosecond laser. They can be smoothly linked in a horizontal line with the moving of XYZ stage by setting its velocity and the repetition rate of the laser. The ripple-to-ripple linking can also be realized through line-by-line scanning on a vertical level. The mechanism analysis shows that the seeding effect plays a key role in the linking of ripples.

Laser-induced damage threshold in HfO_2/SiO_2 multilayer films irradiated by β-ray

Post-processing can effectively improve the resistance to laser damage in multilayer films used in a high power laser system. In this work, HfO_2/SiO_2 multilayer films are prepared by e-beam evaporation and then β-ray irradiation is employed as the post-processing method. The particle irradiation affects the laser induced damage threshold(LIDT),which includes defects, surface roughness, packing density and residual stress. The residual stress that is relaxed during irradiation changes from compressive stress into tensile stress. Our results indicate that appropriate tensile stress can improve LIDT remarkably. In view of the fact that LIDT rises from 8 J/cm^2 to 12 J/cm^2, i.e., 50% increase, after the film has been irradiated by 2.2×10^(13)/cm^2 β-ray, the particle irradiation can be used as a controllable and desirable postprocessing method to improve the resistance to laser induced damage.

STRUCTURE AND SURFACE STUDIES OF Mg_xZn_(1-x)O FILMS GROWN BY PULSED LASER DEPOSITION

The structural and surface properties of high-quality epitaxial cubic MgxZn1-xO films deposited by pulsed laser deposition (PLD) were studied by X-ray diffracti on and atomic force microscopy respectively. For films of about 500nm thick, sca ns over a 30μm × 30μm area revealed a surface roughness Ra of about 100nm. Th is relatively large surface roughness is primarily attributed to the particulate and outgrowth during the PLD process. A good epitaxial growth on LaAlO3 (LAO ) (100) substrates, however has been obtained for composition x = 0.9, 0.7 and 0 .5 with the heteroepitaxial relationship of (100)■∥(100)LAO (out-of-plane) and (011)■∥(010)LAO (in-plane). These structural qualities suggest that cubic Mgx Zn1-xO alloys films have good potential in a variety of optoelectronic device ap plications.

Effect of Oxygen Partial Pressure on Epitaxial Growth and Properties of Laser-Ablated AZO Thin Films

Al-doped ZnO（AZO） thin films were grown on c-sapphire substrates by laser ablation under different oxygen partial pressures（P_（O2））.The effect of P_（O2） on the crystal structure,preferred orientation as well as the electrical and optical properties of the films was investigated.The structure characterizations indicated that the as-grown films were single-phased with a wurtzite ZnO structure,showing a significant c-axis orientation.The films were well crystallized and exhibited better crystallinity and denser texture when deposited at higher P_（O2）.At the optimum oxygen partial pressures of 10- 15 Pa,the AZO thin films were epitaxially grown on c-sapphire substrates with the（0001） plane parallel to the substrate surface,i e,the epitaxial relationship was AZO（000 1） // A1_2O_3（000 1）.With increasing P_（O2）,the value of Hall carrier mobility was increased remarkably while that of carrier concentration was decreased slightly,which led to an enhancement in electrical conductivity of the AZO thin films.All the films were highly transparent with an optical transmittance higher than 85%.

Preparation and Properties of Copper Fine Wire on Polyimide Film in Air by Laser Irradiation and Mixed-Copper-Complex Solution Containing Glyoxylic Acid Copper Complex and Methylamine Copper Complex

Formation of copper wiring on a polyimide film by laser irradiation to a stable copper-complex film consisting of glyoxylic acid copper complex and methylamine copper complex in air has been investigated. A stable metallic copper on the polyimide film was precipitated even in air. Since this copper was generated only in the laser-irradiated parts, direct patterning of copper wiring was possible. It was also found that copper was precipitated by electroless copper plating on the laser-deposited copper wiring and it was possible to thicken the copper wiring by this precipitation. The resistivity of the copper wiring was almost the same as that of the bulk of metallic copper. The developed method—combining laser irradiation to a copper-complex-coated film and electroless copper plating—enables the high-speed deposition of fine copper wiring on a polyimide film in air by a printing process, indicating an inexpensive and useful process for fabricating copper wiring without high vacuum facility and heat-treatment under inert gas.

Laser Ablated Superconducting and Related Thin Films:A Microscopical Investigation

Laser ablated high temperature superconducting and related thin films are investigated with a microscopical point of view.The microstructure and microchemistry of three thin films(Y-Ba-Cu-O, Bi-Pb-Sr-Ca-Cu-O and Sr-Ca-Cu-O)are demonstrated as examples of laser ablation products.

Comparison of ZnO Films Grown on before- and after-vapor Transport Equilibration (VTE) LiAlO_2 Substrates by Pulsed Laser Deposition (PLD)

About φ45 mm LiAlO2 single crystal was grown by Czochralski （Cz） technique. However, the full-width at half-maximum （FWHM） value was high to 116.9 arcsec. After three vapor transport equilibration （VTE） processes, we can obtain high-quality LiAlO2 slice with the FWHM value of 44.2 arcsec. ZnO films were fabricated on as-grown slices and after-VTE ones by pulsed laser deposition （PLD）. It was found that ZnO films on the two slices have similar crystallinity, optical transmittance and optical band gap at room temperature. These results not only show that LAO substrate is suitable for ZnO growth, but also prove that the crystal quality of LAO substrate slightly affects the structural and optical properties of ZnO film.

Preparation of Highly Textured Bi and MnBi Films by the Pulsed Laser Deposition Method

Textured Bi and MnBi/Bi thin films are prepared by the pulsed laser deposition method. The highly c-axis textured MnBi films are obtained by annealing the bilayer consisting of textured Bi and Mn films. The eoercivities of the MnBi/Bi film are 1.5 T and 2.35 T at room temperature and at 373K, respectively, showing a positive temperature coefficient. Microstructural investigations show that the textured MnBi film results from the orientated growth induced by the textured Bi under-layer.

Using Narrow Line-Width Laser to Measure the Thickness and Refractive Index of the Film

We demonstrate applications of a novel setup which is used for measuring the relative phase difference between S and P polarization at an oblique incidence point in optically denser medium by analyzing the relative frequency shift of adjacent axial modes of S and P resonances of a monolithic folded Fabry-Perot cavity (MFC). The relative phase difference at a reflection point A in an optically denser medium is inferred to be around -167.4° for a confocal cavity and -201.1° for a parallel cavity. Given the n1, n3, φ1, φ3, λ, and Δ, the elliptic formula tan(ψ)exp(iΔ) = Rp/Rs is used to find a solution for thickness d and refractive index n2 of the thin film coated on point A, where Rs and Rp are total refractive index of s and p component of light related to two unknown values. Since it is hard to deduce an analytical solution for thickness and refractive index of the film, we firstly used exhaustion method to find the set of solution about thickness and refractive index when assumed there is no light absorption by the film and then Particle Swarm Optimization (PSO) to find a set of solution of thickness and complex refractive index which accounts the light absorption by the film.