Use of Nd: YAG laser forin situ growth of thin films of Y1Ba2Cu3O7−δ

As-deposited superconducting films of Y₁Ba₂Cu₃O_7−δ with zero resistance at a temperature of ⋍ 80 K have been successfully grown using a Nd:YAG laser. A substrate temperature in the range 450–550°C was found most appropriate. The use of a Nd:YAG laser instead of an excimer laser is likely to improve the cost effectiveness of the laser ablation technique.     

Effect of laser irradiation on structural,electrical and optical properties of SnO2 films

Thin films of SnO₂ were prepared using a spray pyrolysis technique. Films were irradiated with Nd:YAG laser pulses of various energy densities (2–50 mJ cm^–2) with varying number of pulses from 1–50. X-ray diffraction studies were made to investigate the structural changes due to laser irradiation. An improvement in crystallinity and an increase in grain size were observed in laser-irradiated films. Hall coefficient and Hall mobility studies were made in the temperature range 77–300 K for the as-grown as well as laser-irradiated films. An increase in mobility and a decrease in carrier concentration were observed in the films after laser irradiation. Optical transmission studies revealed that the refractive index increased as a result of laser irradiation.     

Polycarbonate surface cell's adhesion examination after Nd:YAG laser irradiation

Nd:YAG laser treatment was used in order to increase surface cell adhesion aspects of polycarbonate (PC) films prepared via melt process. The treatment was carried out under different wavelengths and beam diameters. ATR-FTIR and UV spectra obtained from different samples before and after laser treatment in air showed that laser irradiation has induced some chemical and physical changes in surface properties. The irradiated films were also characterized using scanning electron microscopy (SEM) and contact angle measurements. Effect of pulse numbers on the surface properties was also investigated. Cell culture test was used to evaluate cell adhesion property on the PC films before and after treatment. The results obtained from this test showed that after laser treatment, the cells were attached and proliferated extensively on the Nd:YAG laser treated films in comparison with the unmodified PC. Moreover, it was revealed that a decrease in the laser beam diameter and an increase in the irradiated pulse numbers increased surface wettability and caused a better cell attachment on the polymer surface.The obtained results also showed that a decrease in the laser beam diameter and an increase in the irradiated pulse numbers increased surface wettability and caused a better cell attachment on the polymer surface.     

Microstructuring of UV-transparent functionalised films on glass by excimer laser irradiation

KrF excimer laser irradiation was used to remove organic moieties from UV-transparent films of organosilanes on borosilicate glass. High-resolution patterns with different functional groups on glass were obtained by a combination of laser modification and silanisation steps. The local material modification near the ablation threshold of glass was investigated by white light interference microscopy. Change in chemical properties of irradiated surface areas were studied by fluorescence microscopy after an appropriate dying of exposed samples. From the results, the domination of thermo-chemical effects induced by the laser irradiation is derived. Finally, an example is given how the patterned organosilane films can be applied to influence cell growth on glass.     

Growth of metal-oxide semiconductor nanocomposite thin films by a dual-laser, dual target deposition system

Nanocomposite formed by gold nanoparticles embedded in a titanium dioxide matrix thin films have been synthesized by a synchronized two laser system. An ArF? excimer (λ = 193 nm, τ_FWHM ∼ 12 ns) laser and a frequency tripled Nd:Yttrium Aluminium Garnet (YAG; λ = 355 nm, τ_FWHM ∼ 10 ns) laser were used for the irradiation of titanium dioxide and gold targets. The investigations showed that there exists the possibility for tailoring the optical properties of gold-titanium dioxide nanocomposites by the proper choice of the laser irradiation parameters. The band gap narrowing and additional absorption in the visible spectral region induced by the incorporation of gold in the host TiO₂ matrix allows for the design of nanostructured thin films for new generation of photocatalysts or solar energy converters.     

Properties of vacuum-deposited polyimide films

Vacuum-deposited polyimide (PI) thin films have been prepared by co-deposition of precursor pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) followed by thermal treatment. The dependency of the optical and electrical properties, chemical resistivity and mechanical stability on the composition (ODA:PMDA) and the degree of imidization of the PI layers have been investigated and discussed. The experimental results have yielded possibilities to microstructure the vacuum-deposited PI films by excimer laser irradiation or reactive ion etching in gas mixture CF₄/O₂.     

氧化锌脱膜和激光刻蚀制备亚微米自支撑聚酰亚胺薄膜及其性能

探讨小于1 μm自支撑聚酰亚胺薄膜的制备及其性能。以稀盐酸为腐蚀剂, 对涂于氧化锌衬底上的聚酰胺酸薄膜进行剥离, 经热亚胺转化为聚酰亚胺薄膜, 再用准分子激光对其刻蚀减薄。采用原子力显微镜、傅里叶变换红外光谱仪和分光光度计对薄膜的微观结构和光谱性能进行了表征。结果表明, 以室温下溅射的氧化锌薄膜为脱膜剂, 制备了厚度约950 nm的自支撑薄膜, 而激光刻蚀使聚酰亚胺薄膜厚度减薄至150 nm。厚度分别为950和150 nm薄膜的红外谱中均出现了聚酰亚胺特征吸收峰(1775、1720、1380和725 cm^-1), 且两者在400~2500 nm范围的平均透过率分别为80.3% 和83.5%。     

Parametric study of an excimer-pumped, nitrogen Raman shifter for lidar applications

A krypton fluoride (KrF) excimer-pumped, nitrogen Raman shifter has been studied for use in a wavelength-optimized solar-blind Raman lidar. First Stokes conversion efficiencies (248 ? 263 nm) as high as 12% have been observed in N2:He gas mixtures. Both oscillator-amplifier and self-seeded configurations were investigated. Wavelength-dependent effects were investigated with a Nd:YAG laser operating at 532 and 266 nm. A comparison of KrF- and Nd:YAG-pumped Raman shifting has shown that the beam quality of the excimer laser was a major factor in limiting the maximum first Stokes conversion efficiency.     

Effect of a pulsed Nd:YAG laser irradiation on multi-walled carbon nanotubes film

Multi-walled carbon nanotubes (MWCNTs) film have been analyzed by Raman spectroscopy to clarify the effect of a pulsed Nd:YAG laser heating. The MWCNTs film surface was flashed with the fundamental harmonic (λ = 1064 nm) or the second harmonic (λ = 532 nm) of a single pulse of Nd:YAG laser in the air. The dynamics of pulsed nanosecond laser heating process was simulated by the solution of the one-dimensional heat conduction equation. At the laser fluence of 500 mJ/cm² with Nd:YAG laser (λ = 1064 nm), the surface reached the maximum temperature 1395 °C at 12 ns. Moreover, the Raman spectroscopy of MWCNTs films before and after irradiation were measured. The intensity of the two characteristic Raman shifts I_D (defect-mode) and I_G (graphite-mode) was measured by the Raman spectroscopy. The maximum surface temperature was calculated and compared with the I_G/I_D ratio of MWCNTs film. The graphitization occurred on the sample after irradiation.     

Investigation on the panchromaticity of silver-doped poly(vinyl alcohol)/acrylamide photopolymer

An investigation on the panchromaticity of a silver-doped poly(vinyl alcohol)/acrylamide photopolymer system is presented in this paper. Frequency-doubled Nd:YAG (532 nm) and Ar? (488 nm) lasers were used for the characterization of the films. Previous studies using an He-Ne laser (632.8 nm) showed that plane-wave transmission grating with a high diffraction efficiency of 75% could be stored in the optimized film. From the present study, it was noted that transmission gratings with 70% diffraction efficiency could be recorded using Ar? and Nd:YAG lasers, thereby elucidating the possibility of using the developed photopolymer system as a competent panchromatic recording medium.     

Thin film deposition on plastic substrates using silicon nanoparticles and laser nanoforming

Reduced melting temperature of nanoparticles is utilized to deposit thin polycrystalline silicon (c-Si) films on plastic substrates by using a laser beam without damaging the substrate. An aqueous dispersion of 5 nm silicon nanoparticles was used as precursor. A Nd:YAG (1064 nm wavelength) laser operating in continuous wave (CW) mode was used for thin film formation. Polycrystalline Si films were deposited on flexible as well as rigid plastic substrates in both air and argon ambients. The films were analyzed by optical microscopy for film formation, scanning electron microscopy (SEM) for microstructural features, energy dispersive spectroscopy (EDS) for impurities, X-ray photoelectron spectroscopy (XPS) for composition and bond information of the recrystallized film and Raman spectroscopy for estimating shift from amorphous to more crystalline phase. Raman spectroscopy showed a shift from amorphous to more crystalline phases with increasing both the laser power and irradiation time during laser recrystallization step.     

Application of polyimide Langmuir-Blodgett films to deep UV resists

The preparation of Langmuir-Blodgett (LB) films based on a photosensitive polyimide precursor 2 and their application to deep UV resists have been studied. LB films fabricated from a mixed monolayer of polyimide precursor 2-octadecyl alcohol-benzoin ethylether (molar ratio, 3:3:1) were found to act as negative working resists with a resolution of 0.5 μm space and 1.0 μm line, a sensitivity of 100 mJ cm^-2 and good plasma etching resistance. They are promising for application as KrF and ArF excimer laser resists corresponding to 16 and 64 Mbit dynamic random access memories.     

Working beyond the static limits of laser stability by use of adaptive and polarization-conjugation optics

Strong thermo-optical aberrations in flash-lamp-pumped Nd:Cr:GSGG rods were corrected to yield TEM(00) output at twice the efficiency of Nd:YAG. A hemispherical resonator operating at the limit of stability was employed. As much as 3 W of average power in a Gaussian beam (M(2) approximately 1) was generated. Unique features were zero warm-up time and the ability to vary the repetition rate without varying energy, near- and far-field profiles, or polarization purity. Thermal focusing and astigmatism were corrected with a microprocessor-controlled adaptive-optics backmirror composed of discrete elements (variable-radius mirror). A reentrant resonator coupled polarizer losses back into the laser rod and corrected depolarization.     

The irradiation effect of a Nd–YAG pulsed laser on the CeO2 target in the liquid

The irradiation of an Nd–YAG pulsed laser on the CeO₂ target in water was investigated. The reaction products depend mainly on the energy density of the Nd–YAG laser. The CeO₂ nanoparticles with sizes of 20–80 nm were formed in water, while the energy density was larger than 32 kJ/cm². The nanocrystalline films with grain sizes of 50–150 nm were formed on the target with the energy density of 20–25 kJ/cm². Finally, the amorphous films were formed with the energy density of 6–15 kJ/cm². The formation mechanisms of the nanoparticles and the films were discussed according to the triple-point phase diagram of CeO₂.     

Effect of ionizing radiation on optical and lasing properties of Y3Al5O12 single crystals doped with Nd, Er, Ho, Tm, Cr ions

The influence of gamma irradiation on optical and lasing properties of YAG:Er, YAG:CTH, YAG:Nd and YAG:Cr⁴⁺ single crystals were studied. For no thermal annealed rods from YAG:Er and YAG:CTH crystals the increase of laser output energy was established. The mechanisms of radiation sensibilization are discussed.     

Nanocrystalline silicon films formed under the impact of pulsed excimer laser radiation on polyimide substrates

Polycrystalline silicon films on polyimide substrates were obtained by a method based on the crystallization of amorphous films under the impact of nanosecond pulses of excimer laser radiation. Characteristics of the film structure were studied by methods of Raman scattering and high-resolution electron microscopy. For the laser crystallization regimes employed, nanocrystalline silicon films with an average grain size of 5 nm were obtained. The results are of interest for the development of large-scale microelectronic devices (active thin-film transistor matrices) on cheap flexible substrates.     

One-Dimensional, Time-Resolved Raman Measurements in a Sooting Flame made with 355-nm Excitation

Single-shot vibrational Raman measurements were performed along an 11-mm-long line crossing the reaction zone in a premixed, fuel-rich (phi = 10), laminar methane-air flame by use of a frequency-tripled Nd:YAG laser with a 355-nm emission wavelength. This laser source seems to have advantages relative to KrF excimer lasers as well as to Nd:YAG lasers at 532 nm for hydrocarbon combustion diagnostics. The Raman emissions of all major species (N(2), O(2), CH(4), H(2), CO(2), H(2)O) were detected simultaneously with a spatial resolution of 0.4 mm. By integration over selected spectral intervals, the mole fractions of all species and subsequently the local gas temperatures have been obtained. A comparison of the temperatures that were found with results from filtered Rayleigh experiments showed good agreement, indicating the success of what are to the best of our knowledge the first one-dimensional single-shot Raman measurements in a sooting hydrocarbon flame.     

快速凝固高碳铁基合金脉冲激光非平衡热处理

利用脉冲Ｎｄ：ＹＡＧ激光辐照对快速凝固高碳铁基合金进行非平衡相变热处理，发现在高能脉冲激光辐照时，原快速凝固共晶碳化物（Ｆｅ３Ｃ）异常迅速地石墨化，获得了含超细石墨球和既含超细石墨球又含快速凝固共晶Ｆｅ３Ｃ的两种新材料，研究表明，这种快速石墨化及上述两类新型材料的形成主要归因于脉冲激光光速辐照产生强烈周期性起伏温度场的“微退火（ｍｉｃｒｏ－ａｎｎｅａｌｉｎｇ）效应。     

Pulsed laser induced birefringence switching in a biopolymer matrix containing azo-dye molecules

All optical switching has been studied using the Optical Kerr Effect (OKE) configuration in a biopolymer matrix containing an azo-dye: the Disperse Orange 3 (DO3). The biopolymer system consisted of a deoxyribonucleic acid blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride is suitable for optical quality thin film fabrication. The excitation beams inducing birefringence were delivered from a continuous wave laser at 532 nm and another nanosecond pulsed Nd: YAG laser. The birefringence was instantaneously monitored under crossed polarizer system by a weak non-absorbed light from a cw He-Ne laser working at 632.8 nm. Fast all optical switching process (in the range of microseconds) and excellent reversibility have been observed.     

Improvement of physical properties of IGZO thin films prepared by excimer laser annealing of sol–gel derived precursor films

Indium gallium zinc oxide (IGZO) transparent semiconductor thin films were prepared by KrF excimer laser annealing of sol–gel derived precursor films. Each as-coated film was dried at 150 °C in air and then annealed using excimer laser irradiation. The influence of laser irradiation energy density on surface conditions, optical transmittances, and electrical properties of laser annealed IGZO thin films were investigated, and the physical properties of the excimer laser annealed (ELA) and the thermally annealed (TA) thin films were compared. Experimental results showed that two kinds of surface morphology resulted from excimer laser annealing. Irradiation with a lower energy density (≤250 mJ cm⁻²) produced wavy and irregular surfaces, while irradiation with a higher energy density (≥350 mJ cm⁻²) produced flat and dense surfaces consisting of uniform nano-sized amorphous particles. The explanation for the differences in surface features and film quality is that using laser irradiation energy to form IGZO thin films improves the film density and removes organic constituents. The dried IGZO sol–gel films irradiated with a laser energy density of 350 mJ/cm² had the best physical properties of all the ELA IGZO thin films. The mean resistivity of the ELA 350 thin films (4.48 × 10³ Ω cm) was lower than that of TA thin films (1.39 × 10⁴ Ω cm), and the average optical transmittance in the visible range (90.2%) of the ELA 350 thin films was slightly higher than that of TA thin films (89.7%).