斜入射引入动态多重散射机制的激光散斑抑制

散斑抑制一直是激光显示技术的研究热点。对激光光束经SiO₂溶液所形成散斑的特性分析,建立了多重散射与散斑颗粒大小的联系。结合动态光散射理论,提出利用斜入射引入动态多重散射机制的激光散斑抑制方法,并构建由静态散射片和装有粒径为300 nm、摩尔浓度为3.0×10-4 μm-3的SiO₂悬浮液的光通管组成的散斑抑制装置,将其置入激光显示系统的光源部分。针对光束以不同入射角进入SiO₂悬浮液对散斑图像对比度影响进行了系统实验分析。结果表明,光束以约8°进入SiO₂悬浮液能将散斑图像的对比度从0.43降低至0.067。通过该方法实现了散斑颗粒的空间平均和散斑图像的时间平均,提高了散斑抑制的效果。散斑抑制单元无需振动装置且便于集成到激光投影系统中,不仅提高了系统的可靠性也减小了成本。     

Effect of mesh patterning with UV pulsed-laser on optical and electrical properties of ZnO/Ag-Ti thin films

In this study, the ZnO/Ag-Ti structure for transparence conducting oxide (TCO) is investigated by optimizing the thickness of the Ag-Ti alloy and ZnO layers. The Ag-Ti thin film is deposited by DC magnetron sputtering and its thicknesses is well controlled. The ZnO thin film is prepared by sol-gel method using zinc acetate as cation source, 2-methoxiethanol as solvent and monoethanolamine as solution stabilizer. The ZnO film deposition is performed by spin-coating technique and dried at 150 °C on Corning 1737 glass. Due to the conductivity of ZnO/Ag-Ti is dominated by Ag-Ti, the sheet resistance of ZnO/Ag-Ti decrease dramatically as the thickness of Ag-Ti layer increases. However, the transmittances of ZnO/Ag-Ti become unacceptable for TCO application after the thickness of Ag-Ti layer beyond 6 nm. The as-deposited ZnO/Ag-Ti structure has the optical transmittance of 83% @ 500 nm and the low resistivity of 1.2 × 10⁻⁵ Ω-cm. Furthermore, for improving the optical and electrical properties of ZnO/Ag-Ti, the thermal treatment using laser is adopted. Experimental results indicate that the transmittance of ZnO/Ag-Ti is improved from 83% to 89% @ 500 nm with resistivity of 1.02 × 10⁻⁵ Ω-cm after laser drilling. The optical spectrum, the resistance, and the morphology of the ZnO/Ag-Ti will be reported in the study.     

Ru/WCoCN as a seedless Cu barrier system for advanced Cu metallization

The properties of Ru(5 nm)/WCoCN(5 nm) stacked layers as a seedless Cu barrier system has been investigated. Its barrier properties compared to single 10 nm Ru film were investigated by sheet resistances, X-ray diffraction patterns, transmission electron microscopy, energy dispersive spectrometry spot analysis, line scans, and leakage currents. Thermal stability of the Ru(5 nm)/WCoCN(5 nm) improved by over 100 °C than that of Ru(10 nm) barrier. The results show that Ru(5 nm)/WCoCN(5 nm) can effectively block Cu diffusion up to 600 °C for 30 min. The Ru(5 nm)/WCoCN(5 nm) bilayer is a great Cu barrier candidate for seedless Cu interconnects.     

Indium tin oxide sol-gel precursor conversion process using the third harmonics of Nd:YAG laser

We use the third harmonics of Nd:YAG laser (λ = 355 nm) for simultaneous precursor conversion and dopant activation on sol-gel ITO thin films at a laser fluence range of 700-1000 mJ/cm². A minimum resistivity of 5.37 × 10⁻² Ω-cm with a corresponding carrier concentration of 6 × 10¹⁹ cm⁻³ is achieved at laser irradiation fluence of 900 mJ/cm². X-ray photoelectron analysis reveals that extremely high tin concentration of 19.4 at.% and above is presented in the laser-cured ITO thin films compared with 8.7 at.% in the 500 °C thermally cured counterpart. These excess tin-ions form complex defects, which contribute no free carriers but act as scattering centers, causing inferior electrical properties of the laser-cured films in comparison with the thermally cured ones.     

Crystallization of hydrogenated amorphous silicon carbon films with laser and thermal annealing

The crystallization of silicon rich hydrogenated amorphous silicon carbon films prepared by Plasma Enhanced Chemical Vapor Deposition technique has been induced by excimer laser annealing as well as thermal annealing. The excimer laser energy density (E_d) and the annealing temperature were varied from 123 to 242 mJ/cm² and from 250 to 1200 °C respectively. The effects of the two crystallization processes on the structural properties and bonding configurations of the films have been studied. The main results are that for the laser annealed samples, cubic SiC crystallites are formed for E_d ≥ 188 mJ/cm², while for the thermal annealed samples, micro-crystallites SiC and polycrystalline hexagonal SiC are observed for the annealing temperature of 800 and 1200 °C respectively. The crystallinity degree has been found to improve with the increase in the laser energy density as well as with the increase in the annealing temperature.     

Laser Shock Processing of 6061-T6 Al alloy with 1064 nm and 532 nm wavelengths

Laser Shock Processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results in the LSP concept for metal surface treatments in underwater laser irradiation at 532 nm and 1064 nm. The purpose of the work is to compare the effect of both wavelengths on the same material. A convergent lens is used to deliver 1.2 J/pulse (1064 nm) and 0.9 J/pulse (532 nm) in a 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG laser with spots of a 1.5 mm in diameter moving forward along the work piece. A LSP configuration with experimental results using a pulse density of 2500 pulses/cm² and 5000 pulses/cm² in 6061-T6 aluminum samples are presented. High level compressive residual stresses are produced using both wavelengths. It has been shown that surface residual stress level is comparable to that achieved by conventional shot peening, but with greater depths. This method can be applied to surface treatment of final metal products.     

The effect of laser remelting in the formation of tunable nanoporous Mn structures on mild steel substrates

Nanoporous manganese was fabricated by a three-step process involving high power laser cladding of a homogeneous Cu₄₀Mn₆₀ alloy coatings onto a mild steel substrate, laser remelting for tuning the grain size and the composition homogeneity followed by selectively electrochemical de-alloying for removal of Cu element and formation of nanoporous Mn. The microstructure and homogeneity of the precursor Cu₄₀Mn₆₀ alloys have a significant influence on the evolution of nanopores during selectively electrochemical de-alloying. Laser remelting can significantly refine the microstructure. The second dendrite arm spacing decreases with increasing of laser remelting scanning speed. A SDAS of 1.17 μm was obtained at the laser scanning speed of 133 mm/s. When the remelting scanning speed reaches 100 mm/s, a nanoporous structure with average pore size less than 100 nm was achieved under optimized dealloying electrode current density about 2 mA/cm². Nanoporous Mn with nanopore sizes ranging from 80 to 130 nm was fabricated by this method. Surface-enhanced Raman scattering characteristics of the nanoporous materials have been investigated. It is found that smaller nanoporosity leads to significant improvements in surface-enhanced Raman scattering.     

Synthesis of nanosized particles during laser ablation of gold in water

In this paper we report the formation of gold nanoparticles during laser ablation of gold target in water in the absence of any additives. The experiments were carried out by using the radiation of the pulsed Nd:YAG laser, operating at the second (532 nm, 10 ns, 10 Hz), or the fourth harmonic (266 nm) wavelengths. The properties of the nanoparticles were found to be susceptible to the additional 532 and 266 nm laser irradiation. It has been established that both the mean size of the nanoparticles and their stability could be varied by proper selection of the parameters of laser ablation and postirradiation such as laser fluence and wavelength combinations.     

Exact laser line-width requirements evaluation for optical PSK homodyne communication systems with Dither loop

The laser line-width required in PSK homodyne communication systems with Dither phase-locked loop receivers are exactly evaluated. It is shown that second-order phase-locked loops require at least 0.2 pW of signal power per every Hz of laser line-width (this number refers to the system with the detector responsivity 0.94 A/W, damping ratio 0.707, and the phase error standard deviation 10°). This signal power is used for phase locking, and is, therefore lost from the data receiver. This study for the first time shows the imperfect-phase-recovery-induced power penalty as a function of laser line-width. It can be estimated from the theoretical result that an optimal dither phase locked-loop receiver requires the laser line-width as Δυ ≤ 3.14 × 10⁻⁵ × R_b, where R_b is the system bit rate. This number refers to the system with power penalty of 1 dB at BER = 10⁻¹⁰.     

Crystal growth,structural, linear and nonlinear optical studies of 4-methyl-4′-N’-methylstilbazolium tosylate single crystals

Organic 4-methyl-4′-N’-methylstilbazolium tosylate, a new derivative of the stilbazolium tosylate family compound was synthesized by condensation method. The optical quality single crystals with dimension 5 mm × 4 mm × 2 mm were grown by slow evaporation technique at 40 °C. The crystal system and lattice parameters were found from single crystal X-ray diffraction studies. The optical transmittance, cut-off wavelength (402 nm) and band gap energy (3.09 eV) were estimated by UV–visible studies. The surface laser damage threshold study was carried out for MMST crystal using Nd:YAG laser. The third-order nonlinear optical susceptibility (χ³) for MMST crystal was estimated by employing Z-scan technique using 1064 nm laser.     

Chemical composition of ZrC thin films grown by pulsed laser deposition

ZrC films were grown on (1 0 0) Si substrates by the pulsed laser deposition (PLD) technique using a KrF excimer laser working at 40 Hz. The nominal substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that films deposited under residual vacuum or under 2 × 10⁻³ Pa of CH₄ atmosphere were crystalline, exhibiting a (2 0 0)-axis texture, while those deposited under 2 × 10⁻² Pa of CH₄ atmosphere were found to be equiaxed and with smaller grain size. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), showed the usual high oxygen contamination of carbides. Once the topmost 2-4 nm region was removed, the oxygen concentration rapidly decreased, down to around 3-8% only in bulk. Simulations of the X-ray reflectivity (XRR) curves indicated a smooth surface morphology, with roughness values below 1 nm (rms) and films density values of around 6.30-6.45 g/cm³, very close to the bulk density. The growth rate, estimated from thickness measurements by XRR was around 8.25 nm/min. Nanoindentation results showed for the best quality ZrC films a hardness of 27.6 GPa and a reduced modulus of 228 GPa.     

Ageing effects on the wettability behavior of laser textured silicon

In the present work we investigate the ageing of acid cleaned femtosecond laser textured 〈1 0 0〉 silicon surfaces. Changes in the surface structure and chemistry were analysed by Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS), in order to explain the variation with time of the water contact angles of the laser textured surfaces. It is shown that highly hydrophobic silicon surfaces are obtained immediately after laser texturing and cleaning with acid solutions (water contact angle > 120°). However these surfaces are not stable and ageing leads to a decrease of the water contact angle which reaches a value of 80°. XPS analysis of the surfaces shows that the growth of the native oxide layer is most probably responsible for this behavior.     

A study on the biological detection chip through the use of PDMS lens for the reinforcement of fluorescence receiving signal

In this study, MEMS process technology is adopted to produce microfluidic chip and PDMS lens. SU-8 thick film photo resist is coated onto silicon wafer surface in two times of spin coating, then through lithography and mold transfer technology, PDMS chip of minimal line width 100 μm and thickness 200 μm is printed. In fluorescence detection aspect, we use objective lens to couple laser optical source to optical fiber, and then have it incident to excite fluorescence sample, the excited fluorescence then passes through filter and detected by optical detector of experiment group and spectrophotometer of reference group. From the experiment result, the Hex fluorescence detection limit of the system is verified to be 1 pmol/5 μl. In addition, we have integrated PDMS lens into microfluidic chip to make generalized detection experiment, it was found that the signal measured by optical embedded type is higher than that of non-embedded type. Meanwhile, the microfluidic chip with double concave lens (135°) and10 mm PDMS focusing lens can be utilized to obtain optimal fluorescence receiving effect. The fluorescence intensity is raised by 2–3 times, and the measurement limit is lowered to 100 fmol/5 μl.     

Influence of external objects scattering property on self-mixing signal inside fiber laser

The self-mixing sensor based on Er³⁺–Yb³⁺ co-doped Distributed Bragg reflector fiber laser (EYDBR) has been demonstrated for detecting the effect of external objects scattering property on self-mixing signal. Results show that self-mixing interference inside fiber laser with short cavity length especially EYDBR fiber laser can keep high SNR with different types of scattering surfaces even the white print paper. Meanwhile, we have obtained a high and stable SNR at least 29.9 dB in measurements at incident angles smaller than 20°. In this way, the sensing system we demonstrate is suitable for vibration and displacement measurements, particularly for high-precision industrial measurements.     

Epitaxial ZrC thin films grown by pulsed laser deposition

ZrC thin films were grown on (0 0 1)Si, (1 1 1)Si and (0 0 0 1)sapphire substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction, X-ray reflectivity and Auger electron spectroscopy investigations were used to characterize the structure and composition of the deposited films. It has been found that films grown at temperatures higher than 700 °C under very low water vapor pressures were highly textured. Films deposited on (0 0 1)Si grew with the (0 0 1) axis perpendicular to the substrate, while those deposited on (1 1 1)Si and (0 0 0 1)sapphire grew with the (1 1 1) axis perpendicular to the substrate. Pole figures investigations showed that films were epitaxial, with in-plane axis aligned to those of the substrate.     

Effect of pulse repetition rate and number of pulses in the analysis of polypropylene and high density polyethylene by nanosecond infrared laser induced breakdown spectroscopy

Pulse repetition rates and the number of laser pulses are among the most important parameters that do affect the analysis of solid materials by laser induced breakdown spectroscopy, and the knowledge of their effects is of fundamental importance for suggesting analytical strategies when dealing with laser ablation processes of polymers. In this contribution, the influence of these parameters in the ablated mass and in the features of craters was evaluated in polypropylene and high density polyethylene plates containing pigment-based PbCrO₄. Surface characterization and craters profile were carried out by perfilometry and scanning electron microscopy. Area, volume and profile of craters were obtained using Taylor Map software. A laser induced breakdown spectroscopy system consisted of a Q-Switched Nd:YAG laser (1064 nm, 5 ns) and an Echelle spectrometer equipped with ICCD detector were used. The evaluated operating conditions consisted of 10, 25 and 50 laser pulses at 1, 5 and 10 Hz, 250 mJ/pulse (85 J cm⁻²), 2 μs delay time and 6 μs integration time gate. Differences in the topographical features among craters of both polymers were observed. The decrease in the repetition rate resulted in irregular craters and formation of edges, especially in polypropylene sample. The differences in the topographical features and ablated masses were attributed to the influence of the degree of crystallinity, crystalline melting temperature and glass transition temperature in the ablation process of the high density polyethylene and polypropylene. It was also observed that the intensities of chromium and lead emission signals obtained at 10 Hz were two times higher than at 5 Hz by keeping the number of laser pulses constant.     

Laser annealing process of ITO thin films using beam shaping technology

In this study, we develop a laser annealing system for In₂O₃Sn (ITO) to carry out heat treatment on oxides with high melting temperature on substrates with low melting temperature. It is known that the working temperature of traditional heat treatments is usually limited by the melting point of the substrate materials. To overcome this problem, we apply a laser annealing technique to modify the film properties, and to measure the electrical and surface properties, we use Hall measurement, a four-point probe, and an atomic force microscope in our experiment. We will discuss how the annealing is affected by the laser machining parameters, including the beam profile, intensity distribution, laser spot overlap, and laser operation mode. We will further show through experimental results that the beam profile greatly affects the surface roughness of the ITO films. With the use of a uniform beam profile with proper laser intensity, the surface roughness and the sheet resistance of the ITO films can be reduced from 23 nm to 4.2 nm and from 417 Ω/sq to 400.4 Ω/sq, respectively.     

Random distributed feedback fiber laser pumped by an ytterbium doped fiber laser

A random distributed feedback fiber laser operating at 1115 nm has been demonstrated experimentally in standard communication optical fibers by using a LD-pumped Yb-doped fiber laser as the pump source. We have studied the effect of different fiber spans on this new type of random fiber laser output power. It is shown that the generation power is the highest up to 198 mW in a 50 km fiber span. The slope efficiency is more than 28.7%. Stable, high-power continuous-wave (CW) lasing can be generated when the pump power is 3.6 W. The threshold power has also been calculated which well proves a random fiber laser operating via Rayleigh scattering, amplified through the Raman scattering.     

Direct determination of gas velocity and gas temperature in an atmospheric-pressure argon-hydrogen plasma jet

Direct gas temperature and gas velocity measurements made in the exit plane of a subsonic argon-hydrogen thermal plasma jet from high-resolution lineshape analysis of laser light scattered by the plasma are reported. The lineshapes are in general a superposition of the ion feature of the Thomson-scattered light and the lineshape of Rayleigh scattered light. In the center of the jet Thomson scattering dominates while at larger radii Rayleigh scattering dominates. Because of the complexity of the lineshapes of light scattered by multicomponent plasmas, only those that are predominantly due to Thomson scattering can in practice be analyzed for gas temperature. Gas velocity can be determined from the Doppler shift of the lineshapes relative to the frequency of the incident laser if the velocity is greater than about 50 m s⁻¹. The maximum gas temperature measured was 14,500 K±5%. The maximum gas velocity measured was 1100 m s⁻¹±3%. Temperature values and the radial velocity profile are compared with those previously obtained from a subsonic all-argon plasma jet operated under similar conditions.     

Measurements of the linewidth of a continuous-wave distributed feedback quantum cascade laser

Two-sample (Allan) variance with a modified algorithm was applied to the determination of the experimental linewidth of a thermoelectrically-cooled continuous-wave distributed feedback quantum cascade laser at a wavelength of 4.333 μm. From successive laser transmittance scans over the CO₂ ν₃, (01¹1 − 01¹0) P(33) absorption line at 2307.653 cm^− 1, two-sample variances were calculated for the laser frequency difference between different points on the sides of the absorption peak. From the minimum two-sample variance of the laser frequency difference between two adjacent points (5 μs between the points) on the same side of the absorption line the experimental laser linewidth was estimated to be less than 36(7) kHz at a laser power of ~ 25 mW, a laser current of 976 mA and a laser temperature of + 19.5 °C.