Cathodoluminescence property of ZnO nano-phosphors fabricated by pulsed Nd:YAG laser ablation in plasma circumstance

Cathodoluminescence (CL) with energy-controlled electron beams was used to study the inner structure of ZnO nano-phosphors fabricated by YAG laser ablation under oxygen gas and oxygen plasma circumstances. Varying accelerating voltages of electron beams from 1.0 to 3.0 kV, it was clearly seen that the CL spectrum in the case of ZnO nano-phosphors fabricated under the oxygen gas background changed from a broad one centered at approximately 500 nm to a narrow one peaked at 380∼400 nm. This result indicates that there is an oxygen vacancy-rich shell in the surface area and a fine crystalline ZnO structure in the inner core region. Under the oxygen plasma circumstance at 500 Pa, however, we found that there is a crystalline structure in the surface layer of ZnO nano-phosphors due to the sufficient supply of oxygen ions and atoms and suppression of the formation of oxygen vacancy.     

Development of iridium TES by pulsed laser deposition with a Nd:YAG laser

The use of cryogenics micro calorimeters with Transition Edge Sensors for high-resolution spectroscopy for space applications puts several constraints on the detector's performances. Among several requirements, the long term stability of TES from a chemical and physical point of view is one of the most important. Iridium is a very interesting material for TES fabrication due to its excellent chemical stability and low transition temperature. Starting from the promising results we had with a cryogenic microcalorimeter with TES made of an Ir single crystal, we are developing a procedure to produce patterned Ir thin films by means of the Pulsed Laser Deposition (PLD). PLD with an infrared laser, in UHV, allows very clean evaporation process, good efficiency (about 4 nm/shot) and low dissipated power in the vacuum chamber (about 1 W). We have applied a lift-off mask technique that allows to heat the substrate during the deposition, which improves the adhesion and the thermal conductivity and circumvents the needs of very aggressive etchant solutions.     

Amorphous carbon-silicon heterojunctions by pulsed Nd:YAG laser deposition

Amorphous carbon (a-C) films were deposited at 10^− 4 Pa on n-Si (Si-111) and p-Si (Si-100) substrates using a pulsed Nd:YAG laser with fundamental, second- and third-harmonic outputs. These unhydrogenated and undoped a-C films were characterized by visible and UV Raman spectroscopy which indicated the presence of substantial amount of sp³ hybridized carbon network depending on the laser wavelength. The bulk resistivity in the Au/a-C/indium tin oxide structure varied between (10⁹-10¹³) Ω cm — the lowest resistivity was obtained for films deposited by the fundamental laser output at 1064 nm while the highest value was by the third-harmonic laser output at 355 nm. All the a-C/Si heterostructures exhibited a nonlinear current density-voltage characteristic. Under light illumination, by taking into consideration the fill factor of ~ 0.2 for a-C/n-Si, the conversion efficiency at the highest photovoltage and photocurrent, at an illumination density of 0.175 mW/cm² was estimated to be ~ 0.28%.     

Raman spectroscopic investigation of solid samples using a low-repetition-rate pulsed Nd:YAG laser as the excitation source

We tried to investigate the possibility of using a low-repetition-rate pulsed Nd:YAG laser as an excitation source in Raman measurements for solid samples. Based on the results from the Raman spectra excited by continuous wave (CW) 532 and 325 nm lasers, we studied the influence of laser energy and irradiation time of 532 and 355 nm pulsed Nd:YAG lasers (10 Hz repetition rate) on the thermal stability of (NH4)6Mo7O(24).4H2O, NH4VO3, and Ce(NO3)(3).6H2O samples, which usually decompose at relatively low temperatures. It is observed that the heating temperature estimated at these samples caused by the irradiation of 532 nm pulsed laser with 22 mJ is no higher than 100 degrees C even for 60 min exposure. The 355 nm pulsed laser with energies below 8.0 mJ hardly causes thermal damage to hydrated (NH4)6Mo7O24 and hydrated Ce(NO3)3 SAMPLES: However, a 355 nm pulsed laser with only 2.2 mJ causes heating temperatures as high as 200 degrees C in the NH4VO3 SAMPLE: These great differences should be attributed to the electronic absorbance of the above three samples at 355 nm. We also found that a 532 nm pulsed laser with even 22 mJ and a 355 nm pulsed laser with even 8.0 mJ do not cause the phase transition of TiO2 and ZrO2, whose phase transformation easily takes place at elevated temperatures, but pulsed lasers could remove some oxygen atoms from these samples. In addition, for L-alanine and DL-beta-phenylalanine biological samples, it is surprisingly found that they are not damaged by the 355 nm pulsed laser even when the laser energy is increased to 8.0 mJ, possibly because they do not absorb the 355 nm laser. Based on these results, it is demonstrated that low-repetition-rate pulsed lasers with appropriate wavelength and energy can be employed as the excitation sources of Raman spectroscopy for characterizing some solid samples, even the thermally unstable samples.     

Diode-laser-pumped Nd:YAG laser injection seeding system

We have designed and tested a compact injection seeding system consisting of a diode-laser-pumped Nd:YAG master oscillator and a permanent-magnet Faraday isolator. With active resonator frequency stabilization, this system permits highly reliable single-axial-mode operation of a Q-switched Nd:YAG laser over a period of hours. The system is capable of injection seeding both stable and unstable resonator designs and is suitable for injection seeding commercial lasers with only minor modifications.     

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.     

Efficient pulsed 946-nm laser emission from Nd:YAG pumped by a titanium-doped sapphire laser

Efficient pulsed room-temperature laser emission at 946 nm is obtained from a Nd:YAG rod pumped by a Ti-doped sapphire laser in the free-running mode. Three bonded YAG rods of 3-mm diameter with different Nd concentrations and active lengths were tested. A maximum output energy of 83.5 mJ at 3 Hz was obtained with a slope efficiency of 32.3% in an end-pumping configuration.     

Localized boriding of low-carbon steel using a Nd:YAG laser

Localized boriding of low-carbon steel by the conventional technique requires tedious preboriding treatment and a long processing time. Laser boriding of low-carbon steel can be performed faster, and without any preboriding treatment. The feasibility of selective boriding of AISI 1018 steel using a NdYAG laser has been investigated. High hardness in the range 950–2200 H_v was obtained during laser boriding of AISI 1018 steel. The wide range of hardness is due to the variety of microstructures possible during laser boriding. Electron microprobe analysis showed that the highest hardness (2200 H_v) was due to the formation of FeB, and the lowest hardness was due to a mixture of Fe₂B and eutectic (_Fe+Fe₂B). The most desirable microstructure in laser boriding of AISI 1018 steel was found to be Fe₂B, which incorporates a combination of a high hardness, in the range of 1300–1700 H_v, and a compressive stress at the treated surface.     

Deposition of hydroxyapatite thin films by Nd:YAG laser ablation: a microstructural study

Hydroxyapatite (HA) thin films has been successfully deposited by Nd:YAG laser ablation at λ = 532 nm. The morphology and microstructure of the deposited layers was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). Polycrystalline HA films were directly obtained with the substrate at 300 °C and without introducing water vapors in the deposition chamber. Electron paramagnetic resonance (EPR) measurements show that the oxygen stoichiometry in the HA films is also maintained. Depositions performed at λ = 335 nm laser wavelength and 300 °C substrate temperature resulted in polycrystalline layers of mixed composition of HA and tricalciumphosphate (TCP).     

Determination of laser ablation threshold of Teflon at different harmonics of Nd:YAG laser using photothermal deflection technique

We report the measurement of the laser ablation threshold of Teflon using photothermal beam deflection at 1.06 m, 0.532 m, and 0.355 m irradiation in air. The measured ablation threshold at various wavelengths is used to estimate the absorption coefficient. It is observed that the absorption coefficient increases with a decrease in wavelength.     

Direct patterning of double-layered metal thin films by a pulsed Nd:YAG laser beam

Metal thin-film patterning is of technological significance because modern electronic devices commonly require an electrode or metallization pattern. There are many cases where this pattern consists of two different metallic layers in order to improve the mechanical and electrical contact. We here show that double-layered metal thin films evaporated on glass can be directly patterned by a spatially-modulated pulsed Nd-YAG laser beam incident from the backside of the substrate. This method utilizes a pulsed laser-induced thermo-elastic force exerting on the film which plays a role to detach it from the substrate. Since the film is polycrystalline with nano-sized grains, a spatially-modulated thermo-elastic force may enable selective removal of the material by shearing along the weakly-bonded grain boundary regions. Many different combinations of Al, Ag, and Au layers have been investigated and their pattern fidelity and morphology are discussed, along with the simulation results for double-layered nanocystalline films.     

Time-resolved measurements of statistics for a Nd:YAG laser

Time-resolved measurements of the fluctuating intensity of a multimode frequency-doubled Nd:YAG laser have been performed. For various operating conditions the enhancement factors in nonlinear optical processes that use a fluctuating instead of a single-mode laser have been determined up to the sixth order. In the case of reduced flash-lamp excitation and a switched-off laser amplifier, the intensity fluctuations agree with the normalized Gaussian model for the fluctuations of the fundamental frequency, whereas strong deviations are found under usual operating conditions. The frequencydoubled light has in the latter case enhancement factors not so far from values of Gaussian statistics.     

Strategies for formaldehyde detection in flames and engines using a single-mode Nd:YAG/OPO laser system

This paper presents technical developments for the detection of formaldehyde (CH2O) using laser-induced fluorescence. The easily accessible third harmonic of the Nd:YAG laser at 355 nm was used for excitation of formaldehyde. In order to investigate potential background fluorescence, e.g., from large molecules such as polyaromatic hydrocarbons, special attention was paid to investigating the possibility of scanning the wavelength of a single-mode Nd:YAG laser under the gain profile, approximately 3 cm(-1), on and off resonance. Furthermore, a technique for simultaneous detection of formaldehyde and OH using one laser system is presented. The single-mode Nd: YAG laser at 355 nm in combination with an optical parametric oscillator (OPO) laser tuned to 283 nm was used for simultaneous two-dimensional imaging of both species using one charge-coupled device (CCD) detector equipped with a dual filter image separator. The techniques are demonstrated with measurements in laboratory flames and the combined measurements are also demonstrated in an engine.     

Nd:YAG激光辐照碳纤维复合材料的质量烧蚀

通过实验研究了连续Nd:YAG激光辐照下碳纤维环氧树脂复合材料的质量烧蚀规律.结果表明:当激光功率密度大于10 kW/cm2时,材料烧蚀质量与激光辐照能量成正比关系;在同样激光辐照能量下,半径为0.65 mm的激光辐照引起的复合材料的质量烧蚀率比半径为5.5 mm的激光辐照的结果大一倍;激光功率在燃烧阈值附近时,燃烧现象引起质量烧蚀率的波动.     

Investigation of the misalignment sensitivity of a birefringence-compensated two-rod Nd:YAG laser system

A system for the compensation of thermally induced birefringence in laser rods that consists of two identical Nd:YAG laser rods, a telescope to image the principal planes of the rods onto each other and a 90 degrees quartz rotator to change the state of polarization between the rods has been set up, and its sensitivity to transversal and longitudinal misalignment has been investigated experimentally. A theoretical model to describe the increase of depolarization that is due to misalignment has been developed and compared with the experimental results.     

Investigation of diamond-like carbon/silicon heterojunctions deposited by pulsed Nd:YAG laser

Diamond-like carbon (DLC) films were deposited on p-type silicon (Si-100) substrates by using a pulsed Nd:YAG laser for the ablation of a pyrolytic graphite target at a background pressure of 10⁻⁶ Torr. For a fixed distance of 3 cm between the target and substrate, samples of DLC/Si heterojunction were prepared for two different laser wavelengths of 355 nm and 1064 nm. All DLC films showed typical D and G bands in their Raman spectra. DLC films were also deposited on glass substrates for resistivity measurement by four-point probe. The electrical properties for DLC/Si heterojunctions were analyzed current-voltage measurement at room temperature in the dark and also under illumination. The dependencies of the electrical characteristics on the depositing parameters were discussed.     

Laser-diode-pumped Nd:YAG active-mirror laser

We describe a simple design, laser-diode-pumped cw Nd:YAG active-mirror laser and present a thermal analysis of the crystal. A cw output power of 2.4 W and an M(2) beam quality value of less than 1.9 at an incident pumping power of 8.9 W were obtained. From the thermal analysis we predict that the output power can be increased by increasing the pump beam diameter and the pump power at a constant excitation density.