Fourth Harmonics Of Nd Research Articles

Nitriding of 4H-SiC by irradiation of fourth harmonics of Nd:YAG laser pulses in liquid nitrogen

This study presents surface nitriding of 4H-SiC by the irradiation of the fourth harmonics of Nd:YAG laser pulses in liquid nitrogen. A nitride layer with a depth of 1 μm is formed on the irradiated area. The irradiated area has a bumpy morphology. On the other hand, we also find a nitride layer with a smooth surface morphology in the outside of the irradiated area. The concentration of nitrogen is dependent on the laser fluence, and is 1–5%. The diffusion coefficient of nitrogen, which is deduced from the depth profile of the nitrogen number density, is much greater than the diffusion coefficient in solid SiC, suggesting the transport of nitrogen in melted SiC. Considering the fact that SiC does not have a melted state at the atmospheric pressure, it is revealed by the present work that the melted SiC is realized transiently with the help of the high pressure driven by the laser irradiation.

Magnetic field influence on the intensity of ZnO random lasing and exciton luminescence

The effect of the magnetic field on the exciton radiation of ZnO films formed by randomly packed nanorods and covered with Ag nanoparticles has been discovered and studied at room temperature. Photoexcitation was performed by third and fourth harmonics of Nd:YAG laser. The radiation of the investigated samples consisted of exciton luminescence and random lasing in the near UV range. Several percent enhancement of the exciton radiation intensity was observed at some areas of the films subjected to the magnetic field H ∼ 1 T. The enhancement depends slightly on the excitation level. At the same time, in some other areas of the same films, the effect was negligible or absent. It is supposed that the observed effect is related to magnetoexcitons, which are possibly formed due to increasing of the exciton momentum nearby the Ag nanoparticles. The probability of magnetoexciton recombination increases significantly even in a weak magnetic field due to strong stretching of its wave function.

Wavelength dependence on the formation of SiO2 films by ultraviolet-laser-induced photochemical deposition using silicone rubber

We have proposed a novel method which permits to grow silicon dioxide (SiO2) films on various substrates at room temperature using silicone rubber. In the method, two F2 laser (157 nm) beams are used. One is used for generation of source gases from the silicone rubber (1st laser). Another is used for illumination of a substrate to deposit the films (2nd laser). We study on characteristics of the deposited films using laser beams which have longer wavelengths than the F2 laser beam. When a fourth harmonics of Nd:YAG laser (266 nm) is used as the 1st laser, SiO2 films with no carbon contaminants are grown as same as the case that an F2 laser is used. The films are consisted of granular structures and the grain size become small as the laser fluence of 2nd laser beam increase. When an ArF laser (193 nm) is used as the 2nd laser, the deposition rate of the films is very low and the films have carbon contaminants. It shows that the 2nd laser beam plays an important role not only in the growth of the films but also in the prevention of carbon contaminants being mixed into the film.

Influence of argon gas pressure on the crystallinity of α-SiC epitaxial films fabricated by Nd:YAG pulsed-laser deposition

Abstract Fabrication of SiC crystalline films at low temperatures is examined by pulsed-laser deposition (PLD), since it is important for SiC device technology. The growth temperature of α-SiC hetero-epitaxial films is considerably reduced to 820 °C by fabricating under argon (Ar) atmosphere using a very high fluence of the fourth harmonics of Nd:YAG laser. Influence of the Ar gas pressure on the crystallinity of α-SiC film is studied with X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED). It is found that the optimal pressure is critical and is ∼50 Pa for the following experimental conditions: laser fluence F=20 J/cm2/pulse, distance between a substrate and target dTS=20 mm, and substrate temperature TS=820 °C. Under lower pressure than 40 Pa, the film becomes amorphous. On the other hands, higher pressure than 50 Pa results in poly-crystalline films. These results are plausibly explained by the high kinetic energy of ejected species by laser ablation with high fluence and their collision with the atmospheric Ar gas atoms.

Bi 2Sr 2Ca 1Cu 2O X film prepared using 266 nm YAG laser

Epitaxial growth of Bi 2Sr 2Ca 1Cu 2O X (Bi-2212) was achieved on MgO(1 0 0) substrate using the fourth harmonics of Nd:YAG pulsed laser. The repetition rates of both 10 and 2 Hz were used to deposit Bi-2212. In order to change the repetition rate without any optical adjustment, another function generator was employed to modulate only the Q-switch (slower Q-switched). The axis of plume was strongly affected by the beam incidence angle of YAG. By adjusting the beam incidence angle, epitaxial growth was verified for Bi-2212 deposited at the repetition rate of 2 Hz.

超短パルスレーザによる材料加工現象 ４ ピコ秒パルスレーザアブレーションにおける微粒子の飛散シミュレーション

Ablation phenomena when the fourth harmonics of Nd: YAG laser is irradiated to an aluminum substrate during picoseconds were simulated using the modified molecule dynamics method that Ohmura and Fukumoto have developed. Scattering velocity of ablation particles were displayed by vectors, and both molten pool and slip planes in the material were visualized. At the same time, the angle, size and velocity distributions of the scattering particles, both potential and kinetic energies per ablation atom, and ablation energy were examined quantitatively. Authors have already clarified that there are two types in ablation form under constant laser fluence. One is explosive ablation and the other is relatively calm ablation. The former occurs when pulse width is extremely short. The simulation results showed that the angle and size of scattering particles depend on the ablation forms. These differences appear because ablation energy in the explosive process is much larger than that in the relatively calm ablation, that is, kinetic energy per ablation atom becomes very large when the pulse width is extremely short. Velocity of particles also depends on the ablation forms, but the tendency is comparatively weak. Scattering angle in both ablation forms has almost a normal distribution, but the standard deviation in the explosive ablation is much smaller.

超短パルスレーザアブレーション現象の分子動力学解析

Laser ablation phenomena of aluminum with the fourth harmonics of Nd:YAG laser is analyzed using the modified molecular dynamics (MD), which has been developed previously by Ohmura and Fukumoto. In the modified MD method, the MD calculation for metal is carried out compensating the heat conduction by free electrons at each time step. Main conclusions are summarized as follows: (1) When the fluence is constant, there is an optimal irradiance of the laser pulse to make the number of evaporated atoms be the maximum. The ratio of evaporation energy to the laser energy absorbed in the material becomes the maximum at this optimal irradiance. (2) There are two types in laser ablation process. One is explosive evaporation which occurs when pulse width is extremely short, and the other is relatively calm evaporation which occurs when pulse width is comparatively long. In the former process, a comparatively large particles scatter, and in the latter process, the size of scattering particles is relatively small. (3) For the ultrafast laser irradiation, the evaporation threshold fluence of aluminum is about 20 mJ/cm2.

Preparation of thin epitaxial YBCO films by ablation using fourth harmonics of Nd:YAG laser

We have grown high-quality YBCO epitaxial films with c-axis orientation on MgO(100) and SrTiO 3(100) crystalline substrates by pulsed laser deposition method using the fourth harmonics of Nd:YAG laser. The deposition conditions are followings: substrate temperature T s=760°C, oxygen pressure P o=50Pa, laser frequency v=1Hz, and laser energy density σ=1J/cm 2/pulse, which differ slightly from those of excimer laser. Those conditions originate from the feature of YAG laser which has a smaller pulse width and a higher peak-energy than that of excimer laser.