Thermal relaxation behavior of residual stress in laser hardened 17-4PH steel after shot peening treatment

In order to investigate the residual stress relaxations of shot peened layer, isothermal annealing treatments were carried out on tempered and laser hardened 17-4PH steel after shot peening with different temperatures from 300 °C to 600 °C. The results showed that the residual stresses were relaxed in the whole deformation layer especially under higher temperature. The maximum rates of stress relaxation took place at the initial stage of annealing process in all conditions. The relaxation process during isothermal annealing could be described by Zener-Wert-Avrami function. The thermal stability of residual stress in tempered 17-4PH was higher than that in laser hardened 17-4PH as well as that in α-iron, which was due to the pinning effects of ?-Cu precipitates on the dislocation movement. As massive ?-Cu precipitates formed in the temperature about 480 °C, the activation enthalpies for stress relaxation in laser hardened 17-4PH were the same as that in tempered 17-4PH in the conditions of isothermal annealing temperatures of 500 °C and 600 °C.     

Influence of substrate temperature and post-treatment on the properties of ZnO:Al thin films prepared by pulsed laser deposition

Highly transparent conductive Al₂O₃ doped zinc oxide (AZO) thin films have been deposited on the glass substrate by pulsed laser deposition technique. The effects of substrate temperature and post-deposition annealing treatment on structural, electrical and optical properties of AZO thin films were investigated. The experimental results show that the electrical resistivity of films deposited at 240 °C is 6.1 × 10⁻⁴ Ω cm, which can be further reduced to as low as 4.7 × 10⁻⁴ Ω cm by post-deposition annealing at 400 °C for 2 h in argon. The average transmission of AZO films in the visible range is 90%. The optical direct band gap of films was dependent on the substrate temperature and the annealing treatment in argon. The optical direct band gap value of AZO films increased with increasing annealing temperature.     

Fabrication and vacuum annealing of transparent conductive Ga-doped Zn0.9Mg0.1O thin films prepared by pulsed laser deposition technique

In this study, highly transparent conductive Ga-doped Zn_0.9Mg_0.1O (ZMO:Ga) thin films have been deposited on glass substrates by pulsed laser deposition (PLD) technique. The effects of substrate temperature and post-deposition vacuum annealing on structural, electrical and optical properties of ZMO:Ga thin films were investigated. The properties of the films have been characterized through Hall effect, double beam spectrophotometer and X-ray diffraction. The experimental results show that the electrical resistivity of film deposited at 200 °C is 8.12 × 10⁻⁴ Ω cm, and can be further decreased to 4.74 × 10⁻⁴ Ω cm with post-deposition annealing at 400 °C for 2 h under 3 × 10⁻³ Pa. In the meantime, its band gap energy can be increased to 3.90 eV from 3.83 eV. The annealing process leads to improvement of (0 0 2) orientation, wider band gap, increased carrier concentration and blue-shift of absorption edge in the transmission spectra of ZMO:Ga thin films.     

Thermal stability of titanium nitride coatings prepared by the mixing technology with laser and plasma

Titanium samples were treated by the mixing technology with laser and plasma (LPN) using different laser power densities. These nitrided samples were then annealed at 473 K, 673 K, 873 K, and 1073 K for 2 h in vacuum, respectively. The samples before and after annealing were characterized at room temperature and compared in terms of microstructure. X-ray diffraction and cross-sectional optical microscopy studies showed that the layer structure of the titanium nitride coating is preserved after annealing at 1073 K when the coating is formed using a laser power density of 8.0 × 10⁵ W/cm². Therefore, titanium nitride coatings produced by LPN demonstrate excellent thermal stability and are potential candidates for high temperature tribological applications.     

Analysis of the spectral structure of CuBr laser lines

The spectral structure of spontaneous emission of copper atom at 510.6 nm and 578.2 nm was calculated considering the hyperfine structure of energy levels and the isotope shift. The spectral structure of the 510.6 nm and 578.2 nm laser lines was measured in a sealed-off CuBr laser tube with periodic refreshment of the neon buffer gas under different work temperature and excited voltage. The spectral structure of the spontaneous emission of copper atom was found to have similar outline with its laser lines. The spectrum of the 510.6 nm laser line maintains similar outline with three peaks at various discharging parameters while the spectrum of the 578.2 nm laser line is strongly dependent on the reservoir temperature and the discharge voltage.     

Characterization of boron carbon nitride film modified by excimer laser annealing

Boron carbon nitride (BCN) shows promise as a field emitter material because of its mechanical hardness, chemical inertness, and low electron affinity. This study investigated the modification of a BCN film with an amorphous area using KrF excimer laser (wavelength: 248 nm, photon energy: 5.0 eV) annealing without substrate heating. This achieved significant variation in characteristics, such as an increase in bandgap energy and decrease in electron affinity. Laser annealing reduced electron affinity from 0.7 to 0.3 eV. The results indicate that the modification of the BCN film by KrF excimer laser annealing achieves characteristics similar to hexagonal BN (h-BN) film without losing the desirable properties of the BCN film, such as physical stability.     

Structural characterization of AlN films synthesized by pulsed laser deposition

We obtained AlN thin films by pulsed laser deposition (PLD) from a polycrystalline AlN target using a pulsed KrF* excimer laser source (248 nm, 25 ns, intensity of ∼4 × 10⁸ W/cm², repetition rate 3 Hz, 10 J/cm² laser fluence). The target-Si substrate distance was 5 cm. Films were grown either in vacuum (10⁻⁴ Pa residual pressure) or in nitrogen at a dynamic pressure of 0.1 and 10 Pa, using a total of 20,000 subsequent pulses. The films structure was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectral ellipsometry (SE). Our TEM and XRD studies showed a strong dependence of the film structure on the nitrogen content in the ambient gas. The films deposited in vacuum exhibited a high quality polycrystalline structure with a hexagonal phase. The crystallite growth proceeds along the c-axis, perpendicular to the substrate surface, resulting in a columnar and strongly textured structure. The films grown at low nitrogen pressure (0.1 Pa) were amorphous as seen by TEM and XRD, but SE data analysis revealed ∼1.7 vol.% crystallites embedded in the amorphous AlN matrix. Increasing the nitrogen pressure to 10 Pa promotes the formation of cubic (≤10 nm) crystallites as seen by TEM but their density was still low to be detected by XRD. SE data analysis confirmed the results obtained from the TEM and XRD observations.     

Mid-infrared,wide-tunable,continuous-wave Nd:YVO4/PPMgLN intracavity optical parametric oscillator

We obtain a continuous-wave (CW) Nd:YVO₄/PPMgLN intracavity singly resonant optical parametric oscillator (ISRO). The threshold value of the CW-ISRO system is only 2.8 W at 808 nm. When the pump power is 5.5 W, an idle laser output power of 410 mW, and a signal laser output power of 345 mW have been achieved. By changing the grating periods of the domain structure on the PPMgLN wafer, we enable a wide-tunable mid-infrared spectrum of 2.95–4.16 μm and near-infrared spectrum of 1.43–1.66 μm.     

Thermally tunable microfiber knot resonator based erbium-doped fiber laser

A compact and tunable erbium-doped fiber laser is demonstrated using a highly doped fiber and a microfiber knot resonator (MKR) structure which is laid on the surface of a small peltier. The MKR functions as both a reflector and a tunable filter where tunability is achieved by varying the temperature of the resonator by heating the peltier. A stable laser output is achieved at the 1533 nm region with an optical signal to noise ratio (OSNR) of 27 dB using a 65 mW of 980 nm pump power. The operating wavelength of the laser can be tuned from 1532.60 nm to 1533.49 nm as the temperature is increased from the room temperature of 24 to 90 °C. It is observed that the operating wavelength shifts to a longer wavelength as the temperature increases with an efficiency of 12.4 pm/°C. This is due to the thermally induced optical phase shift attributable to the changes in effective refractive index and optical path length of the MKR loop.     

Formation of periodic structures by the space-selective precipitation of Ge nanoparticles in channel waveguides

Thermally stabilized channel waveguides with Bragg gratings were fabricated by the space-selective precipitation technique of crystalline Ge nanoparticles using KrF excimer laser irradiation. The periodic structures consisting of Ge nanoparticles were formed in Ge-B-SiO₂ thin glass films after exposure to an interference pattern of the laser followed by annealing at 600 °C. The channel waveguides with the periodic structures were fabricated by the cladding of the patterned Cr layers on the films. The diffraction peak for the TE-like mode of 11.8 dB depth was observed clearly at a wavelength of 1526.4 nm, indicating that the periodic structure also served as the optical band-pass filter in optical communication wavelength. The spectral shape, diffraction efficiency, and diffraction wavelength remained unchanged even after annealing at 400 °C. Furthermore, a low temperature dependence of the diffraction wavelength - as low as 8.1 pm/°C - was achieved. The diffraction efficiency was further enhanced after subsequent annealing at 600 °C. The space-selective precipitation technique is expected to be useful for the fabrication of highly reliable optical filters or durable sensing devices operating at high temperature.     

Electrical, structural, and optical properties of ITO thin films prepared at room temperature by pulsed laser deposition

Indium tin oxide (ITO) thin films were prepared by pulsed laser deposition (PLD) on glass substrate at room temperature. Structural, optical, and electrical properties of these films were analyzed in order to investigate its dependence on oxygen pressure, and rapid thermal annealing (RTA) temperature. High quality ITO films with a low resistivity of 3.3 × 10⁻⁴ Ω cm and a transparency above 90% were able to be formed at an oxygen pressure of 2.0 Pa and an RTA temperature of 400 °C. A four-point probe method, X-ray diffraction (XRD), atomic force microscopy (AFM), and UV-NIR grating spectrometer are used to investigate the properties of ITO films.     

Femtosecond pulsed laser deposition of diamond-like carbon films: The effect of double laser pulses

The bonding structure of carbon films prepared by pulsed laser deposition is determined by the plasma properties especially the change of the kinetic energy. Using double laser pulses the ablation process and the characteristics of the generated plasma can be controlled by the setting of the delay between the pulses. In our experiments, amorphous carbon films have been deposited in vacuum onto Si substrates by double pulses from a Ti:sapphire laser (180 fs, λ = 800 nm, at 1 kHz) and a KrF laser system (500 fs, λ = 248 nm, at 5 Hz). The intensities have been varied in the range of 3.4 × 10¹² to 2 × 10¹³ W/cm². The morphology and the main properties of the thin layers were investigated as a function of the time delay between the two ablating pulses (0-116.8 ps) and as a function of the irradiated area on the target surface. Atomic force microscopy, spectroscopic ellipsometry and Raman-spectroscopy were used to characterize the films. It was demonstrated that the change of the delay and the spot size results in the modification of the thickness distribution of the layers, and the carbon sp²/sp³ bonding ratio.     

Competition between green and infrared emission in Er:YLiF4 upconversion lasers

The competition between two laser transitions in Er:YLiF₄ (⁴S_3/2 → ⁴I_15/2 at 551 nm and ⁴S_3/2 → ⁴I_13/2 at 850 nm) is studied using a model based on rate equations. The laser emission is pumped by upconversion at 795 nm; for comparison, we also discuss upconversion pumping by another mechanism, at 970 nm. The conditions that favor laser emission in various regimes on these two transitions are found.     

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.     

1097 nm Nd:YVO4 self-Raman laser

An acousto-optically Q-switched self-Raman laser emitting at 1097 nm is demonstrated with a c-cut Nd:YVO₄ crystal, using a fiber-coupled 880 nm diode laser as the pumping source. Raman laser performances in concave-plane and plane-plane oscillating cavities are studied and compared. With an absorbed diode power of 12.4 W and a pulse repetition rate of 50 kHz, the highest output power of 1.45 W is obtained from the plane-plane cavity, corresponding to an optical-to-optical conversion efficiency of 11.7%.     

Structural modification of laser annealed a-Si1−xCx:H films

Hydrogenated amorphous silicon carbon films, with relatively low hydrogen content and carbon fraction x, C/(C + Si), ranging from 0.20 to 0.57 have been deposited by RF-plasma enhanced chemical vapor deposition (PECVD) for excimer laser annealing experiments. After the laser treatments all the films show structural modifications. It has been obtained that with increasing x the crystallinity degree of the Si phase decreases, while that of the SiC phase increases and becomes predominant for x = 0.39. In the overstoichiometric samples only the c-SiC phase has been observed. In all the treated samples 3C-SiC crystallites have been detected.     

Reactive pulsed laser deposition of gold nitride thin films

We report on the growth and characterization of gold nitride thin films on Si 〈1 0 0〉 substrates at room temperature by reactive pulsed laser ablation. A pure (99.95%) Au target was ablated with KrF excimer laser pulses in nitrogen containing atmosphere (N₂ or NH₃). The gas ambient pressure was varied in the range 0.1-100 Pa. The morphology of the films was studied by using optical, scanning electron and atomic force microscopy, evidencing compact films with RMS roughness in the range 3.6-35.1 nm, depending on the deposition pressure. Rutherford backscattering spectrometry and energy dispersion spectroscopy (EDS) were used to detect the nitrogen concentration into the films. The EDS nitrogen peak does not decrease in intensity after 2 h annealing at 250 °C. Film resistivity was measured using a four-point probe and resulted in the (4-20) × 10⁻⁸ Ω m range, depending on the ambient pressure, to be compared with the value 2.6 × 10⁻⁸ Ω m of a pure gold film. Indentation and scratch measurements gave microhardness values of 2-3 GPa and the Young's modulus close to 100 GPa. X-ray photoemission spectra clearly showed the N 1s peak around 400 eV and displaced with respect to N₂ phase. All these measurements point to the formation of the gold nitride phase.     

Properties of Zn3N2-doped ZnO films deposited by pulsed laser deposition

The optical properties of N-doped ZnO films grown by pulsed laser deposition are examined for which zinc nitride is used as the source of nitrogen. The motivation for this study is to determine if nitrogen-related acceptor state formation can be achieved in ZnO films using Zn₃N₂ doping in the ablation target. The films were deposited in oxygen or nitrogen on c-plane sapphire. Photoluminescence measurements at 20 K reveal a 3.31 eV acceptor-bound exciton emission due to nitrogen substitution on the oxygen site, donor-acceptor pair emission at 3.23 ± 1 eV and free electron-acceptor at 3.27 eV. The binding energy of the N-related acceptor is estimated to be in the range of 170-15 meV. While the as-deposited films were n-type, thermal annealing in oxygen yielded insulating behavior, consistent with compensating acceptor states.     

Effects of rapid thermal annealing on the structural and electrical properties of Na-doped ZnMgO ?lms

Rapid thermal annealing (RTA) is a general approach to improve the crystallinity of thin solid films. In this study, we investigated the effects of RTA on the structural and electrical properties of Na-doped ZnMgO ?lms grown by pulsed laser deposition. X-ray diffraction (XRD) results showed that the crystallinity of the Na-doped ZnMgO ?lms was improved with RTA at 400-700 °C, and the grain size became larger as the annealing temperature increased. Moreover, room-temperature photoluminescence (PL) measurements demonstrated decent optical quality of the as-deposited and annealed Na-doped ZnMgO ?lms. Hall-effect measurements showed that the hole concentration increased from 4.9 × 10¹⁴ to 6.6 × 10¹⁵ cm⁻³ to 1.9 × 10¹⁷ to 8.3 × 10¹⁷ cm⁻³ while the resistivity and the Hall mobility decreased after the RTA treatments. The conduction type of the films converted from p to n when the annealing temperature is higher than 800 °C. Therefore a wide temperature window to obtain reasonable p-type Na-doped ZnMgO films by RTA is achieved. It is important because RTA is generally needed to obtain p-type Ohmic contact in the fabrication processes of light-emitting diodes (LEDs).     

Theoretical study of the electro-optic effect of aperiodically poled lithium niobate in a Q-switched dual-wavelength laser

The electro-optic effect of aperiodically poled lithium niobate (APLN) has been theoretically investigated and proposed to use as a Q-switch in a simultaneous dual-wavelength laser. Our analysis shows that the polarization planes of the z-polarized (or y-polarized) dual-wavelength beams can be simultaneously rotated by 90° through a well-constructed APLN with an external electric field applied along the y-axis, which enables Q-switch function in a dual-wavelength laser cavity. Using a Nd:YVO₄ laser operating at 1.0643 μm and 1.3419 μm as an example, we present a design method of APLN by using the so-called simulated annealing algorithm. The influence of the domain errors in fabricating an APLN device is also studied. The results show that the device is not susceptible to the fabrication errors.