Q.P. Wang

The mechanisms of blue emission from ZnO films deposited on glass substrate by r.f. magnetron sputtering

ZnO thin films have been deposited on Corning 7059 glass at room temperature using r.f. magnetron sputtering. Strong monochromatic blue emission located at 446 nm is observed when excited with 270 nm light. The photoluminescence intensity of the blue emission peak decreases with increasing oxygen pressure and substrate temperature during film deposition and it increases markedly by annealing in vacuum. The experiments proved that the 446 nm emission corresponds to the electron transition from the shallow donor level of oxygen vacancy and zinc interstitials to the valence band.

Photoluminescence of ZnO films excited with light of different wavelength

Abstract Different photoluminescence (PL) spectra were observed for rf sputtered ZnO films when excited with light of different wavelength. When the wavelength of the excitation light was 270xa0nm, a UV emission peak (356xa0nm) and a blue peak (446xa0nm) were generated for the films on sapphire, silicon and quartz substrates. For the films on glass substrates only the 446xa0nm blue emission appeared. With increasing the wavelength of the excitation light up to 300 and 320xa0nm, the UV emission disappeared for films on various substrates and the wavelength of the PL peaks increased up to 480 and 510xa0nm, respectively. When the wavelength of the excitation light increased to 340–395xa0nm, the PL spectrum became a wide band which was consistent with three emission peaks.

The blue photoluminescence emitted from ZnO films deposited on glass substrate by rf magnetron sputtering

ZnO films have been deposited on Corning 7059 glass substrates using rf magnetron sputtering. Strong monochromatic blue emission located at 446 nm is observed when excited with 270 nm light at room temperature (RT). The photoluminescence (PL) intensity decreases with increasing oxygen pressure during film deposition and it increases pronouncedly by annealing in vacuum. The blue emission may correspond to the electron transition from the shallow level of oxygen vacancies to the valence band.

Photoluminescence of ZnO films prepared by r.f. sputtering on different substrates

Polycrystalline ZnO films with good orientation were deposited on sapphire, quartz, Si and 7059 glass substrates by r.f. magnetron sputtering. A strong UV photoluminescence (PL) peak (located at 356 nm) and a weak blue emission peak (located at 446 nm) were observed at room temperature (RT) for the films deposited on sapphire, quartz and Si substrates when excited with 270 nm light. For the films prepared on Corning 7059 glass, only a strong 446 nm blue emission peak was found, and the PL intensity decreased with increasing oxygen pressure during films deposition. The intensity of the UV emission increased 7 and 14 times, respectively, for the films on sapphire and quartz substrates after high temperature annealing in vacuum. The UV emission originates from the inter-band transition of electrons and the blue emission is due to transition of electrons from the shallow donor level of the oxygen vacancies to the valence band.

High power and highly efficient Nd:YAG laser emitting at 1123 nm

A diode-end-pumped continuous-wave (CW) Nd:YAG laser emitting at 1123 nm is realized efficiently in a 25-mm-long cavity. A composite Nd:YAG (cNd:YAG) crystal is selected as the gain medium. With an incident diode power of 26.1 W, an output power of up to 9.3 W is obtained, corresponding to an optical-to-optical conversion efficiency of 35.6%. The laser performances at 1123 nm are compared between composite Nd:YAG and common Nd:YAG crystals. The results show that composite Nd:YAG is a better choice for 1123-nm laser generations.

A fiber bragg grating acceleration sensor interrogated by a DFB laser diode

A fiber Bragg grating (FBG) acceleration sensor interrogated by a DFB laser diode is demonstrated; the sensor is fabricated by packaging a FBG on to a cantilever; the interrogation scheme takes advantage of the intensity modulation of the narrow spectral bandwidth light of a distributed feedback laser diode, when the reflection spectrum curve of a FBG moves due to the strain which is applied on the sensor. The sensor’s response to the frequency and acceleration is measured by the experiment, and the factors which have an impact on the sensor’s sensitivity are also discussed.

Impulse transfer to the surface of aluminum and copper from a pulsed Nd: YAG laser

Impulse coupling coefficients in air from 1.06 μm, 10 ns, Nd: YAG pulsed-laser radiation to aluminum and copper targets are measured using the ballistic pendulum method in the laser power-density range from 2.0×108 W/cm2 to 4.0×109 W/cm2. A modified laser-supported detonation (LSD) wave and cylindrical blast wave theory incorporating the vaporization model is proposed to calculate the impulse coupling coefficients. It is found that the theoretical results obtained with the modified model agree well with the experimental data.

Laser ablation of Si, Ge, ZrO2 and Cu in air

Si, Ge, ZrO2 and Cu were irradiated by air by 1.06 mu m 10 ns laser pulses with a high intensity of 6.4*109 W cm-2. Detailed scanning electron microscopy (SEM) and ablation crater profile measurements were made. The results indicated that the ablation rates of these materials under intense pulsed laser irradiation are quite high. The refractory oxide ZrO2 has the highest material removal rate. Evidence of liquid material flushed out of the ablation craters was observed for all the materials studied with the exception of Cu. Gas dynamic velocities of transient thermal vaporization were calculated using self-similar solutions of the gas dynamic equations. Using these parameters, material removal rates were calculated and the results compared with the experimentally measured values. Possible ablation mechanisms of these materials under the irradiation conditions used in the present work were discussed.

Laser characteristics of a new crystal Nd:Sr5(PO4)3F at 1.059 μm

Abstract The absorption spectrum of a new crystal Nd : Sr 5 (PO 4 ) 3 F or Nd : S-FAP, was measured, its two strong absorption peaks and broad effective absorption band showed that Nd : S-FAP can be appropriately pumped at 575 nm and 805.4 nm as well as with a xenon flashlamp. By using a tunable dye-laser (570.0~600.0 nm), a laser-diode (805 nm) and a xenon flash lamp as pump sources, respectively, the performance of a low threshold and high efficiency Nd:S-FAP laser at 1.059 (μm) (including pulse run, cw run, free-run and Q-switch run) has been demonstrated. The laser characteristics, such as the emission spectrum, the output energy, the output power, the pulse width, etc, were measured. In addition, the prospect of a Nd:S-FAP crystal for low-threshold high-efficiency miniature lasers is discussed.

The control effect of surrounding rock with different combinations of the bolt anchoring lengths and pre-tightening forces in underground engineering

The anchoring length and the pre-tightening force are the two main factors influencing the control effect of surrounding rock in bolt support. To study the influences, a theoretical analysis is made on the stress distribution law of the surrounding rock with different anchoring lengths and pre-tightening forces; a high pre-tightening force quantitative exerting device for high strength bolts is developed with a function of automatic anchor retreat; and four field test plans are designed and carried out with different combinations of bolt anchoring lengths and pre-tightening forces to comparatively analyze their control effect of surrounding rock. The theoretical analysis shows that as the bolt anchoring length is constant, the effective compressive stress area in the surrounding rock of the bolt non-anchoring section increases along with the increase of the pre-tightening force; a certain length of non-anchoring section is helpful to play the bolt support function, but the anchoring length should not be too short. The field test shows that increasing pre-tightening force is an effective way to improve the control effect of surrounding rock; under certain conditions, an appropriate reduction of the bolt anchoring length will not significantly weaken the control effect of surrounding rock. That verifies the theoretical analysis. The study provides some useful guidance for the selection of the parameters of the bolt support in underground engineering.