导模法生长晶体研究进展

导模法是一种极具应用潜力的晶体生长方法,具有生长速度快,加工成本低的优点,广泛用于生长各种形状的晶体。对导模法的原理、特点和发展历史进行了简单介绍,着重论述了导模法在生长有形蓝宝石和硅晶体中的发展和应用,对目前导模法生长晶体过程中存在的问题做了简单的介绍。

Judd-Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

This paper reports that the TM3+:Lu2SiO5 (Tm:LSO) crystal is grown by Czochralski technique. The room-temperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Omega(2)=9.3155 x 10(-20) cm(2), Omega(4)=8.4103 x 10(-20) cm(2), Omega(6)=1.5908 x 10(-20) cm(2), the fluorescence lifetime is calculated to be 2.03 ms for F-3(4) -> H-3(6) transition, and the integrated emission cross section is 5.81 x 10(-18) cm(2). Room-temperature laser action near 2 mu m under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuous-wave maximum output power of 0.67 W. The emission wavelengths of Tm:LSO laser are centred around 2.06 mu m with spectral bandwidth of similar to 13.6 nm.

Holmium laser in-band pumped by a thulium laser in the same host of YAlO3

We report on the room-temperature continuous-wave (CW) operation of a Ho:YAlO3 laser that is resonantly end pumped at 1.94 mu m by a diode-pumped thulium-doped laser in the same host. Through the use of a 1 at % Ho3+-doped 20-mm-long YAlO3 crystal (b cut), the Ho:YAlO3 laser generated 1 W of linearly polarized (E//c) output at 2118 nm and 0.55 W of E//a output at 2128.5 nm for an incident pump power of 5 W, with an output coupler transmission of 14 and 3%, respectively. An optical-to-optical conversion efficiency of 20% and a slope efficiency of 33% were achieved at 2118 nm corresponding to an incident pump power.

Tm:Y_2SiO_5晶体的生长和光谱性质研究

采用中频感应提拉法生长了高质量的Tm:Y2SiO5(Tm:YSO)晶体,测定了晶体的晶格常数和分凝系数.运用劳厄照相法确定了单斜晶系Tm:YSO晶体的三个偏振轴〈010〉,D1和D2,在室温下测量了三个偏振轴方向的吸收光谱、荧光光谱和荧光寿命,计算了晶体吸收峰的吸收线宽和吸收截面.研究发现,相对于其他两个偏振轴方向,D1方向在790 nm处出现较强的吸收峰,同时在2μm附近出现了一定强度的发射峰,D1方向的吸收截面较大,荧光寿命较长.Tm:YSO晶体适用于AlGaAs二极管抽运固体激光器,在2μm波段固体激光器的应用上将有很大的发展潜力.

Continuous-wave and Q-switched operation of a resonantly pumped Ho:YAlO3 laser

We demonstrated continuous-wave ( CW) and Q-switched operation of a room-temperature Ho: YAlO3 laser that is resonantly end-pumped by a diode-pumped Tm: YLF laser at 1.91 mu m. The CW Ho: YAlO3 laser generated 5.5 W of linearly polarized (E parallel to c) output at 2118 nm with beam quality factor of M-2 approximate to 1.1 for an incident pump power of 13.8 W, corresponding to optical-to-optical conversion efficiency of 40%. Up to 1-mJ energy per pulse at pulse repetition frequency (PRF) of 5 kHz, and the maximum average power of 5.3-W with FWHM pulse duration of 30.5 ns at 20 kHz were achieved in Q-switched mode. (C) 2008 Optical Society of America.

沉积参量及时效时间对SiO2薄膜残余应力的影响

SiO2薄膜由电子束蒸发方法沉积而成。用GPI数字波面光学干涉仪测量了不同沉积条件下玻璃基底镀膜前后曲率半径的变化，并确定了SiO2薄膜中的残余应力。在其他条件相同的情况下，当沉积温度由190℃升高到350℃时，SiO2薄膜中的压应力由一156MPa增大为-289MPa。氧分压由3．0×10^-3Pa升高到13．0×10^-3Pa时，SiO2薄膜中的应力由-223．5MPa变为20．4MPa。通过对薄膜折射率的测量，发现薄膜的堆积密度随沉积条件的改变也发生了规律性的变化。应力的变化主要是由于沉积时蒸发粒子

Stress, absorptance and laser-induced damage threshold properties of 355-nm HR coatings

A number of 355-nm Al2O3/MgF2 high-reflectance (HR) coatings were prepared by electron-beam evaporation. The influences of the number of coating layers and deposition temperature on the 355-nm Al2O3/MgF2 HR coatings were investigated. The stress was measured by viewing the substrate deformation before and after coating deposition using an optical interferometer. The laser-induced damage threshold (LIDT) of the samples was measured by a 355-nm Nd:YAG laser with a pulse width of 8 ns. Transmittance and reflectance of the samples were measured by a Lambda 900 spectrometer. It was found that absorptance was the main reason to result in a low LIDT of 355-nm Al2O3/MgF2 HR coatings. The stress in Al2O3/MgF2 HR coatings played an unimportant role in the LIDT, although MgF2 is known to have high tensile stress.

Overcoat dependence of laser-induced damage threshold of 355 nm HR coatings

A series of HR coatings, with and without overcoat, were prepared by electron beam evaporation using the same deposition process. The laser-induced damage threshold (LIDT) was measured by a 355 nm Nd:YAG laser with a pulse width of 8 ns. Damage morphologies of samples were observed by Leica-DMRXE Microscope. The stress was measured by viewing the substrate deformation before and after coatings deposition using an optical interferometer. Reflectance of the samples was measured by Lambda 900 Spectrometer. The theoretical results of electric field distributions of the samples were calculate by thin film design software (TFCalc). It was found that SiO2 overcoat had improved the LIDT greatly, while MgF2 overcoat had little effect on the LIDT because of its high stress in the HR coatings. The damage morphologies were different among HR coatings with and without overcoats. (c) 2005 Elsevier B.V. All rights reserved.

Investigation on the properties of high reflective mirror prepared by ion-beam sputtering

The single-sided and dual-sided high reflective mirrors were deposited with ion-beam sputtering (IBS). When the incident light entered with 45 degrees, the reflectance of p-polarized light at 1064 nm exceeded 99.5%. Spectrum was gained by spectrometer and weak absorption of coatings was measured by surface thermal lensing (STL) technique. Laser-induced damage threshold (LIDT) was determined and the damage morphology was observed with Lecia-DMRXE microscope simultaneously. The profile of coatings was measured with Mark III-GPI digital interferometer. It was found that the reflectivity of mirror exceeded 99.9% and its absorption was as low as 14 ppm. The reflective bandwidth of the dual-sided sample was about 43 nm wider than that of single-sided sample, and its LIDT was as high as 28 J/cm2, which was 5 J/cm2 higher than that of single-sided sample. Moreover, the profile of dual-sided sample was better than that of substrate without coatings.

沉积温度对HfO2薄膜残余应力的影响

用电子柬蒸发方法制备了HfO2薄膜，根据镀膜前后基片曲率半径的变化，用Stoney公式计算了薄膜应力。讨论了沉积温度对薄膜残余应力的影响。结果发现，HfO2薄膜的残余应力均为张应力，应力值随沉积温度的升高先增大后减小，在280℃左右出现极大值。对样品进行了XRD测试，从微观结构上对实验结果进行了分析，发现微结构演变引起的内应力变化是引起薄膜残余应力改变的主要因素，HfO2薄膜在所选沉积温度60～350℃内出现了晶态转变，堆积密度随温度升高而增大。

Influence of substrate temperature on properties of MgF2 coatings

Thermal boat evaporation was employed to prepare MgF2 single-layer coatings upon both JGS1 and UBK7 substrates at different substrate temperatures. Microstructure, transmittance and residual stress of these coatings were measured by X-ray diffraction, spectrophotometer, and optical interferometer, respectively. Measurement of laser induced damage threshold (LIDT) of the samples was performed at 355 nm, 8 ns pulses. The results showed that high substrate temperature was beneficial to crystallization of the film. Above 244 degrees C, the refractive index increased gradually with the substrate temperature rising. Whereas, it was exceptional at 210 degrees C that the refractive index was higher than those deposited at 244 and 277 degrees C. The tensile residual stresses were exhibited in all MgF2 films, but not well correlated with the substrate temperature. In addition, the stresses were comparatively smaller upon JGS1 substrates. A tendency could be seen that the LIDTs reached the highest values at about 244 degrees C, and the films upon JGS1 had higher LIDTs than those upon UBK7 substrates at the same temperature. Meanwhile, the damage morphologies showed that the laser damage of the coating resulted from an absorbing center at the film-substrate interface. The features of the damages were displayed by an absorbing center dominated model. Furthermore, the reason of the difference in LIDT values was discussed in detail. (C) 2007 Elsevier B.V. All rights reserved.

Influences of oxygen partial pressure on structure and related properties of ZrO2 thin films prepared by electron beam evaporation deposition

ZrO2 thin films were prepared by electron beam evaporation at different oxygen partial pressures. The influences of oxygen partial pressure on structure and related properties of ZrO2 thin films were studied. Transmittance, thermal absorption, structure and residual stress of ZrO2 thin films were measured by spectrophotometer, surface thermal lensing technique (STL), X-ray diffraction and optical interferometer, respectively. The results showed that the structure and related properties varied progressively with the increase of oxygen partial pressure. The refractive indices and the packing densities of the thin films decreased when the oxygen partial pressure increased. The tetragonal phase fraction in the thin films decreased gradually as oxygen partial pressure increased. The residual stress of film deposited at base pressure was high compressive stress, the value decreased with the increase of oxygen partial pressure, and the residual stress became tensile with the further increase of oxygen pressure, which was corresponding to the evolution of packing densities and variation of interplanar distances. (c) 2007 Elsevier B.V. All rights reserved.

沉积温度对LaF3薄膜性能的影响

abstract {LaF₃ single-layer coatings were prepared by thermal boat evaporation at the deposition temperatures of 189, 255, 277 and 321°C respectively. The crystal structures of the coatings were characterized by X-ray diffraction (XRD). A spectrophotometer was employed to measure its transmittance. Moreover, refractive index, extinction coefficient and cut-off wavelength were obtained from the measured transmittance spectral curve. The residual stress was evaluated by the Stoney's equation and optical interferometer. Laser induce damage threshold (LIDT) was performed by a tripled Nd:YAG laser system. The results show that the crystallization status becomes better with the deposition temperature increasing. Correspondingly, the grain size also gets larger. Meanwhile, the coatings become more compact and the refractive index increases. However, the absorption of coatings seriously rises and the cut-off wavelength drifts to the long wave. In addition, the residual stress also increases and the intrinsic stress plays a determinant role in the coating. The LIDT of the coating also enhances at high temperature.}

薄膜厚度对HfO2薄膜残余应力的影响

HfO2薄膜是用电子束蒸发方法制备的，利用ZYGO干涉仪测量了基片镀膜前后曲率半径的变化，计算了薄膜应力。对样品进行了XRD测试，讨论了膜厚对薄膜残余应力的影响。结果发现不同厚度HfO2薄膜的残余应力均为张应力，应力值随薄膜厚度的增加而减小，当薄膜厚度达到一定值后，应力值趋于稳定。从微观结构变化对实验结果进行了分析，发现微结构演变引起的本征应力变化是引起薄膜残余应力改变的主要因素。

Influences of CO2 laser annealing on mechanical and laser-induced damage properties of ZrO2 thin films

Zirconium dioxide (ZrO2) thin films were deposited on BK7 glass substrates by the electron beam evaporation method. A continuous wave CO2 laser was used to anneal the ZrO2 thin films to investigate whether beneficial changes could be produced. After annealing at different laser scanning speeds by CO2 laser, weak absorption of the coatings was measured by the surface thermal lensing (STL) technique, and then laser-induced damage threshold (LIDT) was also determined. It was found that the weak absorption decreased first, while the laser scanning speed is below some value, then increased. The LIDT of the ZrO2 coatings decreased greatly when the laser scanning speeds were below some value. A Nomarski microscope was employed to map the damage morphology, and it was found that the damage behavior was defect-initiated both for annealed and as-deposited samples. The influences of post-deposition CO2 laser annealing on the structural and mechanical properties of the films have also been investigated by X-ray diffraction and ZYGO interferometer. It was found that the microstructure of the ZrO2 films did not change. The residual stress in ZrO2 films showed a tendency from tensile to compressive after CO, laser annealing, and the variation quantity of the residual stress increased with decreasing laser scanning speed. The residual stress may be mitigated to some extent at proper treatment parameters. (c) 2007 Elsevier GmbH. All rights reserved.