激光扫描声学显微镜光学系统的设计

半导体激光器具有半导体和固体器件的许多优点：结构紧凑、效率高、价格便宜、长寿命，在许多方面优于气体激光器，因此在一些测量领域有较好的应用前景。本文基于棱镜对光的一维压缩及新型半导体激光器，对激光扫描声学显微镜的光学系统进行了新的设计，给出了相关数据及具体技术指标，实验证实其光学性能满足要求。整个光学系统具有结构紧凑、可靠性高、使用方便等特点，现已用于激光扫描声学显微镜定型设计。     

柱面透镜准直LD光场的计算建模方法研究

为了简化LD光场准直柱面透镜繁琐的理论设计过程,便于进行实际操作,利用Matlab计算建模的方法,计算理想准直柱面透镜上的各个离散点的坐标值,通过拟合或二次曲面方程逼近的方法来获得准直柱面透镜的面型参数.分析表明,二次曲面柱面透镜非常适合做半导体激光器的准直透镜,可以根据具体需要来选择相应的面型.相比于其他方法,该方法简单直观,易于设计和加工,参数的优化调整迅速,可以根据加工工艺的难易程度来选择合理的透镜参数.     

A mode-locked dye laser pumped by a xenon ion laser

Passive mode-locking of a rhodamine 6G dye laser has been achieved, using a pulsed xenon ion laser as a pumping source. A pulse width of 5 ps and a peak power of 4 kW have been obtained. Thermal problems were encountered, which adversely affected the operation of the dye laser. Work is in progress to improve these results.     

1.6 W of TEM00 cw output at 1.06 μm from Nd:CNGG laser end-pumped by a fiber-coupled diode laser array

In this paper we demonstrated and analyzed a high-power cw Nd:CNGG laser end-pumped by a fiber-coupled diode laser array in a convex–concave-type cavity. TEM₀₀ mode output power of 1.63 W was obtained with 27% optical-to-optical conversion efficiency and slope efficiency of 44.5%. Thermal lensing and its variation with the incident pump power for this crystal have been measured. The coefficient for pump power induced diffraction losses of Nd:CNGG crystal have also been estimated for this laser configuration.     

一种新颖的激光准直系统的研究

本文用等效望远镜系统的方法研究了锥形梯度折射率纤维透镜用作激光准直系统的原理和特性,指出这种新颖的激光准直元件可望在微型光学和波导光学中获得新应用。     

Validity of Scalar Approaches to Radiation Modes of the GaAs-Based 1.3-μm Diode Lasers Designed for the Optical–Fibre Communication

The work presents a comparison between results of optical simulations based on the scalar and vectorial models applied to both stripe – geometry Fabry-Perot (FPL) as well as vertical-cavity surface-emitting (VCSEL) diode lasers designed for the 1.3-μm optical–fibre communication. As compared to vectorial optical approaches, scalar ones are known to be less exact but simultaneously they need as many as approximately 100 times shorter computation time, which favours those models in many applications. Therefore, vectorial models should be applied only in cases of confirmed faulty performance of scalar ones. While the Effective Index Method and the Effective Frequency Method have been chosen as scalar approaches to FPLs and VCSELs, respectively, simulations, the Method of Lines has been used in both cases as a vectorial one. Scalar models have been found to be quite exact in the case of a determination of the effective refractive index and wavelength of emitted radiation, whereas their exactness in the lasing threshold analysis is much worse, especially in the case of higher-order modes. Our analysis is concluded with the determination of the regions where both models give satisfactorily close results.     

用于太阳光泵浦激光器的菲涅耳透镜设计方法

建立并分析了太阳光点聚焦型菲涅耳透镜的理论模型。提出了适用于太阳光泵浦激光器的设计方法。综合考虑会聚总功率和功率密度提高倍数两个因素,合理设计了菲涅耳透镜口径,相对孔径以及环形小棱镜的宽度(环距)三个参数,获得了用于太阳光泵浦激光器的菲涅耳透镜。     

Research and production of laser crystals in China

A general review of the progress in the research and production of laser crystals in China is presented. In the past quarter century, a considerable foundation and strength has been built up in this field and through further effort China's laser crystals will soon reach world level.     

Operational characteristics of dual gain single cavity Nd:YVO4 laser

Operational characteristics of a dual gain single cavity Nd:YVO₄ laser have been investigated. With semiconductor diode laser pump power of 2 W, 800 mW output was obtained with a slope efficiency of 49%. Further, by changing the relative orientation of the two crystals the polarization characteristics of the output could be varied. In particular by keeping the two Nd:YVO₄ crystals with their c-axes orthogonal to each other and adjusting the gain of the crystals so that both operate at approximately the same power level, completely unpolarized beams could be obtained.     

A long-pulse xenon ion laser as a pumping source for dye lasers

A simple xenon ion laser that is either sealed or has a gas flow mode is described. The laser delivered long pulses ( 15 μs) of almost 1 kW peak power. It has been used to pump a dye laser employing the same configuration as cw dye lasers. The system is inexpensive and can be mode-locked, enabling it to yield ultrashort pulses comparable in duration to those delivered by cw argon laser-pumped dye lasers but with much higher peak powers.     

Dispersion-tuned multiwavelength actively mode-locked fiber laser using a hybrid gain medium

We demonstrate a multiwavelength 10 GHz pulse source using a dispersion-tuned actively mode-locked fiber ring laser incorporated with a semiconductor optical amplifier and an erbium-doped fiber amplifier. Simultaneous seven-wavelength operation of the laser is obtained. The side-mode suppression of all wavelengths is above 30 dB. Smooth wavelength tuning is achieved over more than 12 nm by changing the modulation frequency or the length of the optical delay line. Pulse characteristics are almost constant over the entire tuning span. Wavelength spacing can also be varied from 0.9 to 10 nm by adjusting the dispersion of the cavity. These experimental observations agree well with theoretical analyses.     

Design of aspheric collimation system for semiconductor laser beam

In this paper, semiconductor laser beam collimation lenses system has been optimum simulated and designed. The new design methods for aspheric cylinder lenses collimation system have been discussed in detail and the system parameters are calculated and optimized by using a geometrical ray optics approximation. The optical system has been further simulated by software MATLAB, and the simulation results showed that the emergence angle can be collimated effectively, and the output beam can be expanded to a circular spot in centimeter level beam radius.     

Injection locking properties of a microchip laser

An injected microchip laser is theoretically studied, with the use of two models: in the first model, which is traditional, the field is represented by a single frequency component in the slowly-varying envelope approximation. In the second model, referred to as the Fabry-Perot model, two field components are considered which are respectively centered around the frequency of an eigenmode of the injected laser and the frequency of the injected field. Computation of locking ranges, bistability do mains are performed and the results compared. They show not only an improved precision of the second model but also a necessity to use it to describe some effects such as the bistable domains in the limits of the locking domains. Received: 1st April 1998 / Accepted: 21 August 1998     

A technique for the alignment of a ring laser cavity

An alignment technique for a ring laser cavity is presented which is suitable for a resonator into which auxillary laser beams cannot pass.     

Structure optimisation of short-wavelength ridge-waveguide InGaN/GaN diode lasers

Room-temperature (RT) continuous-wave (CW) operation of the 405-nm ridge-waveguide (RW) InGaN/GaN quantum-well diode lasers equipped with the n-type GaN substrate and two contacts on both sides of the structure has been investigated with the aid of the comprehensive self-consistent simulation model. As expected, the mounting configuration (p-side up or down) has been found to have a crucial impact on the diode laser performance. For the RT CW threshold operation of the otherwise identical diode laser, the p-side up RW laser exhibits as high as nearly 68°C maximal active-region temperature increase whereas an analogous increase for the p-side down laser was equal to only 24°C. Our simulation reveals that the lowest room-temperature lasing threshold may be expected for relatively narrow and deep ridges. For the structure under consideration, the lowest threshold current density of 5.75 kA/cm² has been determined for the 2.2-μm ridge width and the 400-nm etching depth. Then, the active-region temperature increase was as low as only 24 K over RT. For wider 5-μm ridge, this increase is twice higher. An impact of etching depth is more essential for narrower ridges. Quite high values (between 120 and 140 K) of the characteristic parameter T₀ convince very good thermal properties of the above laser.     

Fundamental studies on laser radiation therapy: dispersion of a laser beam passing through optical fibres

For laser internal therapy in medical applications, optical fibres are required to propagate the laser beam. The far-field pattern of the laser beam at the exit face of the optical fibre is studied using a multimode step-index fibre and a graded index Selfoc fibre. The degree of dispersion, or the output angular distribution, of the beam passing through the Selfoc fibre is much smaller than that passing through the multimode step-index fibre. Consequently, the energy density in the far-field pattern of the beam passing through the Selfoc fibre is very much larger than that for the beam passing through the multimode step-index fibre. It is concluded that the Selfoc fibre is more effective in laser internal therapy.     

Experimental study of high-power pulse side-pumped Nd:YAG laser

The paper reports on the characterization of a compact and simple side-pumped 0.538 J×100 Hz pulse Nd:YAG laser. A side-pumping configuration with 100 laser diode bars is used in the laser head. We also experimentally studied the laser performance of the diode-pumped Nd:YAG laser head in the free running and Q-switched operation under different repetition rates.     

Power efficiency of a semiconductor laser with an external cavity

Optical feedback modifies the power vs. current diagram of a laser diode as well as its spectrum. Though optimization of the spectral characteristics is usually the main goal in the design of an external cavity source, power efficiency is also important, especially with relatively high power devices, where temperature variations due to dissipation can have an impact on the wavelength stability and on the laser lifetime. A useful parameter to describe the total power efficiency of the stabilized laser, relative to that of the solitary laser, is proposed in this paper. The dependence of this parameter on the characteristics of the active device, and of the external cavity, is investigated.