激光二极管相干长度的压缩

激光二极管的相干长度在高频调制的驱动电流下可以减小，在实验中对一个９８０ｎｍ的激光二极管进行了测量，表明要干长度已减小了近２０倍。     

半导体激光器在医学上的应用

半导体激光器于１９６２年问世以来，在很多领域有了迅速的发展。近年来，国际上各种波长的激光二极管的报道令人目不暇接，从而半导体激光器在医学上的应用也随着波长的扩展、高功率激光阵列的出现以及可兼容的光纤导光和激光能量参数微机控制的出现而迅速发展起来。半导体激光器具有体积小、重量轻、成本低、波长可选择等优点，在眼科、矫形、皮肤、肿瘤、牙科、妇科、泌尿科和普外科等都有应用。尤其是半导体激光器作为激光针灸与原来的中医针灸理论中的腧穴、经络理论相结合，成为一种新兴的激光针灸仪。本文主要叙述了激光与生物组织的相互作用以及半导体激光在基础医学中的一些具体应用。     

Lateral characteristics improvements of DBR laser diode with tapered Bragg grating

Broad area semiconductor laser (BAL) has poor lateral beam quality due to lateral mode competition, which limits its application as a high-power optical source. In this work, the distributed Bragg reflector laser diode with tapered grating (TDBR-LD) is studied. By changing the lateral width, the tapered grating increases the loss of high-order lateral modes, thus improving the lateral characteristics of the laser diode. The measuring results show that the TDBR-LD can achieve a single-lobe output under 0.9 A. In contrast to the straight distributed Bragg reflector laser diode (SDBR-LD), the lateral far field divergence of TDBR-LD is measured to be 5.23° at 1 A, representing a 17% decline. The linewidth of TDBR-LD is 0.4 nm at 0.2 A, which is reduced by nearly 43% in comparison with that of SDBR-LD. Meanwhile, both of the devices have a maximum output power value of approximate 470 mW.     

Thin Nd:YAG slab laser pumped by lens duct coupled diode laser stacks

High power continuous wave operation of a diode face-pumped thin Nd:YAG slab laser is reported. A novel pumping geometry for a thin Nd:YAG slab using cylindrical lens duct coupled diode laser stacks is demonstrated. In a close-coupled resonator, a maximum laser output power of 260 W in multimode operation is obtained. This corresponds to a slope efficiency of 34% and an optical-to-optical efficiency of 27%, respectively. In high-brightness operation, a polarized laser output of 70 W has been obtained with a beam quality factor close to 4 in both directions. The polarization contrast ratio is >100. PACS 42.55.Xi; 42.60.Pk; 42.60.By     

一种五波长半导体激光生物组织辐照仪

采用GaAlAs单量子阱半导体激光器和LD泵浦的Nd:YVO4－KTP倍频激光器等研制了国内首台可从光导纤维输出5种波长的半导体激光生物组织辐照仪,该仪器已在激光生物医学领域投入应用．     

Synchronous Injection Locking Operation of Monolithic Diode Lasers Mode-Locked Diode Lasers

Synchronized mode-locking of monolithic mode-locked diode lasers has been demonstrated by injecting the light output from a master monolithic mode-locked diode laser. The master diode laser is a 10 GHZ hybridly mode-locked two section InGaASP quantum well laser. The slave lasers are a 10 GHz two section laser which is similar to the master laser, and a 20 GHz three section colliding pulse mode-locking laser. Both the slave lasers were greatly stabilized at 10 GHz frequency by a synchronous mode-locking mechanism under the injection of master laser pulses.     

Optimal fill factor for laser diode arrays applied to transversally pumped erbium laser

A relationship between the laser diode array (LDA) near field fill factor, the power of the amplified spontaneous emission fluxes developed within the LDA active layer and the operation efficiency of the ytterbium–erbium glass laser transversally pumped by the laser diode arrays has been studied taking into account the electric and optical processes in the LDA heterostructure layers. It has been found that there is a critical value of the fill factor (0.65–0.85) below of which an abrupt rise of the ytterbium–erbium laser threshold as well as the decrease of the laser operation efficiency is observed. It has been shown that the increase in the InGaAs/AlGaAs LDA fill factor leads to the increase in the LDA threshold current related with the increase of the ASE flux power. For a suppression of the ASE flux power value it has been proposed to etch the LDA heterostructure emitter layer between the stripe contacts.     

Laser Doppler vibrometry based on self-mixing effect

In this paper, a simple, compact and low cost laser Doppler vibrometer is presented. It is simply composed of a laser diode (9 mm in diameter, 2 g of weight, emitting at 825 nm) and by a two-lens optical system designed to focus the laser radiation on the vibrating target. This sensor can measure target velocity. The working principle is based on the self-mixing effect that occurs in a semiconductor laser diode when the emitted radiation is back reflected toward the cavity and then re-introduced inside. The target velocity is calculated measuring the frequency of the peak of the spectrum of the signal generated by a photodiode mounted on the back facet of the laser diode. In this article, the design and the realisation of the vibrometer is reported. The self-mixing vibrometer has been calibrated in the range 0–300 mm/s, using a rotating disk covered with white paper. The effect of the angle of measurement and target distance are reported. Finally, the sensor has been compared with a commercial laser Doppler vibrometer using a vibrating surface as a target.     

二极管激光器侧泵浦波导耦合系统设计

 为了提高面阵二极管激光器侧泵浦板条激光器泵浦光的利用率，本文采用光线追迹的方法，通过数字模拟设计出了高耦合效率的波导耦合系统。实验测试结果表明，其耦合效率达到85%以上，泵浦光在板条内分布均匀。     

Intra-cavity spectroscopy with diode lasers

A multi-mode diode laser with an external cavity is studied experimentally and theoretically for its application to intra-cavity spectroscopy. One facet of a typical Ga_0.89Al_0.11As laser diode was antireflection-coated by deposition of HfO₂ such that 10^–3 residual reflectivity was left over. This diode was placed in an external optical cavity. The emission spectrum of this diode laser is highly sensitive to any frequency-dependent loss in the cavity, and the detectivity of such a loss grows with the pump rate. Even close to threshold, the absorption at 780 nm of Rb atoms with a density of 5×10¹⁰ cm^–3 has been detected. An adequate model for diode lasers based on rate equations and including frequency-dependent gain saturation is developed and applied to the calculations of output spectra. The sensitivity of these spectra to intra-cavity absorption is determined by the overall cavity loss — which is rather high — and the fraction of spontaneous emission in the total emission, in contrast with dye lasers where it is limited by nonlinear mode coupling. Various criteria for the sensitivity are suggested. The smallest detectable absorption with a perfectly antireflection-coated laser is 10^–6 cm^–1. Improvement of the characteristics of the laser diode would increase the sensitivity.     

880nm半导体激光主动照明光纤耦合模块

为降低半导体激光主动照明红曝,选择波长880 nm大功率半导体激光器作为新型激光主动照明成像系统光源。根据光纤耦合过程光参数积不变原理,研制出波长880 nm大功率半导体激光器阵列单光纤耦合模块,利用光纤匀光作用使激光光束匀化整圆后用于激光主动照明。首次在波长880 nm大功率半导体激光器上采用阶梯反射镜光束整形方法,使激光光参数积与光纤匹配,激光高效耦合进入纤芯400μm、数值孔径0.22的光纤。室温条件下光纤耦合模块连续输出功率44.9 W,电光转化效率35%,波长880 nm大功率半导体激光器阵列光纤耦合模块,不仅其红曝小而且对应CMOS图像传感器光谱响应度较高,系统成像质量好。     

Self-injection locking of an extraordinarily wide broad-area diode laser with a 1000-microm-wide emitter

The experimental results of self-injection locking of an antireflection-coated broad-area diode laser with a 1000-microm-wide emitting area are presented. To our knowledge, it is the broadest single-element diode laser that has been used in an external-feedback cavity until now. Usually, wide diode lasers suffer from filamentation, which leads to poor spatial beam quality. We show, however, that the beam quality of the diode laser is improved significantly when we use asymmetric self-injection locking. An output power of 2.05 W is obtained with a beam quality factor M2 of 2.7. The self-injection locking technique improves the beam quality by a factor of 107. By comparing the results with those obtained with an ordinarily coated diode laser with a 1000-microm-wide emitter we show that antireflection coating on the front facet is decisive for this improvement in the beam quality.     

LD泵浦Nd：BGO晶体的自调Q激光器

首次实现了ＬＫ泵浦Ｎｄ∶ＢＧＯ固体激光器的１．０６４μｍ的激光输出，泵浦阈值功率为２５ｍＷ，在连续运转状态下得到最大为４０ｍＷ的ＴＥＭ００模输出，光－光效率为１３．３％，根据法拉第磁光效庆理论，了ＬＤ泵浦Ｎｄ∶ＢＧＯ自调Ｑ激光器的各种参数，并研制成该激光器，在该器件中，作为损耗调制元件的磁光调制器就是绕有线圈的Ｎｄ∶ＢＧＯ晶体本身，实验在重复率为１ＫＨｚ的条件下得到了ＦＷＨＭ为１００ｎｓ的稳定脉冲     

线阵激光二极管侧面抽运Nd∶YAG激光器特性研究

依据四能级系统速率方程 ,推导出了多横模振荡固体激光器输出与输入参量的关系。对二极管抽运固体激光器中线阵激光二极管三向对称侧面抽运结构 ,计算了抽运光强分布 ,并就激光器的阈值抽运功率、近阈值条件下的斜率效率、输出功率和光束质量等与抽运参量的关系 ,进行了数值计算。由计算结果看出 ,线阵激光二极管侧面抽运Nd∶YAG激光器中晶体半径和抽运光束腰半径是影响输出激光功率和光束质量的主要因素 ,并通过在谐振腔中加小孔选模 ,使光束质量得到明显改善。选择了一组三向侧面抽运结构参量进行了实验验证 ,实验结果与理论计算一致。     

Narrow bandwidth interference filter-stabilized diode laser systems for the manipulation of neutral atoms

We present and investigate different external cavity diode laser (ECDL) configurations for the manipulation of neutral atoms, wavelength-stabilized by a narrow-band high transmission interference filter. A novel diode laser, providing high output power of more than 1 W, with a linewidth of less than 85 kHz, based on a self-seeded tapered amplifier chip has been developed. Additionally, we compare the optical and spectral properties of two laser systems based on common laser diodes, differing in their coating, as well as one, based on a distributed-feedback (DFB) diode. The linear cavity setup in all these systems combines a robust and compact design with a high wavelength tunability and an improved stability of the optical feedback compared to diode laser setups using diffraction gratings for wavelength discrimination.     

Study on the Beam Quality of Uncoupled Laser Diode Arrays

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Study on the Beam Quality of Uncoupled Laser Diode Arrays

The beam quality of uncoupled laser diode array is studied theoretically and experimentally. By calculating the second order moments of the beam emitted from the laser diode array, the dependence of the M2-factor of the laser diode array on the M2-factor of the single emitter, the ratio of the emitting region to the non-emitting space, and the number of emitters, has been deduced. From the measurement of the beam propagation the M2-factor of a laser diode bar is experimentally determined. The measured M2-factor of the laser diode bar agrees with the theoretical prediction.     

基于二次谐波特性的DFB激光器稳频新方法研究

窄线宽稳频激光器在工业生产控制中具有广泛的应用,但自由运转的半导体激光器的频率漂移限制了激光器的使用。为稳定半导体激光器的频率,提出了一种基于二次谐波吸收特性来实现窄线宽二极管激光器的稳频新方法,利用1.396 μm的DFB二极管激光器测量水汽的二次谐波信号来实现激光的稳频,实验结果表明在100 h内激光器输出波长漂移有效的抑制在±0.16 pm范围内,激光稳频后,其吸收峰的位置不随环境温度的变化而漂移。该方法具有简单、可靠等优点,对二极管激光频率的稳定具有广阔的应用前景。     

大功率激光脉冲二极管触发高增益光导开关实验研究

研究了一种新型大功率激光脉冲二极管的输出特性,该激光二极管主要用于触发工作在高增益模式下的砷化镓光导开关。研制了基于射频金属-氧化物半导体场效应管的激光二极管驱动电路,可以为激光二极管提供上升沿、半高宽和峰值电流分别为4 ns,20 ns和130 A的脉冲驱动电流。研究了激光二极管输出的激光脉冲波形、能量、功率、光场分布等特性,并在Blumlein传输线结构中,研究了该大功率激光脉冲二极管的输出特性对工作于高增益模式下的光导开关的导通电阻、开关抖动等主要导通性能参数的影响规律。实验结果表明,激光脉冲的能量和功率越大,光斑面积越大、分布越均匀,在相同偏置电压条件下,光导开关的导通性能越好。     

Near-diffraction-limited segmented broad area diode laser based on off-axis spectral beam combining

The beam quality of a 500-μm-wide broad area diode laser with five active segments has been improved beyond the beam quality of the individual segments. The principle of this new laser system is based on off-axis feedback in combination with spectral beam combining. By using a double-feedback scheme we are able to improve the beam quality of the laser by a factor of 23 from M²=55 for the free-running diode laser to M²=2.4 for the laser with feedback at a drive current of 2.2 A. The improved M² value is a factor of 3.4 below M²=8.2 for a single free-running segment. This is the first time that the beam quality of a segmented broad area diode laser has been improved beyond the beam quality of the individual segments. PACS 42.55.Px; 42.60.Da; 42.60.Jf