Polarization manipulated solid-state lasers with crystalline-orientations

The polarization states of 〈111〉-cut Yb:YAG crystal microchip lasers were investigated by pumped with the elliptically polarized pump beam from fiber-coupled laser-diode. The manipulated polarized lasers were achieved in laser-diode pumped Yb:YAG microchip laser by controlling the crystalline-orientations in 〈111〉-growth Yb:YAG crystal. Generally elliptically polarized lasers were obtained in laser-diode pumped Yb:YAG microchip lasers. However, crystalline-orientation manipulated linearly polarized laser was obtained when six different sites with different crystalline orientations were set to parallel to the major axis direction of the elliptically polarized pump beam. Six different sites in Yb:YAG crystal were separated with 30° and 90°, which were responsible for the linearly polarized laser oscillations. Circularly polarized lasers were observed when a Yb:YAG crystal was aligned to a special position between two sites responsible for linearly polarized laser oscillation. Effects of the polarization states of pump source on the laser polarization states of Yb:YAG microchip lasers and polarization direction of different polarized lasers with respect to Yb:YAG crystal rotation was addressed.     

大功率半导体激光器的可靠性研究

对InGaAs/AlGaAs和InGaAsP/GaAs有源区含铝的915nm和无铝的808nm腔面镀膜及未镀膜的大功率半导体激光器进行了老化实验。在老化前通过综合参数测试仪测试两种激光器的斜率效率、阈值电流，发现有腔面膜的激光器比无腔面膜的激光器的阈值电流降低25％以上。在1.2倍阈值电流下，恒流老化40h左右，老化后再分别测试它们的阈值电流、功率参数，我们发现在老化后未镀膜的激光器的阈值电流和镀有腔面膜的激光器相比增加25mA以上，输出功率也比镀过腔面膜的减小到了原来的1／2，可见腔面保护对于延长激光器的寿命是很重要的。     

LD泵浦单频种籽激光器及其线宽的测试

研究了 L D泵浦的单频种籽激光器。以 Nd:YAG和 Nd:YL F晶体为工作介质 ,采用微片腔的谐振腔形式 ,获得了 1.0 6μm和 1.0 5 3μm的单频激光输出 ,其输出功率分别为 90 m W和 10 m W。采用光纤延迟自零差拍法测量了单频固体激光的线宽 ,其线宽为 30 0 k Hz。     

Proton radiation effects in quantum dot lasers

Proton beams with energies of 10 and 200 MeV were irradiated onto InAs quantum dot lasers with a wavelength of 1.3 μm. The increase in threshold current by proton irradiation was small compared with those of the previously reported other quantum dot lasers with larger active region and 1.3-μm InGaAsP quantum well lasers. These results were discussed by taking account of non-ionizing energy loss and effective volume of active region.     

Bistable phase locking in rocked lasers

We investigate analytically and numerically the dynamics of single mode lasers with periodic ac injection (rocked lasers). Such lasers show phase bistability as the phase of the light emitted by such lasers can lock to either of two values shifted by π. Locking regimes for different lasers are studied showing that the system response is strongly modified in class B lasers due to the influence of relaxation oscillations.     

Buried waveguide double-heterostructure PbEuSe-lasers grown by MBE

Buried heterostructure (BH) lasers with a PbSe active layer and Pb_0.97Eu_0.03Se confinement layers were fabricated using molecular beam epitaxy (MBE). The waveguide was defined by photolithography and an ion milling process. By MBE overgrowth of the etched structure with a PbEuSe layer the BH-laser was formed.The lasers operated cw with low threshold currents (8 mA at 80 K) in the spectral range from 1280 cm⁻¹ (30 K) to 1800 cm⁻¹ (160K). The spectral characteristics of these lasers were superior to comparable DH stripe lasers. These lasers were the first with IV/VI-MBE overgrowth process of etched lateral structures.     

Nonlinear distortions in the current modulation of non-self-pulsing and weakly self-pulsing GaAs/GaAlAs injection lasers

Nonlinear distortion characteristics of GaAs/GaAlAs injection lasers under analog current modulation were experimentally investigated. In non-self-pulsing lasers, relaxation oscillation (R.O.) plays a heavy role in generating harmonic distortions, in good agreement with theory. Additional distortions generated by microwave mixing in weakly self-pulsing lasers make such lasers unacceptable for wideband analog transmissions unless suitable negative feedback is applied. With such measure taken, both fundamental and the harmonic responses of a self-pulsing laser is indistinguishable from that of a laser with no R.O. resonance.     

高功率808nm InGaAsP—GaAs分别限制结构的半导体激光器

介绍了研究分别限制结构ＩｎＧａＡｓＰ－ＧａＡｓ半导体激光器所得到的最新成果。利用引进的俄国技术，基于量子阱结构的ＩｎＧａＡｓＰ－ＧａＡｓ激光器，可用短时间液相外延技术制造。在ＧａＡｓ衬底上制成的ＩｎＧａＡｓＰ－ＧａＡｓ分别限制结构的激光器，主要参数如下：发射波入λ＝８０８ｎｍ，阈值电流密度Ｊ＝３００Ａ／ｃｍ＾２，对于条宽ω＝１００μｍ的激光器，连续功率为１－２Ｗ。     

The tuning characteristics of optically pumped fir cavity laser

Based on the quantum mechanics theory of density matrix and the principle of multiple-beam interference, the tuning characteristics of optically pumped NH₃ FIR lasers were studied. A series of metallic mesh Fabry-Perot cavity lasers with sample tubes of 10cm, 20cm and 100cm in length were constructed and operated successfully, and the FIR laser spectra of the NH₃ cavity lasers pumped by a TEA-CO₂ laser were measured. Supported by the Natural Sciences Foundation of Guangdong Province, PRC     

分布反馈光纤激光器弯曲特性的实验研究

为了研究分布反馈光纤激光器的弯曲特性,对光纤激光器输出波长和弯曲半径的关系进行了理论分析和实验研究.理论分析表明,光纤激光器输出波长变化量与弯曲半径平方的倒数为线性相关,并且随着弯曲半径的增大布拉格波长向短波长方向移动|实验中通过对3支不同波长的光纤激光器在弯曲半径分别为10 mm、20 mm、90 mm时输出波长的测量,验证了理论分析的正确性.实验中采用参考光纤激光器法排除环境干扰,对光纤激光器的激射功率进行了耐弯曲测试,并验证了光纤激光器斜率效率优越的抗弯曲特性.结果表明,在测试的32天内,待测光纤激光器激射功率变化量均小于2 dB,为分布反馈光纤激光器做为弯曲类传感应用的研究提供了重要的参考依据.     

Intensity coupling and synchronization of chaotic lasers

The synchronization of chaotic lasers was studied considering the coupling scheme with the intensity of light pulses from one laser saturating the other one. The experimental synchronization of two single mode CO2 lasers with saturable absorber is reviewed. Numerical simulations are presented for diode lasers made chaotic by optical feedback. Optical intensity saturation coupling was introduced in Lang-Kobayashi equations. Parameters were chosen such that both lasers were uncorrelated and chaotic before coupling and partially synchronize after coupling. Correlation functions for the numerical solutions were used to characterize the properties of the synchronism. They show partial in-phase and antiphase synchronism for the pulse intensities, depending on the coupling mechanism. These synchronisms are independent of optical interferometric effects and so, relevant for communication applications.     

Efficiency improvement of multimode Tm3+ doped double cladding silica fiber laser by in-line biconical tapers

Efficiencies improvement of LD (laser diode) pumped multimode large mode area (LMA) Tm³⁺ doped double cladding silica fiber lasers with different in-line biconial tapers were reported. Two types of multimode Tm³⁺ doped fiber were used in this experiment. Each type of fiber was made into three fiber lasers, a uniform geometry fiber laser and two tapered fiber lasers with different taper parameters. Biconical tapers located several centimeters from the output end of the multimode fiber lasers were made by heating and stretching method. Although the threshold of the best tapered fiber laser was added 200 mW, the slope efficiency (25.3%) and the maximum output power (1.31 W) of the fiber laser increased by 10.3% and 350 mW respectively, in comparison with the un-tapered one. Pre and post output laser power ratio was 6.3–15.6. Simultaneously, the laser spectrum moved to shorter wavelengths. The same trends of these characteristics were also observed in the other three tapered fiber lasers.     

Synchronization of Chaotic Intensities and Phases in an Array of N Lasers

A linear array of N mutually coupled single-mode lasers is investigated. It is shown that the intensities of N lasers are chaotically synchronized when the coupling between lasers is relatively strong. The chaotic synchronization of intensities depends on the location of the lasers in the array. The chaotic synchronization appears between two outmost lasers, the second two outmost lasers, etc. There is no synchronization between nearest neighbors of the lasers. If the number of N is odd, the middle laser is never synchronized between any lasers. The chaotic synchronization of phases between nearest lasers in the array is examined by using the analytic signal and the Gaussian filter methods based on the peak of the power spectrum of the intensity. It can be seen that the message of chaotic intensity synchronization is conveyed through the phase synchronization.     

猝灭式染料激光器理论研究

理论上研究了由准分子激光泵浦的猝灭式染料激光器的猝灭机理，对于一些具体的泵浦情况，通过激光速率方程理论上探讨了激光器的猝灭效果，并且对激光器的一些重要参数进行了一些研究。     

基于DFB激光器的光学微波信号的产生

采用量子阱混杂的材料集成技术制备并联分布反馈激光器和Y形波导耦合器集成的新型光电器件.两个并联分布反馈激光器的激射模式在频率上稍有差别,这两束不同频率的激光在Y形波导耦合器拍频产生光学微波信号.分别独立调节注入到两个激光器的电流大小,可以得到从13 GHz到42 GHz连续可调的光学微波信号. 关键词： 光学微波信号生成 分布反馈激光器 Y形波导 拍频     

Attosecond‐precision ultrafast photonics

We review our recent progress toward attosecond‐precision ultrafast photonics based on ultra‐low timing jitter optical pulse trains from mode‐locked lasers. In femtosecond mode‐locked lasers, the concentration of a large number of photons in an extremely short pulse duration enables the scaling of timing jitter into the attosecond regime. To characterize such jitter levels, we developed new attosecond‐resolution measurement techniques and show that standard fiber lasers can achieve sub‐fs high‐frequency jitter. By leveraging the ultra‐low jitter of free‐running mode‐locked lasers, we pursued high‐precision optical‐optical and optical‐microwave synchronization techniques. Optical signals spanning 1.5 octaves were synthesized by attosecond‐precision timing and phase synchronization of two independent mode‐locked lasers. High‐stability microwave signals were also synthesized from mode‐locked lasers with drift‐free sub‐10‐fs precision. We further demonstrated the attosecond‐precision distribution of optical pulse trains to remote locations via timing‐stabilized fiber links. Finally, the application of optical pulse trains for high‐resolution sampling and analog‐to‐digital conversion is discussed.     

Modeling and experimental study of 780–808-nm AlGaAs/GaAs injection lasers with electron superlattice barriers

Electron superlattice barriers (ESBs) were used in AlGaAs/GaAs injection lasers to improve the electron confinement of the active layer by Bragg reflection of electron waves. The design of a separate-confinement heterostructure (SCH) laser with ESBs operating at 780–808 nm was optimized. Conventional SCH and SCH-ESB were prepared by low-pressure MOCVD epitaxy. Oxide stripe lasers with stripe widths of 100 and 200µm were prepared. The threshold current density of 0.3 kA/cm² and the characteristic temperature constantT ₀=220 K were measured at a wavelength of 808 nm for SCH-ESB lasers with an active-layer thickness of 40 nm and a resonator length of 0.4–0.5 mm. For conventional SCH lasers with the same geometry, a threshold current density of 0.42 kA/cm² andT ₀=160 K were obtained. Experimental results on the low-temperature photoluminescence characterizing ESB regions are presented and are compared with the calculated miniband energy spectrum of the superlattice structure. The leakage currents for ordinary SCH and SCH-ESB lasers were analyzed. Experimental verification of a reduction in the leakage current for SCH-ESB lasers was obtained.     

铒激光脉冲消融泌尿结石和胆结石比较研究

利用光学弱相干显微成像系统对脉冲激光消融硬生物组织后形成的凹坑二维和三维形貌进行了扫描,分析了Erbium∶YAG激光脉冲消融生物硬组织特性.结果表明:相同激光参量条件下,消融胆结石比消融泌尿结石具有更高的消融效率;消融胆结石或消融泌尿结石时,脉冲能量越大,消融效率越高;消融效率提高主要体现在凹坑表面直径更宽、高度更深...     

Micromachining and surface processing of the super-hard nano-polycrystalline diamond by three types of pulsed lasers

Laser beam micromachining was applied to super-hard nano-polycrystalline diamond (NPD) synthesized by the direct conversion of graphite at high pressure and high temperature. Three types of pulsed lasers were tested: nanosecond near-infrared, nanosecond near-ultraviolet, and femtosecond near-infrared lasers. The latter two were also applied for synthetic single crystal of diamond to compare the results with those of the NPD. It was demonstrated that the nanosecond near-infrared laser was the most efficient device for rough shaping of the NPD, while the ultraviolet and femtosecond lasers give satisfactory results for precise surface finishing of it. The properties of the laser-processed surfaces were analyzed by scanning and transmission electron microscopy, laser scanning microscopy, and micro Raman spectroscopy. These analyses demonstrated that the three types of lasers play different and complementary roles, and that their combination is the best suitable solution for micromachining of the hardest diamond into any desired shapes.     

Laser-jamming analysis of combined fiber lasers to imaging CCD

To complete a successful laser jamming to imaging charge coupled device (CCD) based on combined fiber lasers, the interactions between CCD and combined fiber lasers were analyzed in detail. The saturation and crosstalk thresholds of CCD were achieved, which are lower than 10 mW/cm². Through theoretical analysis and numerical simulations, the thermal processes under single pulse, multi-pulses and continuous laser irradiations were developed. The simulation results have proved the possibility of hard damage caused by multi-pulses and continuous laser irradiations. The combined fiber lasers is suitable to deploy optical saturation jamming at present. The further applications of combined fiber lasers need a more powerful laser source and a more accurate tracking and pointing system.