离子注入GaAs实现双包层掺镱光纤激光器被动调Q锁模

用离子注入的半绝缘GaAs晶片作为吸收体和输出镜，在双包层掺镱光纤激光器上实现了调Q锁模. 离子注入的能量为400keV的As+离子，注入剂量为1016/cm2，然后在600℃下退火20min. 当抽运功率为5W时, 脉冲平均输出功率为200mW, 调Q包络重复频率为50kHz, 半高宽为4μs，锁模脉冲重复频率为15MHz. 关键词： 离子注入GaAs 掺镱光纤激光器 被动调Q锁模     

Passively mode-locked Nd:LuVO(4) laser with a GaAs wafer

We report on the passive mode locking of a diode-pumped Nd:LuVO(4) laser with a GaAs wafer as output coupler. Using the interference modulation effect of the GaAs wafer, high-power continuous-wave mode locking with a pulse width of about 7.1 ps and an average output power of 3.11 W was achieved. Our result shows that Nd:LuVO(4) could be an excellent gain medium for diode-pumped high-power mode-locked lasers.     

Nd: Sr5 (PO4) 3F Crystal Laser Characteristics Using GaAs as Passive Q-switch

It is investigated the properties of a diode-pumped Nd: Sr5 ( PO4 )3F laser that is passively Q-switched by a thin, single crystal GaAs wafer. The short high-peak-power pulses of the laser have been obtained. The pulse energies, pulse widths and pulse repetition rates for different conditions have been measured and the experimental results show that GaAs is an excellent passive Q-switch of the diode-pumped Nd: Sr5(PO4)3F lasers.     

Nd: Sr_5 (PO_4 )_3 F Crystal Laser Characteristics Using GaAs as Passive Q-switch

1 IntroductionQ- switching Of diode-pumped lasers iS an effective technique because they provideshort duration optical pulses required for laser ranging, nonlinear studies, medidne andother important applications[1--#]. It is obvious that the replacement of an organic dyewith a solid-state one makeS a laser more convenient tO use. Semiconductor materialsare attractive for saturable absorber because Of the large optical nonlinearities that can beobtained, particularly in quantum--well .t..t..…     

激光二极管抽运的GaAs被动Q开关Nd：YVO4激光器

利用固体可饱和吸收体砷化镓（GaAs）作为被动调Q元件，实现了激光二极管抽运平－凹腔掺钕钒酸钇（Nd:YVO4）激光调Q运转，详细测量了砷化镓被动调QNd:YVO4激光输出特性，获得脉宽15ns，重复频率470kHz，光束质量M^2=1.31的激光输出，调Q激光运转阈值为500mW，并数值求解了砷化镓被动调Q速率方程，讨论了被动调Q机理以及调Q脉冲宽度和脉冲重复频率对抽运速率的依赖关系，理论计算结果与实验结果相一致。     

脉冲LDA泵浦Nd∶YVO4/GaAs被动调Q锁模激光器

用脉冲激光二极管阵列（LDA）作为泵浦源、微柱透镜阵列和透镜导管作为耦合系统,以As＋注入GaAs可饱和吸收片作为被动调Q锁模元件,实现了Nd∶YVO4激光器调Q锁模运转.调Q运转阶段,激光器每泵浦脉宽内输出一个调Q脉冲,调Q脉宽7ns.调Q锁模运转阶段,初始透过率60％的GaAs晶片对调Q包络内的锁模脉冲的调制深度达到95％以上,锁模脉冲重复频率991 MHz.研究了加在LDA上的电压、方波脉冲的脉宽和重复频率对调Q锁模脉冲特性的影响,并对实验结果进行了讨论.     

Short pulse passively Q-switched Nd:GdYVO4 laser using a GaAs mirror

We report on a diode pumped passively Q-switched Nd:Gd_0.64Y_0.36VO₄ laser with a Cr⁴⁺:YAG saturable absorber. We show experimentally that by using an appropriately coated GaAs wafer as output coupler, the Q-switched pulse width can be significantly suppressed. Stable Q-switched pulse train with pulse width of 2.2 ns, peak power of 26.3 kW, repetition rate of 15.38 kHz have been obtained under an absorbed pump power of 8.54 W. The physical mechanism of pulse width narrowing by the GaAs wafer was also experimentally investigated.     

Diode-pumped passively Q-switched Nd:GGG crystal with GaAs saturable absorber

We have experimentally studied the passive Q-switching performance of a diode-pumped Nd-doped gadolinium gallium garnet (Nd:GGG) laser with a GaAs saturable absorber. Stable Q-switched pulses as short as 9 ns with a repetition rate of 196.1 kHz have been obtained with an appropriately coated GaAs wafer used as the output coupler. At 12.44 W of the absorbed pump power, an average output power of 1.03 W has been obtained and the corresponding pulse energy and peak power are 5.25 μJ and 0.58 kW, respectively.     

Control of the pulse duration in a diode-pumped passively Q-switched intracavity frequency-doubling laser

Different techniques to control the pulse duration of a diode-pumped passively Q-switched intracavity frequency-doubled laser are studied, which shows that varying the pump beam radius in the gain medium and mode-spot sizes on a saturable absorber are two efficient ways to control the pulse duration. The output pulse durations obtained from a diode-pumped passively Q-switched Nd:GdVO₄/KTP laser with a GaAs wafer can be controlled in a wide range over 100 ns, which indicates a simple way of controlling the pulse duration of the intracavity frequency-doubled passively Q-switched laser.     

Diode-pumped passively mode-locked Nd:GdVO<Subscript>4</Subscript> laser with a GaAs saturable absorber mirror

We report on a diode end-pumped passively mode-locked Nd:GdVO₄ laser. By using a GaAs wafer simultaneously as the saturable absorber and the output coupler, stable continuous-wave mode locking was achieved. The pulse width was measured to be 18.9 picoseconds at a repetition rate of 370 MHz. The most remarkable property of the laser is that its repetition rate can be changed from 370 MHz to 3.348 GHz by simply changing the cavity length. An average output power of 3.46 W at a 3.348 GHz repetition rate was obtained with a 14 W pump power. To our knowledge, this is the first demonstration of a passively mode-locked Nd:GdVO₄ laser using a GaAs wafer as the saturable absorber. PACS 42.55.Rz; 42.60.Fc; 42.55.Xi.     

Photoexcited GaAs surfaces studied by transient terahertz time-domain spectroscopy

The transmission characteristics of an air-GaAs interface and the transient absorption and index spectra of the thin, photoexcited surface layer are investigated subsequent to excitation by a femtosecond laser pulse. We find that the total phase change and transmission of a terahertz (THz) probe pulse are dominated by interface effects. This observation has important implications in the interpretation of THz time-domain spectroscopy data of absorbing media. We also observe that the THz pulse apparently arrives at the detector as much as 60 fs earlier when it is transmitted through an optically excited GaAs wafer. This effect is fully explained in terms of a frequency-dependent transmission and phase shift at the air-GaAs interface and is not associated with superluminal propagation.     

线性模式下GaAs光电导开关的时间抖动特性

针对线性模式下GaAs光电导开关时间抖动特性的研究,对提高精密同步控制系统的输出性能具有重要意义.根据电脉冲的概率分布和时间与电脉冲波形的对应关系,结合载流子的输运过程,对光电导开关时间抖动进行了定性的理论推导.此外,通过搭建实验平台,利用正交光栅分光,将一束激光同时触发两路并联的GaAs光电导开关,改变触发激光脉冲宽度及外加偏置电压测试开关时间抖动,根据实验值的对比分析,得出在不同的外加偏置电压下,随着触发激光脉冲宽度的减小,开关时间抖动值随之减小.验证了触发激光脉冲宽度对开关时间抖动的影响及理论分析的正确性.研究结果对GaAs光电导开关时间抖动的进一步减小具有一定的指导意义.     

Ultrafast opto-terahertz photonic crystal modulator

We present an agile optically controlled switch or modulator of terahertz (THz) radiation. The element is based on a one-dimensional photonic crystal with a GaAs wafer inserted in the middle as a defect layer. The THz electric field is enhanced in the photonic structure at the surfaces of the GaAs wafer. Excitation of the front GaAs surface by ultrashort 810 nm laser pulses then leads to an efficient modulation of the THz beam even at low photocarrier concentrations (approximately 10(16) cm(-3)). The response time of the element to pulsed photoexcitation is about 130 ps.     

离子注入SI—GaAs做激光器被动调Q元件的研究

本文从半导体材料GaAs的能级结构出发，探讨了GaAs做固体激光器被动调Q器件的可行性，对离子注入半绝缘GaAs用做Nd：YAG激光器中被动调Q元件的机理进行了实验研究，实验中腔型选择直腔式平平腔，Nd：YAG采用脉冲氙灯抽运，在腔型1Hz下获得了单脉冲宽度为62ns的调Q波形输出。     

Athermal annealing of Mg-implanted GaAs

High-resolution X-ray diffraction scans and electrical resistivity measurements were performed on Mg-implanted GaAs exposed to laser shock annealing on both the implanted and the unimplanted surfaces of the wafer. Measurements on the sample that was subjected to a laser pulse exposure on the implanted side indicate that annealing had occurred within 3 mm of the center of the laser-exposed spot. X-ray scans and the topographs indicate the propagation of a mechanical wave propagating in the radial direction from the laser-exposed spot. No evidence of annealing, however, was observed at any position on the Mg-implanted GaAs sample that was subjected to a laser pulse exposure on the unimplanted side. The Mg implant did not show any redistribution for the laser-shocked annealing, in contrast to the conventional rapid thermal annealing. PACS 61.72.Vv; 62.50.+p; 71.55.Eq; 79.20.Ds; 81.05.Ea     

Temperature behavior of implanted and pulsed laser irradiated GaAs

Recent studies have shown that the Low-Power Pulsed-Laser Annealing (LPPLA) of ion-implanted GaAs specimens can be realized in a power-density window in which a complete structural reordering is guaranted. As the experimentally employed conditions allow us to describe the theoretical problem in an unidimensional space domain, we describe here a method to investigate the in-depth temperature behavior during the low-power pulsed-laser irradiation of ion-implanted semiconductors. The application of this method to GaAs specimens shows that the upper limit of the energy density window is connected with the exceeding of the critical temperature T _c below which the As evaporation rate is negligible.     

Generation and detection of acoustic solitons in crystalline slabs by laser ultrasonics

Acoustic solitons have been recently observed in different systems (Si, Sapphire, MgO, alpha-quartz). Such acoustic waves could lead to sub-picosecond acoustic pulses. In this paper, we report on the formation of acoustic solitons in a GaAs crystalline slab. A short picosecond acoustic pulse is generated by absorption of a femtosecond laser pulse in an aluminum thin film deposited on one side of the slab. This strain pulse travels through the sample up to the opposite side where it is detected by a time delayed laser pulse reflected by an aluminum transducer. We use interferometric detection to measure independently the real and imaginary parts of the relative change in optical reflectivity induced by the acoustic pulse. We find that, at low temperature and with a laser pump pulse energy of 10 nJ, an acoustic soliton clearly separates from the acoustic pulse in GaAs slab. The soliton shape is compared with numerical simulations for different excitation conditions. From the very unique properties of solitons, we infer a soliton pulse duration of about 2.3 ps which corresponds to a spatial extent of only 12 nm.     

Diode-pumped passively Q-switched mode-locked Nd:YLF laser with uncoated GaAs saturable absorber

We have demonstrated passively Q-switched mode-locked all-solid-state Nd:YLF laser with an uncoated GaAs wafer as saturable absorber and output mirror simultaneously. Q-switched mode-locking pulses laser with about 100% modulation depth were obtained. The average output power is 890 mW at the incident pump power of 5.76 W, corresponding to an optical slop efficiency of 20%. The temporal duration of mode-locked pulses was about 21 ps. At the Q-switched repetition rate of 30 kHz, the energy and peak power of a single pulse near the maximum of the Q-switched envelope was estimated to be about 1.6 μJ and 76 kW.     

雪崩倍增GaAs光电导太赫兹辐射源研究进展

在飞秒激光激励下用GaAs光电导开关作为太赫兹(THz)辐射天线, 已经广泛用于太赫兹时域光谱系统, 但目前国际上都是使用GaAs光电导开关的线性工作模式, 而GaAs光电导开关的雪崩倍增工作模式所输出的超快电脉冲功率容量远大于其线性工作模式, 迄今为止, 还没有人提出用雪崩倍增机理的GaAs 光电导开关作为辐射源产生THz电磁辐射. 本文探讨了用 雪崩倍增工作模式的GaAs光电导开关作为光电导天线产生THz电磁波的可能性及研究进展. 通过理论分析及实验研究, 在实验上实现了: 1) 利用nJ量级飞秒激光触发GaAs光电导天线, 可以进入雪崩倍增工作模式; 2) 利用光激发电荷畴的猝灭模式, 可以使GaAs光电导天线载流子雪崩倍增模式的延续时间(lock-on 时间)变短. 这为利用具有雪崩倍增机理的GaAs光电导天线产生强THz辐射奠定了基础.     

Passively Q-switched laser operation in a composite Nd:YVO4/Nd:YVO4/Nd:YVO4 crystal with a GaAs saturable absorber

By using a piece of GaAs wafer as the saturable absorber, the performance of the passively Q-switched composite Nd:YVO₄ laser with different output couplers has been demonstrated for the first time as far as we know. The largest continuous wave output power of 1.52 W is obtained at the incident pump power of 5.31 W, giving an optical conversion efficiency of 28.7% and a slope efficiency of 30.2%. The shortest pulse width of 11 ns, the largest single-pulse energy of 2.49 μJ and the highest peak power of 190 W are also obtained.