Optically pumped semiconductor nanowire lasers

This paper reviews our recent work on fabrication,optical characterization and lasing application of semiconductor nanowires,with brief introduction of related work from many other groups.     

Optically pumped semiconductor platelet lasers

Tunable CW laser action of platelet semiconductors is reported in both mode-locked and unmode-locked configurations. The gain media are platelets of CdS, CdSe, CdSSe, and InGaAsP cooled to 85 K and longitudinally pumped by an argon-ion laser. Antireflection (AR) coating of the crystal face and external bandwidth restriction have been used to generate pulses as short as 4 ps. The pulses observed are chirped, with nontransform limited time-bandwidth products of about 1.7. The energy conversion efficiency is 20 percent into the TEM00mode, with output powers of over 10 mW from CdS.     

Optically pumped submillimeter wave semiconductor lasers

An optically pumped multiple quantum well (MQW) submillimeter wave (SMMW) laser is proposed and designed. The laser can potentially generate significant power in the far-infrared regime. It is based on pumping of a series of InGaAs-GaAs quantum wells with a CO₂ laser. The excited electrons created by the pumping process tunnel into the upper of two subband states in an AlGaAs-GaAs quantum well grown in series with the absorption wells, and thereby give rise to a population inversion between these two states which are tuned to the SMMW frequency desired. The authors present the key concepts of the new device and some designed device structures     

A comparison of amplitude-phase coupling and linewidth enhancementin semiconductor quantum-well and bulk lasers

The amplitude-phase coupling factor α (linewidth enhancement factor) is compared for typical semiconductor quantum-well and bulk double heterostructure lasers. As a direct consequence of the reduction of the differential gain, there is no reduction of α in single-quantum-well lasers compared to bulk lasers. The number of quantum wells strongly affects the amplitude-phase coupling in quantum-well lasers. It is shown that the interband transition induced amplitude-phase coupling dominates that induced by the plasma effect of carriers in typical quantum-well lasers. By considering the spontaneous emission factor in the spectral linewidth, the authors show that there is an optimal number of quantum wells for achieving the narrowest spectral linewidth     

Optically pumped CW dimer lasers

Bound-bound electronic transitions in simple molecules are generally suited to realize efficient multiline laser oscillation in the visible and ultraviolet spectral region. By means of optical excitation with argon and krypton lasers, CW laser oscillation could be obtained for various homonuclear diatomic (dimer) molecules such as Li2, Na2, K2, Bi2, S2, Te2, and I2, with emission of several hundred laser lines in the spectral range of about 400-1350 nm. The principles of these lasers and the general dependence of threshold and output power on temperature, pressure, length of vapor zone, and some other parameters is discussed. To achieve satisfactory CW operation, low quenching losses for the upper laser level population and a sufficiently fast relaxation of the population of the lower laser level are necessary. Under optimum operation conditions, efficiencies up to 15 percent, multiline output powers up to 400 mW, and single line-single frequency output powers up to 200 mW were achieved. These dimer lasers are three-level laser systems. In case of coherent optical excitation, two-photon or Raman-type processes contribute to the amplification process. Due to these mechanisms the forward direction is strongly favored and in a ring laser system spontaneous unidirectional oscillation is obtained. By means of a suitable three-level model, analytical and numerical calculations of gain profiles are performed and compared with experiments. These optically pumped molecular lasers are suited for various spectroscopic and kinetic investigations, for frequency standards or as simple and efficient systems to convert pump laser radiation into other spectral regions.     

Optically pumped atomic thulium lasers

A thulium vapor column is irradiated with the fourth harmonic of a Nd:YAG laser at 266 nm. The near coincidence with a dipole allowed transition from ground state results in efficient optical pumping yielding 87 simultaneous superfluorescent laser transitions from 300 to 900 nm. Many of the emissions are due to inversions to the ground state of both neutral and singly ionized Tm atoms.     

Triggerable semiconductor lasers

A triggerable semiconductor laser emits light in very short (0.1 ns) intense (0.1 W) pulses with a few nanosecond periods when biased a fraction of a milliampere above a threshold current. Single uniform lightwave pulses can be triggered by fractional milliampere current pulses up to several nanoseconds in duration. This behavior was first seen in computer simulations of devices with a high electron-trap density (other causes are possible). Devices exhibiting this behavior have been found among the population of AlGaAs stripe lasers made by deep proton bombardment. A simple lightwave pulse regenerator has been built by adding a photodiode with less than unity gain. This circuit emits lightwave pulses with 6 pJ energy, less than 0.2 ns in duration, and with an amplitude that is up to 15 times larger than the input pulse.     

波长(频率)可调谐半导体激光器

波长或频率可调谐的半导体激光器在光通信等实际应用领域中有着重要而广泛的应用。文章立足于实际应用,从谐振腔的结构出发,以调谐机理为研究对象,对可调谐半导体激光器进行了分类研究,并对它们的调谐特性做了总结     

半导体微腔激光器

文章简要叙述了微腔激光器的基本工作原理。采用先进的ＬＰＥ及反应离子刻蚀等微细加工技术制作了盘型－ 图钉式微腔结构,测得其有源区的光荧光谱的半宽度为０ ．０３２ ｅＶ,波长为８１５ ．３３ ｎｍ 。     

分别限制异质结半导体激光器

研制成功分别限制异质结(SCH)激光器在2.5～3倍阈值时,单向输出峰值功率为8～13W,垂直于结平面方向和平行于结平面方向的全宽度半功率束发散为θ垂=15°～22°,θ平=14～18°.     

Heavily-doped semiconductor lasers

A theoretical study of the effect of heavily doping the active layer of a semiconductor laser shows that the minority carrier density required to reach inversion decreases with increasing doping. Unfortunately, the minority carrier lifetime also decreases since there is a component of the recombination rate that is proportional to the doping density. It is found that for a dopant with a recombination rate coefficientK_{B}, 5E-10cm³/s (Zn in GaAs), the inversion current density has a local minimum at zero doping, but decreases again for n-type doping above1E18/cm, and is one third of the zero value at4E18/cm. The value of KBfor other dopants and materials is unknown; however, for a dopant with a coefficient smaller than5E-11, the inversion current would be less than one tenth the zero value at4E18n-type, and would also decrease with the addition of p-type dopant. These results indicate that by heavily doping the active layer with the proper dopant, one might obtain both faster response and a lower threshold current, particularly with n-type dopants.     

Advanced semiconductor lasers

Recent research activities in the field of advanced semiconductor lasers are reviewed with emphasis on highly stable single-wavelength lasers and surface-emitting (SE) lasers for wideband lightwave communication systems and optical parallel information processing. The operational characteristics of DSM (dynamic single-mode) lasers are summarized and requirements for high-performance operation as light sources for high-speed transmission or coherent communications are described. A type of DSM laser called the distributed-reflector (DR) laser is described as an advanced DSM laser which enables high efficiency, high power, and narrow linewidth operations. Specific features and the potential of SE lasers are summarized. Research activities and remaining problems to be solved for a breakthrough in optical parallel information processing are presented. The potential of multidimensional quantum-well structures, such as QW lasers and quantum-box lasers, is discussed in terms of superior characteristics in both stationary and dynamic operations. The present fabrication technologies for realizing high-performance lasers based on multidimensional QW structures are also presented     

相对论电子束激励的准分子激光器

我们建立了一台相对论电子束发生器,电子束能为1.2兆电子伏,束流千安,束宽25毫微秒,上升前沿<10毫微秒。用这台电子束装置横向激励准分子激光器,激光盒腔长150毫米,输出口径φ16毫米。采用镀介质膜的平凹腔。输出腔片在351毫微米处透过率T(?)12％,全反镜R=1米。在气压比为NF_3:Xe:Ar=2.5托:19托:2.8大气压,充电电压为25千伏时,成功地实现了XeF准分子激光器B(~2∑_(1/2))→X(~2∑(1/2))态跃迁,获得波长为351毫微米和353毫微米的激光发射。输出能量约为5毫焦耳,用2米光栅光谱仪摄得这二条强激光谱线。     

Optically excited resonant diaphragm pressure sensor

Silicon diaphragms fabricated by anisotropic etching are coated with a thin layer of aluminium. An intensitymodulated laser beam focused on the diphragm generates transverse vibrations which are detected interferometrically. Differential pressure is applied to the diaphragm and the pressure-induced change in the fundamental resonant frequency is reported.     

Optically excited resonant beam pressure sensor

Micromechanical silicon beams fabricated by anisotropic etching techniques are coated with a thin layer of chromium. An intensity-modulated laser beam focused on the beam generates transverse vibrations which are detected interferometrically. In the letter we report how the vibration frequency changes with temperature and pressure applied to the beam.     

Etched-mirror unstable-resonator semiconductor lasers

The operation and performance of the first etched-mirror high-loss (ray unstable) semiconductor diode lasers are reported and discussed. This is an alternate approach to conventional plane-parallel stripe geometry diode lasers or monolithic laser arrays for obtaining improved mode control and higher power.     

完全锁模半导体激光器

本文对含F-P标准具的外腔半导体激光器进行了主动锁模研究。适当选择F-P标准具参数可形成单一的纵模群振荡,并可因此得到完全锁模光脉冲。实验中得到了脉宽为13.5ps、重复频率为925MHz的光脉冲输出。     

Laterally coupled-cavity semiconductor lasers

We analyze the threshold behavior of a pair of laterally coupled semiconductor lasers of different lengths. The predictions include longitudinal mode selectivity leading to single longitudinal mode operation with a periodicity determined by the length mismatch, and ripples in the equipower curves in the current plane due to carrier-induced index shifts. We present experimental measurements that confirm these predictions.