High-bit-rate generation of low chirped pulses from vertical-cavitysurface-emitting lasers via external axial magnetic field

The possibility of generating low chirped, fast optical pulses with linear polarization in vertical-cavity surface-emitting lasers (VCSELs) is numerically explored. We show that, under the influence of an axial magnetic field, polarization modulation at gigahertz rates can be achieved with possible applications in optical clock generation/extraction and optical communications     

双模气体激光器的磁起偏特性

本文从理论上研究了在外加横向均匀磁场作用下双模气体激光器输出光的偏振特性。用导出的双纵模偏振参数运动方程,计算了双模He-Ne激光器632.8nm谱线的偏振参数。当外加磁场大于某值时,可获得高偏振度的线偏振光输出。理论与实验结果相符合。     

Gyrotron with a tapered external magnetic field

Journal of Infrared, Millimeter, and Terahertz Waves -     

Short-pulse generation with broad-band tunability fromsemiconductor lasers in an external ring cavity

Short optical pulses are generated by actively mode locking semiconductor lasers in an external ring cavity with a very broad tuning range from 795 to 857 nm. The wide tunability is possible because the gain bandwidth is broadened by the use of asymmetric dual quantum wells for the semiconductor laser material. Assuming a Gaussian shape, the generated pulses have pulsewidths of 13-21 ps and spectral widths of 24.5 Å for the tuning range. The mode-locked spectrum contains almost no amplified spontaneous emission noise     

Spiking in light pulses from GaAs Q-switched junction lasers

Using a detection system with 150-ps resolution, a spiking behavior has been detected in theQ-switched light output from GaAs junction lasers. At the lower currents in theQ-switching region, a single light spike, whose width is about 300 ps, is observed. At higher currents, additional light spikes appear whose widths and spacings decrease as the current is increased. At the highest pumping levels, only the initial spike is clearly resolved and its width has decreased to less than 200 ps. Qualitative agreement is obtained from a simple theory based on the standard rate equations. The necessary modifications to the theory are discussed and results of computer calculations are presented which predict that the width of the initial spike can be much less than 100 ps at sufficiently high pumping levels.     

外加磁场对微空心阴极放电的影响

采用C语言编程实现三维系综蒙特卡罗模型,外加磁场对微空心阴极放电的影响。研究结果显示,当气体压强和外加电压保持不变时,在微空心阴极放电系统中加入外部磁场后,对阴极方向上的电子密度分布变化不大,轴向和侧向上的电子漂移范围减小,电子能量向低能方向移动,但是外加磁场对高气压微空心阴极放电的影响整体上不如对低气压放电的影响明显。该研究结果对微空心阴极放电等离子体的机理研究具有一定的指导意义。     

Modulation of Fano resonances by an external magnetic field in semiconductor quantum wells

We have studied the dimensionality dependence of the behavior of Fano resonances in the photoluminescence excitation spectra of GaAs---Al_xGa_1−xAs heterostructures in a magnetic field applied in the Faraday configuration. A striking difference is observed between quasi-two and quasi-three-dimensional systems: while the Fano profiles evolve into Lorentzian lineshapes in two-dimensional systems, Fano resonances emerge from the continuum in three-dimensional-systems with increasing magnetic field.     

AC losses in type-II superconductors induced by nonuniform fluctuations of external magnetic field

Magnetic field fluctuations are inevitable in practical applications of superconductors and it is often necessary to estimate the ac losses these fluctuations induce. If the fluctuation wavelength is greater than the size of a superconductor, known estimates for an alternating uniform external magnetic field can be employed. The authors consider the opposite case and analyze, using a model critical-state problem, penetration of spatially nonuniform fluctuations into type-II superconductors. Numerical simulation is based on a variational formulation of the Bean model. The analytical solutions, found in a weak penetration limit, are used to evaluate ac losses for two types of fluctuations: the running and standing waves. It is shown that for spatially nonuniform fluctuations the losses are better characterized by the fluctuation penetration depth than by the fluctuation amplitude. The results can be used to estimate the ac losses in flywheels, electric motors, magnetic shields, etc.     

Analysis of frequency modulation of junction lasers by ultrasonic waves

An analysis of the interaction of ultrasonic waves with the junction-laser modes is performed, using first-order perturbation theory. It demonstrates that in the presence of sound waves, each laser mode is frequency-modulated with negligible harmonic distortion or mode mixing. It is also shown that bandwidths of several GHz, with high-modulation index are possible.     

Resonant modes of GaAs junction lasers

The resonant modes of GaAs junction lasers are obtained from a proposed model and compared with experimental results. Theoretical results are based on an assumed laser medium whose dielectric constant varies both along and perpendicular to the junction plane. The frequency separations of the transverse modes are found to be in very good agreement with presented high-resolution spectral measurements of stripe-geometry laser radiation. Furthermore, the theoretical field distributions are also in good agreement with observed transverse field variations reported previously. The laser output spectrum usually shows a number of "satellites" located adjacent to each longitudinal (Fabry-Perot) resonance. It is shown that each satellite represents the frequency of a transverse resonance having a different mode number along the junction plane and a corresponding Hermite-Gaussian intensity profile along the plane. Theory shows that the frequency separation of two adjacent satellites is related to the falloff rate of the dielectric constant along the junction plane. This focusing is measured from the intensity profile of a far-field pattern. From this information, the theoretical frequency separation is calculated and found to agree well with the measured separation of 6.4 GHz (0.15 Å).     

Gain measurements on semiconductor lasers by optical feedback from an external grating cavity

We report on new methods to determine the curvature around maximum of the mode gain curve of homogeneously line-broadened semiconductor lasers, either by measuring the wavelength dependence of threshold current of the laser coupled to an external grating cavity or by measuring the tuning range of the laser versus the amount of optical feedback. We experimentally found the mode gain width and the current-induced peak-gain wavelength shift of a GaAlAs CSP laser to 175 Å and 2.1 Å/ mA, respectively.     

Radiation propagating transverse to the external magnetic field from an electromagnetic source in an unbounded plasma

The radiation characteristics of a line source of magnetic current embedded in an unbounded plasma are investigated for the case in which a uniform magnetic field is impressed externally throughout the medium in the direction of the source. The plasma is assumed to be a homogeneous and macroscopically neutral mixture of compressible gas of electrons and ions. A two-fluid continuum theory of plasma dynamics is employed. It is shown that it is possible to define three suitable wave functions which satisfy separately simple wave equations whose solutions are written down by inspection. These wave functions specify the three possible modes which are identified, respectively, to be the modified forms of the electromagnetic, the electron plasma and the ion plasma modes. The limiting behavior of these modes are discussed for the following two cases: 1) infinite source frequency and 2) vanishing external magnetic field. The dispersion relations for the three modes are examined in detail for the general case using a perturbation procedure. It is shown that the modified ion plasma (MIP) mode propagates for all frequencies whereas both the modified electron plasma (MEP) mode and the modified electromagnetic (MEM) mode have a low-frequency cutoff. Explicit expressions for the cutoff frequencies are obtained. The power radiated in each of the three modes is also evaluated. It is found that the power radiated in the MEM mode is always lower than that due to the line source in free space, whereas the power radiated in the two plasma modes is higher than that value for certain ranges of frequency.     

The second harmonic generation in semiconductors in the DC magnetic field

The second harmonic radiation in millimeter wave region is found in semiconductors in the absence of the dc electric field. The observed resonant maximum of radiation intensity is shown to be related to the excitation of the free-electron plasma oscillations in the dc magnetic field.     

Highly circular-polarized single photon generation from a single quantum dot at zero magnetic field

Origin of sharp photoluminescence lines observed from an InAlAs quantum dot was identified with the measurements of excitation-power dependences and polarization correlations, together with photon correlation measurements. Single photon emission with high degree of circular polarization (DCP) up to 60% was observed from a positively charged exciton (trion) state in the single quantum dot under non-resonant excitation at zero magnetic field.     

Power enhancement in argon II narrow-tube lasers due to zeeman effect by a transverse magnetic field

The role of the Zeeman effect for the power enhancement of a small-bore argon ion laser (488.0 nm) by applying the transverse magnetic field has been investigated both experimentally and theoretically. The σ-polarized laser has a larger output power than the π-polarized laser in the wide range of magnetic field strength. Specifically, at weak magnetic fields, enhancement occurred only for the σ-polarized laser. The experimental results are interpreted in terms of the semiclassical theory of the Zeeman laser. A narrow spectrum envelope is observed in the σ-polarized laser. In the case of internal mirrors without Brewster window, it is demonstrated experimentally that π and σ polarization coexist and compete with each other.     

Transform-limited pulses from low chirp DFB lasers with external feedback

Transform-limited pulses with time-bandwidth product as low as 0.34 are obtained from a microwave modulated low-chirp MQW-DFB laser diode coupled to a long, external cavity. Pulsewidths from 20 to 30 ps are measured for repetition frequencies tunable from 2.5 to 5 GHz in steps of approximately 100 MHz.<>     

Linewidth reduction of cleaved-coupled-cavity lasers by optical feedback from a single-mode polarisation-preserving fibre external cavity

Linewidth characteristics of a cleaved-coupled-cavity laser with a single-mode polarisation-preserving fibre external cavity have been investigated as a function of feedback power level and side-mode suppression ratio. The optimum power feedback ratio is near 2×10?4 for a minimum linewidth of about 30 kHz. A weak dependence of linewidth on side-mode suppression ratio is observed as long as the suppression ratio is greater than 500:1.     

Hybrid magnetic tunnel junction/vertical cavity surface emittinglaser field sensor device

A hybrid magneto-optoelectronic device is demonstrated, composed of a magnetic tunnel junction and a vertical cavity surface emitting diode laser. External magnetic field changes are translated into amplitude modulation of the laser output power with sensitivity that suggests applications in wireless and remote sensing of magnetic fields