Simulation of optically pumped intersubband laser in magnetic field

Simulations of an optically pumped intersubband laser in magnetic field up to 60 T are performed within the steady-state rate equations model. The electron-polar optical phonon scattering is calculated using the confined and interface phonon model. A strong oscillatory optical gain vs. magnetic field dependence is found, with two dominant gain peaks occurring at 20 and 40 T, the fields which bring appropriate states into resonance with optical phonons and thus open additional relaxation paths. The peak at 20 T exceeds the value of gain achieved at zero field.     

Optical pumping and population transfer of nuclear-spin states of caesium atoms in high magnetic fields

Nuclear-spin states of gaseous-state Cs atoms in the ground state are optically manipulated using a Ti:sapphire laser in a magnetic field of 1.516T, in which optical coupling of the nuclear-spin states is achieved through hyperfine interactions between electrons and nuclei. The steady-state population distribution in the hyperfine Zeeman sublevels of the ground state is detected by using a tunable diode laser. Furthermore, the state population transfer among the hyperfine Zeeman sublevels, which results from the collision-induced modification \delta a(\bm S \cdot \bm I) of the hyperfine interaction of Cs in the ground state due to stochastic collisions between Cs atoms and buffer-gas molecules, is studied at different buffer-gas pressures. The experimental results show that high-field optical pumping and the small change \delta a(\bm S \cdot \bm I) of the hyperfine interaction can strongly cause the state population transfer and spin-state interchange among the hyperfine Zeeman sublevels. The calculated results maybe explain the steady-state population in hyperfine Zeeman sublevels in terms of rates of optical-pumping, electron-spin flip, nuclear spin flip, and electron-nuclear spin flip-flop transitions among the hyperfine Zeeman sublevels of the ground state of Cs atoms. This method may be applied to the nuclear-spin-based solid-state quantum computation.     

Characterizing bifurcations and chaos in multiwavelength lasers with intensity-dependent loss and saturable homogeneous gain

We consider the nonlinear dynamics of multiwavelength laser cavities with saturable transmitter and saturating homogeneous gain using a simple and general discrete model. Saturable transmitter is an intensity dependent loss in which the transmittance decreases when the incident optical power increases. We determine the condition under which the saturable transmitter will generate behaviors such as stable steady-state lasing states, periodic lasing states, and chaotic lasing states. Indeed, for sufficiently large power, steady-state operation is first destabilized through a Hopf bifurcation which generates periodic lasing solutions. This is followed by a sequence of period doubling bifurcations to chaotic lasing. The bifurcation structure leading to chaos is characterized by three key methods of dynamical systems: a Feigenbaum series, the calculation of Lyapunov exponents and the computation of the correlation dimension of the system. We found that even single wavelength operation can exhibit complex nonlinear dynamics if the loss element is a saturable transmitter.     

Optical amplification using raman transitions between spin-singlet and spin-triplet states of a pair of coupled in-GaAs quantum dots

We report the observation of steady-state optical amplification in Raman transitions between the lowest-energy spin states of a single quantum-dot molecule. Absorption and resonance fluorescence experiments demonstrate that the entangled two-electron singlet and triplet states have electric-dipole coupling to a common optically excited state. Fast spin relaxation ensures optical gain on the triplet transition when the singlet transition is driven resonantly. By embedding the quantum-dot molecule in a cavity of modest quality factor, a solid-state single-emitter laser can be realized.     

Real-time analysis of nonlinear transient response of weakly confined excitons

By means of the nonlocal transient-response theory, we elucidate the characteristics of the femtosecond transient response of thin films with a thickness beyond the long wavelength approximation (LWA) regime. In this regime, the contribution of higher excitonic states with a nondipole-type spatial structure becomes dominant and the interplay between the spatial structures of excitonic wavefunction and the radiation field plays an important role, causing an anomalous enhancement of nonlinear signal at specific size-energy resonant conditions. In addition, in the femtosecond pulse excitation, the interference of the signals from the multiple excitonic states, which are excited simultaneously by the incident pulse with a wide spectral width, can generate a greater diversity of optical response than expected by the steady-state analysis. This suggests the possibility that we can control the optical function of the nano-materials by the selective excitation of the aimed excitonic states using the laser pulse. This study serves as a theoretical basis for the nonlinear transient response by ultrashort pulse excitation of excitons confined in nano-structures.     

基于光反馈半导体激光器的多开关状态检测系统

为了能够同时检测多个开关的状态,提出了一种基于光反馈半导体激光器的多开关状态检测系统.该系统由半导体激光器、多开关传感网络和数据采集与处理单元组成.多开关传感网络包括多个反馈光路,每个光路由耦合器、光纤和强度反射式光开关构成.所有开关都闭合时,系统没有反馈,激光器输出连续光.当有开关被打开时,光反馈使系统工作在混沌状态.根据系统输出信号的自相关曲线中与各开关位置对应处的峰值是否大于预设阈值来判断开关的状态,通过编程令其它位置处的峰值为零来消除干扰峰.搭建了3个开关的实验系统,分别对不同开关状态下的系统进行检测,结果表明该系统可以准确检测单个或多个开关的状态.     

Manipulation on human red blood cells with femtosecond optical tweezers

Different types of femtosecond optical tweezers have become a powerful tool in the modern biological field. However, how to control the irregular targets, including biological cells, using femtosecond optical tweezers remains to be explored. In this study, human red blood cells (hRBCs) are manipulated with femtosecond optical tweezers, and their states under different laser powers are investigated. The results indicate that optical potential traps only can capture the edge of hRBCs under the laser power from 1.4 to 2.8 mW, while it can make hRBCs turn over with the laser power more than 2.8 roW. It is suggested that femtosecond optical tweezers could not only manipulate biological cells, but also subtly control its states by adjusting the laser power.     

CdSe/ZnS核-壳结构量子点的非线性光学吸收

利用开孔Z扫描技术研究了吸收峰分别为553 nm和503 nm的两种尺寸CdSe/ZnS核-壳结构量子点溶液的非线性吸收性质.对于532 nm,6 ns激光脉冲,两种材料均表现出饱和吸收向反饱和吸收转化的现象.数值模拟结果表明：当吸收峰波长大于激光波长时,饱和吸收过程由快、慢两种机制组成,分别对应基态载流子被激发至不同的激发态,而强光下的反饱和吸收与快过程相关;当吸收峰波长小于激光波长时,饱和吸收主要由快过程机制引起,强光下的反饱和吸收源自激发态吸收和双光子吸收.我们的研究结果表明半导体量子点是研制光开关和光限制器件的理想候选材料.     

High-power diode-pumped Yb-doped fiber laser at 1150 nm

A model of steady-state rate equations including amplified spontaneous emission for long-wavelength Yb doped fiber laser is set up, which provides design principle for a practical laser system. We demonstrate a diode-pumped all-fiber Yb-doped fiber laser at 1150 nm with an output power of 33.6 W, the optical efficiency is 60%.     

多有源区隧道再生半导体激光器稳态热特性

 利用有限元软件ANSYS结合傅里叶定律,对制约适用于光纤耦合输出的新型高功率多有源区隧道再生半导体激光器长寿命工作的稳态热特性进行了系统计算、分析。获得了这种新型器件工作时各有源区温度分布特征及与传统单有源区器件稳态热特性的区别,并给出了多有源区隧道再生半导体激光器工作时各有源区温度的估算方法,同时对有效降低这种新型器件热阻的方法进行了讨论。结果表明:连续工作时,多有源区隧道再生半导体激光器比同材料体系传统结构器件更易获得较高的输出功率。     

双环掺铒光纤激光器混沌控制产生周期脉冲及多周期现象研究

研究了双环掺铒光纤激光器混沌控制产生周期脉冲以及多周期现象,并提出了光调制器调制泵浦控制、外部光注入控制、光衰减器控制、光延时时间控制器控制以及相位控制器控制和连续键控反馈光等多种双环掺铒光纤激光器的混沌控制方法.结果表明:用光调制器调制泵浦光能控制激光到周期态及多周期态;用外部光注入能控制激光到单周期态、双周期态、三周期态、四周期态、五周期态以及多种高周期态等,能形成多种形式相空间图样,产生双环掺铒光纤激光器独特的激光单锁模拟和双锁模拟现象;用外部光路反馈控制时,在负反馈条件下,用时间控制器控制反馈光的延时时间能控制激光到不同的周期态和双周期态,用光衰减器控制光的强度能控制激光到稳定态及周期态,用相位调制器控制反馈光的相位进行负反馈和正反馈转换时能有效地控制激光进入到稳定态及周期态;连续键控反馈光相位能控制激光到多周期态等.整个控制系统能动态、有效地控制产生周期光脉冲以及多种新颖的多周期态等.     

Quadrature squeezing in an isolated pulse of light

Quantum properties of pulsed radiation obtained by cutting out a part of the signal from steady-state squeezed-light sources are investigated. The considered sources include a degenerate optical parametric oscillator, a sub-Poissonian injection-locked laser, and a synchronously pumped femtosecond optical parametric oscillator. Based on the statistical properties of steady-state radiation from these sources, we analyzed to what extent preservation of these properties is sensitive to the observation time.     

Robust quantum dot exciton generation via adiabatic passage with frequency-swept optical pulses

The energy states in semiconductor quantum dots are discrete as in atoms, and quantum states can be coherently controlled with resonant laser pulses. Long coherence times allow the observation of Rabi flopping of a single dipole transition in a solid state device, for which occupancy of the upper state depends sensitively on the dipole moment and the excitation laser power. We report on the robust population inversion in a single quantum dot using an optical technique that exploits rapid adiabatic passage from the ground to an excited state through excitation with laser pulses whose frequency is swept through the resonance. This observation in photoluminescence experiments is made possible by introducing a novel optical detection scheme for the resonant electron hole pair (exciton) generation.     

利用光纤光栅对实现双波长增益控制掺铒光纤放大器特性的实验研究

控制激光的弛豫振荡和空间烧孔现象的存在 ,对全光增益控制掺铒光纤放大器 (EDFA)的性能产生劣化影响。采用一种新颖简单的利用两对光纤光栅对形成谐振腔结构 ,实现双波长增益控制掺铒光纤放大器。由两个不同波长的激光共同承担增益控制的任务 ,降低了控制激光引起的空间烧孔现象和瞬态输出变化。在动态工作条件下 ,双波长激光增益控制掺铒光纤放大器显示出优越的特性 ,适用范围扩展为普通单波长增益控制掺铒光纤放大器的两倍 ,能够适应 0～ 43kHz的上下载频率。     

Study on the method of controlling chaos in an Er-doped fiber dual-ring laser via external optical injection and shifting optical feedback light

Controlling chaos in an erbium-doped fiber dual-ring laser is studied by injecting an external light and shifting the phase of an optical feedback light. First, the parameters of the externally injected optical signal are adjusted to bring the chaotic laser into a single-period state and a multiperiod state, respectively. In addition, the single-mode locking in a single ring of the laser as well as the dual-mode locking in dual ring of the laser are found. Secondly, the method of optical feedback is used to stabilize chaos by controlling the parameters of the optical devices in an external optical path. We show that the optical negative feedback can stabilize the chaotic laser into a single-period state, while the optical positive feedback can stabilize the chaotic laser into another single-period state and a period-doubling state. Lastly, various dynamical states are produced in the laser by shifting the phase of the optical feedback light.     

Generating large steady-state optomechanical entanglement by the action of Casimir force

In this paper,we study an optomechanical device consisting of a Fabry-P′erot cavity with two dielectric nanospheres trapped near the cavity mirrors by an external driving laser.In the condition where the distances between the nanospheres and cavity mirrors are small enough,the Casimir force helps the optomechanical coupling to induce a steady-state optomechanical entanglement of the mechanical and optical modes in a certain regime of parameters.We investigate in detail the dependence of the steadystate optomechanical entanglement on external control parameters of the system,i.e.,the effective detuning,the pump powers of the cavity,the cavity decay rate and the wavelength of the driving field.It is found that the large steady-state optomechanical entanglement,i.e.EN=5.76,can be generated with experimentally feasible parameters,i.e.the pump power P=18.2μW,the cavity decay rateκ=0.5 MHz and the wavelength of the laserλL=1064 nm,which should be checked by optical measurement.     

Effect of squeezed vibrational states on the optical properties of molecular systems in a field of laser radiation

Specific features of optical and nonradiative transitions in molecular systems in the field of an intense electromagnetic wave are studied with account of squeezed vibrational states. It is shown that a field of laser radiation considerably enhances the tunneling processes in electronic vibrational systems and makes it possible to obtain the generation of higher harmonics. Conditions are found under which squeezed vibrational states can lead to some stabilization of excited electronic states with respect to the processes of luminescence.     

Computer simulations for a common-cavity two section (CCTS) bistable laser

In this paper a computer simulation about the characteristics of steady-state and transient response for a CCTS bistable laser under inhomogeneous electrical injection or external optical injection is reported. The rate equations are analysed in terms of typical parameters, such as electrical injection currents, spontaneous emission coupling factor, external optical injection intensity, etc. It shown that bistability and self-pulsation come mainly from the absorbing section constituting a saturable absorber in this device. A weak optical signal can be amplified by the laser, the amplification factor being dependent on the direction of the incident light. Some interesting results for the transient response under certain external optical injections are also discussed.     

具有腔内光放大的单共振光参量振荡器

推导了描述稳态运行，具有腔内光放大的环形腔单共振光参量振荡器(ICOASRO)的功率特性的高斯光束理论.在这种结构的单共振光参量振荡器(SRO)中，适当地选择光放大器的参数，可以很大程度地降低单共振光参量振荡器的抽运阈值.在平均场近似下无二阶非线性交叉耦合作用的具有腔内光放大的环形腔单共振光参量振荡器的工作范围分成四个工作区域，且存在最小的单共振光参量振荡器的抽运阈值.文中的分析考虑了作为光放大器的激光增益介质的端面抽运特性，考虑了一般化单共振光参量振荡器的特性. 关键词： 单共振光参量振荡器 光放大 阈值     

Transfer and storage of vortex states in light and matter waves

We theoretically explore the transfer of vortex states between atomic Bose-Einstein condensates and optical pulses using ultraslow and stopped light techniques. We find shining a coupling laser on a rotating two-component ground state condensate with a vortex lattice generates a probe laser field with optical vortices. We also find that optical vortex states can be robustly stored in the atomic superfluids for times, in Rb-87 condensates, limited only by the ground state coherence time.