强脉冲信号在光纤参变放大器中的放大特性研究

考虑到抽运损耗、走离、色散和非线性等效应,用分步傅里叶方法求解耦合的非线性薛定谔方程组,就强脉冲信号在连续光抽运光纤参变放大器中的放大情况进行了理论研究。研究结果表明,强脉冲信号除经历振幅放大,脉冲时域展宽等过程外,还会发生令人感兴趣的脉冲分裂现象,即一个脉冲信号分裂为两个子脉冲。而且即使在连续光抽运的情况下,走离效应对强脉冲信号的放大也产生了显著影响,即促使两个子脉冲振幅不等以及脉冲漂移。最后,强脉冲信号独特的放大特性用光纤参变放大器的饱和增益特性做了很好的解释,并指出脉冲分裂现象在信号抽样、脉冲压缩、光时分复用系统中有潜在用途。     

Autlerben Townes splitting in photoelectron spectra of K2 molecule

We investigate Autler-Townes splitting in the photoelectron spectra of K₂ molecule driven by pump-probe pulses via employing the time-dependent wave packet approach. It is found that the magnitude of Aulter-Townes splitting varies with the wavelength of the intense laser pulse. In particular, the phenomenon of Aulter-Townes splitting vanishes for the far-off resonance of the pump pulse. Also, the split peaks of Autler-Townes in the case of resonant pump pulse give us an approach to directly obtaining the transition dipole moment of a molecule.     

Stimulated generation of superluminal light pulses via four-wave mixing

We report on the four-wave mixing of superluminal pulses, in which both the injected and generated pulses involved in the process propagate with negative group velocities. Generated pulses with negative group velocities of up to v(g)=-1/880c are demonstrated, corresponding to the generated pulse's peak exiting the 1.7 cm long medium ≈50 ns earlier than if it had propagated at the speed of light in vacuum, c. We also show that in some cases the seeded pulse may propagate with a group velocity larger than c, and that the generated conjugate pulse peak may exit the medium even earlier than the amplified seed pulse peak. We can control the group velocities of the two pulses by changing the seed detuning and the input seed power.     

Photoluminescence Properties of Thin-Film Nanohybrid Material Based on Quantum Dots and Gold Nanorods

The dynamics of coherent propagation of a unipolar subcycle pulse of a large electric-field area (the integral of the electric-field strength with respect to time) in a nonlinear two-level resonant medium is studied theoretically. The propagating pulse is shown to be capable of splitting into a pair of individual components, each of which behaves like a pulse of self-induced transparency. This phenomenon is similar to the well-known phenomenon of splitting of a 4π or 6π pulse into a pair of 2π pulses of self-induced transparency, which occurs in the case of propagation of long pulses, when the notion of the pulse area is applicable and the area theorem holds.     

Attosecond time-resolved autoionization of argon

Autoionization of argon atoms was studied experimentally by transient absorption spectroscopy with isolated attosecond pulses. The peak position, intensity, linewidth, and shape of the 3s3p?np 1P Fano resonance series (26.6-29.2 eV) were modified by intense few-cycle near infrared laser pulses, while the delay between the attosecond pulse and the laser pulse was changed by a few femtoseconds. Numerical simulations revealed that the experimentally observed splitting of the 3s3p?4p 1P line is caused by the coupling between two short-lived highly excited states in the strong laser field.     

Observation of the Kondo effect in a spin-3/2 hole quantum dot

We report the observation of Kondo physics in a spin-3/2 hole quantum dot. The dot is formed close to pinch-off in a hole quantum wire defined in an undoped AlGaAs/GaAs heterostructure. We clearly observe two distinctive hallmarks of quantum dot Kondo physics. First, the Zeeman spin splitting of the zero-bias peak in the differential conductance is independent of the gate voltage. Second, this splitting is twice as large as the splitting for the lowest one-dimensional subband. We show that the Zeeman splitting of the zero-bias peak is highly anisotropic and attribute this to the strong spin-orbit interaction for holes in GaAs.     

Determination of Quality Factor for Highly Overcoupled EPR Resonators

We reported determination of the loaded quality factor (Q) of highly overcoupled (dielectric, loop-gap, and cavity) resonators used in time-domain electron paramagnetic resonance. We introduced a microwave absorber into resonators and achieved critical-coupling. Due to the deep “Q-dip” of critical-coupling, we can easily determine the loaded Q as low as 10. The loaded Q of resonators with and without the microwave absorber was examined under various overcoupling conditions. We found that the radiation Q (Q _r) can be calculated from the loaded Q of the resonator that contains the microwave absorber. We proposed a simple model that represents the loaded Q of the overcoupled resonator in terms of two parameters, Q ₀ and Q _r. Q ₀ is the effective unloaded Q of the resonator determined for the critically coupled resonator without the microwave absorber and is independent of a degree of coupling. The model can be applied to overcoupling in which the coupling parameter (Q ₀/Q _r) is in the range of 1 to ca. 20.     

Wave-vector conservation upon hybridization of 4f and valence-band states observed in photoemission spectra of a Ce monolayer on W(110)

Angle-resolved resonant photoemission data for a hexagonally ordered monolayer of Ce on W(110) are presented. The spectra reveal a splitting of the 4f(0) ionization peak around a point in k space where a degeneracy with a valence-band state is expected. The phenomenon is described within a simple approach to the periodic Anderson model. It is found that the Ce 4f state forms a band and hybridization predominantly occurs between the 4f and the valence-band states at the same wave vector.     

Low-energy structure in the ionization of argon: Comparison of experiment with theory

The above-threshold ionization of argon in an intense 70-fs,400-nm linearly polarized laser pulse has been investigated by the velocity map imaging techniques,combined with an attosecond-resolution quantum wave packet dynamics method.There is a quantitative agreement in all dominant features between the experiment and the theory.Moreover,a peak-splitting phenomenon in the first energy peak has been observed at high pulse intensity.Further,through the theoretical analysis,an ac Stark splitting with evident resonant and nonresonant ionization pathways has been found to be the physical reason for the experimental observations.     

Spike Phenomenon in Raman Spectrum of Optically Pumped Ear-Infrared Laser

Based on the theory of semi-classical density matrix, spike phenomenon of multi-longitudinal-mode CO2-9R(30) optically pumped miniature NH₃ molecules far-infrared cavity laser was theoretically studied and the reason of forming spike phenomenon was approved as two aspects: one was the competitive effect caused by the process of AC Stack splitting two photons, which made that the output optical spectral intensity of one AC Stark splitting peak was stronger than that of the other AC Stark splitting peak; the other was the longitudinal-mode spectral characteristics of laser resonant cavity.     

复合结构粉末直流电致发光(CS—DCEL)屏的双光脉冲现象的初步研究

本文首次报导了粉末ZnS:Mn.Cu复合结构直流电致发光(CS—DCEL)屏在电脉冲激发下出现现的双光脉冲现象。这种结构的屏与普通DCEL屏的不同之处在于,其发光层和ITO导电膜层之间镀有一厚约0.4μm绝缘性良好的绝缘介质层。当用电脉冲激发时,黄色光(～5850Å)脉冲不仅出现于电脉冲前沿,还出现于其后沿附近;且正向电脉冲激发时,前沿光脉冲强度大于后沿,反向电脉冲激发时前沿小于后沿。 在电脉冲后沿附近出现第二个光脉冲的现象以及在实验中观察到的其它现象都可利用一个我们建立的模型——发光层与绝缘层界面附近自由电荷层的积累——予以较满意的解释。 另外,CS—DCEL屏在交变电压驱动下具有较好的老化特性和较高的发光效率,它可能成为将来很有前景的一种发光显示器件。     

LD-pumped passively Q-switched Nd:GdVO<Subscript>4</Subscript> laser at 1342 nm with high initial transmission V:YAG saturable absorber

We have realized, for the first time to our knowledge, the passive Q-switching operation of an LD-pumped Nd:GdVO₄ laser at 1342 nm with V:YAG saturable absorber of initial transmission as high as 96%. This laser is investigated under different transmissions of the output coupler. The dependences of average output power, pulse width, pulse repetition rate, single-pulse energy and peak power on incident pump power are also measured. The shortest pulse width of 80 ns, the maximum single-pulse energy of 19.5 μJ and the highest peak power of 244 W are obtained with the output coupler of T = 15% and the pump power of 7.93 W. We find a special experimental phenomenon that the pulse repetition rate begins to drop after reaching the peak with the increase of the pump power. This phenomenon is analyzed and the theoretical calculations are consistent with the experimental results.     

飞秒激光参数对三态阶跃型分子Autler-Townes分裂的影响

利用三态模型和含时波包法, 研究了K₂分子在强飞秒泵浦-探测激光场中泵浦/探测场强、波长对光电子能谱Autler-Townes(AT)分裂的影响．通过分别改变两激光场的场强或者波长预测AT峰移和间距,并且首次量化了AT分裂的峰移和间距．光电子能谱在共振时显示为对称双峰,失谐时为非对称双峰。AT分裂间距随泵浦场强增大而增大,但不因探测场强改变而改变．     

Separatrices splitting for Birkhoff's billiard in symmetric convex domain,closed to an ellipse

An example of a convex domain on the plane with the phenomenon of the transversal intersection of separatrices of the corresponding billiard mapping is presented. This example is constructed as an analytic global symmetric perturbation of an ellipse and we investigate the global symmetric analytic perturbation of the integrable billiard mapping in the ellipse. We establish a theorem on the separatrices splitting of the perturbed billiard mapping and derive the asymptotic formulas for a homoclinic invariant as well as for a "principal" splitting angle of separatrices, arising from the hyperbolic fixed point of the mapping. (c) 1994 American Institute of Physics.     

Measurements of Kondo and spin splitting in single-electron transistors

We measure the spin splitting in a magnetic field B of localized states in single-electron transistors using a new method, inelastic spin-flip cotunneling. Because it involves only internal excitations, this technique gives the most precise value of the Zeeman energy Delta=/g/mu(B)B. In the same devices we also measure the splitting with B of the Kondo peak in differential conductance. The Kondo splitting appears only above a threshold field as predicted by theory. However, the magnitude of the Kondo splitting at high fields exceeds 2/g/mu(B)B in disagreement with theory.     

混响场中脉冲超声空化效应的研究

本文实验研究了不同脉冲宽度的８２０ｋＨｚ超声波的空化效应，结果得出，空化致自基产量随脉冲宽度及声强呈现规律性变化，尤其观察到了“脉冲空化峰”现象，本文从液面受迫振动角度出混响场中“脉冲空化峰”现象的机制。     

负折射介质中超短脉冲的反常分裂现象

对超短脉冲在负折射介质中的传输特性进行了研究,着重分析其不同于常规介质的反常脉冲分裂现象。结果表明:由于负的折射率影响,介质将通过反常群速度色散与自散焦非线性的相互作用机理来诱导脉冲的对称分裂。同时,分析由色散磁导率所导致的可控自陡效应对脉冲分裂的影响,发现负折射介质中正负的自陡效应都会引脉冲非对称分裂。其中负的自陡效导致脉冲裂变后其后沿比前沿高,这与常规介质自陡效应（恒为正）情形相同;而负折射介质正的自陡效应对脉冲分裂影响刚好与前者相反,即裂变后脉冲后沿比前沿低。     

Double-peak Splitting in High-order Harmonics Generation

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Design of electron wave filters in monolayer graphene with velocity modulations

We compare the transport properties of electrons in monolayer graphene by modulating the Fermi velocity inside the barrier. A critical transmission angle is found only when the Fermi velocity in the barriers is larger than the one outside the barriers. It is shown that the transmission exhibits periodicity with the incident angle below the critical transmission angle, and attenuates exponentially in the opposite situation. For both situations, peak splitting occurs in the transmission as the number of the velocity barriers increases, and the characteristics of the transmission suggest an interesting application of an excellent band-pass filter. The dependence of the conductance on the Fermi energy through an identical velocity- modulation structure differs wildly with different Fermi velocities of the barrier. The counterpart of the peak splitting is the sharp oscillations in the conductance profile. Furthermore, some oscillations for the multiple barriers are so sharp that the structure may be used as an excellent sensor.     

Small signal intensity modulation of external cavity lasers with fiber Bragg gratings

The small signal intensity modulation (IM) of a hybrid soliton pulse source (HSPS) utilizing Gaussian apodized fiber Bragg grating (FBG) is described using electric field approach. The HSPS is modeled by a time-domain solution of the coupled-mode equations. It is shown that type of external cavity is important effect on resonance peak spectral splitting (RPSS) in IM response as well as effect of laser and FBG parameters. It is also shown that the RPSS can be suppressed by using linearly chirped Gaussian apodized FBG as an external cavity insted of Gaussian apodized FBG.