Quantum frequency doubling based on tripartite entanglement with cavities

We analyze the entanglement characteristics of three harmonic modes,which are the output fields from three cavities with an input tripartite entangled state at fundamental frequency.The entanglement properties of the input beams can be maintained after their frequencies have been up-converted by the process of second harmonic generation.We have calculated the parametric dependences of the correlation spectrum on the initial squeezing factor,the pump power,the transmission coefficient,and the normalized analysis frequency of cavity.The numerical results provide references to choose proper experimental parameters for designing the experiment.The frequency conversion of the multipartite entangled state can also be applied to a quantum communication network.     

高功率高重复频率多波长飞秒激光系统的研究

以大模场面积光子晶体光纤飞秒激光系统为基频光源,利用非线性频率上转换的方法,获得了高功率高重复频率多波长的飞秒激光脉冲.理论分析并实验验证了聚焦透镜的焦距对倍频光横向模场分布的影响,透镜焦距越长,模场质量越好.在基频光平均功率为218 W,脉冲宽度为110 fs,重复频率为50 MHz的条件下,经过二倍频、三倍频和四倍频获得波长分别为520,347和261 nm的飞秒激光,其平均功率分别达105,47和214 W.二倍频和三倍频的转换效率分别为482%和216%,二倍频到四倍频的转换效率为20 关键词： 超快光学 紫外飞秒激光 频率上转换 光子晶体光纤激光器     

腔内I类非临界相位匹配倍频LBO温度分布对转化效率的影响

在腔内倍频激光器中,非线性晶体的温度梯度造成的相位失配是影响谐波转化效率的关键.用半解析热分析方法得出了非线性晶体LBO在不同基频光参量条件下的温度分布,分析了不同参量对晶体温度分布的影响.分析了温度梯度引起的相位失配对谐波转化总效率的影响,并在不同参量情况下对谐波相对转化效率进行了计算.对腔内倍频激光系统的设计有指导...     

Er3+-Yb3+共掺磷酸盐玻璃放大器的大信号增益与量子效率理论分析

研究大信号工作状态下的Er^3 -Yb^3 共掺磷酸盐玻璃波导放大器的增益与量子转换效率。从量子转换效率的定义出发，得出了增益、抽运光功率以及量子转换效率三者之间关系的解析表达式。通过数值求解大信号工作状态下的Er^3 -Yb^3 共掺系统的速率方程与光功率传输方程，讨论了Er^3 浓度、Yb^3 浓度、Yb^3 与Er^3 浓度比率、抽运光功率以及放大器长度等因素对量子转换效率的影响。结果表明提高Er^3 浓度与增加放大器长度均有助于提高量子转换效率，高Er^3 浓度掺杂需要相应的高Yb^3 浓度与之相匹配以减小由于高浓度Er^3 掺杂引起的上转换效应，Yb^3 浓度的提高将降低器件的量子转换效率，Yb^3 -Er^3 浓度之比取1～2较好。     

Coherent enhancement of broadband frequency up-conversion in BBO crystal by shaping femtosecond laser pulses

An optimal feedback control of broadband frequency up-conversion in BBO crystal is experimentally demonstrated by shaping femtosecond laser pulses based on genetic algorithm, and the frequency up-conversion efficiency can be enhanced by ∼16%. SPIDER results show that the optimal laser pulses have shorter pulse-width with the little negative chirp than the original pulse with the little positive chirp. By modulating the fundamental spectral phase with periodic square distribution on SLM-256, the frequency up-conversion can be effectively controlled by the factor of about 17%. The experimental results indicate that the broadband frequency up-conversion efficiency is related to both of second harmonic generation (SHG) and sum frequency generation (SFG), where the former depends on the fundamental pulse intensity, and the latter depends on not only the fundamental pulse intensity but also the fundamental pulse spectral phase.     

Mode-coupling phenomena in intracavity second harmonic generation

The dependence of intracavity second harmonic generation efficiency on the linear phase detunings in crystal and air is studied both theoretically and experimentally. It is shown that in the presence of feedback at the second harmonic frequency an optimum conversion efficiency can be achieved by a mutually correlated choice of phase mismatch in a nonlinear crystal and the position of the latter inside the cavity.     

Operating the SDUV-FEL with the echo-enabled harmonic generation scheme

Using the recently proposed echo-enabled harmonic generation (EEHG) free-electron laser (FEL) scheme, it is shown that operating the Shanghai deep ultraviolet FEL (SDUV-FEL) with single-stage to higher harmonics is very promising, with higher frequency up-conversion efficiency, higher harmonic selectivity and lower power requirement of the seed laser. The considerations on a proof-of-principle experiment and expected performance in SDUV-FEL are given.     

高效外腔倍频产生426 nm激光的实验研究

利用与铯原子吸收线对应的852 nm半导体激光作为基频光,泵浦基于周期极化磷酸钛氧钾(PPKTP)晶体的环形腔,进行高效外腔谐振倍频并产生426 nm激光.在理论分析小角度环形腔内的热透镜效应基础上,发现晶体中等效热透镜中心位置并非在晶体的几何中心.在理论分析的基础上,实验上通过精密平移台精细调节PPKTP晶体在腔内位置,使得等效热透镜中心位置与谐振腔的腰斑位置重合,进而减小晶体热透镜效应导致的模式失配对倍频效率的影响.在泵浦功率为515 mW时产生了428 mW的426 nm激光输出,对应的倍频转换效率为83.1%.此高效倍频过程为制备与铯原子吸收线相匹配的非经典光场提供有效泵浦光,为推动量子非经典光场的应用以及量子信息科学的发展奠定基础.     

Control of efficiency of photon energy up-conversion in CdSe/ZnS quantum dots

Efficient photoluminescence (PL) up-conversion in CdSe/ZnS quantum dots prepared by an organometallic approach is reported. It is demonstrated that the efficiency of photon energy up-conversion and the magnitude of the spectral shift can be controlled by (i) the thickness of the ZnS layers, (ii) the temperature dependence of the excited-state absorption coefficient, and (iii) the dependence on the excitation intensity. From the analysis of the experimental data, it is proposed that intrinsic gap states are involved as intermediate states in the PL up-conversion, rather than nonlinear two-photon absorption or Auger processes.     

Single photon frequency up-conversion and its applications

Optical frequency up-conversion is a technique, based on sum frequency generation in a non-linear optical medium, in which signal light from one frequency (wavelength) is converted to another frequency. By using this technique, near infrared light can be converted to light in the visible or near visible range and therefore detected by commercially available visible detectors with high efficiency and low noise. The National Institute of Standards and Technology (NIST) has adapted the frequency up-conversion technique to develop highly efficient and sensitive single photon detectors and a spectrometer for use at telecommunication wavelengths. The NIST team used these single photon up-conversion detectors and spectrometer in a variety of pioneering research projects including the implementation of a quantum key distribution system; the demonstration of a detector with a temporal resolution beyond the jitter limitation of commercial single photon detectors; the characterization of an entangled photon pair source, including a direct spectrum measurement for photons generated in spontaneous parametric down-conversion; the characterization of single photons from quantum dots including the measurement of carrier lifetime with escalated high accuracy and the demonstration of the converted quantum dot photons preserving their non-classical features; the observation of 2nd, 3rd and 4th order temporal correlations of near infrared single photons from coherent and pseudo-thermal sources following frequency up-conversion; a study on the time-resolving measurement capability of the detectors using a short pulse pump and; evaluating the modulation of a single photon wave packet for better interfacing of independent sources. In this article, we will present an overview of the frequency up-conversion technique, introduce its applications in quantum information systems and discuss its unique features and prospects for the future.     

Internal resonantly enhanced frequency doubling of continuous-wave fiber lasers

In this Letter we describe a simple method for frequency doubling in high-power CW fiber lasers that offers the prospect of very high conversion efficiency and high power in the visible wavelength regime. Our approach is based on second harmonic generation in an enhancement resonator within the fiber laser cavity and does not require active cavity length stabilization. This technique has been applied to a cladding-pumped Yb-doped fiber laser to generate 19 W of linearly polarized CW green output at 540 nm, with excellent temporal stability for 90 W of absorbed diode pump power at 975 nm. The prospects for further improvement in performance with respect to conversion efficiency and output power are considered.     

稀土掺杂材料的上转换发光

稀土掺杂材料的上转换发光是实现光波频率转换的重要途径,也是稀土掺杂发光材料研究的重要内容。本文从介绍与上转换相关的基本概念出发,阐述了稀土离子上转换发光的发展历史;对稀土离子掺杂材料的能量传递、激发态吸收、合作敏化、合作发光、双光子吸收激发及光子吸收雪崩等上转换发光机制进行了概述,并对各机制进行了比较;对不同稀土离子掺杂体系中上转换发光的机制进行了总结;对以往研究的稀土掺杂上转换发光材料的基质,包括粉体材料、晶体材料、非晶材料进行了概括;最后对影响稀土离子上转换发光效率的因素进行了分析,提出了在上转换发光材料的设计中应重点考虑基质对泵浦光及上转换发射光的吸收、基质材料的声子能量、稀土离子的掺杂方案及泵浦途径等因素。     

激光间接驱动聚变柱形靶腔内光束传输研究

应用衍射积分理论, 对激光在间接驱动聚变柱形靶腔内的传输特性进行了研究, 给出了柱形腔靶注入孔以及内壁上的光强分布, 并与几何光学方法所得结果进行比较, 得出几何光学方法的适用条件。     

Up-conversion detection of mid-infrared light carrying orbital angular momentum

Frequency up-conversion is an effective method of mid-infrared (MIR) detection by converting long-wavelength photons to the visible domain, where efficient detectors are readily available. Here, we generate MIR light carrying orbital angular momentum (OAM) from a difference frequency generation process and perform up-conversion on it via sum frequency conversion in a bulk quasi-phase-matching crystal. The maximum quantum conversion efficiencies from MIR to visible are 34.0%, 10.4%, and 3.5% for light with topological charges of 0, 1, and 2, respectively, achieved by utilizing an optimized strong pump light. We also verify the OAM conservation with a specially designed interferometer, and the results agree well with the numerical simulations. Our study opens up the possibilities for generating, manipulating, and detecting MIR light that carries OAM, and will have great potential for optical communications and remote sensing in the MIR regime.     

High-efficiency frequency doubling of continuous-wave laser light

We report on the observation of high-efficiency frequency doubling of 1550?nm continuous-wave laser light in a nonlinear cavity containing a periodically poled potassium titanyl phosphate crystal (PPKTP). The fundamental field had a power of 1.10?W and was converted into 1.05?W at 775?nm, yielding a total external conversion efficiency of 95±1%. The latter value is based on the measured depletion of the fundamental field being consistent with the absolute values derived from numerical simulations. According to our model, the conversion efficiency achieved was limited by the nonperfect mode matching into the nonlinear cavity and by the nonperfect impedance matching for the maximum input power available. Our result shows that cavity-assisted frequency conversion based on PPKTP is well suited for low-decoherence frequency conversion of quantum states of light.     

Large-signal theory of gyro traveling wave tubes at cyclotronharmonics

A nonlinear theory of gyrotron traveling wave tubes (gyro-TWTs) at cyclotron harmonics has been developed taking into account the electron velocity spread and the possibility of operating with significant Doppler frequency up-shift (CARM operation). It is shown that the orbital efficiency of the relativistic gyro-TWT operating at the second cyclotron harmonic with large frequency up-conversion may exceed 60%. It is also shown that the influence of the axial inhomogeneity of the wave field on the relation between amplitudes of electric and magnetic fields of the wave causes small changes in the efficiency of gyro-TWTs. The results obtained demonstrate the sensitivity of the harmonic gyro-TWT efficiency with respect to electron velocity spread at different axial wave numbers. The expressions for the gain are derived and discussed,     

以一定重复频率工作的KTP倍频效率的演化规律

基于导带电子密度和材料的有效介电函数的表达式,推导了KTP晶体对532 nm光波的吸收系数. 对比研究了不同峰值功率密度和重复频率下KTP晶体的导带电子密度和532 nm吸收系数的演化规律,以及倍频转换效率的演化规律. 结果表明,随着导带电子密度的增加,KTP晶体532 nm吸收系数随之增加,其倍频转换效率随之减小;当基频光入射功率密度一定时,不同重复频率脉冲作用引起的导带电子密度存在积累效应,导致KTP晶体532 nm透过率及倍频转换效率均随着作用时间的增加呈指数形式变化,随着脉冲重复频率的增加其积累效果更加明显,但随着作用时间的增加,导带电子密度、吸收系数均趋于同一稳定值. 关键词： KTP晶体 灰迹 倍频转换效率     

两模腔中的参量上转换和下转换

提出了一种通过建立双线性二次哈密顿量在量子腔中实现参量上转换和下转换的方案.通常在非线性过程中,介质本身不参与能量的净交换,但光波频率可以发生转换的作用称为参量转换作用.此方案建立在一个四能级原子同时与两经典场和两量子场相互作用的基础上,理论属于非线性光学四波混频范畴.将原子制备在合适的能级上,经典光场与相应的能级发生共振,而同时量子光场与相应的能级产生大失谐相互作用,在强相互作用区域内,原子和腔场失耦合,进而实现腔模的参量转换.根据所制备初始能级的不同以及光场激发能级的差异,分别实现了参量上转换和参量下转换.在利用参量下转换制备压缩算符后,对实验的可行性进行了讨论,并且给出了理论值.结果表明：在级联三能原子中采用一个级联双光子过程代替了原来的两个偶极禁戒跃迁间的经典驱动,可以保证高的不同频率之间的转换效率,并且用于光的量子操控和量子信息处理.     

Nonreciprocal Single Photon Frequency Conversion via Chiral Coupling between a V-Type System and a Pair of Waveguides

The single photon frequency conversion is investigated theoretically in the system composed of a V-type system chiral coupling to a pair of waveguides. The single photon scattering amplitudes are obtained using the real-space Hamiltonian. The calculated results show that the probability of single photon frequency down-or up-conversion can reach a unit by choosing appropriate parameters in the non-dissipative system with perfect chiral coupling.We present a nonreciprocal single photon beam splitter whose frequency of the output photon is different from that of the input photon. The influences of dissipations and non-perfect chiral coupling on the single frequency conversion are also shown. Our results may be useful in designing quantum devices at the single-photon level.     

Common properties of free electron lasers

A general theory of microwave devices (in particular, ubitron, gyrotron) based on the ultrarelativistic Doppler up-conversion of electron oscillation frequency is developed. The wave growth rate for the amplifier and the start current for the generator are obtained. A universal relation between the frequency conversion factor and the efficiency of the laser is derived.