Rovibrational State-Selectivity in Photoassociation through Multi-photon Transitions

The rovibrational state-selectivity in photoassociation （PA） is investigated for the ground electronic state of OH radical. The calculated results show that population can be transferred from continuum state to the target states through three-, four-, and nine-photon transitions by choosing suitable pulse parameters and initial collision energy. To control population transfer to a lower rovibrational state, a shorter pulse frequency has to be chosen and the photon number transferred to target state should be increased. In PA process, some associated OH radicals can be dissociated via intermediate and background states, which decreases the nal population of the target state.

Influence of multi-photon pulses on practical differential-phase-shift quantum key distribution

The influence of multi-photon pulses on practical differcBtial-phase-shift quantum key distribution （DPS-Qt（D） is analysed. We have estimated the information which Eve obtained by PNS （photon-number splitting） attack and BS （beam splitting） attack. The result indicates that the PNS attack and BS attack will not limit the transmission distance as long as we select an appropriate mean photon number. Also, the maximum mean photon number under BS attack in practical DPS-QKD system and the set of practical assumptions about Eve＇s capabilities are presented.

Evolution of Electron Phase Orbits of Multi-photon Nonlinear Compton Scattering in High Power Laser-plasma

The evolution of the electron phase orbits based on the multi-photon nonlinear Compton scattering with the high power laser-plasma is discussed by using Kroll-Morton-Rosenbluth theory. The random evolution of the un-captured electron phase orbits from periodicity to non-periodicity is found after the energy has been exchanged between the electron and photons. With the increase of the absorbed photon number n by an electron,this evolution will be more and more intense, while which is rapidly decreased with the enhancement of the collision non-flexibility ξ and their initial speeds of the electrons and photons,but this evolution is lower than that in the high power laser field. When the electrons are captured by the laser field,the evolution is finished,and the electrons will stably transport,and the photons don’t provide the energy for these electrons any more.

Preparation of multi-photon Fock states and quantum entanglement properties in circuit QED

We demonstrate the controllable generation of multi-photon Fock states in circuit quantum electrodynamics （circuit QED）. The external bias flux regulated by a counter can effectively adjust the bias time on each superconducting flux qubit so that each flux qubit can pass in turn through the circuit cavity and thereby avoid the effect of decoherence. We further investigate the quantum correlation dynamics of coupling superconducting qubits in a Fock state. The results reveal that the lower the photon number of the light field in the number state, the stronger the interaction between qubits is, then the more beneficial to maintaining entanglement between qubits it will be.

Polarization control of multi-photon absorption under intermediate femtosecond laser field

It has been shown that the femtosecond laser polarization modulation is a very simple and well-established method to control the multi-photon absorption process by the light-matter interaction. Previous studies mainly focused on the multi- photon absorption control in the weak field. In this paper, we further explore the polarization control behavior of multi- photon absorption process in the intermediate femtosecond laser field. In the weak femtosecond laser field, the second- order perturbation theory can well describe the non-resonant two-photon absorption process. However, the higher order nonlinear effect （e.g., four-photon absorption） can occur in the intermediate femtosecond laser field, and thus it is necessary to establish new theoretical model to describe the multi-photon absorption process, which includes the two-photon and four-photon transitions. Here, we construct a fourth-order perturbation theory to study the polarization control behavior of this multi-photon absorption under the intermediate femtosecond laser field excitation, and our theoretical results show that the two-photon and four-photon excitation pathways can induce a coherent interference, while the coherent interference is constructive or destructive that depends on the femtosecond laser center frequency. Moreover, the two-photon and four- photon transitions have the different polarization control efficiency, and the four-photon absorption can obtain the higher polarization control efficiency. Thus, the polarization control efficiency of the whole excitation process can be increased or decreased by properly designing the femtosecond laser field intensity and laser center frequency. These studies can provide a clear physical picture for understanding and controlling the multi-photon absorption process in the intermediate femtosecond laser field, and also can provide a theoretical guidance for the future experimental realization.

Multi-photon resonance enhanced super high-order harmonic generation

This paper proposes highly charged ions pumped by intense laser to produce very high order harmonics. Numerical simulations and full quantum theory of Ne^9＋ ions driven by laser pulses at 1064 nm in the power range of 109 W/cm^2 1015 W/cm^2 show that the emission spectrum corresponds to the electronic transitions from the excited states to the ground state, which is very different from the spectrum of general high-order harmonic generation. In such situation, harmonic order as high as 1000 can be obtained without producing lower order harmonics and the energy conversion efficiency is close to general high order harmonic generation of hydrogen atom in the same laser field.

The Physical Transient Spectrum for a Multi-Photon V-Type Three-Level Atom Interacting with a Squeezed Coherent Field in the Presence of Nonlinearities

We study the interaction of a multi-photon three-level atom with a single mode field in a cavity, taking explicitly into account the existence of forms of nonlinearities of both the field and the intensity-dependent atom-field coupling. The analytical forms of the emission spectrum is calculated using the dressed states of the system. The effects of photon multiplicities, mean photon number, detuning, Kerr-like medium and the intensity-dependent coupling functional on the emission spectrum are analyzed.

Influence of Heat-radiating on Multi-photon Compton Scattering High-energy Electron

Using the model of the inverse Compton scattering between high-energy electrons and heat-radiation photons, the influence of heat-radiating photons on multi-photon Compton scattering high-energy electrons is studied . The results show that the energy loss, power loss, light resistance and light pressure of the high-energy electron formed by heat radiating are all proportional to the temperature T4 of the vacuum cavity of the electron,the Lorentz factor γ2 of the high-energy electrons, the scattering section of the electron and the number of photons acting at the same time with high-energy electrons. A good method for lessening the energy loss of the high-energy electron by using the one-photon Compton scattering between high-energy electrons and heat radiation photons is proposed.

Multi-Photon Ionization in Background of Plasma

Multi photon ionization (MPI) in plasma is examined in terms of optical metric, and the quantum Volkov state in curved space time is derived. The cross section of MPI is derived by virtue of the corrected Volkov state within the framework of quantum electrodynamics (QED) formal scattering theory. It shows that the plasma medium acts as a suppression on MPI.

A multi-photon(7×7)-focus 3D laser printer based on a 3D-printed diffractive optical element and a 3D-printed multi-lens array

One of the challenges in the field of multi-photon 3D laser printing lies in further increasing the print speed in terms of voxels/s.Here,we present a setup based on a 7×7 focus array(rather than 3×3 in our previous work)and using a focus velocity of about 1 m/s(rather than 0.5 m/s in our previous work)at the diffraction limit(40×/NA1.4 microscope objective lens).Combined,this advance leads to a ten times increased print speed of about 108 voxels/s.We demonstrate polymer printing of a chiral metamaterial containing more than 1.7×10^(12) voxels as well as millions of printed microparticles for potential pharmaceutical applications.The critical high-quality micro-optical components of the setup,namely a diffractive optical element generating the 7×7 beamlets and a 7×7 lens array,are manufactured by using a commercial two-photon grayscale 3D laser printer.

Decoherence-free subspace and entanglement sudden death of multi-photon polarization states in fiber channels

The construction of quantum networks requires long-distance teleportation of multi-qubit entangled states.Here,we investigate the entanglement dynamics of GHZ and W states in fiber channels.In a fiber channel,the two most important phenomena that affect polarization entanglement are polarization mode dispersion(PMD)and polarization-dependent loss(PDL).We theoretically characterize how PMD and PDL vectors affect three-qubit states.In particular,upon quantifying the entanglement at the output states using concurrence and entanglement witnesses,we reveal the occurrence of entanglement sudden death and the appearance of decoherence-free subspaces in tripartite systems.Finally,we explore the evolution of GHZ and W state with an arbitrary number of photons in a fiber network and discuss the decoherence mechanism of the 4-party cluster state.

波长可调的量子点纠缠光源(特邀)

可按需产生纠缠光子对的量子光源是光量子网络中的重要组成部分。半导体量子点可确定性地产生高纠缠保真度的光子对。基于量子点构建量子网络所需的量子中继单元时,需要多个发光波长一致的高质量纠缠光源。然而量子点形貌、组分和应力的不均一性严重限制了基于量子点的量子中继器的可扩展性。国内外研究团队发展了多种量子点生长后调节技术,成功调节量子点精细结构劈裂并通过联合多个调节自由度实现多维度的调节。本文综述了目前联合多个调节自由度实现发光波长和精细结构劈裂均能调控的实验方案,总结了不同方案的调节方法和研究现状,并介绍了将量子点与光学微腔相结合通过Purcell效应能进一步提升纠缠光源的性能。最后,对该领域的未来发展进行展望。

应用于高密度多层光存储的聚合物基存储介质

飞秒微爆多层光存储是一种新型光存储技术,它通过在介质内部记录多层数据,成倍地扩充了光盘容量极限,有望解决传统光盘容量过低的问题。但由于飞秒微爆多层光存储信息记录过程受到多种材料因素的共同影响,导致长期缺乏介质材料选择的理论依据。文中选择误码率作为光存储性能的关键指标,测试对比了不同光学树脂的光存储性能。采用相关系数量化了材料的力学性质、热性质、光学性质、介电常数和高分子链结构与光存储性能之间的依赖关系,从而揭示出光学树脂的高分子链结构才是影响光存储性能的决定性影响因素。基于此发现,在聚甲基丙烯酸甲酯材料中实现了60层高密度多层光存储信息读写测试,容量密度达到1600 Gbits/cm^(3)。

多光子成像技术及其在化妆品评估中的应用

多光子成像技术是一种观察人体皮肤组织结构的光学成像方法,其原理是利用不同波长的近红外激光使皮肤组织中特定的内源性或外源性荧光物质发出不同的荧光信号,从而观测、区分皮肤不同层的特定组织结构。近年来,该方法开始逐步应用于化妆品的评估中,如评估化妆品紧致抗皱、祛斑美白、透皮吸收的效果等。多光子成像技术能够通过监测皮肤形态或代谢的变化评估化妆品紧致抗皱的作用、定量黑色素分布和含量评估化妆品祛斑美白成分的功效性或判断特定皮肤的类型、可视化化妆品成分透皮吸收的过程评估其功效性或安全性。该方法获得的客观、可视化图像可以为化妆品评估提供定量的数据结果,在皮肤成像领域有着广阔的应用前景,本文综述了这种在体、无创、精准的三维成像方法在化妆品评估中的应用和进展。

Investigations on multi-photon emissions of Nd^3＋-sensitized core/shell nanoparticles

The past few years witnessed extensive emergence of short-wavelength upconversion（UC） emission stimulated photoactivation studies. However, low efficiency of multi-photon process greatly limits further applications. Here, ultraviolet（UV） upconversion emissions originated from multi-photon process of Tm^3＋ were studied with Nd^3＋-sensitized NaGdF4：Yb,Tm@NaYF4：Nd,Yb core/shell nanoparticles. Crucial factors, including the contents of sensitizers Nd^3＋, Yb^3＋ and activator Tm^3＋, as well as the excitation power density were investigated based on the UV emission. Spectral results showed that high contents of Nd^3＋ in shell region up to 50%（molar fraction hereafter） and Yb^3＋ of 10% were essential to mediate the energy transfer via the core/shell interface and facilitate multi-photon UV emissions. Compared with segregated activator and sensitizer, a core/shell strategy with isolated Nd^3＋ in the shell was important for higher UV emission. Although the upconverting process was initiated with Nd^3＋→Yb^3＋, the short-wavelength emissions were intrinsically coming from four- and five-photon process. The optimized nanoparticles were found to be able to manipulate the configuration transition of azobenzene molecules, and it could be promising for near infrared（NIR） triggered optical switches applications.

Superconducting nanowire multi-photon detectors enabled by current reservoirs

Single-photon detectors are ubiquitous devices in quantum-photonic-based communication,computation,metrology,and sensing.In these applications,N-fold coincidence photon counting is often needed,for example,to characterize entanglement.However,N-fold coincidence photon counting typically requires N individual singlephoton detectors and associated bias and readout electronics,and these resources could become prohibitive if N goes large and the detectors need to work at cryogenic temperatures.Here,to break this limit on N,we propose a device architecture based on N cascaded photosensitive superconducting nanowires and one wider nanowire that functions as a current reservoir.We show that by strategically designing the device,the network of these superconducting nanowires can work in a synergic manner as an n-photon detector,where n can be from 1 to N,depending on the bias conditions.We therefore name the devices of this type superconducting nanowire multi-photon detectors(SNMPDs).In addition to its simple one-port bias and readout circuitry,the coincidences are counted internally in the detector,eliminating the need for external multi-channel,time-correlated pulse counters.We believe that the SNMPDs proposed in this work could open avenues towards conveniently measuring high-order temporal correlations of light and characterizing multi-photon entanglement.

Towards in-situ diagnostics of multi-photon 3D laser printing using optical coherence tomography

In recent years,multi-photon 3D laser printing has become a widely used tool for the fabrication of micro-and nanostructures for a large variety of applications.Typically,thorough sample characterisation is key for an efficient optimisation of the printing process.To date,three-dimensional microscopic inspection has usually been carried out on finished 3D printed microstructures,that is,using ex-situ approaches.In contrast,in-situ 3D characterization tools are desirable for quickly assessing the quality and properties of 3D printed microstructures.Along these lines,we present and characterise a Fourier-domain optical coherence tomography(FD-OCT)system that can be readily integrated into an existing 3D laser lithography setup.We demonstrate its capabilities by examining different 3D printed polymer microstructures immersed in a liquid photoresist.In such samples,local reflectivity arises from the(refractive-index)contrasts between the polymerised and non-polymerised regions.Thus,the refractive index of the printed material can be extracted.Furthermore,we demonstrate that the reflectivity of polymer-monomer transitions exhibits time-dependent behaviour after printing.Supported by transfer-matrix calculations,we explain this effect in terms of the time-dependent graded-index transition originating from monomer diffusion into the polymer matrix.Finally,we show exemplary 3D reconstructions of printed structures that can be readily compared with 3D computer designs.

Adiabatic and Non-Adiabatic Berry Phases in Generalized J-C Model of Multi-Photon Process

We derive the adiabatic and non-adiabatic Berry phases in the generalized Jaynes-Cummings model of multi-photon process. The results show that the adiabatic Berry phase is kept a constant π independent of all the parameters, while the non-adiabatic approximate Berry phase is parameter-dependent, proportional to the average photon number m, and tends to be constant with the increasing detuning. In the ease of exact n-photon resonance and an integer ratio of m/n, the two results coincide with each other, otherwise there appears an additional non-trivial phase factor.

全数字PET关键器件硅光电倍增器研究进展

近年来,硅光电倍增器(SiPM)凭借其出色的性能表现,已经成为正电子发射断层成像(PET)中的首选光电转换器件。SiPM具有单光子分辨能力和低于100 ps的时间分辨率,使得精确测量光子到达时间成为可能,催生了飞行时间PET、光子计数计算机断层扫描、正电子素寿命显像等新兴应用领域,这些应用又对SiPM的性能提出了更高的挑战。因此,如何将SiPM性能推进至其物理极限已成为新一代SiPM的研究的关键方向。在传统的SiPM架构中,信号经过多次处理和模数转换,带来噪声增加和时间性能恶化的问题,从而限制了SiPM的性能潜力。随着半导体制造工艺的快速发展,SiPM可在标准CMOS工艺节点上制造,标志着可以将数字逻辑集成在SiPM器件内,这是SiPM领域的一次重大突破,使我们能在单一SiPM内实现更精确的时间、能量、位置信息获取,为推进SiPM达到性能极限提供了一条可能的途径。本文综述SiPM的发展历史、工作原理和性能参数,分析传统SiPM的局限性,梳理数字SiPM研究的关键问题,介绍当前几种数字化SiPM架构,最后对数字SiPM的关键技术进行总结和展望。

基于X切薄膜铌酸锂的4×4 MMI耦合器的设计和制造

针对多模干涉(MMI)耦合器存在尺寸大、插入损耗高、工艺复杂的问题,在基于X切薄膜铌酸锂(X-cut TFLN)平台上设计了一种基于横电(TE)模式的4×4 MMI耦合器,采用三维时域有限差分(FDTD)方法对MMI区域长度及宽度进行仿真优化,最后根据优化结果并利用电感耦合等离子体(ICP)刻蚀方法在该平台上制造4×4 MMI耦合器。仿真结果表明,优化后的4×4 MMI耦合器总插入损耗为0.36 dB,实际测量插入损耗为0.78 dB。