Characterization of probe lasers for thin-film optical measurements

The peak-power-density stability and beam-wander precision of a probe laser are important factors affecting the inspection results in precise thin-film optical measurements. These factors are also key to evaluating a probe laser for in-line long-time operation of precise thin-film optical measurements. The peak-power density and beam wander of liner helium–neon (He–Ne) lasers, random He–Ne lasers, and diode lasers as functions of time are investigated experimentally using a beam profiler. It is found that the linear polarized He–Ne laser is considered to be a promising candidate for a probe laser employed in precise thin-film optical measurements due to better peak-power-density stability and beam-wander precision. Both the peak-power-density stability and beam-wander precision of He–Ne lasers are usually better than that of diode lasers, but an adequate warm-up of He–Ne laser for 30 min is required before thin-film optical measurements are made. After 12 h operation, the linear polarized He–Ne laser is suitable for precise thin-film optical measurements because both the peak-power-density stability and the beam-wander precision reach the minimum level. A cost-effective system composed of two linear polarized He–Ne lasers for long-term operation is proposed. This system can operate for around 0.5–1.2 years in precise thin-film optical measurements under the normal operating life of a He–Ne laser by switching the probe laser every 18 h.     

Influence of lasers propagation delay on the sensitivity of atom interferometers

In atom interferometers based on two photon transitions, the delay induced by the difference of the laser beams paths makes the interferometer sensitive to the fluctuations of the frequency of the lasers. We first study, in the general case, how the laser frequency noise affects the performance of the interferometer measurement. Our calculations are compared with the measurements performed on our cold atom gravimeter based on stimulated Raman transitions. We finally extend this study to the case of cold atom gradiometers.     

自混频激光理论模型及应用

建立了在同一块非线性激光晶体上实现自混频激光的理论模型。该模型计入了具有任意腰斑大小的泵浦光和腔内基频光的空间分布,并将该模型应用到NYAB和Nd:GdCOB的自混频蓝光实验。理论分析预测和证实了一些实验结果,同时,讨论和总结了提高自混频激光输出效率的途径。     

Narrow bandwidth operation of high-power broad-area diode laser using cascaded phase-conjugate injection locking

A broad-area laser is injection-locked by another broad-area laser that is also injection-locked by a single-mode diode laser. Two double-phase conjugate mirrors of photorefractive BaTaO₃ are used to couple the master laser beams to the first slave laser, and the first slave laser output to the second slave laser. One of the double-phase conjugate mirrors is built up with the beams from two broad-area lasers. Two slave lasers are oscillating in single longitudinal mode at 808.5 nm and the spectral width is the same as that of the master laser. Final single-mode output power from the second slave broad-area laser is 840 mW, which is limited by the power of the injection beam. This work verifies the possibility of the multi-stage cascaded injection locking of high-power diode lasers with phase-conjugate injection. Received: 18 November 1998 / Revised version: 29 January 1999 / Published online: 7 April 1999     

The effects of nonuniform gain in ruby lasers

A Monte Carlo method is used to examine the pumping density distribution in the active elements of cw ruby lasers. It is shown that when elliptical reflectors are used in conditions typical for such lasers the transverse dimension of the pumped region in the ruby is about 0.6 mm. A direct measurement of the pumping distribution confirms this conclusion. The effect of a nonuniformity in the gain of a cw ruby laser on the mode parameters and lasing threshold is studied experimentally. The measurements are in satisfactory agreement with the theory of Gaussian beams in a medium with a parabolic distribution of the gain coefficient and the theory may be used to evaluate the threshold and other characteristics of a laser.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 92–97, October, 1976.In conclusion the authors thank A. A. Kashkan for important help in the calculations for the first section of this article.     

用于原子能级结构研究的激光共振电离光谱系统

激光共振电离光谱技术是一种利用一路或多路激光将待测原子选择性共振激发与电离,通过测量离子信号来研究原子能级结构的光谱技术。研建了一套激光共振电离光谱装置,用于原子高激发态能级结构参数的测量。分别从该装置的总体结构、关键技术和应用实例等方面进行了详细介绍。该套装置主要包括高调谐精度的染料激光器系统、高效的激光离子源系统和高分辨率的飞行时间质量分析器。染料激光器系统包括3台多纵模可调谐染料激光器和1台单纵模可调谐染料激光器,均为脉冲工作方式,重复频率为10 kHz,泵浦源均为532 nm的Nd∶YAG固体激光器。激光离子源系统包括原子化源、激光与原子相互作用区和离子光学透镜组三部分组成,样品在原子化源中被电加热实现原子化,喷射出的原子被激光选择性激发、电离,产生的离子被离子传输透镜整形成能量分散小、束窄的离子束。飞行时间质量分析器采用了反射式结构设计、脉冲垂直推斥技术和偏转板调节技术。利用此装置,实验测定了U原子的自电离态光谱,获得了U原子一条较佳的三色三光子共振电离路径,对应激光的波长分别为591.7,565.0和632.4 nm。此系统还可用于测量同位素位移和原子超精细结构等参数。另外,由于此系统中联用了质量分析器,因此可用于样品多元素分析、痕量元素分析、同位素丰度分析。     

Quasiparity‐Time Symmetric Microdisk Laser

Recent developments in parity‐time (PT) symmetric systems have ushered in unique photonic devices with enhanced functionalities. While single‐mode laser emission has been demonstrated in such systems, the current designs face severe challenges in applications, either due to their stringent requirement on fabrication precision or nonscalability to larger devices. Here, we demonstrate a general mechanism to achieve single‐mode lasing in coupled cavities, which relies on external mode coupling and overcomes these drawbacks. We find significant gain enhancement for selected modes by external coupling, and our experiments have confirmed the resulting single‐mode laser emission in size‐mismatched photonic molecules (PMs), when only one constituent cavity is pumped. This behavior persists for a wide range of pump power, from transparent threshold to gain saturation, and it is highly tolerant of fabrication imprecisions. In addition, the output intensity of such single‐mode lasers also displays enhancement when compared with the same PMs under uniformly pumping. We believe our results will both advance the understanding of different coupling scenarios in coupled cavities and improve the characteristics of onchip laser sources for practical applications.     

Propagation instabilities of high-intensity laser-produced electron beams

Measurements of energetic electron beams generated from ultrahigh intensity laser interactions (I>10(19) W/cm(2)) with dense plasmas are discussed. These interactions have been shown to produce very directional beams, although with a broad energy spectrum. In the regime where the beam density approaches the density of the background plasma, we show that these beams are unstable to filamentation and "hosing" instabilities. Particle-in-cell simulations also indicate the development of such instabilities. This is a regime of particular interest for inertial confinement fusion applications of these beams (i.e., "fast ignition").     

Laser intracavity absorption spectroscopy

Emission spectra of multimode lasers are very sensitive to spectrally selective extinction in their cavity. This phenomenon allows the quantitative measurement of absorption. The sensitivity of measurements of intracavity absorption grows with the laser pulse duration. The ultimate sensitivity obtained with a cw laser is set by various perturbations of the light coherence, such as quantum noise, Rayleigh scattering, four-wave mixing by population pulsations, and stimulated Brillouin scattering. It depends on the particular laser type used, and on its operative parameters, for example pump power, cavity loss, cavity length, and length of the gain medium. Nonlinear mode-coupling dominates the dynamics of lasers that feature a thin gain medium, such as dye lasers, whereas Rayleigh scattering is more important in lasers with a long gain medium, such as doped fibre lasers, or the Ti:sapphire laser. The highest sensitivity so far has been obtained with a cw dye laser. It corresponds to 70000 km effective length of the absorption path. The ultimate spectral resolution is determined by the spectral width of mode emission, which is 0.7 Hz in this dye laser. High sensitivity and high temporal and spectral resolution allow various practical applications of laser intracavity spectroscopy, such as measurements and simulations of atmospheric absorption, molecular and atomic spectroscopy, process control, isotope separation, study of free radicals and chemical reactions, combustion diagnostics, spectroscopy of excited states and nonlinear processes, measurements of gain and of spectrally narrow light emission. Intracavity absorption in single-mode lasers shows enhanced sensitivity as well, although not as high as in multimode lasers. Received: 10 May 1999 / Published online: 29 July 1999     

Laser-driven generation of fast particles

The great progress in high-peak-power laser technology has resulted recently in the production of ps and subps laser pulses of PW powers and relativistic intensities (up to 10²¹ W/cm²) and has laid the basis for the construction of multi-PW lasers generating ultrarelativistic laser intensities (above 10²³ W/cm²). The laser pulses of such extreme parameters make it possible to produce highly collimated beams of electrons or ions of MeV to GeV energies, of short time durations (down to subps) and of enormous currents and current densities, unattainable with conventional accelerators. Such particle beams have a potential to be applied in numerous fields of scientific research as well as in medicine and technology development. This paper is focused on laser-driven generation of fast ion beams and reviews recent progress in this field. The basic concepts and achievements in the generation of intense beams of protons, light ions, and multiply charged heavy ions are presented. Prospects for applications of laser-driven ion beams are briefly discussed.     

Photonic band gap of three dimensional magnetized photonic crystal with Voigt configuration

We study Bessel beams of two-level atoms that are driven by a linearly polarized laser field. Starting from the Schrödinger equation, we determine the states of two-level atoms in a plane-wave field respecting propagation directions both of the atom and the field. For such laser-driven two-level atoms, we construct Bessel beams beyond the typical paraxial approximation. We show that the probability density of these atomic beams obtains a non-trivial, Bessel-squared-type behavior and can be tuned under the special choice of the atom and laser parameters, such as the nuclear charge, atom velocity, laser frequency, and propagation geometry of the atom and laser beams. Moreover, we spatially and temporally characterize the beam of hydrogen and selected (neutral) alkali-metal atoms that carry non-zero orbital angular momentum (OAM). The proposed spatiotemporal Bessel states (i) are able to describe, in principle, twisted states of any two-level system which is driven by the radiation field and (ii) have potential applications in atomic and nuclear processes as well as in quantum communication.     

飞秒激光氘团簇聚变

简要介绍了原子团簇的产生方法和特点以及激光惯性约束核聚变的基本原理,氚团簇在飞秒激光的作用下,大量吸收激光能量,产生了高离化态高能离子,从而实现了氚团簇桌面台式聚变。     

Space continuous atom laser in one dimension

Cold atom physics in space station arouses a lot of interest of scientists. We investigate the dynamical output process of the space continuous atom laser by solving nonlinear Gross-Pitaevksii equations numerically. Slow-moving continuous atom beams in two directions are observed simultaneously. The slow-moving coherent atom beams can be used as a source of atom interferometer to realize long-time measurements. We also control the output of space atom laser by adjusting the output coupling strength.     

Lasers as Light Sources for Analytical Atomic Spectrometry

Abstract

Lasers have advantages compared to conventional light sources, which include high power, a monochromatic emission profile, stability, and rapid tuning across an atomic line. These advantages have resulted in superior analytical figures of merit and methods of background correction compared to conventional light sources. The most widely used lasers for atomic spectrometry include dye laser systems, optical parametric oscillator systems, and diode lasers. Three principal techniques employ lasers as light sources. Laser‐excited atomic fluorescence spectrometry (LEAFS) involves the use of laser light to excite atoms that emit fluorescence and serves as the analytical signal. Laser‐enhanced ionization (LEI) involves laser excitation of atoms to an excited state energy level at which collisional ionization occurs at a higher rate than from the ground state. Diode laser atomic absorption spectrometry (DLAAS) employs a DL as a source to excite atoms in an atom cell from the ground state to an excited state. The analytical signal is involves the ratio of the incident and transmitted beams. Recent applications of these techniques are discussed, including practical applications, hyphenated techniques employing laser‐induced plasmas, and work to characterize fundamental spectroscopic parameters.     

A compact and efficient four-wavelength Q-switched Nd:YAP laser

In this paper, a four-wavelength electro-optic (E-O) Q-switched solid-state laser system was presented. This laser system only use one Nd:YAP laser crystal, which irradiates 1079.5 nm and 1341.4 nm fundamental wavelengths. Both of these wavelength lasers and their second harmonic generation (SHG) compose a four-wavelength Nd:YAP Q-switched laser. The Q-switched output energies of 277 mJ for 1079.5 nm and 61 mJ for 539.8 nm and that of 190 mJ for 1341.4 nm and 51 mJ for 670.7 nm wavelengths were achieved. The pulse durations of 1079.5 and 539.8 nm lasers and that of 1341.4 and 670.7 nm lasers are 20 and 40 ns, respectively. Due to this laser system has the larger chance and convenience for selecting the wavelengths and operation modes by moving a stepping motor and controlling the Q-switched devices, it will broaden applications in the fields of laser cosmetology, dermatotis therapy, material processing and laser display etc.     

亚微米局域空心光束的产生及其在单原子囚禁与冷却中的应用理论研究

提出了一种采用单模光纤、环形二元相位板和微透镜组成的光束整形系统产生亚微米局域空心光束的方案. 根据瑞利-索莫菲衍射积分公式, 数值计算了微透镜焦平面附近的场分布, 详细研究了空心光束的暗斑尺寸与单模光纤模场半径和微透镜焦距的关系. 数值计算结果表明: 在微透镜焦平面附近光场分布近似对称, 在焦点处场强近似为零, 周围场强逐渐增大, 形成半径约为0.4 μm的三维封闭的球形空心光场区域, 即亚微米局域空心光束. 当局域空心光束为蓝失谐时, 光场中的原子将被囚禁在光场最弱处. 若加上抽运光, 原子将受到蓝失谐局域空心光束与抽运光共同激发的强度梯度Sisyphus冷却. 本文利用该方案产生的亚微米局域空心光束构建单原子的囚禁与冷却器件, 并以单个⁸⁷Rb原子为例, 利用Mont-Carlo方法研究亚微米局域空心光束中单原子囚禁与强度梯度冷却的动力学过程, 结果表明利用该器件可以获得温度在5.8 μK量级的超冷单原子.     

40K-87Rb原子冷却的半导体激光系统

对⁴⁰K-⁸⁷Rb原子冷却的半导体激光系统提出了一种实验方案，并进行了初步实验.采用三台外腔光栅反馈半导体激光器(ECDL)、四台注入锁定从激光器和一台半导体激光放大器组成激光系统.三台ECDL通过声光调制器产生四束光，分别作为⁴⁰K和⁸⁷Rb原子的冷却光和再抽运光，四束不同频率成分的激光分别注入锁定四台从激光器，然后Rb 冷却光、K冷却光和K再抽运光再同时注入半导体激光放大器进行放大.该装置可同时产生冷却⁴⁰K和⁸⁷Rb原子的冷却光和再抽运光，结构紧凑、工作稳定. 关键词： 简并费米气体 激光器系统 外腔光栅反馈半导体激光器 半导体激光放大器     

Tapered diode lasers and laser modules near 635nm with efficient fiber coupling for flying-spot display applications

Flying-spot displays require light sources in the red, green and blue with a high optical output power and nearly diffraction limited beams. In this paper we present experimental results of red-emitting, AlGaInP based, tapered diode lasers and their integration into diode laser modules. The laser modules emit a collimated, almost diffraction limited beam with an optical output power as high as 1W at a wavelength close to 635 nm. The tapered laser chips were designed with emphasis on achieving a good beam quality in vertical and lateral directions of a collimated beam. To test the suitability for flying-spot display applications, we performed fiber coupling experiments with a low mode number optical fiber with an etendue as low as 6 × 10^?6 mm² sr. A maximum transmission of 70% of the launched power behind the uncoated fiber as well as a usable power in excess of 580mW were measured.     

Magneto-optical trapping of radioactive atoms for test of the fundamental symmetries

We are planning test experiments of fundamental symmetries based on the intrinsic properties of francium. It is expected that the laser cooling and trapping of francium will produce precision measurements. The pilot experiment using rubidium was performed with the goal of francium trapping. The ion beam generated with a francium ion source was investigated using a Wien filter. Each piece of equipment still must be studied in more detail, and the equipment should be upgraded in order to trap radioactive atoms.     

Spectral filtering of dual lasers with a high-finesse length-tunable cavity for rubidium atom Rydberg excitation

We propose and demonstrate an alternative method for spectral filtering and frequency stabilization of both 780-nm and 960-nm lasers using a high-finesse length-tunable cavity(HFLTC). Firstly, the length of HFLTC is stabilized to a commercial frequency reference. Then, the two lasers are locked to this HFLTC using the Pound–Drever–Hall(PDH) method which can narrow the linewidths and stabilize the frequencies of both lasers simultaneously. Finally, the transmitted lasers of HFLTC with each power up to about 100 μW, which act as seed lasers, are amplified using the injection locking method for single-atom Rydberg excitation. The linewidths of obtained lasers are narrowed to be less than 1 k Hz, meanwhile the obtained lasers' phase noise around 750 k Hz are suppressed about 30 d B. With the spectrally filtered lasers, we demonstrate a Rabi oscillation between the ground state and Rydberg state of single-atoms in an optical trap tweezer with a decay time of(67 ± 37) μs, which is almost not affected by laser phase noise. We found that the maximum short-term laser frequency fluctuation of a single excitation lasers is at ～ 3.3 k Hz and the maximum long-term laser frequency drift of a single laser is ～ 46 k Hz during one month. Our work develops a stable and repeatable method to provide multiple laser sources of ultra-low phase noise, narrow linewidth, and excellent frequency stability, which is essential for high precision atomic experiments, such as neutral atom quantum computing, quantum simulation, quantum metrology, and so on.