Laser cooling of a natural isotope mixture of Yb+ storedin an RF trap

We demonstrate laser cooling of Yb⁺, produced by ionization of a natural isotope mixture, stored in an RF trap. One of the three major even isotopes was directly laser cooled and other isotopes were simultaneously trapped as a result of sympathetic cooling. It was possible to carry out laser cooling to the temperature at which the cloud-to-crystal phase transition occurs for ¹⁷⁴Yb⁺ , as observed in the case where enriched isotopes are used. We observed sudden drops of fluorescence owing to pumping to the ² F_7/2 state in the case of a small number of trapped Yb ⁺ ions     

Frequency shifts of iodine stabilized He-Ne lasers at higherharmonic order stabilization

The frequency shifts of an ¹²⁷I₂ stabilized He-Ne laser at 633 nm have been measured at the third, fifth, and seventh harmonic stabilization using a digital signal processing lock-in amplifier. The observed frequency shifts confirmed the previous theoretical prediction that the laser frequency depends on the harmonic order of stabilization. The lower effects of modulation amplitude shift, power shift, and iodine pressure shift at the fifth harmonic stabilization indicate a potential improvement of the frequency reproducibility of the laser standard. A model is suggested to describe the power shifts of the laser. The mechanism explains the lower power shift of some lasers when they are operated at relatively high intracavity power     

On the enrichment of low-abundant isotopes of light chemical elements by gas centrifuges

A brief review of the main areas for the application of the isotopes ¹⁵N and ¹³C is made. Separation of the nitrogen isotopes in a single gas centrifuge in the form of pure nitrogen, ammonia, and trifluoride of nitrogen as well as the carbon isotopes in the form of carbon dioxide has been studied by means of numerical simulation. The parameters of the centrifugal machine investigated were close to the parameters of the Iguassu machine. The dependence of the efficiency criterion versus the basic parameters of the separation process has been explored in the computational experiments. Comparisons of the calculated results with the experimental data have shown good agreement. The results obtained have demonstrated the possibility of using gas centrifuge technology to enrich successfully the low-abundant isotopes of light chemical elements.     

Design of a Triangular Active Ring Laser 13 m on a Side

The design and testing of a proof-of-principle triangular active ring laser interferometer ~13 m on a side is discussed. Issues such as lock in, multimode interference, mode hopping, and neon isotope mixtures are examined as they relate to large He-Ne ring lasers. Responses of the ring laser to Earth's rotation and perturbations that change its tilt or area are presented. Some potential applications are suggested for large interferometers.     

Large-size bismuth silicate (Bi4Si3O12) scintillating crystals of good quality

We have achieved a considerable improvement in the growth of large Bi₄Si₃O₁₂ crystals, offering the possible application in γ-ray detectors at high energies. Clear blocks with transverse/longitudinal dimensions as large as 25 mm/200 mm were produced with good reproducibility. The pulse height uniformity along the longitudinal axis is within ±2%. The internal attenuation is less than 0.1%/cm at wavelengths above 400 nm. The radiation-induced optical absorption, which is about 2.5 m⁻¹ at 10⁴ rad (10² Gy) for the absorption coefficient at 480 nm, does not increase greatly even if the accumulated dose increases up to 10⁸ rad. Spontaneous recovery continues for at least several tens of days, although the recovery is never complete. UV annealing occurs to some extent, in contrast to the case of BGO which darkens upon exposure to UV light. The scintillation characteristics are similar to those of small crystals reported previously. The light output is 25% of BGO and typical decay constants are 2.1 ns (for 6% of intensity), 40 ns (13%) and 112 ns (81%).     

Mode behavior in ultralarge ring lasers

Contrary to expectations based on mode spacing, single-mode operation in very large He-Ne ring lasers may be achieved at intracavity power levels up to approximately0.15 times the saturation intensity for the He-Ne transition. Homogeneous line broadening at a high total gas pressure of 4-6 Torr allows a single-peaked gain profile that suppresses closely spaced multiple modes. At startup, decay of initial multiple modes may take tens of seconds. The single remaining mode in each direction persists metastably as the cavity is detuned by many times the mode frequency spacing. A theoretical explanation requires the gain profile to be concave down and to satisfy an inequality related to slope and saturation at the operating frequency. Calculated metastable frequency ranges are > 150 MHz at 6 Torr and depend strongly on pressure. Examples of unusual stable mode configurations are shown, with differently numbered modes in the two directions and with multiple modes at a spacing of approximately 100 MHz.     

Precision interferometric frequency measurement of the 674 nm2S1/2-2D5/2 transition in asingle cold Sr+ ion

The narrow linewidth 674 nm ²S_1/2-² D_5/2 transition in a cold Sr⁺ ion confined within an RF Paul trap has been probed using an optically narrowed 674 nm diode laser offset-locked to a second diode laser stabilized to a high-finesse ultra-low-expansion reference cavity. The transition frequency has been measured by means of interferometric comparison with an iodine-stabilized 633 nm He-Ne reference standard. A preliminary value for the ²S_1/2-²D_5/2 transition line center is 444 779 045 (9) MHz, limited by residual micromotion and low magnetic field Zeeman splitting     

双纵模He-Ne激光器的热稳频技术研究

介绍了双纵模He-Ne激光器的热稳频技术原理,设计了热稳频控制系统,并进行了相关的实验。根据实验结果可知,本热稳频系统实现了将两个纵模频率稳定在增益曲线中心频率对称位置和不对称位置上。根据拍频结果可知,当稳定在对称位置上时,激光器的频率稳定度达10^-10量级;当稳定在不对称位置上、维持频率稳定度10^-10量级时,激光器输出单纵模的功率最高达总功率的80%。     

Bandwidth dependence of pulse duration in intra-cavity frequency-doubled lasers: theory and experiment

A model is presented of pulse evolution in broadband intra-cavity frequency-doubled lasers. The model utilizes normalized coupled rate equations for each mode, including terms that represent the loss due to nonlinear mixing between longitudinal modes. The pulse energy, shape, peak power and duration are calculated by numerical solution of these equations. The model shows that the pulse duration depends not only on the initial population inversion, photon lifetime and the effective nonlinear coupling coefficient, as is the case for narrowband lasers, but also on the fundamental bandwidth. A gain-switched Ti:sapphire laser, pumped by a Q-switched Nd-doped yttrium aluminium garnet laser at 532?nm, was frequency doubled using an intra-cavity β-barium borate crystal. The bandwidth was reduced from about 25?nm to about 1.5?nm in two steps using a series of prisms, and the resulting changes in experimental pulse durations and energies agree well with the model.     

Frequency dependent electrical conductivity and dielectric relaxation behavior in amorphous (90V2O5–10Bi2O3) oxide semiconductors doped with SrTiO3

We report on the experimental results of frequency dependent a.c. conductivity and dielectric constant of SrTiO₃ doped 90V₂O₅–10Bi₂O₃ semiconducting oxide glasses for wide ranges of frequency (500–10⁴ Hz) and temperature (80–400 K). These glasses show very large dielectric constants (10²–10⁴) compared with that of the pure base glass (≈10²) without SrTiO₃ and exhibit Debye-type dielectric relaxation behavior. The increase in dielectric constant is considered to be due to the formation of microcrystals of SrTiO₃ and TiO₂ in the glass matrix. These glasses are n-type semiconductors as observed from the measurements of the thermoelectric power. Unlike many vanadate glasses, Long's overlapping large polaron tunnelling (OLPT) model is found to be most appropriate for fitting the experimental conductivity data, while for the undoped V₂O₅–Bi₂O₃ glasses, correlated barrier hopping conduction mechanism is valid. This is due to the change of glass network structure caused by doping base glass with SrTiO₃. The power law behavior (σ_ac=A(ω^s) with s<1) is, however, followed by both the doped and undoped glassy systems. The model parameters calculated are reasonable and consistent with the change of concentrations (x).     

Fixed-wavelength operation of a copper-laser-pumped dye laser injection seeded by low-power He-Ne lasers

The design and operating characteristics of a dye laser pumped by a 3-W copper-vapor laser (CVL) and injection seeded by low-power (1-5 mW) He-Ne lasers at 633 nm are reported. An extremely simple optical arrangement is used wherein the output mirror of the He-Ne laser and a third mirror form the dye laser cavity. Laser efficiency in fixed-wavelength operation has been investigated for variable CVL pump power, He-Ne injection power and polarization, and cavity output coupling for a standard Rhodamine 590/Rhodamine 640 dye solution. Over 90% of free-running (unseeded) laser power is obtained in fixed-wavelength (seeded) operation at low CVL pump powers (≤1 W), dropping to approximately 60% at 3-W pump power. Maximum CVL pump to dye laser optical conversion efficiency in narrow-band, fixed-wavelength operation at 633 nm was 12%.     

不同负载对太阳能电池输出功率的影响

利用直流电子负载对太阳能电池进行了恒压、恒流和恒阻三种模式下的测试,得到了太阳能电池的输出功率响应曲线,又用陶瓷电阻进行了恒阻模式下的测试和对比.实验结果表明,太阳能电池的输出特性随不同类型的负载变化趋势基本一致.通过比较得出了在利用直流电子负载进行太阳能电池特性测试时,恒压、恒流模式下的测试结果比较可信,恒阻模式下的测试结果存在突变现象,输出响应存在问题,不推荐使用;而在纯电阻的恒阻模式下,太阳能电池的输出特性与恒压、恒流模式下的测试结果一样可信.     

Observation of a Sub-10-Hz Linewidth 88Sr+ 2S1/2–2D5/2 Clock Transition at 674 nm

In this paper, a pair of diode lasers at 674 nm, locked to two independent ultralow-expansion high-finesse cavities, have been characterized by monitoring the beat frequency between them. The individual laser linewidth of 1.4 Hz for a 3-s averaging time broadened to 4 Hz at 30 s. The relative frequency stability of the beat at 1s is 2.5 10^-15. One of the lasers has been used to interrogate the ⁸⁸Sr^{+ 2}Si_1/2-²D _5/2 transition at 674 nm, and a transition linewidth of 9 Hz has been observed     

International comparison of 127I2-stabilizedHe-Ne Lasers at λ≈633 nm using the third and the fifthharmonic locking technique

In an international comparison of ¹²⁷I₂-stabilized helium-neon lasers at λ≈633 nm, lasers from the CMI and the BIPM were stabilized by the third (THT) and the fifth (FHT) harmonic locking techniques. A frequency shift to the blue was measured when using the FHT technique. The influence of weak components of the rotational-vibrational transition P(33) 6-3 of the molecule ¹²⁷I¹²⁹I on the frequency shift of components d, e, f, and g of the line R(127) 11-5 is evaluated     

Linewidth reduction by 6 orders of magnitude of a broad-area 729-nm diode laser

Diode lasers with a power output superior to 100 mW are in widespread use in medical as well as research applications. However, for such diodes lasing oscillation generally occurs simultaneously in several longitudinal and transverse modes that are unsuitable for high-resolution spectroscopy. We spectrally narrow a 100-mW broad-area diode laser by first using an extended cavity and then an electrical feedback produced by a Pound-Drever-Hall stabilization on a low-finesse reference cavity. Reduction of the linewidth by more than 6 orders of magnitude is achieved (the output linewidth is narrowed from 1 THz to less than 500 kHz), making possible its use for high-resolution spectroscopy. The power and the spectral qualities of this diode laser allow us to induce quantum jumps toward the D5/2 metastable level of single Ca+ ions.     

Calculating parameters of high-power He-Ne Lasers operating at λ = 0.63 μm

The existing methods of calculation of the parameters of He-Ne lasers agree with experiment for laser powers not exceeding 30–50 mW. We propose a method applicable to lasers operating at λ = 0.63 μm with a maximum output power exceeding 100 mW.     

Laser operation with two orthogonally polarized transverse modes

Laser resonator configurations, which enable laser operation with two orthogonally polarized transverse modes, are presented. The intensity distributions of these two modes can be chosen to be complementary, so the gain medium can be exploited more efficiently than with a single mode, leading to improved output power. Moreover, the two modes can be combined and efficiently transformed into a single high-quality beam. Basic principles and experimental results with Nd:YAG lasers are presented.     

Coupled cavity InGaAsP/InP laser for synthetic optical coherence tomography and other applications

The authors describe widely tunable coupled cavity semiconductor lasers with sub-microsecond switching times between modes over the operating range of ˜100 nm. With appropriate modulation of injection currents and time averaging of the output, these devices provide short coherence lengths and can be an excellent source for synthesised optical coherence tomography (OCT). The depth resolution was found to be ˜15 mm for a 100 nm wavelength tuning range centred at 1580 nm. High-output power and brightness together with a short coherence length confers on these asymmetric multiple quantum well (AMQW) C³ laser some advantages over conventional sources for OCT. Also, a rapid wavelength switching capability allows the AMQW C³ lasers to be used in real-time OCT and other applications needing wavelength agile sources.     

Results of International Comparisons Using Methane-Stabilized He-Ne Lasers at 3.39 ?m and Iodine-Stabilized He-Ne Lasers at 633 nm

The results of international comparisons of methane-stabilized He-Ne lasers at ? = 3.39 ?m and iodine-stabilized He-Ne lasers at 633 nm, made by beat frequency techniques, between Bureau International des Poids et Mesures (BIPM) and eleven national laboratories are presented. Generally, the measured frequency differences were inside ±4 × 10-11; but greater frequency differences were observed with some iodine cells (probably as a result of contamination) or when the output power of one laser was two or three times greater than the power of the other laser.     

A Study of Fullerene Preparation Technique

A new homemade are fullerene generator used in this experiment is reported. The comparation of yields of fullerenes (C₆₀/C₇₀ mixture) was studied by different power supplies (AC and DC), different gaps of two graphite rods and different He pressure between 0.4×10⁴- 2.8×10⁴ Pa. In our experiment, the highest yield up to 13% was achieved, when DC discharge was used and the optimum He pressure was near 0.8×10⁴ - 1.6×10⁴ Pa.

The mixed fullerene was analyzed by electron impact masa spectnun (EIMS). The relative amount af C₆₀ to C₇₀ was 4.2 to 1. After column chromatography aeperation with hexane on alumina, 99.9% Cso was obtained. FTIR and ^1aC-NMR epectrum were ueed to characterize the pure C₆₀ samples.