Rb atomic absorption line reference for single Sr+ laser cooling systems

85 Rb, 5s²S_1/2(F”=2)→6p²P_1/2(F’=2,3) absorption resonance with the ⁸⁸Sr⁺, 5s²S_1/2→5p²P_1/2 transition is exploited to provide a simple, effective frequency reference for a laser cooling/fluorescence excitation source applied to single Sr⁺ ions. A modulation-free frequency stabilization system has been designed which uses the differential signal from two frequency-displaced beams traversing a Rb cell and which probe the Doppler-broadened Rb S–P lineshape at microwatt power levels. The method is applied to frequency lock a 422-nm frequency-doubled diode laser system that is used for excitation of a single ⁸⁸Sr⁺ ion. Stable, long-term laser cooling and fluorescence are achieved using the frequency-stabilized 422-nm source resulting in observed ion confinement times without adjustment of over 8 h, together with an improvement in single-ion loading efficiency. Received: 12 February 1998     

Blue laser cooling transitions in Tm I

We have studied possible candidates for laser cooling transitions in ¹⁶⁹Tm in the spectral region of 410–420 nm. By means of saturation absorption spectroscopy, we have measured the hyperfine structure and rates of two nearly closed cycling transitions from the ground state 4f¹³6s²(²F₀)(J_g=7/2) to upper states 4f¹²(³H₅)5d_3/26s²(J_e=9/2) at 410.6 nm and 4f¹²(³F₄)5d_5/26s²(J_e=9/2) at 420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and 48(6) ns, respectively. Decay rates from these levels to neighboring opposite-parity levels are evaluated by means of Hartree–Fock calculations. We conclude that the strong transition at 410.6 nm has an optical leak rate of less then 2×10^-5 and can be used for efficient laser cooling of ¹⁶⁹Tm from a thermal atomic beam. The hyperfine structure of two other even-parity levels, which can be excited from the ground state at 409.5 nm and 418.9 nm, is also measured by the same technique. In addition, we give a calculated value of 7(2) s^-1 for the rate of magnetic-dipole transition at 1.14 μm between the fine structure levels (J_g=7/2)↔(J’_g=5/2) of the ground state which can be considered as a candidate for applications in atomic clocks. PACS 32.70.Cs; 32.10.Fn; 32.80.Pj     

锶原子三重态谱线的观测及在光钟中的应用

实验中通过互组跃迁689 nm激光抽运形成三重态最低能态原子布居,引入688 nm激光改变三重态最低能态间的原子布居,利用抽运光与探测光空间分离的方法观测碱土金属锶原子的三重态能态间跃迁(5s6s)³S₁ → (5s5p)³P_j(j=0,1,2)的吸收谱线,对应三条跃迁线的激光波段为679 nm, 688 nm和707 nm.探测三重态原子跃迁谱线可以用于锶原子冷却中再抽运光707 nm和679 nm激光频率的直接锁定,相比于通常利用的腔传递技术,可以把再抽运光频率锁定在原子跃迁谱线上,有利于提高锶原子冷却中俘获原子数目的长期稳定性.     

Optical frequency measurement of the 1S–3S two-photon transition in hydrogen

This article reports the first optical frequency measurement of the 1S–3S transition in hydrogen. The excitation of this transition occurs at a wavelength of 205 nm which is obtained with two frequency doubling stages of a titanium sapphire laser at 820 nm. Its frequency is measured with an optical frequency comb. The second-order Doppler effect is evaluated from the observation of the motional Stark effect due to a transverse magnetic field perpendicular to the atomic beam. The measured value of the 1S_1/21\mathrm{S}_{1/2}(F = 1)-3S_1/2(F = 1) frequency splitting is 2 922 742 936.729(13) MHz with a relative uncertainty of 4.5 × 10^-12. After the measurement of the 1S–2S frequency, this result is the most precise of the optical frequencies in hydrogen.     

Inverse Laplace transforms of osculatory and hyperosculatory interpolation polynomials

In the numerical calculation of f(t), the inverse Laplace transform of F(p), where f(′) = (1/2πi) °_c−i∞^c+i∞ e^pt F(p)dp, sufficient accuracy is usually obtainable when p³F(p), s > 0, is replaced by an interpolating polynomial in 1/p. From the values of F(p) with F′(p), or with F′(p) and F″(p), for p at points equally spaced on the real axis, an osculatory or hyperosculatory interpolation polynomial for p⁸F(p), namely L_2n−1(x) or L_3n−1(x), where x = 1/p, is obtained in barycentric form. Then f(t) is calculated by a Gaussian-type quadrature formula employing complex values of L_2n−1 or L_3n−1 and instead of p^sF(p) which may be unknown or more difficult to compute. For calculating L_2n−1 and L_3n−1, auxiliary coefficients, suitable for economical storage in the program, are given exactly for n = 2(1)11 and n = 2(1)7, furnishing up to 21st and 20th degree accuracy, respectively.     

Measurements of electron density, temperature and photoionization cross sections of the excited states of neon in a discharge plasma

In the present work emission and absorption spectroscopy have been used to determine the plasma parameters of neon in a hollow cathode discharge lamp. The excitation temperature is determined using the intensity ratio method and Boltzmann's plot method whereas the electron density is determined from the Stark broadening of the spectral lines. The behavior of the optogalvanic signal as a function of laser energy has been studied for three transitions from the 2p⁵3s [1/2]₂ metastable state following ΔJ=ΔK=0, ±1 dipole selection rules. The saturation technique has been used to measure the photoionization cross section from three intermediate states 2p⁵3p′ [1/2]_1, 2p⁵3p′ [3/2]₂ and 2p⁵3p [5/2]₃ up to the 2p^{5 2}P_1/2 ionization threshold.     

Frequency Stabilization of 421.671 nm Second-Harmonic Generation for Studies of 88 Sr+ Ions Confined in an RF Trap

The frequency of a SHG of a high power laser diode has been stabilized to the 5s²S_1/2#x2212;5p²P_1/2 transition of ⁸⁸Sr^#x002B; at 421.671 nm using the differential detection of the absorption signal of a hollow-cathode lamp. The frequency fluctuation never exceeded 10 MHz. The fluorescence signal of ⁸⁸Sr^#x002B; ions was detected.     

应用于白光显示的Tm3+/Ho3+/Yb3+共掺碲酸盐玻璃上转换发光特性研究

用高温熔融法制备了Tm³⁺/Ho³⁺/Yb³⁺共掺碲酸盐玻璃(TeO₂-ZnO-La₂O₃)样品,测试了玻璃样品的吸收光谱和上转换发光光谱,分析了上转换发光机理.结果发现:在975 nm波长激光二极管(LD)激励下,制备的碲酸盐玻璃样品可以观察到强烈的红光(662 nm)、绿光(546 nm)和蓝光(480 nm)三基色上转换发光,红光对应于Tm³⁺离子 关键词： 碲酸盐玻璃 上转换发光 白光 3+/Ho³⁺/Yb³⁺共掺')" href="#">Tm³⁺/Ho³⁺/Yb³⁺共掺     

Laser cooling of Cd<Superscript>+</Superscript> ions using a microwave transition as a repumping process

Cadmium ions trapped in a linear Paul trap have been laser cooled by use of a microwave transition as a repumping process. A 15.2-GHz microwave transition between a ground-state hyperfine splitting is used for repumping, while an all-solid-state laser with the wavelength of 214 nm drives the cooling transition between the ² S _1/2 and ² P _3/2 states. A phase transition from the cloud state to the crystal state of trapped ions has been observed both in fluorescence spectra and in images of an ion string. Cadmium ions have potential of application for quantum information processing where the ground-state microwave transition is used for both a repumping process and manipulation of quantum states of trapped ions. PACS 32.80.Pj     

Ultraviolet and visible upconversion luminescence of Tm(0.1)Yb(5):FOV oxyfluoride nanophase vitroceramics

The ultraviolet upconversion luminescence of Tm³⁺ ions sensitized by Yb³⁺ ions in oxyfluoride nanophase vitroceramics when excited by a 975 nm diode laser was studied. An ultraviolet upconversion luminescence line positioned at 363.6 nm was found. It was attributed to the fluorescence transition of ¹D₂→³H₆ of Tm³⁺ ion. Several visible upconversion luminescence lines at 450.7 nm, (477.0 nm, 462.5 nm), 648.5 nm, (680.5 nm, 699.5 nm) and (777.2 nm, 800.7 nm) were also found, which result respectively from the fluorescence transitions of ¹D₂→³F₄, ¹G₄→³H₆, ¹G₄→³F₄, ³F₃→³H₆ and ³H₄→³H₆ of Tm³⁺ ion. The careful measurement and analysis of the variation of upconversion luminescence intensity F as a function of the 975 nm pumping laser power P prove that the upconversion luminescence of ¹D₂ state is partly a five-photon upconversion luminescence, and the upconversion luminescence of ¹G₄ state and ³H₄ state are respectively the three-photon and two-photon upconversion luminescence. The theoretical analysis suggested that the upconversion mechanism of the 363.6 nm ¹D₂→³H₆ upconversion luminescence is partly the cross energy transfer of {³H₄(Tm³⁺), ³F₄(Tm³⁺), ¹G₄(Tm³⁺)→¹D₂(Tm³⁺)} and {¹G₄(Tm³⁺)→³F₄(Tm³⁺), ³H₄(Tm³⁺)→¹D₂(Tm³⁺)} between Tm³⁺ ions. In addition, the upconversion luminescence of ¹G₄ and ³H₄ state results respectively from the sequential energy transfer {²F_5/2(Yb³⁺)→²F_7/2(Yb³⁺), ³H₄(Tm³⁺)→¹G₄(Tm³⁺)} and {²F_5/2(Yb³⁺) →²F_7/2(Yb³⁺), ³F₄(Tm³⁺)→³F₂(Tm³⁺)} from Yb³⁺ ions to Tm³⁺ ions. Supported by the National Natural Science Foundation of China (Grant No. 10674019)     

A narrow linewidth and frequency-stable probe laser source for the <Superscript>88</Superscript>Sr<Superscript>+</Superscript> single ion optical frequency standard

In this paper, we describe in detail a narrow linewidth and frequency-stable laser source used to probe the 5s ² S _1/2–4d ² D _5/2 clock transition of the ⁸⁸Sr⁺ optical frequency standard. The performance of the laser system is investigated with studies of its frequency drift rates and with high resolution spectra of the ⁸⁸Sr⁺ clock transition. The observed short-term drift rates are typically in the range of 10 to 23 mHz/s, and the current long-term drift rate is 13.9(3) mHz/s. The laser stability, after subtraction of linear drifts, reaches 5×10⁻¹⁶ at an averaging time of 3000 s. This high level of stability is attributed for the most part to stabilization of the reference cavity at the temperature where the coefficient of linear thermal expansion crosses zero. An upper bound for the laser linewidth is given by the observation of a Fourier-transform limited resonance of 4.3 Hz (Δν/ν=1×10⁻¹⁴) on the ⁸⁸Sr⁺ clock transition. The effective averaging time during the linewidth measurements was about 100 s.     

Exchange currents in electric transitions and the rôle of siegert's theorem: A case study in deuteron photodisintegration

The hyperfine structure (hfs) splittings of the metastable 1s2s ³ S ₁ state of⁷Li⁺ have been measured with combined laser optical pumping and microwave resonance. A lowenergy Li⁺ ion beam, optically excited by an intersecting laser beam, passed a waveguide where radio frequency transitions were induced. The resulting population transfer among the hfs levels of the³ S ₁ was detected via the change in intensity of the fluorescence light from a second crossing region of laser light and ion beam located past the waveguide. The magnetic hfs constantA(⁷Li⁺, 1s2s ³S₁) was measured and compared with theory. A deviation of the two transition frequenciesν(F=3/2?F=5/2) andν(F=1/2?F=3/2) from the interval rule is due to a depression of theF=3/2 hfs sublevel, caused by mixing of the 2³ S ₁ and 2¹ S ₀ states via hyperfine interaction. This shift was never observed so far in a two-electron spectrum, because of absence ofI>1/2 isotopes in He, the only two-electron atom investigated spectroscopically with high precision. The size of the shift is in fair agreement with a theoretical estimate.     

Laser desorption jet-cooling of organic molecules

Laser desorption followed by jet-cooling allows wavelength-selective as well as mass-selective detection of molecules desorbed from a surface without fragmentation. The cooling characteristics and detection sensitivity of laser desorption jet-cooling of organic molecules are investigated. From the rotational contour of the electronic origin of the S ₁ S ₀ transition of laser-desorbed anthracene, rotational cooling to 5–10 K is demonstrated. Vibrational cooling is studied for laser-desorbed diphenylamine, a molecule with low-energy vibrations, and a vibrational temperature below 15 K is found. The absolute detection sensitivity is determined for the perylene molecule. Using two-color (1+1) resonance enhanced multi-photon ionization (with a measured ionization efficiency of 0.25) for detection, it is found that one ion is produced in the detection region for every 2×10⁵ perylene molecules evaporated from the desorption laser spot. A two-color (1+1) REMPI spectrum (400 points) of perylene is recorded using only 30 picogram of material.     

Preliminary frequency measurement of the electric quadrupole transition in a single laser-cooled 40Ca+ ion

The trapping and laser cooling of ⁴⁰Ca⁺ ion on the way toward optical frequency standards have been developed. A single ⁴⁰Ca⁺ ion is trapped in the miniature Paul trap and laser cooled by two frequency-stabilized diode lasers. A commercial Ti:Sapphire laser system at 729 nm is referenced to a high-finesse cavity to meet the requirements of ultra narrow linewidth of the 4s²S_1/2-3d²D_5/2 electric quadrupole transition. Its center frequency is preliminarily measured to be 411 042 129 686.1 (2.6) kHz. The attempt to finally lock the 729-nm laser system to atomic transition is made. Further work to improve the accuracy of measurement and the stabilization of system locking is in consideration and preparation.     

Frequency response measurement of high-speed photodetectors using the spectrum power method in a delay self-heterodyne system

We report on a photoionization scheme for controlled loading of ⁸⁸Sr⁺ ions into a radio-frequency (rf) ion trap. The two-step doubly-resonant process drives the ⁸⁸Sr atom on the 5s^{2 1} S ₀ – 5s5p¹ P ₁ transition at 461 nm using a frequency-doubled diode laser, and then excites the atom to the autoionizing (4d²+5p²) ¹ D ₂ state with 405 nm light from a free-running diode laser. This method of trap loading is quantitatively compared to electron bombardment loading, and shown to reduce the Sr vapour pressure required to load by four orders of magnitude. It also provides more than an order of magnitude reduction in the day-to-day variation of the voltages required to compensate micromotion. We additionally introduce a two-step atomic source consisting of an oven and hotplate, which reduces the number of impurities evaporated towards the trap. This is shown to significantly reduce fluctuations in required micromotion compensation voltages. The demonstrated reduction in flux and increased source purity are expected to improve the reliability of trap operation for precision ion-trap experiments. PACS 32.80.Fb; 32.80.Pj; 39.10.+j     

Growth,spectroscopic and laser properties of Yb<Superscript>3<Emphasis Type="Bold">+</Emphasis></Superscript>-doped GdAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystal: a candidate for infrared laser crystal

Yb³⁺:GdAl₃(BO₃)₄ (hereafter Yb³⁺:GAB) crystals with large sizes and good optical quality have been grown by the top-seed solution growth (TSSG) method. The polarized absorption and emission spectra have been investigated at room temperature. For the σ-polarization, the intensities of both absorption and emission spectra are stronger than those for the π-polarization, the σ-absorption cross section of Yb³⁺ in GAB being 3.43×10^-20 cm² at 977 nm, and the σ-emission cross section being 0.98×10^-20 cm² at 1045 nm. The fluorescence lifetime of the ² F _5/2→² F _7/2 transition was measured to be 800 μs in the 5% doped sample used for our laser experiments, 993 μs in a 10% doped sample and 569 μs in a 0.5% doped sample. The laser parameters were estimated as: β_min=0.022, I_sat=10.4 kW/cm² and I_min=0.23 kW/cm². About 0.4 W laseroutput at the wavelength of 1043 nm was achieved when the Yb³⁺:GAB crystal was pumped by a 974 nm laser diode, with 27.4% slope efficiency. PACS 42.55.-f; 42.70.Hj; 78.20.-e; 81.10.Dn     

Tunable frequency-controlled laser source in the near ultraviolet based on doubling of a semiconductor diode laser

Continuously tunable ultraviolet laser radiation at 397 nm was generated by doubling the output of a semiconductor diode laser. The fundamental radiation was provided by a 150 mW AlGaAs laser diode injected by a low-power AlGaAs laser diode which was frequency stabilized by optical feedback using a new scheme of a miniature external cavity. Second-harmonic generation was produced in a lithium-triborate crystal placed in a compact enhancement cavity. The fundamental radiation was used for sub-Doppler spectroscopy of the Ar I 4s ³ P ⁰ ₀–4p ¹ P ₁ transition at 795 nm; the second-harmonic radiation was used for spectroscopy of the Ca II 4² S _1/2–4² P _1/2 transition at 397 nm.     

All solid-state continuous-wave Nd:YAG laser at 1319 and 659.5 nm under direct 885 nm pumping

The continuous-wave high efficiency laser emission of Nd:YAG at the fundamental wavelength of 1319 nm and its 659.5-nm second harmonic obtained by intracavity frequency doubling with an LBO nonlinear crystal is investigated under pumping by diode laser at 885 nm (on the ⁴ F _3/2 → ⁴ I _13/2 transition). An end-pumped Nd:YAG crystal yielded 9.1 W at 1319 nm of continuous-wave output power for 18.2 W of absorbed pump power. The slope efficiency with respect to the absorbed pump power is 0.55. Furthermore, 5.2 W 659.5 nm red light is acquired by frequency doubling, resulting in an optical-to-optical efficiency with respect to the absorbed pump power of 0.286. Comparative results obtained for the pump with diode laser at 808 nm (on the ⁴ F _5/2 → ⁴ I _13/2 transition) are given in order to prove the advantages of the 885 nm wavelength pumping.     

Observation of new laser transitions and saturation effects in optically pumped NO

We report investigations of an NO laser employing specially profiled magnetic fields of up to 3.4T, and F₂ pump laser intensities as great as 20 MW cm^–2. We have observed laser oscillation at 226 nm on a rotational branch of the B'-X/it(3–11) band of NO for the first time, in addition to the previously reported oscillation at 218 nm on the B'-X/it(3–10) band. We have also observed visible laser emission on a rotational branch of the B ²-B ² II(3–1) band of NO. Saturation of the NO laser pulse energy with pump intensity has been observed, the total NO laser pulse energy having been increased to 490 J. The possibility of increasing the NO laser pulse energy towards 1 mJ per transition is discussed.     

Nonlinear refraction and nonlinear absorption of As2S3 aqueous solution

We report for the first time to our knowledge on the preparation of colloidal solution of chalcogenide semiconductor As₂S₃ by laser ablation and the measurements of its nonlinear-optical characteristics using Z-scan method at the wavelength of Nd:YAG laser radiation ( = 1064 nm, = 25 ns). The nonlinear refractive index was measured to be –7.5 × 10^–18 m² W^–1. Nonlinear absorption coefficient of chalcogenide solution was measured to be 1 cm GW^–1.