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Physical Review A

Laser spectroscopy of the 4s4p 3P2 – 4s3d 1D2 transition on magnetically trapped calcium atoms

Umakanth Dammalapati, I. Norris, C. Burrows, Erling Riis

Published Jun 27, 2011• 2 citations
Publisher

Abstract

Laser excitation of the $4s4p {}^{3}{P}_{2} -- 4s3d {}^{1}{D}_{2}$ transition in atomic calcium has been observed and the wavelength determined to 1530.5298(6) nm. The metastable $4s4p {}^{3}{P}_{2}$ atoms were magnetically trapped in the quadrupole magnetic field of a magneto-optical trap. This state represents the only ``loss'' channel for the calcium atoms when laser cooled on the $4{s}^{2} {}^{1}{S}_{0} -- 4s4p {}^{1}{P}_{1}$ transition. A rate equation model shows that an order of magnitude more atoms are trapped in this state compared with those taking part in the main cooling cycle. Excitation of the ${}^{3}{P}_{2}$ atoms back up to the $4s3d {}^{1}{D}_{2}$ state provides a means of accessing these atoms. Efficient repumping is achieved if the 1530-nm laser is used in conjunction with a 672-nm laser driving the $4s3d {}^{1}{D}_{2} -- 4s5p {}^{1}{P}_{1}$ transition. In the present experiment, we detected about $4.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ trapped ${}^{3}{P}_{2}$ atoms, a relatively low atom density, and measured a lifetime of approximately 1 s, which is limited by background collisions.

DOI
10.1103/physreva.83.062513

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Laser excitation of the 4s4p3P2−−4s3d1D24s4p {}^{3}{P}_{2} -- 4s3d {}^{1}{D}_{2}4s4p3P2​−−4s3d1D2​ transition in atomic calcium has been observed and the wavelength determined to 1530.5298(6) nm. The metastable 4s4p3P24s4p {}^{3}{P}_{2}4s4p3P2​ atoms were magnetically trapped in the quadrupole magnetic field of a magneto-optical trap. This state represents the only ``loss'' channel for the calcium atoms when laser cooled on the 4s21S0−−4s4p1P14{s}^{2} {}^{1}{S}_{0} -- 4s4p {}^{1}{P}_{1}4s21S0​−−4s4p1P1​ transition. A rate equation model shows that an order of magnitude more atoms are trapped in this state compared with those taking part in the main cooling cycle. Excitation of the 3P2{}^{3}{P}_{2}3P2​ atoms back up to the 4s3d1D24s3d {}^{1}{D}_{2}4s3d1D2​ state provides a means of accessing these atoms. Efficient repumping is achieved if the 1530-nm laser is used in conjunction with a 672-nm laser driving the 4s3d1D2−−4s5p1P14s3d {}^{1}{D}_{2} -- 4s5p {}^{1}{P}_{1}4s3d1D2​−−4s5p1P1​ transition. In the present experiment, we detected about 4.5\ifmmode×\else\texttimes\fi1044.5\ifmmode\times\else\texttimes\fi{}{10}^{4}4.5\ifmmode×\else\texttimes\fi104 trapped 3P2{}^{3}{P}_{2}3P2​ atoms, a relatively low atom density, and measured a lifetime of approximately 1 s, which is limited by background collisions.
We investigate a repumping scheme for magneto-optically trapped calcium atoms. It is based on excitation of the 4s3d1D24s3{d}^{1}{D}_{2}4s3d1D2​--4s5p1P14s5{p}^{1}{P}_{1}4s5p1P1​ transition at 672672672 nm with an extended cavity diode laser. The effect of the repumping is approximately a factor of three increase in trap lifetime and a doubling of the trapping efficiency from a Zeeman slowed thermal beam. Added to this, the 672-nm laser repumps atoms from an otherwise dark state to yield an overall increase in detected fluorescence signal from the magneto-optic trap (MOT) of more than an order of magnitude. Furthermore, we report isotope shift measurements of the 672672672-nm transition, for the first time, for four naturally occurring even isotopes. Using available charge radii data, the observed shifts, extending up to 4.34.34.3 GHz, display the expected linear dependence in a King plot analysis. The measured shifts are used to determine the isotope shifts of the remaining 41,43,46Ca^{41,43,46}\mathrm{Ca}41,43,46Ca isotopes. These might be of interest where less abundant isotopes are used enabling isotope selective repumping, resulting in enhanced trapping and detection efficiencies.
We report the magnetic trapping of metastable 3P2{}^{3}{P}_{2}3P2​ atomic strontium. Atoms are cooled in a magneto-optical trap (MOT) operating on the dipole-allowed ${}^{1}{S}_{0}{\ensuremath{-}}^{1}{P}_{1}$ transition at 461 nm. Decay via ${}^{1}{\stackrel{\ensuremath{\rightarrow}}{{P}_{1}}}^{1}{\stackrel{\ensuremath{\rightarrow}}{{D}_{2}}}^{3}{P}_{2}$ continuously loads a magnetic trap formed by the quadrupole magnetic field of the MOT. Over 108{10}^{8}108 atoms at a density of $8\ifmmode\times\else\texttimes\fi{}{10}^{9}{\mathrm{cm}}^{\ensuremath{-}3}$ and temperature of 1 mK are trapped. The atom temperature is significantly lower than what would be expected from the kinetic and potential energies of atoms as they are transferred from the MOT. This suggests the occurrence of thermalization and evaporative cooling in the magnetic trap.
This thesis reports an optical dipole trap for atomic calcium. The dipole trap is loaded from a magneto-optical trap (MOT) of calcium atoms cooled near the Doppler limit (~1 mK). The dipole trap is formed by a large-frame argon ion laser focused to 20 microns into the center of the MOT. This laser runs single-line at 488 nm with a maximum power of 10.6 watts. These parameters result in a trap of 125 mK for calcium atoms in the 4s3d 1D2 state. The 488 nm light also photo-ionizes the trapped atoms due to a near-resonant transition to the 4s4f 1F3 level. These ions leave the trap and are detected to determine the trap decay rate. By measuring this decay rate as a function of 488 nm intensity, we determine the 1F3 photo-ionization cross section at this wavelength to be approximately 230 Mb.
We report magnetic trapping of Yb in the excited 3P2{}^{3}{P}_{2}3P2​ state. This state, with a lifetime of 15 s, could play an important role in studies ranging from optical clocks and quantum computation to the search for a permanent electric dipole moment. Yb atoms are first cooled and trapped in the ground state in a 399-nm magneto-optic trap. The cold atoms are then pumped into the excited state by driving the ${}^{1}{S}_{0}\ensuremath{\rightarrow}{}^{3}{P}_{1}\ensuremath{\rightarrow}{}^{3}{S}_{1}$ transition. Atoms in the 3P2{}^{3}{P}_{2}3P2​ state are magnetically trapped in a spherical quadrupole field with an axial gradient of 110 G/cm. We trap up to 106{10}^{6}106 atoms with a lifetime of 1.5 s.
Spectroscopy of the 5s5p5s5p5s5p $ ^3 P_0 \rightarrow 5s5d$ $ ^3 D_1 $ transition of strontium using laser cooled atoms
This article presents spectroscopy results of the 5s5p  3P0→5s5d  3D15s5p{\;^3}P_0 \rightarrow 5s5d{\;^3}D_15s5p3P0​→5s5d3D1​ transition in all isotopes of laser cooled Sr atoms and the utility of this transition for repumping application. By employing the $5s5p{\;^{3} P_{0}} \rightarrow 5s5d{\;^3}D_1 $ (483 nm) transition in combination with the excitation of 5s5p  3P2→5s6s  3S15s5p{\;^3}P_2 \rightarrow 5s6s{\;^3}S_15s5p3P2​→5s6s3S1​ (707 nm) transition, we observe a significant increase (∼\sim∼ 13 fold) in the steady state number of atoms in the magneto-optic trap (MOT). This enhancement is attributed to the efficient repumping of Sr atoms that have decayed into the dark 5s5p  3P25s5p{\;^3}P_25s5p3P2​ state by returning them to the ground state 5s2  1S05s^2{\;^1}S_05s21S0​ without any loss into the other states. The absolute transition frequencies were measured with an absolute accuracy of 30 MHz. To support our measurements, we performed Fock-space relativistic coupled-cluster calculations of the relevant parameters in Sr. To further increase the accuracy of the calculated properties, corrections from the Breit, QED and perturbative triples were also included. The calculated branching ratio for the repumping state confirms the significantly increased population in the 3P1{^3}P_13P1​ state. Thereby, leading to an increase of population of atoms trapped due to the enhanced repumping. Our calculated hyperfine-splitting energies are in excellent agreement with the measured values. Moreover, our calculated isotope shifts in the transition frequencies are in good agreement with our measured values.
Optical pumping of 5s4d1D2{\mathrm{5s4d} ^1\mathrm{D}_2}5s4d1D2​ strontium atoms for laser cooling and imaging
We present a faster repumping scheme for strontium magneto-optical traps operating on the broad 5s21S0−5s5p1P1{\mathrm{5s^2} ^1\mathrm{S}_0} - {\mathrm{5s5p} ^1\mathrm{P}_1}5s21S0​−5s5p1P1​ laser cooling transition. Contrary to existing repumping schemes, we directly address lost atoms that spontaneously decayed to the 5s4d1D2{\mathrm{5s4d} ^1\mathrm{D}_2}5s4d1D2​ state, sending them back into the laser cooling cycle by optical pumping on the 5s4d1D2−5s8p1P1{\mathrm{5s4d} ^1\mathrm{D}_2} - {\mathrm{5s8p} ^1\mathrm{P}_1}5s4d1D2​−5s8p1P1​ transition. We thus avoid the ∼100 μs\sim 100 \, \mathrm{μs}∼100μs-slow decay path from 5s4d1D2{\mathrm{5s4d} ^1\mathrm{D}_2}5s4d1D2​ to the 5s5p3P1,2{\mathrm{5s5p} ^3\mathrm{P}_{1,2}}5s5p3P1,2​ states that is part of other repumping schemes. Using one low-cost external-cavity diode laser emitting at 448 nm448 \, \mathrm{nm}448nm, we show our scheme increases the flux out of a 2D magneto-optical trap by 60 %60 \, \%60% compared to without repumping. Furthermore, we perform spectroscopy on the 5s4d1D2−5s8p1P1{\mathrm{5s4d} ^1\mathrm{D}_2} - {\mathrm{5s8p} ^1\mathrm{P}_1}5s4d1D2​−5s8p1P1​ transition and measure its frequency ν88Sr=(668917515.3±4.0±25) MHzν_{\mathrm{^{88}Sr}} = (668917515.3 \pm 4.0 \pm 25) \, \mathrm{MHz}ν88Sr​=(668917515.3±4.0±25)MHz. We also measure the frequency shifts between the four stable isotopes of strontium and infer the specific mass and field shift factors, δνSMS88,86=−267(45) MHzδν_\text{SMS} ^{88,86} = -267(45) \, \mathrm{MHz}δνSMS88,86​=−267(45)MHz and δνFS88,86=2(42) MHzδν_\text{FS} ^{88,86} = 2(42) \, \mathrm{MHz}δνFS88,86​=2(42)MHz. Finally, we measure the hyperfine splitting of the 5s8p1P1{\mathrm{5s8p} ^1\mathrm{P}_1}5s8p1P1​ state in fermionic strontium, and deduce the magnetic dipole and electric quadrupole coupling coefficients A=−4(5) MHzA = -4(5) \, \mathrm{MHz}A=−4(5)MHz and B=5(35) MHzB = 5(35) \, \mathrm{MHz}B=5(35)MHz. Our experimental demonstration shows that this simple and very fast scheme could improve the laser cooling and imaging performance of cold strontium atom devices, such as quantum computers based on strontium atoms in arrays of optical tweezers.