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Acta Sinica Quantum Optica

Measurement of the Temperature of Strontium Atoms by Doppler Cooling

Hong Chang

Published Jan 1, 2010• 0 citations
OpenAlex

Abstract

After the realization of Doppler cooling based on(5s2)1S0→(5s5p)1P1 in alkaline-earth metal strontium,the temperature of two isotopes of strontium which is 88Sr(bosons)and 87Sr(fermions) are measured using time of flight and expansion measurement.And the result of the two isotopes are～9 mK(88Sr) and～2 mK(87Sr).According the theory of Doppler cooling limited temperature,the experimental results are analyzed.This can be the well basis for the next step,1S0→3P1 narrow line cooling of strontium.

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ISOTOPE SHIFT SPECTROSCOPY OF ULTRACOLD STRONTIUM

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We describe the design, construction, and performance of a laser system to probe the ultra-narrow (Γ/2π ≈ mHz) clock transition 1S0 → 3P0 in strontium. We present the first reported spectroscopy of this transition in two of the bosonic isotopes, 84Sr and 86Sr. Furthermore, we measure the complete set of isotope shifts between all four stable isotopes on the clock line and the narrow intercombination line 1S0 → 3P1, permitting a King plot analysis of the isotope shifts. Complications arising from the unambiguous determination of a line center in 87Sr 3P1 prevent us from making claims about the King linearity, but we provide a statistical boot- strap analysis of the isotope shifts 88−84Sr and 88−86Sr to compute a field shift ratio F698/F689 = 0.9979, with a 95% confidence interval [0.9952,1.0008]. The intercept term K698 − (F698/F689) K689 is similarly determined to be -2.0 GHz-amu, with a 95% confidence interval [−3.9, −0.3] GHz-amu. Finally, we describe the design of a next-generation apparatus that will enable improvements on the results described here, as well as other studies that involve coherent manipulation of strontium atoms on the clock line.

•Jan 1, 2019•1 citation
After the realization of Doppler cooling based on(5s2)1S0→(5s5p)1P1 in alkaline-earth metal strontium,the temperature of two isotopes of strontium which is 88Sr(bosons)and 87Sr(fermions) are measured using time of flight and expansion measurement.And the result of the two isotopes are～9 mK(88Sr) and～2 mK(87Sr).According the theory of Doppler cooling limited temperature,the experimental results are analyzed.This can be the well basis for the next step,1S0→3P1 narrow line cooling of strontium.
We present a detailed investigation of strontium magneto-optical trap (MOT) dynamics. Relevant physical quantities in the trap, such as temperature, atom number and density, and loss channels and lifetime, are explored with respect to various trap parameters. By studying the oscillatory response of a two-level 1S0–1P1 88Sr MOT, we firmly establish the laser cooling dynamics predicted by Doppler theory. Measurements of the MOT temperature, however, deviate severely from Doppler theory predictions, implying significant additional heating mechanisms. To explore the feasibility of attaining quantum degenerate alkaline-earth samples via evaporative cooling, we also present the first experimental demonstration of magnetically trapped metastable 88Sr. Furthermore, motivated by the goal of establishing the fermionic isotope 87Sr as one of the highest-quality, neutral-atom-based optical frequency standards, we present a preliminary study of sub-Doppler cooling in a 87Sr MOT. A dual-isotope (87Sr and 88Sr) MOT is also demonstrated.
At present the optical clock with accuracy and stability achieves to 10-18 level, which could be the next generation of time and frequency standard. This paper gives an introduction of the progress of researching on the optical lattice clock of Strontium atom in NTSC (National Time Service Center). We realize the (5s5s)1S0—(5s5p)1P1 cooling (blue MOT) and (5s5s)1S0—(5s5p)3P1 cooling (red MOT) in succession for the optical lattice clock, and loading these cold atoms in a lattice composed by a magic wave-length is studied. By using our narrow line-width diode laser and the fiber femtosecond optical frequency comb, we precisely measure the absolute frequencies of the inter-combination transitions (5s5s)1S0—(5s5p)3P1 of four isotopes of Strontium referenced to an H maser.
To decrease the Doppler broadening and frequency shift,reducing the atomic velocity by laser cooling is necessary.Noting that through the first stage cooling,atoms can only be slowed down to the temperature at the mK level,which is too high to be loaded to the optical lattice,We made further efforts to slow down the velocity of the atoms,and the second stage cooling was implemented.When the first stage cooling stopped,using the 689 nm laser corresponding to(5s2)1S0→(5s5p)3P1further cooling the atoms could attain the temperature at as low asμK level.Using the timing sequence accurately controlling the time of interaction between the electromagnetic field and atoms.calculated the temperature through timeof-flight method.Dropping time of cold atoms in the MOT was accurately controlled,and the atomic photos were taken at 0ms and 20 ms.By analyzing the data,the atomic temperature after the second stage cooling is 4.39μK,uncertainty is only 0.19μK and the number of the atoms 1.2×107.The temperature and number of the Sr atoms offer the important reference for estimating the SNR of signal,which is also the foundation for achieving the high-precision standard of time and frequency.
We observe the fluorescence and the saturated fluorescence spectra of (5s2)1S0(5s5p)3P1 intercombination transition of thermal strontium atomic beam. Experimental investigation of 88Sr(5s2)1S0(5s5p)3P1 intercombination transition is performed on the different experimental conditions. Our study indicates that experimental parameters affect spectra largely, including temperature, intensity of laser and scanning frequency of laser. Intensity of spectrum is reciprocal of scanning frequency of laser due to long lifetime of (5s5p)3P1 state of Sr atom. Owing to Doppler broadening, transit broadening and other experimental factors, the linewidth of (5s2)1S0(5s5p)3P1 fluorescence spectrum is far more than its natural linewidth and proportional scanning frequency of laser.
In this paper we present a method of observing triplet state transitions of strontium. The intercombination transition is employed to pump the atom population from singlet-state (5s2)1S0 to triplet-state (5s5p)3P1 by a laser at 689 nm. Then 688 nm laser is also employed to divide atom population into the two other triplet-state states (5s5p)3P0 and (5s5p)3PP2. We can obtain the absorption signals of triplet-state transition (5s6s)3S1 → (5s5p)3P0 and (5s6p)3S1 → (5s5p)3P3P2. And these atomic absorption signals can be used for stabilizing the repumping light 679 nm and 707 nm directly to transition line of strontium. This method can be used in the Doppler cooling of strontium atoms.
We describe the design, construction, and performance of a laser system to probe the ultra-narrow (Γ/2π ≈ mHz) clock transition 1S0 → 3P0 in strontium. We present the first reported spectroscopy of this transition in two of the bosonic isotopes, 84Sr and 86Sr. Furthermore, we measure the complete set of isotope shifts between all four stable isotopes on the clock line and the narrow intercombination line 1S0 → 3P1, permitting a King plot analysis of the isotope shifts. Complications arising from the unambiguous determination of a line center in 87Sr 3P1 prevent us from making claims about the King linearity, but we provide a statistical boot- strap analysis of the isotope shifts 88−84Sr and 88−86Sr to compute a field shift ratio F698/F689 = 0.9979, with a 95% confidence interval [0.9952,1.0008]. The intercept term K698 − (F698/F689) K689 is similarly determined to be -2.0 GHz-amu, with a 95% confidence interval [−3.9, −0.3] GHz-amu. Finally, we describe the design of a next-generation apparatus that will enable improvements on the results described here, as well as other studies that involve coherent manipulation of strontium atoms on the clock line.