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Conference on Precision Electromagnetic Measurements

Design of a cold atom source for a neutral strontium optical frequency standard

Irène Ventrillard, Audrey Quessada, Richard P. Kovacich, J.‐J. Zondy, Arnaud Landragin, Giorgio Santarelli, P. Lemonde

Published Jun 25, 2003• 0 citations
Publisher

Abstract

We discuss the design of a cold atom source for a neutral strontium optical frequency standard. The cooling laser light at 461 nm is produced by sum frequency generation by a KTP crystal inside a doubly resonant cavity. Up to 120 mW of blue light are generated. We also describe the atomic beam and the Zeeman slower from which the atoms are captured.

DOI
10.1109/cpem.2002.1034801

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Efficient cooling and trapping of strontium atoms

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We report the capture of cold strontium atoms in a magneto-optical trap (MOT) at a rate of 4 x 10(10) atoms/s. The MOT is loaded from an atomic beam decelerated by a Zeeman slower operating with a focused laser beam. The 461-nm laser, used for both cooling and trapping, was generated by sum-frequency mixing in a KTP crystal with diode lasers at 813 nm and a Nd:YAG laser at 1064 nm. As much as 115 mW of blue light was obtained.

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We report the capture of cold strontium atoms in a magnetooptical trap at a rate of 3/spl times/10/sup 10/ atoms/s. This is achieved with high power laser light at 461 nm generated by sum frequency mixing in a potassium titanyl phosphate (KTP) crystal using diode lasers at 813 nm and a Nd:YAG laser at 1064 nm. Up to 115 mW of blue light is obtained. Tuned to the /sup 1/S/sub 0//spl rarr//sup 1/P/sub 1/ of /sup 88/Sr, this light is used both to slow down an atomic beam in a Zeeman slower and to capture the atoms in a magnetooptical trap. Trapping of /sup 87/Sr and /sup 86/Sr is also reported.

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Optical frequency standard with ultra-cold strontium atoms

N. Poli, Robert E. Drullinger, Marco G. Tarallo +2 more

We report on our progress toward the realization of an optical frequency standard referenced to strontium intercombination lines. While first frequency measurement of the weakly allowed 1S 0- 3P 1 transition was done with saturation spectroscopy on a thermal beam, we are preparing the experimental setup for high resolution spectroscopy on ultracold atoms of the doubly forbidden 1S 0- 3P 0 line. Our current setup allows the capture more than 10 7 atoms at 1 μK in 500 ms in two stages of magneto-optical trapping. We also demonstrated the dipole trapping of ultracold strontium isotopes for accurate spectroscopy and collisional measurements. A semiconductor laser source at 698 nm has already been locked to a pre-stabilization cavity obtaining a fast linewidth of less than 1 kHz. Second stage stabilization of the clock laser to ultra-high finesse cavity is in development. Recent measurement of elastic and inelastic cross-sections of the two most abundant 88Sr and 86Sr isotopes are also presented.

•Jan 1, 2006•2 citations
We discuss the design of a cold atom source for a neutral strontium optical frequency standard. The cooling laser light at 461 nm is produced by sum frequency generation by a KTP crystal inside a doubly resonant cavity. Up to 120 mW of blue light are generated. We also describe the atomic beam and the Zeeman slower from which the atoms are captured.
We report the capture of cold strontium atoms in a magnetooptical trap at a rate of 3/spl times/10/sup 10/ atoms/s. This is achieved with high power laser light at 461 nm generated by sum frequency mixing in a potassium titanyl phosphate (KTP) crystal using diode lasers at 813 nm and a Nd:YAG laser at 1064 nm. Up to 115 mW of blue light is obtained. Tuned to the /sup 1/S/sub 0//spl rarr//sup 1/P/sub 1/ of /sup 88/Sr, this light is used both to slow down an atomic beam in a Zeeman slower and to capture the atoms in a magnetooptical trap. Trapping of /sup 87/Sr and /sup 86/Sr is also reported.
A 461 nm laser was constructed for the purposes of studying ultracold neutral strontium. The dipole-allowed 1 S0 → 1P1 transition at 460.862 nm can be used in laser cooling and trapping; optical imaging, Zeeman slowing, and photoassociative spectroscopy. We produce light at this wavelength by converting infrared light at 922nm from various IR sources, notably a Ti:Sapphire laser, via second harmonic generation in a frequency doubling cavity using a potassium niobate crystal. This thesis will discuss the motivation, optical resonator, locking electronics, and characterization of a 461 nm laser.
Optical atomic clocks have proven to be the most stable clocks with the lowest systematic uncertainty which has now reached a record level of (9.4 X10/(^{19}/)). Thus optical clocks now surpass the best fountain Cs atomic clocks by three orders of magnitude which opens the prospect of using optical clocks as frequency standards for timekeeping in the near future. \n \nThis thesis describes the progress that has been made towards a stationary optical lattice clock based on strontium atoms, and reports the results of an ongoing characterization. \n \nAn experimental apparatus was designed and built to efficiently slow, cool, and trap the strontium atoms which represent the heart of the strontium optical lattice clock discussed in this thesis. The novel aspects of the experimental development described in the thesis comprise a frequency doubling cavity for producing 461 nm laser light employed for cooling and trapping the strontium atoms in the first stage cooling. This cavity provided sufficient power for cooling and trapping the strontium atoms for up to 300 mW of 461 nm laser light. Furthermore, a new design of Zeeman slower based on spherical permanent magnets was produced, built and characterized. \n \nThe slower is compact, tunable, easy to assemble and maintain, and cost-effective as the permanent magnets do not require any power supply or water cooling. It is suggested that this kind of Zeeman slower constitutes an ideal solution for portable optical clock systems. A blue magneto-optical trap was realized for the first time with such a Zeeman slower. With about 30 mW of a 461 nm laser, up to 6X10/(^8/) atoms were captured.
Optical frequency standards with the reference to a narrow electronic transition of a laser-cooled collection of neutral atomic particles are becoming essential tools of research in modern precision physics experiments. In the core of a building block of an optical frequency standard is the optical continuous wave laser that has a good spectral purity of the emitted light. Such a stable optical oscillator is highly desirable in high resolution spectroscopy, if it emits in a good quality beam at a short visible wavelength. This Master thesis explores efficient techniques for building such an optical frequency source intended for use in the cooling and trapping of Calcium atoms scheme. The strong dipole transition at the blue wavelength in the atomic Calcium is needed to reduce the kinetic energy of atoms by nearly six orders of magnitude. A further reduction in the thermal energy of the laser cooled atoms is required to locate with ultra-high precision the 400 Hz narrow clock transition of the stable 40Ca isotope. The experimental methods that achieve this and approach sub-microkelvin temperature of the laser cooled bosonic isotopes of alkaline earths are inspected. The blue laser with a uniform intensity distribution in the beam is useful to maintain the trapped number of cold atoms during these experiments. The spectroscopic properties of the relative transitions in Calcium atom are also reviewed following relevant publications in the area. The constructed blue laser can be used as a primary wavelength source in the lasers network for cooling and trapping of Calcium atoms. These experiments will constitute part of the project to build an optical atom clock referenced to 40Ca narrow linewidth transition. The blue laser is constructed by generating second harmonic in a Potassium Niobate crystal, which is temperature controlled to use a type-I noncritical phase-matching of the optical nonlinear process. The power of the intracavity-generated second harmonic depends on the resonance properties of the optical resonator where this nonlinear crystal is placed. The study is aimed at characterising the designed optical resonator and the experimental parameters that describe it. The formula is derived that relates the resonance power enhancement coefficient with finesse and the power coupling contrast of a passive optical cavity. The obtained relationship is verfied during the experiments. The produced efficiency of the intracavity second harmonic generation is approx. 0.0023 mWblue/(mWred)2. The research work also examines the noise characteristics of the infrared diode laser that is used as a pump source for the intracavity generated second harmonic and determines the spectroscopic precision of the produced blue light. The frequency locking experiment is analysed using the unbalanced scheme of the polarisation stabilisation technique. The designed optical buildup cavity became a part of the unbalanced frequency discriminator in such a scheme. The results demonstrate high gain of frequency noise suppression of the stabilised laser. The unbalanced arrangement of the H}ansch-Couillaud technique has been possible due to a very low amplitude noise of semiconductor lasers.
We report on our progress toward the realization of an optical frequency standard referenced to strontium intercombination lines. While first frequency measurement of the weakly allowed 1S 0- 3P 1 transition was done with saturation spectroscopy on a thermal beam, we are preparing the experimental setup for high resolution spectroscopy on ultracold atoms of the doubly forbidden 1S 0- 3P 0 line. Our current setup allows the capture more than 10 7 atoms at 1 μK in 500 ms in two stages of magneto-optical trapping. We also demonstrated the dipole trapping of ultracold strontium isotopes for accurate spectroscopy and collisional measurements. A semiconductor laser source at 698 nm has already been locked to a pre-stabilization cavity obtaining a fast linewidth of less than 1 kHz. Second stage stabilization of the clock laser to ultra-high finesse cavity is in development. Recent measurement of elastic and inelastic cross-sections of the two most abundant 88Sr and 86Sr isotopes are also presented.