Doppler-free spectroscopy of metastable calcium in a discharge heat pipe

Abstract

We report on Doppler-free frequency modulation spectroscopy and polarization spectroscopy in a discharge heat pipe of yet unexplored transitions connecting the metastable 3 P 2 ͑4s4p͒ state of calcium atoms with the multiply excited states 3 P 2 ͑4p4p͒ and 3 D 3 ͑4s3d͒. Calcium vapor is efficiently produced in a heat pipe operating in a small Pyrex cell filled with 2 torr of neon. A dc discharge running at 500 V efficiently populates the metastable triplet states. Narrow resonances with bandwidths of a few tens of MHz with excellent signal-tonoise ratios are observed, well suited as references for laser frequency stabilization. Examination of the Zeeman shifts lets us determine the Landé g factors of the excited states and compare them with the predictions based on the Russel-Saunders coupling scheme. We describe an economic, simple, and robust experimental setup that should work for other alkaline-earth-metal atoms like Mg and Sr, as well as for other solid elements with insufficient vapor pressures at room temperature.Alkaline-earth-metal atoms have attracted renewed interest recently because they offer a unique combination of features favorable for a wide range of applications including atomic interferometry ͓1,2͔, optical time standards ͓3͔, cold collision studies in reach of ab initio calculations ͓4-6͔, and studies of ultracold or quantum degenerate atomic gases outside the alkali-metal domain ͓7,8͔. Many interesting aspects of alkaline-earth-metal atoms are connected to the existence of long-lived metastable states accessible by laser sources in the visible and infrared. The desire to manipulate these states with the powerful techniques of laser cooling has motivated us to explore simple frequency referencing schemes, which provide narrow-band spectroscopic signals used to fix the laser frequency with regard to the atomic resonance of interest ͓9,10͔. In experiments with alkali-metal atoms in their ground states, frequency reference schemes are readily provided via Doppler-free spectroscopy in simple vapor cells owing to the high vapor pressure at room temperature ͓11͔. In contrast, alkaline-earth metals like calcium need to be heated significantly in order to obtain sufficient vapor pressure and the population of the metastable state requires operation of a discharge. A possible strategy is the use of a hollow cathode lamp. In such lamps, the discharge is derived from a hollow cathode made of the material of interest-for example, calcium; i.e., the discharge produces a calcium vapor by sputtering and at the same time populates the metastable state. In Ref. ͓12͔, Doppler-free signals with several tens of MHz linewidths have been obtained both with optogalvanic spectroscopy ͓13͔ and more directly by saturation spectroscopy. In both cases, by means of intermodulation techniques a signal-to-noise ratio of about 10 was achieved. Signal sizes in this approach are limited by the sputtering efficiency, while the use of intermodulation techniques based on mechanical choppers limits servolock applications to a band...

Spectroscopy and isotope shifts of the4s3d1D2–Dammalapati1, Norris2, Burrows3 et al. 2010Phys. Rev. A

“…This method is chosen over using another calcium or molecular transition because of its robustness and simplicity. Stabilization to the calcium 1 D 2 -1 P 1 transition is cumbersome as it requires a discharge-heat pipe oven in a buffer gas to sufficiently populate the 4s3d 1 D 2 state [27,28]. Another option is to use the iodine (I 2 ) molecule, which provides frequency references throughout the visible and near infrared (IR).…”

Reservoir spectroscopy of5s5p3P2–5snStellmer1, Schreck2 2014Phys. Rev. A347441View full textAdd to dashboardCite

“…Elements such as magnesium, calcium [91], ytterbium, and mercury have an electronic structure very similar to strontium. More complex atoms, such as the rare-earth species [92] dysprosium [69,93], holmium [94], erbium [68,95], and thulium [96], which are currently under investigation, all have a wealth of metastable states, which can be trapped in the magnetic field of a MOT and potentially be used for reservoir spectroscopy.…”

An ultraviolet laser system for laser cooling and trapping of metastable magnesium

“…The method can also be applied to other experiments requiring multiple stabilised lasers by an appropriately designed cavity. A few examples are the sub-Doppler cooling of calcium in the metastable manifold [2], the strontium optical clock [6] and the simultaneous magneto-optical trapping of 6 Li, 40 K and 87 Rb [11], among many others.…”

“…This can be achieved via frequency modulation spectroscopy in an atomic vapour cell if the transition originates from the ground state [1]. Applying this method to metastable transitions involves additional complexity of an electric discharge and the associated linewidth broadening [2]. In such cases, as well as in the case that the laser frequency is far from any atomic transition, one can transfer the stability of a reference laser to the target laser via a transfer cavity or a frequency comb [3,4,5].…”