Energy and Radiative Lifetime of the5d96s2D5

Abstract

The Doppler-free, two-photon 5d 10 6s 2 Si/ 2 -5d 9 6s 22 D 5 / 2 transition in singly ionized Hg, attractive as an optical-frequency standard, has been observed for the first time on a small number of 198 Hg + ions confined in a radio-frequency trap. The radiative lifetime of the 2 D 5 / 2 state and the absolute wave number of the two-photon transition were measured to be 0.090(15) s and 17 757.152(3) cm" 1 , respectively. Optical amplitude-modulation sidebands, induced by the secular (thermal) motion of the harmonically bound ions, were observed also for the first time.PACS numbers: 32.70.Fw, 32.30.JcMicrowave or optical transitions of laser-cooled ions that are confined in electromagnetic traps offer the basis for frequency standards of high stability and accuracy. 1 " 5 The advantages of such devices are numerous: Very long interrogation times and, therefore, high transition-line (?'s can be achieved; fractional frequency perturbations that are due to the trapping fields can be held below 10~1 5 ; collisions with background gas and cell walls can be largely avoided; Doppler shifts are directly reduced by trapping and cooling; and finally, nearly unit detection efficiency of transitions to metastable states is possible so that the signal-to-noise ratio need be limited only by the statistical fluctuations in the number of ions that make the transition. 5 Details of ion traps and laser cooling have been published elsewhere. 1 " 3 A particularly attractive candidate for an optical-frequency standard is the Sd l %s 2 Sy 2 -5d 9 6s 22 D 5 / 2 VLg* transition driven either by two photons with a wavelength near 563 nm 4 or by one photon at half this wavelength. 5 The lifetime of the 2 D 5 / 2 state, which decays by the emission of electric quadrupole radiation at 281.5 nm, is calculated to be of order 0.1 s. 6 This gives a potential optical-line Q of about 7x 10 14 . In this Letter we describe the first results of our investigation of the two-photon transition in 198 Hg + (which is free of hyperfine structure) stored in a miniature rf trap.Our trap is similar to the small radio-frequency traps used in the ion-cooling experiments that were conducted at Heidelberg University on Ba + , 7 and at the University of Washington on Mg + and Ba + . 8 A cross section of the trap electrodes is shown in Fig. 1. It is interesting to note that, although the inner surfaces of our trap electrodes were machined with simple conical cuts, the trap dimensions were chosen to make the fourth-and sixth-order anharmonic contributions to the potential vanish. 9 The rf drive frequency was 21 MHz with a voltage amplitude V 0 ^ 1 kV. The partial pressure of the background gas, with the exception of deliberately added mercury and helium, was ^10~7 Pa (133 Pa = 1 Torr). After loading of 50-200 mercury ions the mercury vapor was frozen out in a liquid-nitrogen cold trap and the vacuum vessel was backfilled with He to the order of 10" 3 -10" 2 Pa. This was sufficient to cool the trapped Hg + collisionally to near room temperature as verified by the ...

Optical frequency standards based on mercury and aluminum ions

“…The first proposal to use the 282 nm transition from the ground 5d 10 6s 2 S 1/2 state to the metastable 5d 9 6s 2 2 D 5/2 state of Hg + as an optical frequency was made by Bender et al 1 The metastable state has a natural lifetime of around 90 ms, [2][3][4][5] giving this transition a Q of around 6 × 10 14 . Work began at NIST on mercury ion optical frequency standards several years later.…”

Hybrid quantum systems with trapped charged particles

“…Table II summarizes the resulting trap parameters. Figure 14(a) describes a three-dimensional configuration of electrodes similar to [87]. Here, the trap endcap to endcap distance is set to d = 100 µm in order to yield reasonable coupling while keeping a minimum distance of 50 µm between the ion and the nearest electrode to avoid large heating rates.…”

Pulsed fluorescence measurements of trapped molecular ions with zero background detection

“…To investigate the quantitative capability of these fluorescence techniques, the laser-induced fragmentation of trapped Alexa I on traps provide a controlled environment in which fluorescence measurements can be performed on an ensemble of ions over timescales sufficient to consider small ion numbers and slow reaction rates. Laserinduced fluorescence measurements of trapped ions have been used in spectroscopic studies of atomic structure [1][2][3][4], the vibrational spectra of small molecules [5][6][7][8], as well as to characterize the dynamic cooling [9] and crystallization of atomic ions [10 -12].This paper introduces techniques that eliminate the detection of laser background scattering on trap apertures and internal surfaces allowing measurements to achieve both high sensitivity and large dynamic range. In previous pulsed laser measurements of molecular fluorescence collected from trapped species (discussed in references [5][6][7][8]), the radiative lifetimes were sufficiently long to allow collection of fluorescence radiation after the laser pulse.…”

“…Analysis of photon statistics indicated an average of ϳ10 photons were incident on the PMT detector per 15 ns pulse for ϳ10 3 I on traps provide a controlled environment in which fluorescence measurements can be performed on an ensemble of ions over timescales sufficient to consider small ion numbers and slow reaction rates. Laserinduced fluorescence measurements of trapped ions have been used in spectroscopic studies of atomic structure [1][2][3][4], the vibrational spectra of small molecules [5][6][7][8], as well as to characterize the dynamic cooling [9] and crystallization of atomic ions [10 -12].…”