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Physical Review A

Laser modulation technique for single isotope spectroscopic studies

Jason R. Bochinski, Thomas H. Loftus, THOMAS W. MOSSBERG

Published Mar 17, 2000• 4 citations
Publisher

Abstract

We demonstrate an atomic-beam approach to obtaining isotope specific driven-atom spectra using samples of arbitrary isotopic composition. The method employs modulation of a target isotope ground-state population by an upstream preparation laser. Desired driven-atom signals generated downstream from the preparation laser are isolated using a lock-in amplifier referenced to the preparation laser modulation frequency. In our experiments, an intensity-modulated laser resonant with the barium ${(6s}^{2}{)}^{1}{S}_{0}{\ensuremath{-}(6s6p)}^{3}{P}_{1}$ 791.1-nm intercombination transition selectively pumps ${}^{138}\mathrm{Ba}$ atoms via radiative decays to the ${(6s5d)}^{3}{D}_{1,2}$ metastable states. Dressed-atom gain studies using the ${(6s}^{2}{)}^{1}{S}_{0}{\ensuremath{-}(6s6p)}^{1}{P}_{1}$ 553.5-nm transition demonstrate the efficacy of the method. This technique has general utility for selectively isolating specific isotopic signals in systems possessing optically controllable atomic-beam populations.

DOI
10.1103/physreva.61.041404

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We demonstrate an experimental technique that selects the nuclear spin I=0 isotope $^{138}\mathrm{Ba}$ for spectroscopic measurements from a beam of natural barium containing seven stable isotopes. A cw dye laser is used to optically pump the I=3/2 isotopes $^{135}\mathrm{Ba}$ and $^{137}\mathrm{Ba}$ into the metastable 6s5d $^{1}$${\mathit{D}}_{2}$ and $^{3}$${\mathit{D}}_{1,2}$ levels via the 6s6p $^{1}$${\mathit{P}}_{1}$ excited state, leaving nearly pure $^{138}\mathrm{Ba}$ in the ground state. Photoionization spectra of the excited 5d6p $^{3}$${\mathit{D}}_{1}$ even isotope state recorded with optical pumping of $^{135}\mathrm{Ba}$ and $^{137}\mathrm{Ba}$ to the metastable levels are essentially devoid of forbidden features associated with the hyperfine interaction in the odd isotopes.

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Umakanth Dammalapati

This thesis is written as a part of the TRImP programme. Rare and short-lived radioactive isotopes offer new possibilities for investigating fundamental interactions and symmetries. Radium, a radioactive alkaline earth element has been identified as a new candidate for searches for a permanent electric dipole moment in neutral atoms. The TRImP facility at KVI, Groningen, The Netherlands is being setup to produce and utilize these radioactive isotopes to study fundamental interactions and symmetries. We use atom traps for these studies. We presented the various stages for the production, separation and slowing of the short-lived radioactive isotopes of our interest at the TRImP facility. We need to expand laser cooling and trapping methods to heavy alkaline earth elements barium and radium. Stable barium is well suited as a precursor for radioactive radium, because of its similar level scheme and chemical properties. Because of the radioactivity of radium we have chosen to prepare the cooling and trapping with the homologue barium. Stable isotopes of barium were used in the present study. For spectroscopy, metastable singlet and triplet D-states were populated by optical methods rather than using the conventional method of atomic discharges. The singlet D-state is populated by driving the 1S0-1P1 transition. To populate the triplet D-states efficiently the branching ratio of the 3P1 level was exploited by optical pumping with the intercombination line using the diode lasers at 791.3 nm. Long term frequency stability of these lasers were achieved by referencing the frequency to a nearby transition in molecular iodine. We performed first direct optical spectroscopy of the 1D2-1P1(1500.4 nm), 3D1-1P1(1107.8 nm) and 3D2-1p1 (1130.6 nm) transitions respectively. The hyperfine structure of the 3D1 and 3D2 levels for the Ba-135,137 isotopes were optically resolved. In addition, isotope shifts of the 3D1-1P1 transition were measured. We report the experimental observation of coherent Raman resonances in barium. The relevant Rabi frequencies were extracted for the lambda system and estimated the transition rates, relevant for the laser cooling experiment. We have achieved the first slowing of a barium atomic beam. These results can be applied for atoms, in which a closed cooling cycle can only be found with several laser fields at different wavelengths.

•Jan 1, 2006•4 citations
We demonstrate an atomic-beam approach to obtaining isotope specific driven-atom spectra using samples of arbitrary isotopic composition. The method employs modulation of a target isotope ground-state population by an upstream preparation laser. Desired driven-atom signals generated downstream from the preparation laser are isolated using a lock-in amplifier referenced to the preparation laser modulation frequency. In our experiments, an intensity-modulated laser resonant with the barium (6s2)1S0\ensuremath−(6s6p)3P1{(6s}^{2}{)}^{1}{S}_{0}{\ensuremath{-}(6s6p)}^{3}{P}_{1}(6s2)1S0​\ensuremath−(6s6p)3P1​ 791.1-nm intercombination transition selectively pumps 138Ba{}^{138}\mathrm{Ba}138Ba atoms via radiative decays to the (6s5d)3D1,2{(6s5d)}^{3}{D}_{1,2}(6s5d)3D1,2​ metastable states. Dressed-atom gain studies using the (6s2)1S0\ensuremath−(6s6p)1P1{(6s}^{2}{)}^{1}{S}_{0}{\ensuremath{-}(6s6p)}^{1}{P}_{1}(6s2)1S0​\ensuremath−(6s6p)1P1​ 553.5-nm transition demonstrate the efficacy of the method. This technique has general utility for selectively isolating specific isotopic signals in systems possessing optically controllable atomic-beam populations.
We demonstrate an experimental technique that selects the nuclear spin I=0 isotope 138Ba^{138}\mathrm{Ba}138Ba for spectroscopic measurements from a beam of natural barium containing seven stable isotopes. A cw dye laser is used to optically pump the I=3/2 isotopes 135Ba^{135}\mathrm{Ba}135Ba and 137Ba^{137}\mathrm{Ba}137Ba into the metastable 6s5d 1^{1}1D2{\mathit{D}}_{2}D2​ and 3^{3}3D1,2{\mathit{D}}_{1,2}D1,2​ levels via the 6s6p 1^{1}1P1{\mathit{P}}_{1}P1​ excited state, leaving nearly pure 138Ba^{138}\mathrm{Ba}138Ba in the ground state. Photoionization spectra of the excited 5d6p 3^{3}3D1{\mathit{D}}_{1}D1​ even isotope state recorded with optical pumping of 135Ba^{135}\mathrm{Ba}135Ba and 137Ba^{137}\mathrm{Ba}137Ba to the metastable levels are essentially devoid of forbidden features associated with the hyperfine interaction in the odd isotopes.
We demonstrate that laser cooling, combined with VVV-scheme optical double-resonance spectroscopy, provides a sensitive means to measure isotope shifts and hyperfine splittings. Our technique is illustrated using the 398.8-nm ${(6s}^{2}{)}^{1}{S}_{0}{\ensuremath{-}(6s6p)}^{1}{P}_{1}$ and 555.6-nm ${(6s}^{2}{)}^{1}{S}_{0}{\ensuremath{-}(6s6p)}^{3}{P}_{1}$ transitions in a neutral ytterbium atomic beam having natural isotopic composition. With a precision comparable to existing approaches, our unique method has enabled the most complete single-technique survey to date of the ${}^{1}{S}_{0}{\ensuremath{-}}^{1}{P}_{1}$ isotope shifts and hyperfine splittings.
Trapped single ions provide an ideal platform for studying quantum optics, light-matter interactions, and quantum information processing. Many of these applications rely on the availability of well-defined and reproducible quantum emitters as well as precise control over the internal states of ions. To study both of these concepts, this thesis focuses on the isotope selectivity of neutral Barium (Ba) transitions as well as the state preparation of single trapped 138Ba+ ions. The first part of this thesis introduces the theoretical framework for experiments, focusing on single Ba+ ions and light-matter interactions. Therefore, the working principle of Paul traps is presented, the Ba ion is introduced and fundamental light-matter interaction tightly related to the experiments and simulations presented in this work are established. In the second part, the isotope selectivity of the neutral Ba 6s2 1S0 to 6s6p 1P1 transition at 553 nm is investigated and compared with the isotope selectivity of the 6s2 1S0 to 5d6p 3D1 transition at 413 nm. A secondary photon can be used in both cases to achieve isotope selective ionization of Ba+ ions. The isotope selectivity of the 553 nm transition was tested by carrying out spectroscopy and comparing the results with existing data. The isotope selectivity for other naturally available Ba isotopes is simulated for both transitions (553 nm and 413 nm) and for different angles between atomic beam and laser beam (90°, 85° and 80°). The simulations show, that under ideal conditions (when the atomic beam and ionization laser beam are orthogonal) both transitions perform similarly. However, the 553 nm transition exhibits greater robustness against Doppler shifts as the angle deviates from 90°. At an angle of 80° between the atomic beam and the laser beam, the maximum probability of generating 138Ba+ is 99 % using 553 nm, while the maximum probability of generating the isotope using 413 nm does not exceed 94 %. In the third part of this thesis, we focus on state preparation of Ba+ ions in the 6P1/2 state. A heralding state preparation scheme that exploits the spontaneous emission of a 389 nm photon during the decay of the excited state 6D3/2 is introduced. The detection of a photon at this wavelength projects the ion into the desired state 6P1/2 in a deterministic fashion. A simulation of this scheme shows that the preparation probability may exceed 78 %, and the heralding process ensures state preparation with 100 % fidelity, if a photon at a wavelength of 389 nm is detected. The state preparation method will be adopted in near-future experiments that are provided as an outlook at the end of this thesis.
Summary form only given. Barium (Ba) is a versatile atom for basic quantum optical measurements because it possesses multiple transitions at conveniently accessible wavelengths which allow the creation of a variety of useful systems. This atom has been used as a three-level /spl Lambda/, cascade, and V system for driven atom and lasing without inversion experiments. Other work relied on the (6s/sup 2/)/sup 1/S/sub 0/-(6s6p)/sup 1/P/sub 1/ 553.5 nm transition as a two-level system for cavity quantum electrodynamics, two-photon laser, and single-atom laser experiments. However, these observations, which utilize natural Ba, are complicated by the presence of multiple isotopes with small frequency shifts. These isotopes introduce additional features and under certain conditions mask small structures, making interpretation of the results non-trivial.
Isotope selective optical excitation of atoms is important for experiments with neutral atoms, metrology, and work with trapped ions, including quantum information processing. Polarization-enhanced absorption spectroscopy is used to frequency stabilise a tunable external cavity laser diode system at 398.9 nm for isotope selective photoionization of neutral Yb atoms. This spectroscopy technique is used to measure isotope resolved dispersive features from transitions within a see through configuration Ytterbium hollow-cathode discharge lamp. This Doppler-free dichroic polarization spectroscopy is realised by retro-reflecting a laser beam through the discharge and analysing the polarization dependent absorption with balanced detection. The spectroscopy signal is recovered using lock-in detection of frequency modulation induced by current modulation of the external cavity laser diode. Here, we show the use of polarization-enhanced absorption spectroscopy for isotope selectively loading of 171^{171}171Yb+^++, 172^{172}172Yb+^++, or 174^{174}174Yb+^++ ions into an RF Paul trap.
This thesis is written as a part of the TRImP programme. Rare and short-lived radioactive isotopes offer new possibilities for investigating fundamental interactions and symmetries. Radium, a radioactive alkaline earth element has been identified as a new candidate for searches for a permanent electric dipole moment in neutral atoms. The TRImP facility at KVI, Groningen, The Netherlands is being setup to produce and utilize these radioactive isotopes to study fundamental interactions and symmetries. We use atom traps for these studies. We presented the various stages for the production, separation and slowing of the short-lived radioactive isotopes of our interest at the TRImP facility. We need to expand laser cooling and trapping methods to heavy alkaline earth elements barium and radium. Stable barium is well suited as a precursor for radioactive radium, because of its similar level scheme and chemical properties. Because of the radioactivity of radium we have chosen to prepare the cooling and trapping with the homologue barium. Stable isotopes of barium were used in the present study. For spectroscopy, metastable singlet and triplet D-states were populated by optical methods rather than using the conventional method of atomic discharges. The singlet D-state is populated by driving the 1S0-1P1 transition. To populate the triplet D-states efficiently the branching ratio of the 3P1 level was exploited by optical pumping with the intercombination line using the diode lasers at 791.3 nm. Long term frequency stability of these lasers were achieved by referencing the frequency to a nearby transition in molecular iodine. We performed first direct optical spectroscopy of the 1D2-1P1(1500.4 nm), 3D1-1P1(1107.8 nm) and 3D2-1p1 (1130.6 nm) transitions respectively. The hyperfine structure of the 3D1 and 3D2 levels for the Ba-135,137 isotopes were optically resolved. In addition, isotope shifts of the 3D1-1P1 transition were measured. We report the experimental observation of coherent Raman resonances in barium. The relevant Rabi frequencies were extracted for the lambda system and estimated the transition rates, relevant for the laser cooling experiment. We have achieved the first slowing of a barium atomic beam. These results can be applied for atoms, in which a closed cooling cycle can only be found with several laser fields at different wavelengths.