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Physical Review A

Rydberg atom spectroscopy enabled by blackbody radiation ionization

Xiaoxu Lu, Yuan Sun, Harold J. Metcalf

Published Sep 6, 2011• 6 citations
Publisher

Abstract

We have excited helium atoms from their metastable 2 ${}^{3}\phantom{\rule{-0.16em}{0ex}}S$ state to Rydberg states in the range $13<n<50$ in a two-step process via the 3 ${}^{3}\phantom{\rule{-0.16em}{0ex}}P$ state using light at $\ensuremath{\lambda}=389$ nm and 785--815 nm. Atoms in a thermal beam (100 K) cross partially overlapping laser beams of the appropriate frequencies in the counterintuitive order to exploit the high efficiency of stimulated rapid adiabatic passage. The interaction region is between two plates that can be used for Stark tuning in a few V/cm field or for field ionization. At fields much too low for field ionization, we observe signals attributed to ionization by blackbody radiation. Multiple tests confirm this attribution as the cause of ionization. For example, by heating the plates we observe the expected signal increases. Our experiments reinforce previous work where the interaction between Rydberg atoms and room temperature blackbody radiation is important for experiments.

DOI
10.1103/physreva.84.033402

Related papers

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Driving atoms from an initial to a final state of the same parity via an intermediate state of opposite parity is most efficiently done using STIRAP, because it does not populate the intermediate state. For optical transitions this requires appropriate pulses of light in the counter-intuitive order - first coupling the intermediate and final states. We populate Rydberg states of helium (n = 12 ~ 30) in a beam of average velocity 1070 m/s by having the atoms cross two laser beams in a tunable dc electric field. The &ldquo red &rdquo light near &lambda = 790 ~ 830 nm connects the 33P states to the Rydberg states and the &ldquo blue &rdquo beam of &lambda = 389 nm connects the metastable 23S state atoms emitted by our source to the 33P states. By varying the relative position of these beams we can vary both the order and the overlap encountered by the atoms. We vary either the dc electric field and fix the &ldquo red &rdquo laser frequency or vary the &ldquo red &rdquo laser frequency and fix the dc electric field to sweep across Stark states of the Rydberg manifolds. Several mm downstream of the interaction region we apply the very strong bichromatic force on the 23S &rarr 23P transition at &lambda = 1083 nm. It deflects the remaining 23S atoms out of the beam and the ratio of this signal measured with STIRAP beam on and off provides an absolute measure of the fraction of the atoms remaining in the 23S state. Simple three-level models of STIRAP all predict 100% excitation probability, but our raw measurements are typically around half of this, and vary with both n and l of the Rydberg states selected for excitation by the laser frequency and electric field tuning on our Stark maps. For states with high enough Rabi frequency, after correction for the decay back to the metastable state before the deflection, the highest efficiencies are around 70%. An ion detector readily detects the presence of Rydberg atoms. We believe that the observed signals are produced by black-body ionization at a very low rate, but sufficient to ionize about 0.5 ~ 1.0 % of the atoms in a region viewed by our detector. Many measurements provide support for this hypothesis.

•Dec 1, 2011•0 citations

Effects of blackbody radiation on highly excited atoms

William E. Cooke, Thomas F. Gallagher

Transitions between energetically close-lying Rydberg states are characterized by large electric dipole matrix elements and frequencies low enough that at room temperature the photon occupation number is \ensuremath{\simeq} 10. Consequently the absorption of blackbody radiation and the stimulated emission produced by it lead to an efficient redistribution of population among nearby levels. In some cases dramatic effects are observed, for example, radiative lifetimes that are shortened to a small fraction of their $T=0$ values. In addition, the 300-K blackbody field of \ensuremath{\sim}10 V/cm produces ac Stark shifts of the Rydberg levels. Calculations of the population redistribution effects and ac Stark shifts are presented. Examples are given to illustrate that care must be taken in experiments with highly excited atoms to ensure that only one state is being observed rather than a distribution.

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Sun, Yuan

We investigate the coherent population transfer and associated effects for a three level atomic system, with the third level being a Rydberg state. The scheme adopted here is the stimulated Raman adiabatic passage (STIRAP). An atomic beam of metastable helium is orthogonally crossing two laser beams in a tunable dc electric field. The ir laser of 790 - 830 nm connects the triplet 3P state to the Rydberg states (n = 12 - 50) and the uv laser of 389 nm connects the metastable triplet 2S state to the triplet 3P state. A third laser of 1083 nm driving 2S-2P transition is applied downstream, providing a strong bichromatic force on the atoms remaining in the 2S state to deflect them, establishing the absolute count of Rydberg atoms. Rydberg atoms can be ionized by background thermal radiations at room temperature and it is observed in this experiment. This fact actually enables precise measurement, especially spectroscopy, of Rydberg atoms by simply looking at the ions, which are easy to detect. It is also confirmed that background thermal radiation could significantly redistribute the population between neighboring Rydberg states. The 2S, 3P and the final Rydberg states all have magnetic sub-levels, hence the linkage pattern of the excitation has non-trivial crossings, if the polarizations of the two lasers are not parallel to each other. Those phase differences in different excitation paths induced by the laser polarizations can lead to interference which would determine the excitation probability and the polarization of the excited atom. Theoretical calculations predict interesting interference patterns as a function of laser polarizations and Rabi frequencies. Those interference structures have been experimentally observed. Transverse velocity distribution in the atomic beam turns out to be a limiting factor in the efficiency of production of Rydberg atoms. The transverse velocity of an atom can not only induce one-photon detuning but also two-photon detuning, which could effectively reduce the STIRAP process efficiency. By adding a laser to make Doppler molasses in the transverse direction, we can heat or cool the atomic beam transversely and verify this effect. | 190 pages

•Dec 1, 2013•0 citations

Collisional and thermal ionization of sodium Rydberg atoms: I. Experiment fornS andnD atoms withn= 8–20

I. I. Ryabtsev, Denis B. Tretyakov, Ilya I. Beterov +3 more

Collisional and thermal ionization of sodium n S and n D Rydberg atoms with n = 8–20 has been studied. The experiments were performed using a two-step pulsed laser excitation in an effusive atomic beam at atom density of about 2 × 10 10 cm −3 . Molecular and atomic ions from associative, Penning and thermal ionization processes were detected. It was found that the atomic ions were created mainly due to photoionization of Rydberg atoms by photons of blackbody radiation at the ambient temperature of 300 K. Blackbody ionization rates and effective lifetimes of Rydberg states of interest were determined. The molecular ions were found to be from associative ionization in Na( nL ) + Na(3S) collisions. Rate constants of associative ionization have been measured using an original method based on relative measurements of Na + 2 and Na + ion signals.

arXiv:physics/0501088•Journal of Physics B Atomic Molecular and Optical Physics•Jan 6, 2005•23 citations

STIRAP on helium: Excitation to Rydberg states

Deqian Yuan

Research in optically induced transitions between dierent atomic levels has a long history. For transitions between states driven by a coherent optical eld, the theoretical eciency could be ideally high as 100% but there could be many factors preventing this. In the three state helium atom excitation process, i.e. 23S! 33P! nL , the stimulated emission from intermediate state makes it hard to achieve ecient population transfer to the nal state through an intuitive excitation order. One technique to achieve a higher eciency is Stimulated Raman Adiabatic Passage (STIRAP) which is being studied and under research in our lab. Unlike traditional three level excitation processes, STIRAP actually uses a counter intuitive pulsed laser beams timing arrangement. The excitation objects are metastable helium atoms traveling in a vacuum system with a longitudinal velocity of 1070 m/s. We are using a 389 nm UV laser to connect the 23S and the 33P state and a frequency tunable 790 nm iii IR laser to connect the 33P state and the dierent Rydberg states. A third 1083 nm wavelength laser beam drives the 23S ! 23P transition to transversely separate the residual metastable atoms and the Rydberg atoms for eciency measurements. The data is taken by a stainless steel detector in the vacuum system. As the Rydberg atoms will get ionized by blackbody radiation under room temperature, we can utilize this for their detection. An ion detector sitting on the eld plate is capable to collect the ion signals of the Rydberg atoms for detection. So far the whole system has not been ready for data collection and measurement, so here we are using data and results from previous theses for discussions. The highest transition frequency that has ever been achieved in our lab is around 70% after corrections. | 144 pages

•Jan 1, 2015•0 citations

Collisional and thermal ionization of sodium Rydberg atoms in single and crossed atomic beams

I. I. Ryabtsev, Ilya I. Beterov, Denis B. Tretyakov +4 more

The results of the experimental and theoretical study on associative ionization of laser excited Na Rydberg atoms in collisions with ground-state atoms and on thermal ionization by blackbody radiation in single and crossed effusive atomic beams are reported and discussed.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Mar 1, 2006•0 citations
We have excited helium atoms from their metastable 2 3S{}^{3}\phantom{\rule{-0.16em}{0ex}}S3S state to Rydberg states in the range 13<n<5013<n<5013<n<50 in a two-step process via the 3 3P{}^{3}\phantom{\rule{-0.16em}{0ex}}P3P state using light at \ensuremathλ=389\ensuremath{\lambda}=389\ensuremathλ=389 nm and 785--815 nm. Atoms in a thermal beam (100 K) cross partially overlapping laser beams of the appropriate frequencies in the counterintuitive order to exploit the high efficiency of stimulated rapid adiabatic passage. The interaction region is between two plates that can be used for Stark tuning in a few V/cm field or for field ionization. At fields much too low for field ionization, we observe signals attributed to ionization by blackbody radiation. Multiple tests confirm this attribution as the cause of ionization. For example, by heating the plates we observe the expected signal increases. Our experiments reinforce previous work where the interaction between Rydberg atoms and room temperature blackbody radiation is important for experiments.
Driving atoms from an initial to a final state of the same parity via an intermediate state of opposite parity is most efficiently done using STIRAP, because it does not populate the intermediate state. For optical transitions this requires appropriate pulses of light in the counter-intuitive order - first coupling the intermediate and final states. We populate Rydberg states of helium (n = 12 ~ 30) in a beam of average velocity 1070 m/s by having the atoms cross two laser beams in a tunable dc electric field. The &ldquo red &rdquo light near &lambda = 790 ~ 830 nm connects the 33P states to the Rydberg states and the &ldquo blue &rdquo beam of &lambda = 389 nm connects the metastable 23S state atoms emitted by our source to the 33P states. By varying the relative position of these beams we can vary both the order and the overlap encountered by the atoms. We vary either the dc electric field and fix the &ldquo red &rdquo laser frequency or vary the &ldquo red &rdquo laser frequency and fix the dc electric field to sweep across Stark states of the Rydberg manifolds. Several mm downstream of the interaction region we apply the very strong bichromatic force on the 23S &rarr 23P transition at &lambda = 1083 nm. It deflects the remaining 23S atoms out of the beam and the ratio of this signal measured with STIRAP beam on and off provides an absolute measure of the fraction of the atoms remaining in the 23S state. Simple three-level models of STIRAP all predict 100% excitation probability, but our raw measurements are typically around half of this, and vary with both n and l of the Rydberg states selected for excitation by the laser frequency and electric field tuning on our Stark maps. For states with high enough Rabi frequency, after correction for the decay back to the metastable state before the deflection, the highest efficiencies are around 70%. An ion detector readily detects the presence of Rydberg atoms. We believe that the observed signals are produced by black-body ionization at a very low rate, but sufficient to ionize about 0.5 ~ 1.0 % of the atoms in a region viewed by our detector. Many measurements provide support for this hypothesis.
Transitions between energetically close-lying Rydberg states are characterized by large electric dipole matrix elements and frequencies low enough that at room temperature the photon occupation number is \ensuremath{\simeq} 10. Consequently the absorption of blackbody radiation and the stimulated emission produced by it lead to an efficient redistribution of population among nearby levels. In some cases dramatic effects are observed, for example, radiative lifetimes that are shortened to a small fraction of their T=0T=0T=0 values. In addition, the 300-K blackbody field of \ensuremath{\sim}10 V/cm produces ac Stark shifts of the Rydberg levels. Calculations of the population redistribution effects and ac Stark shifts are presented. Examples are given to illustrate that care must be taken in experiments with highly excited atoms to ensure that only one state is being observed rather than a distribution.
We investigate the coherent population transfer and associated effects for a three level atomic system, with the third level being a Rydberg state. The scheme adopted here is the stimulated Raman adiabatic passage (STIRAP). An atomic beam of metastable helium is orthogonally crossing two laser beams in a tunable dc electric field. The ir laser of 790 - 830 nm connects the triplet 3P state to the Rydberg states (n = 12 - 50) and the uv laser of 389 nm connects the metastable triplet 2S state to the triplet 3P state. A third laser of 1083 nm driving 2S-2P transition is applied downstream, providing a strong bichromatic force on the atoms remaining in the 2S state to deflect them, establishing the absolute count of Rydberg atoms. Rydberg atoms can be ionized by background thermal radiations at room temperature and it is observed in this experiment. This fact actually enables precise measurement, especially spectroscopy, of Rydberg atoms by simply looking at the ions, which are easy to detect. It is also confirmed that background thermal radiation could significantly redistribute the population between neighboring Rydberg states. The 2S, 3P and the final Rydberg states all have magnetic sub-levels, hence the linkage pattern of the excitation has non-trivial crossings, if the polarizations of the two lasers are not parallel to each other. Those phase differences in different excitation paths induced by the laser polarizations can lead to interference which would determine the excitation probability and the polarization of the excited atom. Theoretical calculations predict interesting interference patterns as a function of laser polarizations and Rabi frequencies. Those interference structures have been experimentally observed. Transverse velocity distribution in the atomic beam turns out to be a limiting factor in the efficiency of production of Rydberg atoms. The transverse velocity of an atom can not only induce one-photon detuning but also two-photon detuning, which could effectively reduce the STIRAP process efficiency. By adding a laser to make Doppler molasses in the transverse direction, we can heat or cool the atomic beam transversely and verify this effect. | 190 pages
Collisional and thermal ionization of sodium n S and n D Rydberg atoms with n = 8–20 has been studied. The experiments were performed using a two-step pulsed laser excitation in an effusive atomic beam at atom density of about 2 × 10 10 cm −3 . Molecular and atomic ions from associative, Penning and thermal ionization processes were detected. It was found that the atomic ions were created mainly due to photoionization of Rydberg atoms by photons of blackbody radiation at the ambient temperature of 300 K. Blackbody ionization rates and effective lifetimes of Rydberg states of interest were determined. The molecular ions were found to be from associative ionization in Na( nL ) + Na(3S) collisions. Rate constants of associative ionization have been measured using an original method based on relative measurements of Na + 2 and Na + ion signals.
Research in optically induced transitions between dierent atomic levels has a long history. For transitions between states driven by a coherent optical eld, the theoretical eciency could be ideally high as 100% but there could be many factors preventing this. In the three state helium atom excitation process, i.e. 23S! 33P! nL , the stimulated emission from intermediate state makes it hard to achieve ecient population transfer to the nal state through an intuitive excitation order. One technique to achieve a higher eciency is Stimulated Raman Adiabatic Passage (STIRAP) which is being studied and under research in our lab. Unlike traditional three level excitation processes, STIRAP actually uses a counter intuitive pulsed laser beams timing arrangement. The excitation objects are metastable helium atoms traveling in a vacuum system with a longitudinal velocity of 1070 m/s. We are using a 389 nm UV laser to connect the 23S and the 33P state and a frequency tunable 790 nm iii IR laser to connect the 33P state and the dierent Rydberg states. A third 1083 nm wavelength laser beam drives the 23S ! 23P transition to transversely separate the residual metastable atoms and the Rydberg atoms for eciency measurements. The data is taken by a stainless steel detector in the vacuum system. As the Rydberg atoms will get ionized by blackbody radiation under room temperature, we can utilize this for their detection. An ion detector sitting on the eld plate is capable to collect the ion signals of the Rydberg atoms for detection. So far the whole system has not been ready for data collection and measurement, so here we are using data and results from previous theses for discussions. The highest transition frequency that has ever been achieved in our lab is around 70% after corrections. | 144 pages