Measurement of the Persistence of Excited States of Atoms.

Metastable state produced in mercury vapor at low pressures by electron impacts of 4.9 volts.---The persistence of the "radiation" produced by 4.9 volt impacts in mercury vapor was measured in a four electrode tube of the type usually employed in resonance potential measurements, consisting of an equipotential cathode of simple design, an inner grid $G$ for controlling the velocity of the impacting electrons, an outer photo-electric grid $H$ and a photo-electric plate $P$ . A.c. and d.c. voltages were applied to the two grids in such a way that the electrons had sufficient velocity to excite the radiation only in alternate half-cycles and that the photo-electric current to the electrometer alternated in direction simultaneously. As a result of the persistence of the radiation there resulted a decrease in the current with increasing frequency, reaching a minimum at 1800 cycles for a distance between grids of 17 mm and at 3800 cycles for a distance of 8.5 mm. These results did not vary much with pressure,.003 to.032 mm. They show a lapse of time between the excitation and the arrival of the first radiation at the plate $P$ of about 1/3600 and 1/7600 sec. respectively. A mathematical discussion shows that the diffusion of the radiation by repeated emission and re-absorption (the "imprisonment" of radiation theory) cannot account for these results. A calculation, based on the assumption that the excited atoms remain in a metastable state and carry the energy of excitation to the photo-electric surfaces and there give it up, gives results in very close agreement with the observations. The conclusion is that a metastable state is formed by the atoms excited by the 4.9 volt electron impacts and that these are the effective ones in producing the photo-electric response in the tubes. In these experiments the $2{p}_{2}$ state is the only one excited by the impacts in appreciable amount. How these results can be reconciled with the Bohr theory, according to which the $2{p}_{2}$ state is not metastable, is not clear.Metastable state produced in mercury vapor at low pressures by electron impacts of 4.9 volts.---The persistence of the "radiation" produced by 4.9 volt impacts in mercury vapor was measured in a four electrode tube of the type usually employed in resonance potential measurements, consisting of an equipotential cathode of simple design, an inner grid $G$ for controlling the velocity of the impacting electrons, an outer photo-electric grid $H$ and a photo-electric plate $P$. A.c. and d.c. voltages were applied to the two grids in such a way that the electrons had sufficient velocity to excite the radiation only in alternate half-cycles and that the photo-electric current to the electrometer alternated in direction simultaneously. As a result of the persistence of the radiation there resulted a decrease in the current with increasing frequency, reaching a minimum at 1800 cycles for a distance between grids of 17 mm and at 3800 cycles for a distance of 8.5 mm. These results did not vary much with pressure,.003 to.032 mm. They show a lapse of time between the excitation and the arrival of the first radiation at the plate $P$ of about 1/3600 and 1/7600 sec. respectively. A mathematical discussion shows that the diffusion of the radiation by repeated emission and re-absorption (the "imprisonment" of radiation theory) cannot account for these results. A calculation, based on the assumption that the excited atoms remain in a metastable state and carry the energy of excitation to the photo-electric surfaces and there give it up, gives results in very close agreement with the observations. The conclusion is that a metastable state is formed by the atoms excited by the 4.9 volt electron impacts and that these are the effective ones in producing the photo-electric response in the tubes. In these experiments the $2{p}_{2}$ state is the only one excited by the impacts in appreciable amount. How these results can be reconciled with the Bohr theory, according to which the $2{p}_{2}$ state is not metastable, is not clear.

Physical ReviewAug 1, 192462 citations

A New Method of Measuring the Lifetimes of Excited States of Atoms

R. W. P. McWhirter

Jan 1, 19600 citations

Persistent Photochemical Hole-Burning in the R-Lines of Tetravalent Manganese in Submicron α-Al2O3

Norfadira Binti Wahib, Hans Riesen

Persistent spectral hole-burning in the R-lines of tetravalent manganese in X-irradiated submicron corundum powder is reported for the first time. Two samples were investigated, namely, nominally 0.4 atom % Mn 3+ -doped and 0.4 atom % Mn 4+, Mg 2+ -codoped α-Al 2 O 3 . The samples were produced by a simple combustion reaction method at 600 °C. Spectral hole-burning properties of Mn 4+ ions burned via the R 1 and R 2 lines were measured either by the photoluminescence excitation mode via monitoring the luminescence signal of a vibrational sideband at ∼694 nm or in luminescence, with blue light excitation after the burn period. The hole widths were studied as a function of burn fluence and temperature in the range from 2 to 90 K. We propose a photochemical hole-burning mechanism for both samples based on photoionization and photoreduction of the tetravalent manganese ion. Interestingly, the 0.4 atom % Mn 4+, Mg 2+ sample displayed a higher hole-burning efficiency than the Mn 3+ sample. The hole widths obtained for the persistent spectral holes in the present powder samples were approximately 300 times broader at 2.2 ± 0.1 GHz compared to the ∼6 MHz width observed in transient hole-burning in a macroscopic crystal [ Riesen, H. Chem. Phys. Lett. 2011, 515 (44), 241−244]. We assign this effect to the disruption of the crystal lattice upon the valence state change of the Mn 4+ ion in the hole-burning process. From the hole width, we obtained a decay time of 0.72 ns for the 2 A̅ → E̅ one-phonon relaxation process within the split 2 E excited state. The stability of the spectral holes burned via the R 1 and R 2 lines was investigated for both samples, and we observed a decay of about 20% within 2 h, indicating slow spontaneous hole-filling. A hole area recovery of ∼70 and ∼64% was observed after a temperature cycle from 2.5 to 70 and 90 K for the 0.4 atom % Mn 3+ and 0.4 atom % Mn 4+, Mg 2+ samples, respectively.Persistent spectral hole-burning in the R-lines of tetravalent manganese in X-irradiated submicron corundum powder is reported for the first time. Two samples were investigated, namely, nominally 0.4 atom % Mn 3+ -doped and 0.4 atom % Mn 4+, Mg 2+ -codoped α-Al 2 O 3 . The samples were produced by a simple combustion reaction method at 600 °C. Spectral hole-burning properties of Mn 4+ ions burned via the R 1 and R 2 lines were measured either by the photoluminescence excitation mode via monitoring the luminescence signal of a vibrational sideband at ∼694 nm or in luminescence, with blue light excitation after the burn period. The hole widths were studied as a function of burn fluence and temperature in the range from 2 to 90 K. We propose a photochemical hole-burning mechanism for both samples based on photoionization and photoreduction of the tetravalent manganese ion. Interestingly, the 0.4 atom % Mn 4+, Mg 2+ sample displayed a higher hole-burning efficiency than the Mn 3+ sample. The hole widths obtained for the persistent spectral holes in the present powder samples were approximately 300 times broader at 2.2 ± 0.1 GHz compared to the ∼6 MHz width observed in transient hole-burning in a macroscopic crystal [ Riesen, H. Chem. Phys. Lett. 2011, 515 (44), 241−244]. We assign this effect to the disruption of the crystal lattice upon the valence state change of the Mn 4+ ion in the hole-burning process. From the hole width, we obtained a decay time of 0.72 ns for the 2 A̅ → E̅ one-phonon relaxation process within the split 2 E excited state. The stability of the spectral holes burned via the R 1 and R 2 lines was investigated for both samples, and we observed a decay of about 20% within 2 h, indicating slow spontaneous hole-filling. A hole area recovery of ∼70 and ∼64% was observed after a temperature cycle from 2.5 to 70 and 90 K for the 0.4 atom % Mn 3+ and 0.4 atom % Mn 4+, Mg 2+ samples, respectively.

The Journal of Physical Chemistry CAug 24, 20230 citations

Measurements of Lifetimes of Excited States of Atoms by the Method of Delayed Coincidences

S. HERON, R. W. P. McWhirter, E. H. Rhoderick

NatureSep 1, 195422 citations

Controllable Persistent Atom Current of Bose–Einstein Condensates in an Optical Lattice Ring

Gong-Ping Zheng, Liang Jiu-Qing

In this paper the macroscopic quantum state of Bose–Einstein condensates in optical lattices is studied by solving the periodic Gross–Pitaevskii equation in one-dimensional geometry. It is shown that an exact solution seen to be a travelling wave of excited macroscopic quantum states resultes in a persistent atom current, which can be controlled by adjusting of the barrier height of the optical periodic potential. A critical condition to generate the travelling wave is demonstrated and we moreover propose a practical experiment to realize the persistent atom current in a toroidal atom waveguide.In this paper the macroscopic quantum state of Bose–Einstein condensates in optical lattices is studied by solving the periodic Gross–Pitaevskii equation in one-dimensional geometry. It is shown that an exact solution seen to be a travelling wave of excited macroscopic quantum states resultes in a persistent atom current, which can be controlled by adjusting of the barrier height of the optical periodic potential. A critical condition to generate the travelling wave is demonstrated and we moreover propose a practical experiment to realize the persistent atom current in a toroidal atom waveguide.

arXiv:cond-mat/0506115Communications in Theoretical PhysicsMay 1, 20055 citations

The Excited States of Atoms

Karl Taylor Compton

Scientific AmericanNov 1, 19260 citations

G

for controlling the velocity of the impacting electrons, an outer photo-electric grid

H

and a photo-electric plate

P

. A.c. and d.c. voltages were applied to the two grids in such a way that the electrons had sufficient velocity to excite the radiation only in alternate half-cycles and that the photo-electric current to the electrometer alternated in direction simultaneously. As a result of the persistence of the radiation there resulted a decrease in the current with increasing frequency, reaching a minimum at 1800 cycles for a distance between grids of 17 mm and at 3800 cycles for a distance of 8.5 mm. These results did not vary much with pressure,.003 to.032 mm. They show a lapse of time between the excitation and the arrival of the first radiation at the plate

P

of about 1/3600 and 1/7600 sec. respectively. A mathematical discussion shows that the diffusion of the radiation by repeated emission and re-absorption (the "imprisonment" of radiation theory) cannot account for these results. A calculation, based on the assumption that the excited atoms remain in a metastable state and carry the energy of excitation to the photo-electric surfaces and there give it up, gives results in very close agreement with the observations. The conclusion is that a metastable state is formed by the atoms excited by the 4.9 volt electron impacts and that these are the effective ones in producing the photo-electric response in the tubes. In these experiments the

2{p}_{2}

state is the only one excited by the impacts in appreciable amount. How these results can be reconciled with the Bohr theory, according to which the

2{p}_{2}

state is not metastable, is not clear.