Photoionization of strongly laser-coupled potassium

Laser-induced autoionization, a form of forced autoionization, is discussed. Highly excited atomic Rydberg states generally have a small cross section for photoionization due to their small overlap with the nucleus. The cross section for photoionization can be strongly enhanced if the Rydberg series is perturbed by an atomic state with a relatively large cross section for photoionization. The photoionization dynamics of such a perturbed Rydberg system shows strong similarities to that of an autoionizing Rydberg series. For intense laser pulses, which strongly couple the perturber to the continuum, the photoionization rate is limited by the coupling between the Rydberg states and the perturber or, in other words, the autoionization rate. The model describing this ionization dynamics is applied to the barium 6snd ${(}^{1,3}$ ${\mathit{D}}_{2}$ ) state which is perturbed by the 5d7d ${(}^{1}$ ${\mathit{D}}_{2}$ ) state. The calculations show good agreement with experimental results of photoionization of barium Rydberg states with subpicosecond laser pulses of light of 620 nm in wavelength.Laser-induced autoionization, a form of forced autoionization, is discussed. Highly excited atomic Rydberg states generally have a small cross section for photoionization due to their small overlap with the nucleus. The cross section for photoionization can be strongly enhanced if the Rydberg series is perturbed by an atomic state with a relatively large cross section for photoionization. The photoionization dynamics of such a perturbed Rydberg system shows strong similarities to that of an autoionizing Rydberg series. For intense laser pulses, which strongly couple the perturber to the continuum, the photoionization rate is limited by the coupling between the Rydberg states and the perturber or, in other words, the autoionization rate. The model describing this ionization dynamics is applied to the barium 6snd${(}^{1,3}$${\mathit{D}}_{2}$) state which is perturbed by the 5d7d${(}^{1}$${\mathit{D}}_{2}$) state. The calculations show good agreement with experimental results of photoionization of barium Rydberg states with subpicosecond laser pulses of light of 620 nm in wavelength.

Physical Review ASep 1, 19957 citations

Photoionization of laser excited barium

Lucy-Wenzhong He

Jan 1, 19940 citations

EXCITATION AND PHOTOIONIZATION OF LASER-COOLED ATOMS IN THE AC-DRIVEN MAGNETO-OPTICAL TRAP (AC-MOT), USING RESONANT AND NON-RESONANT RADIATION.

John Chidowerem Agomuo

ABSTRACTCandidate?s Names: John AgomuoDegree Title: PhDThesis Title: Excitation And Photoionization Of Laser-Cooled Atoms In The AC Driven Magneto-Optical Trap (AC-MOT), Using Resonant And Non-Resonant Radiation.Date: 19/12/2014Results of experiments involving the manipulation of atoms using laser radiation are presented. A high-density trap of potassium atoms was created using an AC-driven magneto-optical trap (AC-MOT), loaded from a Zeeman-slowed atomic beam. The AC-MOT was operated in a pulsed mode, with a trapping laser that was detuned by -4?, where ? is the natural line-width of the trapping transition. Under these conditions, the AC-MOT trapped an average of 3.63�0.02�?10?^8 atoms, which were cooled to a mean temperature of 275?K�33?K.Using the AC-MOT, the absolute photoionization cross-section of cold potassium atoms was determined using ionizing laser radiation at 450.4 nm obtained from a high-power diode laser. The measured photoionization cross-section from the 42P3/2 excited state was obtained by measuring the loss rate and the lifetime of the AC-MOT during the loading and decay processes. Using these methods, the cross section was determined to be 1.49�0.13 Mb, and 2.38�0.18 Mb respectively. Precise energy levels of high-n Rydberg states of potassium have also been measured using stepwise-excitation of the trapped atoms, with the intermediate state being the 42P1/2 state that was excited by resonant laser radiation at 389,286,368.12 MHz. Excitation from the 42P1/2 state to the n^2 S_(1/2) states was carried out using blue radiation from a dye laser, for transitions to Rydberg states with principal quantum numbers ranging from n = 18 to ~200. For excitation to the n^2 D_(3/2) states, transitions up to Rydberg states with n ranging from 18 to 167 were studied. Due to the strong interaction between Rydberg atoms, the measured energy levels deviated from their predicted theoretical values at high principal quantum numbers (n?130 for the S-states, and n?100 for the D-states). For principal quantum numbers greater than these values, the spectral lines were found to both broaden and shift in energy, and new features in the Rydberg spectra were observed. These new features have been attributed to the dipole-forbidden n2P1/2 and n2P3/2 states, which cannot be excited directly by the laser. These states must hence be excited due to interplay between the highly excited Rydberg atoms that is occurring due to their large effective size and close proximity in the AC-MOT.ABSTRACTCandidate?s Names: John AgomuoDegree Title: PhDThesis Title: Excitation And Photoionization Of Laser-Cooled Atoms In The AC Driven Magneto-Optical Trap (AC-MOT), Using Resonant And Non-Resonant Radiation.Date: 19/12/2014Results of experiments involving the manipulation of atoms using laser radiation are presented. A high-density trap of potassium atoms was created using an AC-driven magneto-optical trap (AC-MOT), loaded from a Zeeman-slowed atomic beam. The AC-MOT was operated in a pulsed mode, with a trapping laser that was detuned by -4?, where ? is the natural line-width of the trapping transition. Under these conditions, the AC-MOT trapped an average of 3.63�0.02�?10?^8 atoms, which were cooled to a mean temperature of 275?K�33?K.Using the AC-MOT, the absolute photoionization cross-section of cold potassium atoms was determined using ionizing laser radiation at 450.4 nm obtained from a high-power diode laser. The measured photoionization cross-section from the 42P3/2 excited state was obtained by measuring the loss rate and the lifetime of the AC-MOT during the loading and decay processes. Using these methods, the cross section was determined to be 1.49�0.13 Mb, and 2.38�0.18 Mb respectively. Precise energy levels of high-n Rydberg states of potassium have also been measured using stepwise-excitation of the trapped atoms, with the intermediate state being the 42P1/2 state that was excited by resonant laser radiation at 389,286,368.12 MHz. Excitation from the 42P1/2 state to the n^2 S_(1/2) states was carried out using blue radiation from a dye laser, for transitions to Rydberg states with principal quantum numbers ranging from n = 18 to ~200. For excitation to the n^2 D_(3/2) states, transitions up to Rydberg states with n ranging from 18 to 167 were studied. Due to the strong interaction between Rydberg atoms, the measured energy levels deviated from their predicted theoretical values at high principal quantum numbers (n?130 for the S-states, and n?100 for the D-states). For principal quantum numbers greater than these values, the spectral lines were found to both broaden and shift in energy, and new features in the Rydberg spectra were observed. These new features have been attributed to the dipole-forbidden n2P1/2 and n2P3/2 states, which cannot be excited directly by the laser. These states must hence be excited due to interplay between the highly excited Rydberg atoms that is occurring due to their large effective size and close proximity in the AC-MOT.

Mar 27, 20150 citations

Doubly resonant photoionization of He below the N = 2 ionization threshold

A. Mihelič, M. Žitnik, Mateja Hrast

Abstract We present an extended theoretical study of two-colour doubly resonant photoionization of helium involving two doubly excited states below the N = 2 ionization threshold. We model the effects of a strong laser coupling between the lowest 1 P o and the selected 1 S e , 1 P e and 1 D e doubly excited states on the photoelectron (photoion) yield by taking into account the spatio-temporal structure of the pulses and by considering the effects of the neighbouring resonance states. We show that the laser coupling results in a measurable modification of the line profiles and in a reduction of the photoelectron yield under resonant or near-resonant conditions.Abstract We present an extended theoretical study of two-colour doubly resonant photoionization of helium involving two doubly excited states below the N = 2 ionization threshold. We model the effects of a strong laser coupling between the lowest 1 P o and the selected 1 S e , 1 P e and 1 D e doubly excited states on the photoelectron (photoion) yield by taking into account the spatio-temporal structure of the pulses and by considering the effects of the neighbouring resonance states. We show that the laser coupling results in a measurable modification of the line profiles and in a reduction of the photoelectron yield under resonant or near-resonant conditions.

Journal of Physics B Atomic Molecular and Optical PhysicsOct 26, 20176 citations

{(}^{1,3}

{\mathit{D}}_{2}

) state which is perturbed by the 5d7d

{(}^{1}

{\mathit{D}}_{2}

) state. The calculations show good agreement with experimental results of photoionization of barium Rydberg states with subpicosecond laser pulses of light of 620 nm in wavelength.