Three-step Excitation Scheme Research Articles

Observation of interference effects via four-photon excitation of highly excited Rydberg states in thermal cesium vapor.

We report on the observation of electromagnetically induced transparency (EIT) and absorption (EIA) of highly excited Rydberg states in thermal Cs vapor using a four-step excitation scheme. The advantage of this four-step scheme is that the final transition to the Rydberg state has a large dipole moment and one can achieve similar Rabi frequencies to two- or three-step excitation schemes using two orders of magnitude less laser power. This scheme enables new applications such as dephasing free Rydberg excitation. The observed lineshapes are in good agreement with simulations based on multilevel optical Bloch equations.

The VMI study on angular distribution of ejected electrons from Eu 4f76p1/26d autoionizing states**Project supported by the National Natural Science Foundation of China (Grant No. 11174218).

The combination of a velocity mapping imaging technique and mathematical transformation is adopted to study the angular distribution of electrons ejected from the Eu 4f76p1/26d autoionizing states, which are excited with a three-step excitation scheme via different Eu 4f76s6d 8 DJ (J = 5/2, 7/2, and 9/2) intermediate states. In order to determine the energy dependence of angular distribution of the ejected electrons, the anisotropic parameters are measured in the spectral profile of the 6p1/26d autoionizing states by tuning the wavelength of the third-step laser across the ionic resonance lines of the Eu 6s+ → 6p+. The configuration interaction is discussed by comparing the angular distributions of ejected electrons from the different states. The present study reveals the profound variations of anisotropic parameters in the entire region of autoionization resonance, highlighting the complicated nature of the autoionization process for the lowest member of 6p1/26d autoionization series.

Efficient field-free orientation of CO molecules using a three-step excitation scheme

An efficient three-step excitation scheme is proposed to achieve the strong molecular orientation. By taking the CO molecule for example, via the Raman excitation by the femtosecond pulse L 1 and subsequently resonant excitations by a single-cycle THz pulse L 2, the high degree of the field-free orientation of |⟨ cosθ ⟩ |max = 0.8921 can be obtained at the rotational temperature T = 0 K. An additional single-cycle THz pulse L 3 is introduced to further regulate the population distribution on rotational states and decrease the reduction of the orientation originating from the offset phase. With the increase of the central frequency ω 3 of L 3, the optimal |⟨ cosθ ⟩ |max increases monotonically. When ω 3 = 1.0 THz, the degree of the field-free orientation reaches |⟨ cosθ ⟩ |max = 0.9401. Moreover, our scheme is robust against the rotational temperature. Although the molecular orientation weakens with the rise of rotational temperature, |⟨ ⟨ cosθ ⟩ ⟩ | > 0.5 is still obtained until T = 22.8 K.

Three-step resonant photoionization spectroscopy of Ni and Ge: ionization potential and odd-parity Rydberg levels

In preparation of a laser ion source, we have investigated multi-step laser ionization via Rydberg and autoionizing states for atomic Ni and Ge using a mass separator with an ion beam energy of 20 keV. For both elements resonant three-step excitation schemes suitable for modern Ti:sapphire laser systems were developed. Rydberg series in the range of principal quantum numbers 20 ⩽ n ⩽ 80 were localized, assigned and quantum numbers were allocated to the individual resonances. Ionization potentials (IP) were extracted from fits of the individual series and quantum defects of individual levels were analysed for confirmation of series assignment. For Ni the ionization potential could be extracted with significantly increased precision compared to literature with a value of EIP (Ni) = 61 619.77(14) cm−1. Also, at least one notable autoionizing state above the first IP was discovered for both elements, and the different ionization schemes via Rydberg or autoionizing states were compared with respect to line shape, ionization efficiency and selectivity.

Determination of the first ionization potential of einsteinium by resonance ionization mass spectroscopy (RIMS)

The first ionization potential of einsteinium (IP Es) was determined by resonance ionization mass spectroscopy (RIMS) using samples with ≤10 12 atoms of 254Es ( T 1/2=276 days). This method is based on the measurement of photoionization thresholds as a function of applied electric field strength, followed by extrapolation to zero field strength to yield IP Es. An atomic beam of Es was created by heating a filament on which einsteinium was electrodeposited from an aqueous solution onto a tantalum backing and covered with titanium metal. Es atoms were ionized via a three-step excitation scheme, and the ions mass-selectively detected in a time-of-flight (TOF) mass spectrometer. The excitation scheme used included a previously unknown EsI level at 32 924.9 cm −1. Furthermore, an autoionizing state at 51 447.3 cm −1 was also found. The first ionization potential of Es was determined to be 6.3676(5) eV (≡51 358(5) cm −1).

Determination of the Gold Content in Geogas by Resonance Ionization Mass Spectrometry

W. Y. MA, Q. HUI, M. XUE, W. X. JI and D. Y. CHEN, J. Anal. At. Spectrom., 1997, 12, 57 DOI: 10.1039/A606031E

Spectroscopic Properties of Sr 5p1/2ns Autoionizing States

The resonance profile of the Sr 5p1/2ns states and angular dependence of ejected electrons have been studied by using three-step excitation scheme. Energy levels and widths of the 5p1/2ns states with n ranging from 7 to 10 are measured. The electrons originated from the decays to different ionic states are resolved with the time-of-flight detector.

Multistep excitation of autoionizing states of neutral strontium

Resonance profiles of the lowest members of the Sr 5 pns and 5 pnp autoionizing series have been measured using the two- or three-step excitation schemes. Interference between different excitation pathways is manifested as the Beutler-Fano asymmetric profile in the two-step excitation but is absent in the three-step isolated-core-excitation schemes. These spectra are characterized by either Lorentzian or Fano profile. The manifestations involved in the observed spectra are interpreted in detail. The scaled widths of different autoionizing series are compared.

Laser-reduced fluorescence study of the carbon monoxide nd triplet Rydberg series: Experimental results and multichannel quantum defect analysis

The ndσ and ndδ (n=4...9, v=0) triplet Rydberg series of carbon monoxide have been observed for the first time and rotationally resolved with an accuracy of 0.03 cm−1 using a three-step excitation scheme. A multichannel quantum defect theory (MQDT) analysis shows strong perturbations for n=5, 8, and 9 and predicts the positions of the sσ and dπ levels. There is significant mixing between the sσ and dσ states, with a mixing angle between 42 and 45 degrees, as well as some smaller interaction with the np series. The ionization limit for CO is found to be 113 027.5(3) cm−1.

Laser-reduced fluorescence detection of carbon monoxide npσ ( n = 5–8) triplet Rydberg states

Members of the npσ 3Σ + (υ = 0) Rydberg series of the CO molecule in the range n = 5–8 have been detected and rotationally analysed using a three-step excitation scheme via a perturbed valence ‘doorway’ state. Starting from n = 6, l-uncoupling becomes evident. Molecular constants for a p-complex Hamiltonian have been obtained. Strong predissociation, growing with n, was found for all observed members of the series. The N-dependence of the linewidths is explained by the combined effects of l-uncoupling and a homogeneous perturbation of the npπ 3Σ + states.

Resonance ionization mass spectroscopy for trace analysis of neptunium

Resonance ionization mass spectroscopic (RIMS) measurements for trace analysis and spectroscopy of 237Np, the ecologically most important isotope of neptunium, are described. The chemical procedure for the separation of neptunium from aqueous samples as well as the preparation of filaments for RIMS are outlined. Several two- and three-step excitation schemes have been investigated in order to find suitable conditions for the sensitive detection of 237Np. Using a three-step, three-color excitation and ionization scheme an overall detection efficiency of 3×10−8 was obtained, resulting in a detection limit of 4×108 atoms (160 fg) of 237Np. The hyperfine structure splittings of the levels under investigation, which influence the detection limit, were measured. A new method to determine the first ionization potential (IP) was applied to neptunium yielding a value of IP=6.2655(2) eV.