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The response function of energy-dispersive X-ray spectrometers (EDS) has been a topic for investigation as long as EDS has been used. This work systematically investigates soft X-ray peaks with energies below 150 eV in regard to the detector energy calibration linearity. It was found that Si-L (92 eV) and Al-L (73 eV) lines are not shifted in energy position in comparison to higher energy K-lines of boron, carbon and nitrogen. The reason is simply the silicon detector material has a large absorption jump at 99 eV (Si-L2/Si-L3), which causes much higher detection depths of photons with energies below 99 eV. There is also less shift than assumed with older approaches in the energy region 100 to 149 eV (Si-L1). It is also expected that Li-K radiation will not be affected by an energy shift due to detector artefacts. The authors propose a modified shift-correction which corrects this detector artefact and linearizes the energy calibration of measured EDS spectrum below 600 eV. This energy shift effect of the measured X-ray lines is in principle with any silicon-based X-ray detector. But the shift value depends also on the front contact layer design and quality. The novelty with changed correction is that no shift is applied for X-ray peaks below 99 eV. Older applied correction procedures were found to produce a line energy misplacement in spectrum for this energy region.

Absolut System has built a 30 K and a 10 K remote Helium cooling loops used as a vibration free cooling source, respectively for IR detectors electro-optical characterization test bench and two-stage optical cryostat. The circulation loops are based on a by-passed flowrate from either a two-stage Gifford–McMahon cryocooler or a two-stage Pulse Tube cryocooler. Dedicated compact and high efficiency tubes & shell heat exchangers have been designed and produced for the recuperators. The paper describes the design and the performances of the vibration free cooling system produced. The current work towards a 4 K low vibration cooling source will be introduced as well.

The excellent energy resolution and low threshold of cryogenic detectors have brought them to the forefront of the search for low-mass Weakly Interacting Massive Particles. The next generation of large cryogenic detectors for dark matter search promises further improvements in sensitivity, yet it is difficult and in some cases impossible to test and fully characterize these detectors in an unshielded environment. Therefore, the Queen’s SuperCDMS team is installing a well shielded Cryogenic Underground detector TEst facility (CUTE) at SNOLAB to support detector testing and characterization for SuperCDMS and future cryogenic rare event search experiments. Significant effort is put into achieving a very low background environment which may open the door for early science results with the first set of SuperCDMS detectors during the time the main experimental apparatus is being installed. We discuss some of the challenges and solutions implemented in the design of this facility as well as the status and schedule for the start of operations underground at SNOLAB.

The energy-dispersive X-ray spectrometer (EDS or EDX) is a commonly used device to characterise the composition of investigated material in scanning and transmission electron microscopes (SEM and TEM). One major benefit compared to wavelength-dispersive X-ray spectrometers (WDS) is that EDS systems collect the entire spectrum simultaneously. Therefore, not only are all emitted characteristic X-ray lines in the spectrum, but also the complete bremsstrahlung distribution is included. It is possible to get information about the specimen even from this radiation, which is usually perceived more as a disturbing background. This is possible by using theoretical model knowledge about bremsstrahlung excitation and absorption in the specimen in comparison to the actual measured spectrum. The core aim of this investigation is to present a method for better bremsstrahlung fitting in unknown geometry cases by variation of the geometry parameters and to utilise this knowledge also for characteristic radiation evaluation. A method is described, which allows the parameterisation of the true X-ray absorption conditions during spectrum acquisition. An 'effective tilt' angle parameter is determined by evaluation of the bremsstrahlung shape of the measured SEM spectra. It is useful for bremsstrahlung background approximation, with exact calculations of the absorption edges below the characteristic peaks, required for P/B-ZAF model based quantification methods. It can even be used for ZAF based quantification models as a variable input parameter. The analytical results are then much more reliable for the different absorption effects from irregular specimen surfaces because the unknown absorption dependency is considered. Finally, the method is also applied for evaluation of TEM spectra. In this case, the real physical parameter optimisation is with sample thickness (mass thickness), which is influencing the emitted and measured spectrum due to different absorption with TEM measurements. The effects are in the very low energy part of the spectrum, and are much more visible with most recent windowless TEM detectors. The thickness of the sample can be determined in this way from the measured bremsstrahlung spectrum shape.

The 8snl double Rydberg states of barium with l = 5 and n = 12–15 are populated by employing an isolated core excitation (ICE) scheme in conjunction with the Stark switching technique. The recorded spectra show strong configuration interaction with three adjacent 5fjn'l' series. One of the latter series is converging to the 5f5/2 ionization limit and the other two to the higher lying 5f7/2 one. A multichannel quantum defect theory (MQDT) analysis reveals the presence of low-lying members of double Rydberg series converging to higher ionization thresholds and determining the configuration mixing. At least two perturbers, affecting energy level positions, are identified while a comparison between experimental and fitted excitation profiles points towards the presence of a third one. Finally, theoretical calculations of the 8snl(l = 5) series members quantum defects demonstrate the onset of mutual penetration between the two excited electrons. Nevertheless, the most important quantum defect contributions stem from exchange and polarization effects and thus long-range interactions alone are insufficient for a proper description of the double Rydberg states involved.

We examine the energy dependence of the quantum defect of double Rydberg states with a high-l electron moving in Coulomb plus dipole and quadrupole polarization potentials. The polarization quantum defects due to these additional potential terms exhibit an energy dependence which is characteristic of each of them: linear for the dipole part and quadratic for the quadrupole part. For quantum defects which are small enough to guarantee the validity of a perturbative treatment, we derive the energy levels using a simple and accurate dipole quantum defect formula obtained by the semiclassical JWKB theory. At larger polarizabilities which correspond to a non-perturbative situation, the dipolar energy spectrum is calculated by diagonalizing the Hamiltonian matrix built on hydrogenic wavefunctions. In this case the quantum defect always presents a smooth variation versus the energy, but does not exhibit a simple behaviour. For the lower levels it is larger than unity, while it decreases rapidly to smaller values (less than one) as the ionization limit is approached. All the calculations are performed using dipole polarizabilities which are close to values found in the double Rydberg literature.

The present review is devoted to the recent advances performed in alkaline-earth atoms by the selective laser preparation of autoionizing asymmetrical double Rydberg states which have, so far, not been observed in natural environments. Because the great amount of flexibility achieved by the sequential laser electron excitations, a wide choice of two-electron situations have been investigated and analyzed which exhibit spectral features due to long-range effects of the Coulomb electron-electron repulsion. To overcome the autoionization broadening of the lines, double Rydberg states with a non-core penetrating high-l outer electron were produced by combining temporal laser excitation technique with the electric-field switching method. The study of the spectral correlation signatures in Nsnl double Rydberg states versus l allow to understand their evolution from simple spectra (l ≥ 10) due to long-range dipole interaction to more complex data (l ≤ 7) induced by short-range multipole effects when two electrons start to influence more each other.

The authors have studied double ionization of Ba 6snl Rydberg states through resonant two-photon excitation of 8snl double-Rydberg states with n=13 and 14 and different l. The laser intensity dependence of Ba2+ yield measured for l>or=8, when the electrons suffer long-range dipole interaction, shows a decrease from four-photon for l=8 to less than three for l=11. The four-photon dependence is due to autoionization decay populating the Ba+(7p) levels which gives an indirect signature to the Ba2+ production. By increasing l this decay vanishes and the data show evidence of a direct double-ionization process via planetary-electron states for l>or=10. Additional intensity measurements performed for low l=6 states strongly mixed with 5fn'l' ones by short-range multipole interaction, reveal indirect Ba2+ production and an individual case of partial stabilization due to destructive interference leading to direct double ionization.

The authors present an analysis of the effect of a stray electric field on 7snl and 10snl double-Rydberg spectra for n=12-15. To excite these states they use the Stark switching technique to populate high l, along with the isolated core excitation (ICE) method. The 7snl spectra show a single peak for each l excited, while, as observed for 8dnl states, the 10snl spectra show a multiple peak structure common to all l (for n>12). This structure is explained by taking into account a 1 V cm-1 stray electric field which l mixes the 6snl levels from which the 10snl are excited. Application of a small

The even-parity J = 1e, 2e autoionizing spectra of neutral strontium are investigated below the 4d5/2 threshold in a two-step laser experiment via the 4d5p 1P1 level in a strontium atomic beam. The produced Sr+ ions are analysed by a time-of-flight microchannel plate detector. The J final level assignment is obtained by comparing the line intensity dependence from two recorded spectra with pi pi and pi sigma polarizations of the two lasers. More than 400 new resonance lines are measured with an accuracy of +or-0.2 cm-1 for the narrow ones using standard laser calibration procedures. They are assigned to fifteen autoionizing Rydberg series 4dns, 4dn d and 4dng and many perturbers belonging to the 5p6p configuration. Interpretation is made by a combination of the eigenchannel R-matrix and multichannel quantum defect methods (MQDT).

The even parity J=0, 1 and 2 autoionizing spectra of Sr have been observed below the 4d5/2 threshold using two-step laser spectroscopy from the ground state atom 5s2 in an atomic beam. Resonant excitations of the autoionizing states are observed by time-of-flight (TOF) analysis of the produced ions. In this experiment via the 4d5p 1P1 intermediate level, the J=0 resonances are selectively identified among the other J=1 or 2 ones by comparing the line intensities from two spectra recorded with pi pi and pi sigma polarizations of the two laser beams. From the J=0 data, the J=0 4d3/2 nd3/2 and 4d52/nd5/2 series are observed up to n=66 and 64 respectively. In addition the authors also observed the 5p2 1S0level, whose location has been controversial for a long time: this level is now identified with a broad autoionizing resonance at 54 451+or-30 cm-1 . It has also been observed in this work by a direct two-photon excitation.

The odd J=3 autoionising spectrum of Sr between the 5s and the 4d thresholds has been observed. In a Sr atomic beam, the ionised atoms produced by a two-step excitation scheme have been analysed via a time-of-flight spectrometer. A theoretical approach based on the R-matrix method combined with multichannel quantum defect theory calculations provided a good description of the position of the observed lines. Analysis of the observed profiles gave qualitatively good results although the intermediate 5p2 1D2 level is not perfectly described in the model.

The authors present the excitation of highly excited 7p1/2nd and 7p3/2nd states (10 16) have a strong autoionisation channel towards the 7p1/2 state of Ba+. This result confirms that autoionisation occurs predominantly to excited states of Ba+ with the emission of low-energy electrons.

In order to prepare a theoretical analysis of Rydberg series 4f14 6snl the classification of the spectrum of neutral ytterbium has been extended with the help of new observations in the infrared and measurements of Zeeman effect in the visible and near ultraviolet. 176 lines are classified by 70 new levels. The configurations 4f136s26p and 4f146p2 are now complete and the lowest levels of 4f135d26s and 4f145d6p have been recognized, as well as new low members of the Rydberg series. In both parities a parametric study of the configurations taking into account mixing effects has led us to revise and to extend the earlier labeling. All the perturbers of the 4f146snl series have been found or predicted. A reinterpretation of the autoionizing levels observed by Parr and Elder is also needed.

Extensive new data on the even-parity autoionized spectrum of Ba has been provided by two-step optogalvanic spectroscopy. The spectral range below the 5d3/2 ionization limit presents a complicated scheme of interacting levels, which is analyzed using the multichannel quantum defect theory (MQDT). The analysis concerns the 5d3/2nd and 5d3/2ns series converging on the 5d3/2 limit and their perturbers belonging to 5d5/2nd and 5d5/2ns series converging on the higher 5d5/2 limit. This is a favourable case for MQDT since the number of perturbing levels is very large: for each 5d5/2nl perturbing series, nine levels are located below the 5d3/2 limit. A J by J treatment of the energies of the spectra with J value ranging from 0 to 5 was carried out taking into account the 5dnd-5dns mixing. The analyses only concern the position of autoionized levels. In fact the 5dnl autoionized lines observed in this range are relatively narrow and we can neglect the coupling of 5dnl levels with 6sl continua. The MQDT treatments presented here allow us to improve the identification of levels and to describe accurately the behaviour of perturbed series. The lower 5dnl levels are bound, i.e. below the 6s limit and the MQDT treatment of their mixing with the 6snl principal Rydberg series has been previously published. The comparison of the MQDT parameters fitted to the bound or autoionized spectra confirms the large energy dependence of the parameters. This point is discussed and shows the difficulties of extrapolation procedures. For the first time the MQDT parameters are closely related to semi-empirical values of Slater integrals.

Using two-step optogalvanic spectroscopy via the intermediate 5d6p 1P10 level, the position of the 6p2 1S0 level has been identified to a broad profile ( approximately 300 cm-1) about 44800 cm-1. An MQDT analysis of the J=0 spectrum including mixing with the 6s epsilon s 1S0 continuum has been performed. The predicted relative oscillator strength densities between 44000 and 45400 cm-1 are in fairly close agreement with the experimental data. The Fano profiles of the 5d5/28d5/2, 5d3/2 9d3/2 J=0 resonance, the broad 6p2 1S0 profile and the hole profile for the 5d3/2 10d3/2 resonance are explained.

By focusing an excimer pumped dye laser on an atomic beam, the authors have observed multiphoton multiple ionisation of the neutral strontium atom in the tuned wavelength range 532-41 nm. Sr + and Sr ++ yields were measured with a time of flight spectrometer. At least three photons are required to produce Sr + and eight photons to produce Sr ++ . As a function of the wavelength, the Sr + yield exhibits resonances which correspond to two-photon excitation of bound states (5s 2 -5p 2 1 D 2 and 5s 2 -5p 2 1 S 0 ) and three-photon excitation of autoionising states 4d5f J=1 and J=3 of the neutral atom. The Sr ++ yield exhibits four broad smooth resonances that they interpret, from known spectroscopic data, as two-photon (5p 1/2 -4f), three-photon (5s-6p 1/2, 3/2 ) and four-photon (5s-7d) resonances in the singly charged ion. The latter transitions start from a singly charged ion in the 5s or 5p 1/2 state reached after three- or four-photon ionisation of the neutral ground state. The variation of the Sr ++ pattern as a function of the dye laser beam intensity shows that resonances are shifted and broadened when the intensity is increased. These features have been interpreted by a perturbative treatment of Sr + ionisation based on the use of an effective Hamiltonian which takes into account higher-order terms involved in the calculation of resonance effects. Calculated multiphoton ionisation probabilities are in good agreement with experimental data. Journal of Physics B: Atomic, Molecular and Optical Physics

Highly excited levels of ytterbium have been investigated using two-photon absorption spectroscopy and space-charge detection. The authors tuned the 0.2 cm-1 dye laser radiation over the range 3900-4100 AA and observed the even-parity states J=0 and J=2 belonging to the series 4f146s ns 1S0, 4f146s nd 1D2, 4f146s nd 3D2 from n=13-62, from n=11-64 and from n=11-21, respectively. Many strong perturbations appear due to configurations with a 4f13 core.

An extensive study of the configurations 4fN(5d + 6s), using the methods of Racah, which included the configuration interaction for these two configurations and effective electrostatic parameters for the 4f-5d interaction leads to an improved agreement between observed and calculated energies for seven spectra and to find new energy levels for PrIII, PrII and TmII. Because of the regularities of the radial parameters either in the isoelectronic series or in the same stage of ionization sequences, we are able to predict the energy differences of many levels for ErIII and HfV.

In the wavelength range 280-700 nm the authors have observed more than 60 resonances in the production of Ba2+ from neutral Ba. All the strong resonances can be associated with Ba+ transitions originating in the 6s12/, 5dj or 6pj states. The production of Ba2+ is highest for the wavelength range 450-650 nm, where numerous two- and three-photon resonances occur in the multiphoton ionisation of Ba+.

The authors present a novel instrument for the analysis of highly excited Rydberg states of ions. This set-up is applied to study the ns and nd Rydberg levels of Ba+ produced in an atomic beam with values of n varying between 19 and 65. The selective excitation is provided by a two-UV-laser-photon process. The excited Ba+ ions are ionised by a microwave field and detected by a double time of flight mass spectrometer. A UV optogalvanic spectrum, resulting from an iron hollow-cathode discharge, is used as a reference for calibration. The accuracy of the energy level wavenumber determination is +or-0.1 cm-1. These measurements lead the authors to a revised value for the Ba II ionisation limit of 80 686.25+or-0.10 cm-1.

Highly excited Rydberg and autoionized levels were investigated by using selective absorption spectroscopy and the space charge amplification method for detecting ions. The one-photon absorption spectrum from the ground state 6s2 1S0 has been recorded by scanning the emitted continuum from a mercury lamp with a 2 m Czerny-Turner monochromator. With the allowed resolution of 0.1 AA, 6snp 1P10 Rydberg states were observed up to n=45. Furthermore, two-photon absorption spectroscopy was performed using a 0.150 cm-1 tunable dye laser radiation over the range 4200-5600 AA. Even-parity states J=0 and J=2 belonging to the series 6sns and 6snd up to n=46 and n=77, respectively, and new autoionized levels belonging to 5dns and 5dnd configurations were observed.

Even parity levels of neutral barium above the 6s ionization limit have been investigated by using a two-step pulsed laser excitation with optogalvanic detection. From the metastable states, 5d6s, populated by a d.c. discharge in a heat-pipe vapour, we reach the 5dnl even Rydberg series with J values ranging from 0 to 5, the 6p2 1S0 state and the low-lying members (n = 7 and 8) of the 6pnp series above the 5d limits. The 5dnd configurations (18 levels for each n member) are observed from n = 8 up to n = 45 using optogalvanic spectra recorded from five intermediate 5d6p levels: 3P1,20, 3F3,40 and 1P10. These eighteen series are observed for the first time. Fine structure is resolved up to n = 25 and has been analyzed using Slater-Condon parametric calculations. In addition, the 5d3/2ns J = 1 and 5d5/2ns J = 3 series are observed up to n = 38 and 42 respectively, as well as sharp resonances interpreted as 5d3/2ng7/2 J = 2 and 5d5/2ng J = 1, 2 series up to n = 27 and n = 28 respectively. In conclusion, the energies of 636 new levels between 6s and 5d limits are given with their term and configuration identifications. Above the 5d5/2 limit, broad resonances observed from the 5d6p 1P10, 6s7p 1P10 and 3P0,1,20 intermediate levels have been identified with levels of the 6p7p and 6p8p configurations using parametric calculations based on the Slater-Condon theory.

Highly excited even levels of ytterbium have been investigated using both a two-photon absorption, and a two-step process from the 6S2 1S0 ground state. Resonances are detected by the thermoionic-diode method. Most of the observations are between the J=O and J=2 even levels: the series 6sns1S0, and 6snd1D2 and 6snd 3D2 have been observed from n=10 to n=65, n=8 to n=80 and n=10 to n=61 respectively. Several levels of the 4f135d6s6p and 6p2 configurations have been identified. In the autoionising region lines showing a Fano profile have been observed and analysed. The authors observed many lines corresponding to absorption from the excited levels 6s6p 1P1 degrees , 5d6s3D2 and 5d6s3D3. Some J=2, 3 and 4 odd levels have been observed with this method.

The calculation of the energy eigenvalues and the Lande g factors of the configurations 4f12(5d + 6s)2 + 4f136p taken together has led to the interpretation of 155 even levels whose energies are predicted with an rms error of 105 cm-1. The configuration 4f125d2 is correlated with 36 experimental levels, among which is the lowest level at 30 508 cm-1. Eigenvectors of the sub group of configurations f12ds + f13p are given in the J1J2 coupling scheme, which is the closest to the physical coupling.

The calculation of the energy eigenvalues and the Lande g factors of the configuration 4f12(5d+6s)6p taken together has allowed the identification of 175 odd levels with a mean error of 97 cm-1. The configuration 4f125d6p is identified at 44 838 cm-1. The eigen vectors of f12sp and those of f12dp for the matrices with J ≥ 5 are given in the *J1J2 coupling scheme where *J1 is an eigenvector of the real core f12. The four levels of the configuration 4f137s are interpreted and the value of the IP of Tm II fitted by interpolation with the neighbouring elements, which is 12,05 volts, is confirmed.

There are a number of regularities evident when one compares the first four levels of the 4fN5d (in spectra II) and 4fN5d6s2 (in spectra I) for 8 ≤ N ≤ 13. By this empirical method we have found the energies for the low-lying levels of f11d for Ho II and one energy level for Tb II.