Comparison of Resonance Ionization in High and LowVoltage

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Comparison of Resonance Ionization in High- and Low-Voltage Mass Separators Fabian Schneider, Tobias Kron,

Comparison of Resonance Ionization in High- and Low-Voltage Mass Separators Fabian Schneider, Tobias Kron, Sven Richter, Klaus Wendt Institute of Physics, University of Mainz, Germany Laser Resonance Ionization Spectroscopy for Selected Applications 07. 06. 2021 Fabian Schneider 1

Motivation Use of different type offline mass separators for similar purposes: • Search for

Motivation Use of different type offline mass separators for similar purposes: • Search for excitation schemes • Ion source developments • Resonance ionization spectroscopy on stable isotopes General goal is the achievement of • Highest ionization efficiency • High spectral resolution • Optimum background suppression But: How do the characteristics of the mass separator affect these parameters? 07. 06. 2021 Fabian Schneider 2

Offline Mass Separators at Mainz The Mainz RISIKO Mass Separator • • • (RISIKO

Offline Mass Separators at Mainz The Mainz RISIKO Mass Separator • • • (RISIKO – Resonance Ionization Spectroscopy in KOllinear Geometry) 30 k. V ion energy Two step acceleration (ISOLDE 2 design) - intermediate extraction electrode on 18… 22 k. V Atomizer oven: Tantalum, up to 2500 K Ion detection with current readout of a Faraday Cup or ion pulse counting from SEM Source region identical to present ISOLDE sources Ion Detection 0. 6 Tesla Separator Magnet 18 k. V Extraction Electrode Hot Cavity Atomizer Laser Beams 07. 06. 2021 Fabian Schneider 3 Ion Optics for Beam Shaping 30 k. V RILIS Ion Source

RISIKO Mass Separator Laser Beams 30 k. V High Voltage 8 k. V Einzellens

RISIKO Mass Separator Laser Beams 30 k. V High Voltage 8 k. V Einzellens X-Y Deflector Pairs Hot Cavity Atomizer 22 k. V Extraction Electrode 1 m 07. 06. 2021 Fabian Schneider 4

Offline Mass Separators Compact mass separator MABU – Mainz Atomic Beam Unit: • •

Offline Mass Separators Compact mass separator MABU – Mainz Atomic Beam Unit: • • • 30 V ion energy Atomizer oven: Graphite, up to 2300 K – cheaper to change Mass separation with a RF quadrupole Very compact and simple – no HV needed High resolution spectroscopy possible with transversal excitation Ion. Detection RILIS Ion Source RF Quadrupole Extraction Electrode Ion Optics Mass Spectrometer Ion Optics RF Quadrupole Electrostatic Mass Quadrupole Laser Beams Spectrometer RILIS Ion. Deflector Source on Electrostatic Ground Potential Quadrupole Deflector 70 cm 07. 06. 2021 Fabian Schneider 5

Laser System Pockel‘s Cell Driver Tunable Titanium-Sapphire Lasers: • Pulse length of 30 s

Laser System Pockel‘s Cell Driver Tunable Titanium-Sapphire Lasers: • Pulse length of 30 s with a repetition rate of 10 Hz • Wide tuning range from 700 to 1000 m • High output power, up to 4 • Pumped by commercial frequency doubled Nd: YAG with 12. . 20 W Output Coupler Stepper Motor Curved Mirror Ti: Sa Curved Mirror 07. 06. 2021 Fabian Schneider Beam Expander 6 Rotatable Grating Curved Mirror Output Coupler Ti: Sa Etalon Lyot Filter Curved Mirror Pockel‘s Cell End Mirror Grating tuned Titanium-Sapphire Laser: • • For spectroscopy purposes Wavelength selection using a grating Lower output power But allows automated, mode-hop free scans of the complete tuning range

Ytterbium Excitation Scheme Ytterbium as test candidate: 50991. 0 cm-1 AI • Evaporates at

Ytterbium Excitation Scheme Ytterbium as test candidate: 50991. 0 cm-1 AI • Evaporates at intermediate temperatures 50443. 2 cm-1 IP • RIS possible with high efficiency, as high as 35% reported by Alkhazov et al. (1989) – 767 -800 nm 736. 540 nm using a three step resonant scheme 37414. 59 cm-1 1 P 1 • Undisturbed spectrum due to closed shells • Measurements on most abundant isotope 174 Yb 07. 06. 2021 Fabian Schneider 801. 826 nm / 3 = 267. 28 nm 0. 00 cm-1 GS 1 S 0 7

Spectral Scans • Very similar spectra in the two step excitation using an AI

Spectral Scans • Very similar spectra in the two step excitation using an AI transition • Here the AI ion signal is about 10 times stronger than non-resonant ionization 07. 06. 2021 Fabian Schneider 8

Performance Comparison Machine performance: RISIKO: • Overall efficiency of 25%, including separator magnet transmission

Performance Comparison Machine performance: RISIKO: • Overall efficiency of 25%, including separator magnet transmission and ion detection efficiency of 70% • Mass resolution of 400 MABU: • Overall efficiency of 0. 9%, translates to an efficiency of the QMS system of about 2. 5% • Similar mass resolution, even for masses > 240 u 07. 06. 2021 Fabian Schneider 9

Rydberg Spectroscopy Perturber state IP • Long range scan with low laser power using

Rydberg Spectroscopy Perturber state IP • Long range scan with low laser power using the grating tuned Ti: sapph • Several Rydberg series visible, strongly enhanced in RISIKO spectrum • Very strong perturber state at 50244. 3 cm-1 07. 06. 2021 Fabian Schneider 10

Rydberg Series Analysis • Same data plotted against prinicipal quantum number • Peak positions

Rydberg Series Analysis • Same data plotted against prinicipal quantum number • Peak positions converge to the same ionization potential in both spectra • Any shift in the resonances is smaller than the laser linewidth (~8 GHz) 07. 06. 2021 Fabian Schneider 11

Rydberg Series Analysis RISIKO MABU 1 S 0 Series unknown Series Perturber State 1

Rydberg Series Analysis RISIKO MABU 1 S 0 Series unknown Series Perturber State 1 D 2, 3 D 3 P 2 2 Series • Both measurements are in reasonable agreement with literature values for 1 D 2, 3 D and 1 S Rydberg series 2 0 • Some weak peaks belonging to 3 P 2 series visible in the RISIKO data • An additional series is visible, that is unknown in the literature 07. 06. 2021 Fabian Schneider 12

Non-Resonant Ionization IP • Distinct shift in the behaviour for non resonant ionization between

Non-Resonant Ionization IP • Distinct shift in the behaviour for non resonant ionization between the spectra • Amounts to a threshold of 36 cm-1 lower in RISIKO than in MABU • But no absolute shift assignable 07. 06. 2021 Fabian Schneider 13

Electric Field Most likely cause: Lowering the ionization threshold by the electric field of

Electric Field Most likely cause: Lowering the ionization threshold by the electric field of the extraction RISIKO: • Extraction Field Strength: 150… 300 /mm MABU: • Extraction Field Strength: 2… 5 /mm • Field does not penetrate into the oven region 07. 06. 2021 Fabian Schneider 14 Oven Extraction Electrode

Field Penetration Maximum field in the oven: 70 /mm Considerations: • Ions with E

Field Penetration Maximum field in the oven: 70 /mm Considerations: • Ions with E < 29900 e. V are detected on a lower mass • Range of rydberg atoms before decay is only some mm • Mean thermal velocity: 0. 5 mm/µs, radiation lifetime 5 µs for n=20 07. 06. 2021 Fabian Schneider 15

Conclusion Resonance ionization spectroscopy results are transferable between both machines: • Nearly identical excitation

Conclusion Resonance ionization spectroscopy results are transferable between both machines: • Nearly identical excitation spectra for the first excited step and the auto ionizing state • Very similar mass spectra But in case of Rydberg excitation they strongly differ • The penetrating extraction field of 70 V/mm allows field ionisation effects • Increased signal on Rydberg states, even for energies more than 500 cm -1 below the IP • Decreased non-resonant ionization threshold by 40 cm-1 Depending on the specific ion source schemes with Rydberg states have to be considered among the most efficient schemes 07. 06. 2021 Fabian Schneider 16

Thank you very much for attention! Luis Wendt, * 15. 02. 2013 07. 06.

Thank you very much for attention! Luis Wendt, * 15. 02. 2013 07. 06. 2021 Fabian Schneider 17