Fluorescence studies using low energy electron beam excitation

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Johanna Fuhrmann
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1 Fluorescence studies using low energy electron beam excitation a very personal view by Andreas Ulrich with real work done by: Thomas Dandl, Thomas Heindl, and Andrei Morozov * and a lot of help by Jochen Wieser ** Physik Department E12 Technische Universität München * University of Coimbra **Optimare Analytik GmbH & Co KG Air Fluorescence Workshop, Karlsruhe 211 andreas.ulrich@ph.tum.de

2 Spectroscopy: Provides information about the species involved We work with beams in nitrogen and in air

4 Heavy ion beam experiments at the Munich 15 MV Tandem accelerator: PMT Ocean Opt. Spectrometer Fiber Optics Grating Vacuum Monochromator 1/5 Mirror Optics Beam Line Vacuum Gas Cell Faraday Cup Ti Gas Purifier

6 1 MeV 32 S beam stopped in neon

7 7 Intensity e-beam, 5µA Pure nitrogen, 8mbar Some information comes from emission spectra

8 nm NO 6 5 Intensity 2 Intensity N nm 1 Gaydon Herman green (GHG) and Herman Infrared (HIR) Intensity Intensity 5-1nm

9 Extension into the VUV shows N I lines! (nitrogen spectrum)

10 Atomic nitrogen shows up in the VUV spectral range

11 A beam current 8 A beam current (scaled on 337nm) The spectrum depends on beam current! Intensity , N2 / NO 337nm/247nm N2 / GHG 337nm / 557nm ,8 NO / N 2 GHG / N 2,6 Plasma effects and radiation trapping Ratio,4,2, Beam Current ( A)

12 14 12 pure Nitrogen Nitrogen with,1% Oxygen Intensity e-beam 1µA 1mbar gas Huge effect of O

13 4 Intensity at 337nm (a.u.) Stopping the gas flow: 17% in 3min Time (min)

14 Intensity 5 Intensity 1 Intensität nm 1nm 5 A 4mbar fresh 5 A 4mbar after 1min 2 Appearance of CN [nm]

15 6 5 Nitrogen synth. Air (scaled on 337nm) Intensity 4 3 e-beam, 8µA 8mbar gas

16 16 14 Nitrogen Air (scaled on 337nm) 12 Intensity 1 8 e-beam, 8µA 8mbar gas

17 Qualitative results from spectroscopy: Pure nitrogen is very sensitive to impurities NO is often formed Higher lying bands are populated (cascades?) Nitrogen is split to N atoms even excited N atoms Regular air and synthetic air behave differently Next step: relative sensitivity calibration

18 Thomas Dandl has used 3 types calibration lamps: Halogen Lamp (LOT) Wi 17G (Osram) 2x Deuterium Lamp (LOT, Cathodeon) one lamp, 2 data sets to measure the relative response of an Ocean Optics QE65 between 28 and 42nm He used (in part) filters for the wavelength region to suppress stray light

19 Setup for calibration 12 kev electron source MgF 2 windows Calibration lamp Gas cell Fiber optics entrance

21 ,3,25 correction function,2,15,1 Wi17/G 2892 Wi17/G 3261 Halogenlamp,5,

22 1,25 1,,75 Ratio,5 fiber rotated 1 fiber rotated 2 fiber bent fiber tilted,25, Important message: Do not touch the setup after calibration!

23 ,4 correction function,35,3,25,2,15,1,5 Wi17/G 2892 Wi17/G 3261 Deuterium lamp (not our lamp) Deuterium lamp (our lamp) Halogen lamp solid line: with UG11-filter dashed line: without UG11-filter,

24 18 2 Intensity (a.u.) Laborluft M.Ave et al synth. Air percentage wise deviation from synth. air

25 Pure nitrogen, 8μA Intensity mbar 4mbar mbar percentage-wise deviation from 8mbar data

26 Pressure dependence rel. to 337nm line Intensität bezogen auf 337,1nm [%] ,7nm Intensität bezogen auf 337,1nm [%] 23,8 23,6 38,5nm 23,4 23,2 23, 5 to 1% starting at vib. level 7,4??? 22,8 22,6 7,3 22,4 22,2 Intensität bezogen auf 337,1nm [%] 7,6 45,nm 7,5 7,2 I (p) various lines relative to the 337nm line 1 to 1mbar Pressure [mbar] 22, Druck [mbar] Druck [mbar] 13, Intensität bezogen auf 337,1nm [%] ,7nm Druck [mbar] Intensität bezogen auf 337,1nm [%] ,7nm 11,5 3 to 5% at vib. Level 1 11, 1, Druck [mbar] Intensität bezogen auf 337,1nm [%] 12,5 375,6nm 12, 1, 9,5 9, 8, Druck [mbar] Intensität bezogen auf 337,1nm [%] 5, 4,8 399,8nm 4,6 4,4 4,2 4, 3,8 3,6 3,4 3, Druck [mbar] 4,4 9 Intensität bezogen auf 337,1nm [%] 2,8 2,7 2,6 2,5 2,4 328,5nm Intensität bezogen auf 337,1nm [%] 4,2 371,1nm 15% level 3 3% level 2 4, 3,8 3,6 3,4 3,2 Intensität bezogen auf 337,1nm [%] ,4nm N 2 + 1% 2, Druck [mbar] 3, Druck [mbar] Druck [mbar]

27 ,7nm 5% 23,5 23, 38,5nm 63 22,5 Intensität to 9 µa Intensität 22, 21,5 21, Intensität 7,6 7,4 7,2 7, 6, nm 2, Beam current dependence of some lines in pure nitrogen normalized to the 337nm line Quenching by free electrons? 6,

28 Intensity A 4 A A percentage wise deviation from int at 8 A

29 Conclusion: Spectroscopy provides a lot of information about the nitrogen fluorescence. Calibration measurements have to be carefully prepared. Relative intensity measurements of the emission bands would have to be repeated with better wavelength resolution.

30 Thank you for your attention!

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