Measurements of air
fluorescence induced by
low-energy electrons
at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Universidad Complutense de Madrid (Spain)
Motivation
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Scarce data on air fluorescence in the
1keV-1MeV energy region.
Very low pressure (p < 250 mTorr) is
suitable for an experimental analysis of
fluorescence molecular processes.
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Goals
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Absolute measurements of fluorescence
parameters: yield, cross sections,
lifetimes…
Determination of the spatial distribution of
the fluorescence light and its effect in the
light detection depending on the pressure.
Checking a fluorescence deposit model
via simulation.
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Outline
1. Method:
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
3. Simulation:
• Experimental system
• Monte Carlo analysis
• Data taking
• Spatial distributions
• Pressure dependence
2. Results:
• Fluorescence
spectrum
4. On progress:
• Absolute calibration
• Lifetimes
• Spatial distributions
• Pressure dependence
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
1. Method
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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1. Method:
Experimental system
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Basics of the experimental setup
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
1. Method:
Experimental system
Detection
system
Laser
Electron
gun
High
voltage
Gas cell
Overall view
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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1. Method:
Experimental system
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Electron emission
based on a plasma
produced by a pulsed
nitrogen laser
(Spectra-Physics VSL337ND-S)
Electrostatic
acceleration up to 30
kV (Spellman SL1200).
Diffusion-pumped
vacuum system:
p ~ 10-4 Torr.
Schematic view of the electron gun
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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1. Method:
Experimental system
Acceleration
anode
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Cathode
Close-up of the electron gun
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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1. Method:
Experimental system
No entrance window:
differential vacuum
maintained by a gas
impedance.
Electron beam
geometrically well
defined by a collimator.
Peak currents up to 20
mA in 20 ns pulses.
Electron energies from
10 to 30 keV.
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
CCD photo of the beam section
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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1. Method:
Experimental system
Time evolution of the pulse
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Electron energy spectrum
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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1. Method:
Experimental system
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Electron current collection in
a Faraday cup.
Optical system with a quartz
lens focusing the light.
Monochromator of 20 Å
resolution (Mini-Chrom C).
High gain PMT (Phillips
56UVP) supplied at 2 kV.
Absolute pressure
transducer (MKS Baratron
626A01TDE).
Gas cell and detection system
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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1. Method:
Experimental system
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
CCD chip Sony ICX055AL.
Optics efficiency from 350
nm on.
Lateral setup: opposite side
of the PMT.
Frontal setup: ZnS
fluorescent screen.
Beam cross section
CCD system
(lateral setup)
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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1. Method:
Data taking
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Coincidence mode: negligible background, lifetimes.
Event per event data collection (~1000 triggers per
run).
PMT in photon-counting mode.
Tektronix TDS5032B oscilloscope: ns time resolution.
Electron current integration: absolute charge
measurement (thin target).
Specific analysis software.
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Method:
Data taking
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Integrated
electron
current
Photons
Signals recorded by the oscilloscope
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
2. Results
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Fluorescence spectrum
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Relative intensities of the fluorescence bands
[1] F.R. Gilmore et al., J. Chem. Ref. Data 21 (1992) 1005
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2. Results:
Lifetimes
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Time evolution of the light emission for the 391 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Lifetimes
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Stern-Volmer plot for the 391 nm band in air
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
2. Results:
Lifetimes
band
τ0 (ns)
p’air (hPa)
p’nitrogen (hPa)
391 nm
1N(0,0)
62 ± 2
1.7 ± 0.6
1.2 ± 0.3
62 ± 6 [1]
1.3 [3]
1.7 [3]
43 ± 5
> 0.8
>6
42 ± 2 [2]
13.1 [3]
77 [3]
337 nm
2P(0,0)
Very preliminary values summary
[1] S.V. Pancheshnyi et al., J. Chem. Phys. Lett. 294 (1998) 523
[2] S.V. Pancheshnyi et al., J. Chem. Phys. 262 (2000) 349
[3] Reference values used in:
F. Arqueros et al., Astropart. Phys. 25 (2006) 231
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Spatial distributions
Beam
contour
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Halo partly due
to secondary
electrons
Impedance
exit
Faraday
cup
CCD photo of the fluorescence light λ>350 nm
emitted into the gas cell (mainly 1N system)
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Spatial distributions
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Monochromator
input slit scan
Schematics of the data taking for analysis of the
spatial distribution with wavelength resolution
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Spatial distributions
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
CCD photo
strip
Schematics of data taking by using the
central strip of the CCD image
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Spatial distributions
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Spatial distribution for the 391 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Spatial distributions
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Spatial distribution for the 337 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
2. Results:
Pressure dependence
Image of the monochromator input
slit at the beam axis.
Expected pressure dependence.
p
1
eff
light vv ' ( p ) ∝
σ vv ' ( p, E , G ) [1]
p
RT 1 + p ' gas
v
[1] F. Arqueros et al., Astropart. Phys. 25 (2006) 231
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
2. Results:
Pressure dependence
Image of the monochromator input
slit at the beam axis.
Expected pressure dependence.
p
1
eff
light vv ' ( p ) ∝
σ vv ' ( p, E , G ) [1]
p
RT 1 + p ' gas
v
Number of molecules
per unit volume
[1] F. Arqueros et al., Astropart. Phys. 25 (2006) 231
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
2. Results:
Pressure dependence
Image of the monochromator input
slit at the beam axis.
Expected pressure dependence.
p
1
eff
light vv ' ( p ) ∝
σ vv ' ( p, E , G ) [1]
p
RT 1 + p ' gas
v
Quenching correction
[1] F. Arqueros et al., Astropart. Phys. 25 (2006) 231
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
2. Results:
Pressure dependence
Image of the monochromator input
slit at the beam axis.
Expected pressure dependence.
p
1
eff
light vv ' ( p ) ∝
σ vv ' ( p, E , G ) [1]
p
RT 1 + p ' gas
v
Effective optical cross section including contribution from secondary electrons:
complicated dependence on the pressure, the incident energy, the geometry...
[1] F. Arqueros et al., Astropart. Phys. 25 (2006) 231
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Pressure dependence
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Pressure dependence of the light detected
for the 391 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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2. Results:
Pressure dependence
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Pressure dependence of the light detected
for the 337 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
3. Simulation
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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3. Simulation:
Monte Carlo analysis
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Secondary electrons [1]
Differential and total cross
sections [1,2]
Full simulated geometry:
beam, chamber and detection
system
Simulated spectrum of beam
electrons.
Electron interactions [2]
[1] F. Arqueros et al., Astropart. Phys. 25 (2006) 231
[2] A. Muñoz et al., Nucl. Instrum. Meth. Phys. Res. A 536 (2005) 176
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3. Simulation:
Spatial distributions
CCD photo (λ > 350 nm)
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Simulation (391 nm band)
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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3. Simulation:
Spatial distributions
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Spatial distribution for the 391 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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3. Simulation:
Spatial distributions
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Spatial distribution for the 337 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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3. Simulation:
Pressure dependence
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Simulated detected light at the
maximum of the spatial distribution
(focusing at the axis beam).
Characteristic pressures [1]:
– p’air (391) = 1.3 hPa (quenching correction < 25%).
– p’air (337) = 13.1 hPa (quenching correction < 2.5%).
[1] Reference values used in:
F. Arqueros et al., Astropart. Phys. 25 (2006) 231
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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3. Simulation:
Pressure dependence
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Pressure dependence of the light detected
for the 391 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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3. Simulation:
Pressure dependence
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Pressure dependence of the light detected
for the 337 nm band
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
4. On progress
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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4. On progress:
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Increasing the energy of beam electrons
up to 130 keV.
Increasing the pressure into the gas cell
up to 1 atm: hydrocarbon thin film.
Obtaining absolute calibration.
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4. On progress:
Absolute calibration
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Viewgraph of the absolute calibration setup based on the
comparison with Rayleigh scattering measurements
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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4. On progress:
Absolute calibration
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Pulsed nitrogen laser Spectra-Physics VSL-337ND-S
(337 nm, 300 µJ, 4 ns )
Laser beam with the same geometry as the electron
beam.
Minimized background reflections: darkened walls, beam
dump and two stages collimator.
Laser beam intensity:
– Absolute measurement: calibrated Ophir PD10
photodiode.
– Monitoring: FDS100 photodiode.
5th Fluorescence Workshop, San Lorenzo de El EscorialEscorial-Madrid, Spain, 1616-20 September, 2007
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4. On progress:
Absolute calibration
Pressure dependence of
the detected light in
Rayleigh measurements
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Spatial distributions for
the scattered laser light
compared with the 337 nm
fluorescence band
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Conclusions
Measurements of air fluorescence induced by
lowlow-energy electrons at very low pressure
J. Rosado, F. Blanco, F. Arqueros, M. Ortiz
Resolution in wavelength and time.
Results on spatial distributions.
Analysis on the pressure dependence of
the detected fluorescence light.
Good agreement of the simulation with the
experimental data.
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Thank you!