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Transcript
046103-2
Berry et al.
Rev. Sci. Instrum. 86, 046103 (2015)
The difference between M1 and M3 is the yield of D* with
n L ≤ n ≤ nMCP measured as neutrals by the potential energy
mechanism.
nîµ°
nL
MCP
îµ°
[M1 − M3] =
Nn ε PE −
Nn ε PE
=
n=2
nîµ°
MCP
n=2
Nn ε PE = ε PE
Similarly, the yield of D* in the same range of n detected as
ions is given by
∞
∞
îµ°
îµ°
[M4 − M3] − [M2 − M1] =
Nn ε ion −
Nn ε ion
n=n L
n=n MCP
nîµ°
MCP
= ε ion
Nn .
n=n L
measured (Fig. 2)
M1 =
nîµ°
MCP
Nn ε PE,
(1)
n=2
where M1 is the number of measured D* and Nn is the number
produced by the laser in state n. We assume that ε PE is
independent of n, as all excited states are much higher in
energy than the work function of the MCP, and occupy a
narrow energy range (10.2-13.6 eV).
Repeating this measurement with the same EFI , but
switching the field direction so that field-ionized D* are
detected as D+ results in
M2 =
Nn .
n=n L
n=n L
FIG. 1. Schematic of double-sided time-of-flight spectrometer used to measure D* fragments from D2, along with a diagram of the z-stack MCP
detector.10
nîµ°
MCP
nîµ°
MCP
Nn ε PE +
∞
îµ°
Nn ε ion .
(2)
n=n MCP
n=2
In a second pair of measurements, EFI is increased above
the MCP field. The mesh field ionizes D* with n ≥ n L , where
n L < nMCP. Again, in one measurement the field ionized D*
are repelled and in the other they are detected
M3 =
nL
îµ°
Nn ε PE,
As the number of D* in each excited state, Nn , produced by the laser field is unknown, the absolute detection
efficiencies cannot be determined, but the relative efficiency
ε PE/ε ion is given by dividing the two expressions above
[M1 − M3]
=
[M4 − M3] − [M2 − M1]
M5 =
(3)
nîµ°
MCP
M4 =
n=2
Nn ε PE +
Nn ε ion .
Nn
n=n L
n MCP
îµ±
ε PE
.
ε ion
=
Nn
n=n L
M6 =
(4)
nîµ°
MCP
(5)
Nn ε FI ,
(6)
n=n MCP
Nn ε PE +
nH
îµ°
∞
îµ°
Nn ε FI +
n=n MCP
n=2
n=n L
nH
îµ°
Nn ε PE +
n=2
∞
îµ°
ε ion
n MCP
îµ±
In a similar fashion, we can determine the relative
detection efficiency of D* by field ionization inside the
MCP channel, ε FI/ε ion, by performing an additional pair of
measurements. Now, EFI is set to be weaker than the field
inside the MCP, field ionizing n ≥ n H , where n H > nMCP.
D* in the states between nMCP and n H are detected by
field ionization in the MCP while all states below nMCP are
still detected because of their potential energy. Once more,
measurements are performed repelling and detecting the ions
from all the higher excited states ionized between the meshes
n=2
nL
îµ°
ε PE
Nn ε ion .
(7)
n=n H
Computing the differences between the measured yields
as before gives the yield in states nMCP ≤ n ≤ n H detected by
field ionization in the MCP,
nîµ°
nîµ°
nH
MCP
MCP
îµ°
[M5 − M1] =
Nn ε PE +
Nn ε FI −
Nn ε PE
n=2
=
nH
îµ°
n=n MCP
Nn ε FI = ε FI
n=n MCP
n=2
nH
îµ°
Nn ,
n=n MCP
and as field-ionized keV ions,
∞
∞
îµ°
îµ°
[M2 − M1] − [M6 − M5] =
Nn ε ion −
Nn ε ion
n=n
n=n
H
MCP
FIG. 2. Left: schematic diagram of the three pairs of measurements involved
nH
nH
îµ°
îµ°
in determining the relative detection efficiencies, corresponding to measurements M1 − M6 listed in the text. Right: example detector configurations for
=
Nn ε ion = ε ion
Nn .
repelling (top) and detecting (bottom) field ionized D*.
n=n MCP
n=n MCP
Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. IP: 129.130.37.97 On: Wed, 17 Feb 2016
20:54:58