11
HISTOGRAMS
a second photon within a certain time after the first, this exponential decrease will start
only after
τ
D
of the respective detector.
Depending on the time scale of the phenomenon to be observed, this may or may not
be a problem for your measurement. Therefore, we always advise to use cross-correlation
histograms to measure the
g
(2)
function.
11.3.3
Model functions
The most common models for the
g
(2)
correlation function are shown below. With these,
thermal
photons,
antibunching
, and
three-level-systems
can be described.
Thermal
g
(2)
th
(
τ
) =
A
·
e
−
(
τ
−
τ
0)
2
2
c
2
+
B
(6)
Antibunching
g
(2)
ab
(
τ
) = 1
−
e
−
|
τ
−
τ
0
|
τa
(7)
Three-Level-System
g
(2)
tl
(
τ
) = 1 +
p
2
f
c
·
e
−
|
τ
−
τ
0
|
τb
−
(1 +
c
)
·
e
−
|
τ
−
τ
0
|
τa
(8)
Normalization
Please note that the measured histogram data are normalized with a
factor
N
=
R
1
R
2
T W,
(9)
with countrates
R
1
and
R
2
, total integration time
T
and histogram bin width
W
.
11.3.4
Realization in the quTAU GUI
HBT Measurements can be obtained and analyzed in the quTAU GUI, see Figure
. For
testing purposes or if no device is connected, data can also be simulated (and analyzed
normally). Settings can be accessed on the bottom, the retrieved data are shown in the
plot at the top.
11.3.5
DLL Usage
Table 11:
Examples: HBT Measurements
LabView Example
/userlib/labviewXX/examples/hbt measurement.vi
C Example
/userlib/src/example2.c
quTAU/quPSI Manual V4.0 Page 39
