472 CHINESE OPTICS LETTERS / Vol. 6, No. 7 / July 10, 2008
Quantum efficiency calibration of opto-electronic detector
by means of correlated photons method
Jianjun Li (
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), Xiaobing Zheng (
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), Yunjun Lu (
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),
Peng Zou (
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), and Wei Zhang (
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)
Remote Sensing Laboratory, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031
Received November 13, 2007
A new calibration method of detectors can be realized by using correlated photons generated in spontaneous
parametric down-conversion (SPDC) effect of nonlinear crystal. An absolute calibration system of detector
quantum efficiency is performed. And its principle and experimental setup are introduced. A continuous-
wave (CW) ultraviolet (351 nm), diode-pumped, frequency-doubled, and solid-state laser is used to pump
BBO crystal. The quantum efficiencies of the photomultiplier at 633, 702, and 789 nm are measured
respectively. The coincidence peaks are observed using coincidence circuit. Some measurement factors
including the filter bandwidth of trigger channel, the detector position alignment and polarization of the
pump light are analyzed. The uncertainties of this calibration method are also analyzed, and the relative
uncertainties of total calibration are less than 5.8%. The accuracy of this method could be improved in
the future.
OCIS codes: 190.4410, 000.2190, 040.5160, 030.5630.
doi: 10.3788/COL20080607.0472.
In recent years, because of the requirements of quanti-
tative remote sensing, radiometric calibration of sensors
has become a fundamental technique in order to ensure
the precision and availability of data in remote sensing.
In traditional optical radiometry, primary standards are
based on absolute sources or detectors. The common
characteristics of those methods are in need to establish
high-precision primary standards, and a chain of stan-
dard transfer
[1−3]
. They are exactly the factors that re-
strain the improvements of precision, and the transfer
chain is a major source of uncertainty.
A new technique based on correlated photons ob-
tained through parametric downconversion (PDC) was
studied for the absolute calibration of photon-counting
detectors
[4−6]
. The interest in this technique is the es-
tablishment of inherently absolute measurements at very
low light levels, i.e., in the photon-counting regime. So
far the reports about the method paid mainly attention
to demonstrations and feasibility studies, much less em-
phasis was given to the systematic studies of uncertainty.
The goal of this research is to provide some missing parts
of this framework.
Wavelengths of correlated photons can be tuned over a
significant portion of the visible and near-infrared spec-
trum when the phase matching angle is changed
[7]
. By
means of this method, the quantum efficiencies of a pho-
tomultiplier at 633, 702, and 789 nm are systemically
calibrated respectively.
The method of absolute calibration of photodetectors is
based on the rigorous space and time coherence of pho-
ton in the PDC effect. For the process of parametric
downconversion, a nonlinear uniaxial birefringent crystal
is used. The crystal is aligned with its optic axis form-
ing a large angle with the incident short-wavelength laser
beam. A small fraction of the incident photon is sponta-
neously downconverted to pairs of photons satisfying the
condition of energy and momentum conservation.
ω
p
= ω
s
+ ω
i
,
~
k
p
=
~
k
s
+
~
k
i
, (1)
where ω
p
, ω
s
and ω
i
are pump, signal and idler frequen-
cies, respectively.
~
k
p
,
~
k
s
and
~
k
i
are pump, signal and idler
wave vectors, respectively.
If N is the total number of photon pairs emitted from
the crystal in a given time interval. N
1
, N
2
and N
C
are
the mean count rates recorded by signal detector, idler
detector and in coincidence measurement, respectively,
we have the following relationships
[8]
:
N
1
= τ
Trigger
η
Trigger
N, (2)
N
2
= τ
DUT
η
DUT
N, (3)
N
C
= τ
Trigger
τ
DUT
η
Trigger
η
DUT
N, (4)
where η
Trigger
, η
DUT
denote the quantum efficiency of
signal and idler detectors, respectively. τ
Trigger
, τ
DUT
denote the transmittance of signal and idler paths, re-
spectively.
The quantum efficiencies of the two detectors are easily
derived from Eqs. (2)—(4),
η
DUT
=
1
τ
DUT
·
N
C
N
1
, (5)
η
Trigger
=
1
τ
Trigger
·
N
C
N
2
. (6)
According to the principle above, we need to measure
the coincidence count rates, trigger count rates and total
optical losses of detector under test (DUT) path.
We set up a system to calibrate photomultiplier (PMT)
in our laboratory. Figure 1 shows the schematic of
optical setup. The diode-pumped, frequency-doubled
Nd:vanadate laser (Coherent. Inc. Model Verdi V-18)
provides a single-frequency green (532 nm) output, which
is directed to Ti:sapphire laser (Coherent. Inc. Model
MBR110) and then directed to frequency-doubled laser
(Coherent. Inc. Model MBD200). A continuous-wave
(CW) ultraviolet (UV) (351 nm) beam is produced. The
1671-7694/2008/070472-04
c
2008 Chinese Optics Letters