Newport 1815-C, Руководство оператора

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3.3.1 Detector Calibration and Accuracy
Newport Corporation calibrates its detectors using secondary standards
directly traceable to the United States National Institiute of Science and
Technology (NIST) or to Great Britain’s National Physical Laboratory, (NPL).
The details and accuracy of the calibration procedure vary with each detector
model but a detailed description of the calibration results is supplied with
each individually calibrated detector.
In general, detector calibration accuracy ranges from 2% to 5% in absolute
terms and varies with wavelength. Each detector will have some variation in
the response over different sections of its surface. Therefore, for the most
reproducible measurements, light should illuminate the detector as uniformly
as possible over 80% of the detector’s active area.
Caution
Avoid focusing a light source onto the detector surface. Inaccurate
readings and possible detector damage may result. Consult your
detector manual for information on detector saturation or damage
thresholds.
NIST traceability requires that detectors be recalibrated on one year intervals.
As individual detector responses change with time, especially in the ultravio-
let, recalibration is necessary to assure confidence in the accuracy of the
measurement. For the most reproducible measurements, the same detector
should always be used for measurements which are to be directly compared.
3.3.2 Quantum Detector Temperature Effects
Semiconductor based photodiode detector characteristics (Newport Corporation
Low-Power detectors) are significantly affected by temperature. At longer
wavelengths, these quantum detectors typically lose sensitivity with increasing
temperature. However the detector dark current increases exponentially with
temperature. For silicon detectors, dark current is generally on the order of a few
picoamps at room temperatures. With uncooled germanium detectors, however,
this dark current is on the order of a nanoamp, or typically 1,000 to 10,000 times
greater than silicon. These dark currents can be zeroed at any moment in time via
the Model 1815-C’s ZERO knob. Since dark currents drift with temperature, the
ZERO should be adjusted just prior to taking any measurements. The noise or
drift in the dark current sets a lower bound on the measurement resolution which
can be achieved with any given detector.
If the detector temperature is constant, sensitivity changes and dark current
drifts are significantly reduced. In addition, if the detector is cooled, the dark
current and dark current noise will decrease. For the most accurate measure-
ments, particularly with germanium detectors, the user should cool the
detector to approximately 0
°
C and control the temperature to within
±
1
°
C.
3.3.3 Thermopile Detector Temperature Effects
Disk themopile based detector characteristics (Newport Corporation High-
Power detectors) are significantly affected by temperature fluctuations arising
from air flow disturbances. As the detector element is a heat measuring
device, air flow disturbances often set a practical lower limit on the power that
a detector can measure. In order to get the most out of any thermopile
detector, be careful to shield the detector from air flow disturbances. Com-
mon sources of disturbance are air conditioners and people walking past.