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MTN028160-D02
SPDMHx Series
3 Operation
Attention
The avalanche photodiode inside the SPDMHx Series device is an extremely sensitive device.
It can be permanently damaged by over-exposure to intense light.
Excessive light level (even daylight) might damage a powered SPDMHx Series detector. Pre-
cautions should be taken to avoid such situations.
When the SPDMHx Series detector is mounted on another instrument, ensure that the optical
connection is light-tight.
Heat Dissipation
In order to avoid damage to the detector, adequate heat sinking must be provided by placing or
the module onto a suitable heat sink, e.g. an optical table, bread board or base plate.
3.4.1 Gating Function and TTL Output
The SPDMHx Series detectors feature a gating input to disable or enable the output signal.
The output of the detector is disabled when a TTL low level signal is applied to the
Applying a TTL high level will enable the device and permit signal processing and signal output.
If the gate input is left unconnected, the device is enabled by default. Please see the
for the respective TTL levels.
Gating is very useful in applications with rare signals that occur only within a small, defined time
window as gating can deselect longer time periods with no signal. Also, applications with very
weak signal and high background light profit from the gating in that the background signal within
periods without real signal are not recorded.
Attention
Always switch off the device before connecting or disconnecting the gating input and the TTL
output.
3.4.2 Optimizing Performance
Active Sensor Area - Focusing the Beam
The SPDMH2 and SPDMH3 free space detectors show best performance if the light is focused
to on a small spot (<70
m
m diameter) in the center of the sensor active area. Off-center focus-
ing or overfilling the sensor area might lead to a significantly lower detection efficiency and/or
increased FWHM of the photon timing resolution. Mounting the detector on a suitable
or other means of positioning mechanics is therefore recommended.
The SPDMH2F and SPDMH3F detectors with FC/PC-connectors are pre-aligned for fibers spe-
cified in the
and require no further optimization.
Timing Resolution
The single photon timing resolution of the SPDMHx Series detectors depends on three factors
and is different for every single detector. Please see the production report of your SPDMHx
Series detector for details.
·
Detection Wavelength: The best photon timing resolution (i. e. smallest FWHM) is achieved
around 680 nm. The FWHM increases slightly towards blue and NIR detection wavelengths.