THORLABS APD430 Series, Operation Manual

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© 2015 Thorlabs
3 Operating Instruction
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Please note, that coupling losses may occur due to small detector size, which will result in a
reduced output signal. If angled connectors are used the fiber adapter can be rotated from its
original position to check for an improved alignment. For this process use an optical input
power below the saturation power while observing OUTPUT voltage on a digital voltmeter or
other low-frequency measurement device.
The maximum OUTPUT voltage swing is 4.1 V at High-Z termination. Saturation of the
OUTPUT will occur at optical input power greater than CW Saturation Power listed in
specifications . If necessary, use external neutral density filters or attenuators to reduce the
input light level. Please note that the Avalanche Photodetectors are extremely sensitive to
unwanted stray light. Carefully shielding of the Avalanche Photodetectors from any unwanted
light sources is essential. Common techniques to minimize the influence of stray light include
baffling or other opaque barriers like black cloths, beam tubes or using appropriate band pass
filters in front of the detector.
Attention
The optical damage threshold is 1 mW. Exceeding this value will permanently destroy the
Avalanche Photodetector!
3.1.2 Electrical Output
Thorlabs APD430x Avalanche Photodetectors deliver an OUTPUT voltage, which is a function
of incident light power
P
opt
, detector's responsivity
 ( l )
, multiplication factor
M
and
transimpedance gain
G
given by:
·
 ( l )
for a given wavelength can be read from the spectral responsivity curves (see Technical
Data ) to estimate the OUTPUT voltage.The M factor (gain) settings range is 10 to 100
(APD430A and APD430A2) and 4 to 20 for APD430C at 23°C ambient temperature.
· The amplifier’s transimpedance gain
G
is 10 kV/A. Please note that OUTPUT voltage is
reduced by a factor of 0.5 if connected to a 50 W load.
The maximum output voltage swing of OUTPUT is 4.1 V for high impedance loads (2.0 V into
50 W ). Depending on the wavelength responsivity
Â
(
l
)
of the detector and the M factor, the
amplifier will reach saturation at optical input power greater than CW Saturation Power listed in
specifications. To avoid saturation, keep the output signal below the specified maximum output
voltage.
The output of the APD430x Avalanche Photodetectors is a BNC connector.
The amplifier offset voltage is factory set to zero at 23°C ambient temperature. Due to the very
high transimpedance gain, small temperature changes may affect offset voltage. Therefore it is
recommended to use the Avalanche Photodetectors in a constant temperature environment
after a short warm up period (~5 min) for exact DC light level measurements.
In the appendix, typical curves for Output Frequency Response and Spectral Noise
Distribution can be found.
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