THORLABS APD410 Series, Operation Manual

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APD410x
3 Operating Instruction
3.1 Operating Principle
The Thorlabs APD410x series of temperature-compensated, variable gain Avalanche Photode-
tectors combine a high sensitivity Si or InGaAs Avalanche Photodiode with a specially designed
ultra-low noise transimpedance amplifier for detection of optical signals from DC to 10 MHz.
The buffered output stage can deliver up to 2.0 V into a 50
W impedance load. No external
high voltage power supply is required for operation.
APD410x series Avalanche Photodetectors have an exceptionally low NEP, making them ideal
for fast low-level light detection applications, such as spectroscopy, fluorescence measure-
ments, laser radar and optical rangefinders. Due to their very high sensitivity the APD410x
series Avalanche Photodetectors can replace Photomultiplier Tubes (PMT) in many applica-
tions. The Avalanche Photodetectors cannot be damaged by unwanted ambient light, which is
critical for many Photomultiplier Tubes.
Avalanche Photodiodes use an internal gain mechanism to increase the sensitivity. Incident
photons generate electron-hole pairs, like in a normal photo diode. By applying a high reverse
voltage, a strong electric field appears that accelerates these electrons and produces seconda-
ry electrons by impact ionization. This leads to an electron avalanche producing gain factors of
up to several hundreds. The amplification depends on the reverse bias voltage and is described
by the M (multiplication) factor. Due to internal processes, the M factor is temperature depend-
ent. At a fixed reverse bias voltage the M factor will change with temperature: in general, with
lower temperatures the M factor will increase, with higher temperatures - decrease.
The APD410x series Avalanche Photodetectors are temperature-compensated. A thermistor
senses the temperature inside the APD410x enclosure, and a special electronic circuit controls
the applied to the APD reverse voltage in accordance with the temperature change. As the M
(multiplication) factor depends on the applied reverse voltage, the temperature dependency of
the M factor can reduced drastically.
These detectors have a rotary GAIN knob that allows the reverse bias voltage of the avalanche
photodiode to be adjusted within a certain range, resulting in a variation of the M (multiplication)
factor that is equivalent to a gain variation.
The APD410x Series is powered by the included external power supply (±12 V, 250 mA) via a
PICO M8 power connector.
3.1.1 Optical Input
The APD410C uses an InGaAs Avalanche Photodiode with a detector active area diameter of
0.2 mm, operating from 900 to 1700 nm nm.
The APD410A uses a Silicon Avalanche Photodiode with a detector active area diameter of
1 mm, operating from 400 to 1000 nm.
The APD410A2 uses an UV-enhanced Silicon Avalanche Photodiode with a detector active
area diameter of 0.5 mm, operating from 200 to 1000 nm.
The typical responsivity curves can be found in the appendix .
An open beam should be carefully aligned to the detector. Additional focusing lenses can be
easily attached to the Avalanche Photodetectors. The housing is compatible with any number
of Thorlabs 1” and ½” threaded accessories. This allows convenient mounting of external op-
tics, filters, apertures or fiber adapters.
For fiber coupled applications, in order to meet specifications, it is recommended to focus the
optical signal out of the fiber onto the detector. Details please see in the
appendix .
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