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InGaAs Avalanche Photodetectors
Thorlabs' InGaAs Avalanche photodetectors (APDs) are designed to offer increased sensitivity and lower noise compared to standard PIN detectors, making them ideal for applications with low optical power levels. In addition to our standard APDs, versions featuring variable gain (i.e., M factor) and/or temperature compensation are offered.
In general, avalanche photodiodes use an internal gain mechanism to increase sensitivity. A high reverse bias voltage is applied to the diodes to create a strong electric field. When an incident photon generates an electron-hole pair, the electric field accelerates the electrons, leading to the production of secondary electrons by impact ionization. The resulting electron avalanche can produce a gain factor of several hundred times, described by a multiplication factor, M, that is a function of both the reverse bias voltage and temperature. In general, the M factor increases with lower temperatures and decreases with higher temperatures. Similarly, the M factor will increase when the reverse bias voltage is raised and decrease when the reverse bias voltage is lowered.
Our APD130C(/M) temperature-compensated APD features an integrated thermistor that adjusts the bias voltage to compensate for the effect of temperature changes on the M factor. In addition to being temperature compensated, the APD410C(/M), APD430C(/M), and APD450C variable-gain APDs allow the reverse bias voltage across the diode to be adjusted via a rotary knob on the side of the housing, which varies the M factor continuously from 4 to 20.
For extremely light-sensitive applications, Thorlabs offers Menlo Systems' APD310 variable-gain, high-sensitivity avalanche photodectector, which offers high-speed response up to 1 GHz.
A complete list of all of our APDs, including those that have a silicon photodiode for use at UV and visible wavelengths, can be found on the Selection Guide tab. Please note that these packaged APDs are not suitable for use as single photon counters. Thorlabs has single photon counters available here.
BNC Female Output (Photodetector)
APD Male (Power Cables)
APD Female (Photodetector)
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Output from a fiber is coupled into the photodetector using an aspheric lens to focus the signal onto the detector active area.
In fiber coupling applications, we recommend taking into account the divergence of light from the fiber tip to ensure that all of the signal is focused onto the detector active area. When using a standard fiber connector adapter with a detector with an active area smaller than Ø1 mm, high coupling losses and degradation of the frequency response may occur.
To achieve high coupling efficiency, a fiber collimation package, focusing lens, and X-Y translator should be used, as shown in the photo to the right. The avalanche photodetector is shown with a fiber collimator, lens tube collimator adapter, lens tube, and X-Y translation mount. An adapter inside the lens tube holds an aspheric lens (not visible) to focus the collimated light onto the active area of the detector. The X-Y translation mount corrects for any centering issues.
Pulsed Laser Emission: Power and Energy Calculations
Determining whether emission from a pulsed laser is compatible with a device or application can require referencing parameters that are not supplied by the laser's manufacturer. When this is the case, the necessary parameters can typically be calculated from the available information. Calculating peak pulse power, average power, pulse energy, and related parameters can be necessary to achieve desired outcomes including:
Pulsed laser radiation parameters are illustrated in Figure 1 and described in the table. For quick reference, a list of equations are provided below. The document available for download provides this information, as well as an introduction to pulsed laser emission, an overview of relationships among the different parameters, and guidance for applying the calculations.
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Figure 1: Parameters used to describe pulsed laser emission are indicated in the plot (above) and described in the table (below). Pulse energy (E) is the shaded area under the pulse curve. Pulse energy is, equivalently, the area of the diagonally hashed region.
Is it safe to use a detector with a specified maximum peak optical input power of 75 mW to measure the following pulsed laser emission?
The energy per pulse:
seems low, but the peak pulse power is:
It is not safe to use the detector to measure this pulsed laser emission, since the peak power of the pulses is >5 orders of magnitude higher than the detector's maximum peak optical input power.
Avalanche Photodetector Selection Guide
Thorlabs' APD130C(/M) Avalanche Photodetector features an integrated thermistor that maintains an M factor stability of ±3% or better over 23 ± 5 °C by adjusting the bias voltage across the avalanche photodiode, supplying improved output stability in environments with temperature variations.
The orientation of the mechanical and electrical connections, combined with the compact design, ensures that these detectors can fit into tight spaces. Three 8-32 (M4) mounting holes, one on each edge of the housing, further ensure easy integration into complicated mechanical setups. The housing also provides compatibility with both our SM05 and SM1 Lens Tubes. An internally SM1-threaded cap is included.
Fiber Coupling Note:
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The M Factor is controlled by a knob on the side of the APD.
Thorlabs' APD410C(/M), APD430C(/M), and APD450C Avalanche Photodetectors have a variable gain that can be controlled by a knob on the right side of the housing. The gain knob adjusts the reverse bias voltage across the photodiode, allowing the M factor to vary. Like the APD130C detectors above, these devices feature an integrated thermistor that maintains an M factor stability of ±3% or better over 23 ± 5 °C by adjusting the bias voltage across the avalanche photodiode. These detectors offer different bandwidth ranges and sensitivity.
The orientation of the mechanical and electrical connections, combined with the compact design, ensures that these detectors can fit into tight spaces. Three 8-32 (M4) mounting holes, one on each edge of the APD410C(/M) and APD430C(/M) housing, further ensure easy integration into complicated mechanical setups. The APD450C detector offers universal 8-32/M4 mounting holes. The housing also provides compatibility with both our SM05 and SM1 Lens Tubes. An internally SM1-threaded cap is included.
Fiber Coupling Note:
Menlo Systems' APD310 InGaAs Avalanche Photodetector provides an extremely light-sensitive alternative to traditional PIN photodiodes and is sensitive and fast enough for the characterization of pulsed lasers on the order of nanoseconds. The InGaAs avalanche photodiode of the APD310 provides exceptional performance for low-light applications in the 850 - 1650 nm range. This APD maintains high-gain stability over the operating temperature range by utilizing a temperature-compensation circuit, which adjusts the ~150 VDC bias to ensure operation near the breakdown voltage.
A 40 dB gain amplifier is integrated into the housing and is AC-coupled to band the output BNC. The output is matched to 50 Ω impedance. The detector has an electronic bandwidth of 5 MHz to 1 GHz (at 3 dB) and offers user-accessible push buttons providing 100 step gain adjustment. The APD310 has SM05 (0.535"-40) threads for easy integration into Thorlabs' family of lens tubes and cage assemblies. For direct fiber mounting, compatible fiber adapters are available. The bottom of the detector has a metric (M4) mounting hole and an M4 to 8-32 adapter for post mounting. The compact packaging allows the APD to be substituted directly into an existing setup while maintaining a small footprint on the benchtop. A location-specific power adapter is included with the detector; contact Technical Support for more information.
These photodetectors are not suitable for pulses longer than 30 ns or continuous light levels. Please see the FPD510 series for alternatives.
The LDS12B ±12 VDC Regulated Linear Power Supply is intended as a replacement for the supply included with our APD series of avalanche photodetectors sold on this page, except for the APD310 photodetector. The cord has three pins: one for ground, one for +12 V, and one for -12 V (see diagram above). This power supply ships with a location-specific power cord. This power supply can also be used with the PDA series of amplified photodetectors, PDB series of balanced photodetectors, PMM series of photomultiplier modules, and the FSAC autocorrelator for femtosecond lasers.