Single Photon Detectors
- Single Photon Detection or Counting Modules
- Low Dark Counts: 25 Hz - 300 Hz
- Detector Sizes of Ø20 µm, Ø50 µm, or Ø500 µm
- Active Quenching and Temperature Stabilization
Single Photon Counting Module
Single Photon Detection Module with Adjustble Gain
Single Photon Counting Modules Have a Fan-Cooled Heat Sink for Temperature Stabilization
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The Photon Detection Efficiency (PDE) is shown here as a function of wavelength for the SPDMA module at both Max and Min Gain and the SPCMxxA(/M) modules. The operating range of the SPDMA module is 350 nm - 1100 nm, while the operating range of the SPCMxxA(/M) modules is 350 nm - 900 nm.
- Visible and NIR Wavelength Responsivity:
- Single Photon Detector: 350 nm - 1100 nm
- Single Photon Counters: 350 nm - 900 nm
- Low Typical Dark Counts:
- SPDMA: <75 Hz (Min Gain), <300 Hz (Max Gain)
- SPCM20A(/M): 25 Hz
- SPCM50A(/M): 150 Hz
- Three Detector Sizes: Ø20 µm, Ø50 µm, or Ø500 µm Active Area
- Active Quenching
- Temperature Stabilization
- Pulse Output
- TTL Gating/Trigger Input
- Spectroscopy with Single Molecules
- Spectro-Photometrical Measurements
- Flow Cytometry
- Photon Correlation Spectroscopy
- Quantum Optics
Thorlabs' SPDMA Single Photon Detection Module provides an extended wavelength range into the near infrared and continuously adjustable gain with an SMA connection offering a TTL output that can be viewed on an oscilloscope or connected to an external counter. The SPCMxxA(/M) Single Photon Counting Modules have an internal 31-bit photon counter and software included, with a more limited wavelength range and single gain setting. A comparison of the photon detection efficiencies (PDEs) of the detectors is shown at right.
Each of the single photon modules uses a silicon avalanche photodiode. Please see the Tutorial tab for details about the functionality of these photodiodes. The active quenching circuit integrated into the diode of these single photon systems enables high count rates, allowing users to detect a photon every 35 ns - 45 ns, depending on the model chosen. The diodes are actively temperature stabilized to achieve low dark count rates of 25 Hz - 300 Hz, depending on the model and settings, with power level detection down to fW. Please see the Specs tab for complete specifications on all modules.
Software for SPCMxxA(/M) Counting Modules
The Single Photon Counter Modules include a software package with GUI for out-of-the-box operation. The following operating modes can be set by the software:
- Manual Mode for manual operation, where the counter is started and stopped manually by pressing the Start/Stop button (toggle function).
- Free Running Timer Counter for counting incident photons for a certain number of "Time Bin Lengths."
- Externally Triggered Timer Counter for triggering the timer start for counting incident photons for a certain time period.
- Externally Triggered Counter for starting and stopping the counter by an external trigger.
- External Gating for activating the counter and the APD externally.
For more details about the software and its operation modes, please see the Software tab.
|Detector Type||Si Avalanche Photodetector|
|Wavelength Range||350 nm - 1100 nm||350 nm - 900 nm|
|Active Detector Size||Ø500 µm||Ø20 µm||Ø50 µm|
|Gain Adjustment Factor (Typical)||4||N/A|
|Typical Photon Dectection Efficiency||@ Max Gain
58% @ 500 nm
66% @ 650 nm
43% @ 820 nm
|35% @ 500 nm|
|Dark Count Rate||<75 Hz (Typical); <400 Hz (Max) @ Min Gain
<300 Hz (Typical); <1500 Hz (Max) @ Max Gain
|25 Hz (Typical); 60 Hz (Max)||150 Hz (Typical); 200 Hz (Max)|
|Count Rate||20 MHz (Typical @ Max Gain)
>10 MHz (Min @ Max Gain)
|28 MHz (Max)||22 MHz (Max)|
|Dead Time||<35 ns (@ Max Gain)||35 ns (Typical)||45 ns (Typical)|
|APD Gating Delaya||N/A||18 ns (Typical)|
|Gate / Trigger In to Pulse Out Delayb||N/A||28 ns (Typical)|
|Afterpulse Probability||1% (Typical @ Min Gain)||3%|
|APD Temperature Stability||<0.01 K||<0.1 K|
|Trigger Input TTL Signalc
|Output Pulse Amplitude @ 50 Ω Load
|Dimensions||72.0 mm x 51.3 mm x 27.4 mm||85.0 mm x 76.5 mm x 36.2 mm|
|Operating Temperatured||0 °C - 35 °C||0 °C - 40 °C|
|Storage Temperature Range||-40 °C - 70 °C|
|Power Supply||± 12 V, 0.3 A / 5 V, 2.5 A||6 VDC / 1.5 A|
Operating Principle of Single Photon Detectors
Avalanche photodiodes (APDs) operated in the Geiger Mode have the ability to detect single photons. This single photon sensitivity can be achieved by biasing the APD above the breakdown voltage (Point A in Fig. 1). The APD will remain in a metastable state until a photon arrives and generates an avalanche (Point B). This avalanche is quenched by an active quenching circuit inside the APD (Point C), which lowers the bias voltage below the breakdown voltage (labeled VBR in Fig. 1).
Figure 1: Current Voltage Characteristics of an Avalanche Photodiode Operated in Geiger Mode
Afterwards the excess bias voltage can be restored. During this time, which is known as the pulse dead time of the diode, the APD is insensitive to any other incoming photons. Spontaneously triggered avalanches are possible while the diode is in a metastable state. If these spontaneous avalanches occur randomly, they are called dark counts. If the spontaneously triggered avalanches are correlated in time with a pulse caused by a photon, it is called an afterpulse. To block such afterpulses in the measurement, an additional pulse dead time can be set in the software for the counting modules, which will cause the internal counter of the single photon detector to ignore all pulses occurring during this pulse dead time.
In this mode, the diode is operated slightly above the breakdown threshold voltage. Hence, a single electron-hole pair (generated by absorption of a photon or by a thermal fluctuation) can trigger a strong avalanche.
Dark Count Rate:
This is the average rate of registered counts in the absence of any incident light and determines the minimum count rate at which the signal is dominantly caused by real photons. The false detection events are mostly of thermal origin and can therefore be strongly suppressed by using a cooled detector.
Active Quenching occurs when a fast discriminator senses the steep onset of the avalanche current and quickly reduces the bias voltage so that it is below breakdown momentarily. The bias is then returned to a value above the breakdown voltage in preparation for detection of the next photon.
Dead Time is the time interval the detector spends in its recovery state. During this time, it is effectively blind to incoming photons. The dead time fraction, which is an inherent feature of an active quenching circuit, may be defined as the ratio of missed to incident events.
During an avalanche, some charges can be trapped inside the high field region. When these charges are released, they can trigger an avalanche. These spurious events are called Afterpulses. The life of those trapped charges is on the order of a few tenths of a microsecond. Hence, it is likely that an afterpulse occurs directly after a signal pulse.
The SPCMxxA(/M) Single Photon Counting Modules include a software package with GUI for out-of-the-box operation. Please note the SPDMA Single Photon Detector does not include or require any software for operation.
The following operating modes can be set by the software:
The counter is started and stopped manually by pressing the Start/Stop button (toggle function). The timer will be reset at each start.
Free Running Timer Counter:
Both the number of time bins (i.e, the number of measurements) as well as the minimum interval between two subsequent bins can be set.
Externally Triggered Timer Counter:
In this mode, the timer is started by an external trigger signal and counts incident photons during the set time bin length. The active trigger slope (rising or falling) can be selected.
Externally Triggered Counter:
In this mode, the external trigger signal will start and stop the counter.
The counter and the APD are activated externally.
In the array mode, each data value is recorded to an array. In the continuous mode, the measurement is restarted after the preset number. Both modes can be saved as a .txt file. The measurement results can be represented as a bar (XY bar with counts vs. number of measurements), graph (curve), table (numeric) or alignment (numeric with additionally information) display. The number of measurements can be defined, and the measurements can be repeated.
- Extended Wavelength Range: 350 nm - 1100 nm
- Adjustable Gain
- Compact Size: 72.0 mm x 51.3 mm x 27.4 mm
- Ø500 μm Active Detector, Concentrically Aligned to Input Aperture
The SPDMA Single Photon Detection Module provides an extended photon detection efficiency (PDE) into the NIR. The adjustable gain allows the user to optimize for either higher PDE (higher gain) or lower dark counts (lower gain). The status LED on the side of the module has a cover to prevent LED light from disturbing the measurement. Unlike many photomultiplier tubes, this detection module cannot be damaged by unwanted ambient light.
For flexible integration into optical systems, the detection module has external SM1 (1.035"-40) threading for compatibility with Ø1'' lens tubes as well as four 4-40 tapped holes for integration with 30 mm cage components. The SPDMA module can be mounted in metric or imperial systems using the three 8-32 and M4 combi-thread mounting holes, located on both sides and the bottom of the unit.
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The SPDMA detection module has external SM1 threads, is 30 mm cage system compatible, and includes an SM1T1 Internal SM1 Adapter and SM1RR Retaining Ring. The module also includes a gain adjustment screw and status LED with cover.
The detection module includes an SM1T1 SM1 coupler that adapts the external thread to an internal thread, an SM1RR retaining ring, and a reusable protective plastic cover cap. A power supply with a region-specific plug is also included with the module.
- Integrated Counter and Software Included
- Wavelength Range: 350 nm - 900 nm
- Compact Size: 85.0 mm x 76.5 mm x 36.2 mm
The SPCMxxA(/M) Single Photon Counting Modules convert an incoming photon to a TTL signal in the detector, which is then counted by an internal 31 bit counter. The module includes a software package with GUI for out-of-the-box operation. For more details about the software and its operation modes, please see the Software tab.
For flexible integration into optical systems, the detection module has external SM1 (1.035"-40) threading for compatibility with Ø1'' lens tubes. The SPCM20A(/M) provides an active area of Ø20 µm while the SPCM50A(/M) offers Ø50 µm. Two versions of each module are available for mounting in metric or imperial systems.
The module comes with a CD with the operating software, a USB 2.0 cable, Type A to mini Type B, and a power supply.