THORLABS SPDMA User manual

Single Photon Detector
SPDMA
Operation Manual
2021

Version:
Date: 1.0 08-Dec-2021
Copyright © 2021 Thorlabs

Foreword
Contents
1 General Information 1
11.1 Ordering Codes and Accessories
2 Getting Started 2
22.1 Parts List
3 Operating Instructions 3
33.1 Operating Elements 33.2 Mounting 33.3 Setup 43.4 Operating Principle 53.5 Block Diagram and Trigger IN
4 Maintenance and Service 7
74.1 Troubleshooting
5 Appendix 8
85.1 Technical Data 95.2 Definitions 105.3 Performance Plots 105.3.1 Typical Photon Detection Efficiency 105.3.2 Pulse Out Signal 115.4 Dimensions 125.5 Safety 145.6 Certifications and Compliances 155.7 Return of Devices 155.8 Manufacturer Address 155.9 Warranty 155.10Copyright and Exclusion of Liability 165.11Thorlabs Worldwide Contacts - WEEE Policy

© 2021 Thorlabs
We aim to develop and produce the best solutions for your
applications in the field of optical measurement techniques. To help
us to live up to your expectations and constantly improve our
products, we need your ideas and suggestions. We and our
international partners are looking forward to hearing from you.
Thorlabs GmbH
Warning
Sections marked by this symbol explain dangers that might result in
personal injury or death. Always read the associated information
carefully before performing the indicated procedure.
Please read this advice carefully!
This manual also contains "NOTES" and "HINTS" written in this form.
Attention
Paragraphs preceded by this symbol explain hazards that could
damage the instrument and the connected equipment or may cause
loss of data.
Note

Rev: 1.0, 08-Dec-2021 © 2021 Thorlabs Page 1
SPDMA 1 General Information
1 General Information
The Thorlabs' SPDMA Single Photon Detector uses a cooled silicon avalanche photodiode,
specialized for a wavelength range from 350 to 1100 nm with a maximum sensitivity at 600 nm.
Incoming photons are converted into a TTL pulse in the detector. The SMA connection offers a
direct output pulse signal from the module that can be viewed on an oscilloscope or connected
to an external counter.
An integrated Thermo Electric Cooler (TEC) element stabilizes the diode's temperature to re-
duce the dark count rate. The low dark count rate and high photon detection efficiency allow
detection of power levels down to fW. The active quenching circuit integrated into the diode of
the SPDMA enables high count rates. The output signal can further be optimized by continuous
adjustment using the Gain Adjustment Screw.
Using a TTL Trigger IN signal, the SPDMA can be externally triggered to select the time frame
for the detection of single photons.
Optical alignment is simplified by the relatively large active area of the diode with a diameter of
500 m m. The diode is actively aligned at the factory to be concentric with the input aperture,
which adds to the high quality of this device.
For flexible integration into optical systems, the SPDMA accommodates any Thorlabs 1'' lens
tubes as well as the Thorlabs 30 mm Cage System. The SPDMA can be mounted in metric or
imperial systems due to 8-32 and M4 combi-thread mounting holes.
The product includes an SM1T1 SM1 Coupler which adapts the external thread to an internal
thread and holds the SM1RR Retaining Ring and a reusable protective plastic cover cap.
Another advantage is that the SPDMA cannot be damaged by unwanted ambient light, which is
critical for many photomultiplier tubes.
Attention
Please find all safety information and warnings concerning this product in the chapter Safety in
the Appendix.
1.1 Ordering Codes and Accessories
SPDMA
Single Photon Detector, 350 nm - 1100 nm, Active Area Diameter 0.5 mm,
Combi-Thread Mounting Holes Compatible with 8-32 and M4 Threads
Included Accessories
· Power Supply (±12 V, 0.3 A / 5 V, 2.5 A)
· Plastic Cover Cap (Item # SM1EC2B) on an included SM1T1 SM1 Coupler with an
SM1RR SM1 Retaining Ring.
Optional Accessories
· All Thorlabs internal or external SM1 (1.035"-40) threaded accessories are compatible
with the SPDMA.
· The 30 mm Cage System can be mounted on the SPDMA.
Please visit our homepage http://www.thorlabs.com for various accessories like fiber adapters,
posts and post holders, data sheets and further information.

Page 2 MTN025859_D02
SPDMA 2 Getting Started
2 Getting Started
2.1 Parts List
Please inspect the shipping container for damage. Please do not cut through the cardboard, as
the box might be needed for storage or returns.
If the shipping container appears to be damaged, keep it until you have inspected the contents
for completeness and tested the SPDMA mechanically and electrically.
Verify that you have received the following items within the package:
1. SPDMA Single Photon Detector
2. Plastic Cover Cap (Item # SM1EC2B) on SM1T1-SM1 Coupler with an SM1RR-SM1
Retaining Ring
3. Power Supply (±12V, 0.3 A / 5 V, 2.5 A) with Power Cord, Connector According to Ordering
Country
4. Quick Reference

Rev: 1.0, 08-Dec-2021 © 2021 Thorlabs Page 3
SPDMA 3 Operating Instructions
3 Operating Instructions
3.1 Operating Elements
3.2 Mounting
Mounting SPDMA on an Optical Table
Mount the SPDMA on an optical post by using either of the three tapped mounting holes on the
left and right side, and bottom of the device. The combi-thread tapped holes accept both 8-32
and M4 threads, such that using either imperial or metric TR posts is possible.
Mounting External Optics
The customer system can be attached and aligned using either the external SM1 thread or the
4-40 mounting holes for a 30 mm Cage System. The positions are indicated in the Operating
Elements section. The external SM1 thread accommodates Thorlabs’ SM1-threaded (1.035"-
40) adapters that are compatible with any number of Thorlabs 1'' threaded accessories, like ex-
ternal optics, filters, apertures, fiber adapters, or lens tubes. The SPDMA is shipped with an
SM1T1 SM1 coupler that adapts the external thread to an SM1 internal thread. A retaining ring
in the coupler holds the protective cover cap. Please unscrew the coupler if needed.
For accessories, please visit our website or contact Thorlabs.
3.3 Setup
After mounting the SPDMA, set up the detector as follows:
1. Power up the SPDMA using the included power supply.
2. Switch on the SPDMA, using the toggle button on the side of the instrument.
3. Push the cover from the status LED to see the status:
a. Red: The LED will initially be red upon connection to the power supply to indicate this
connection and the need to wait until the detector has reached the operating temperature.
Within a few seconds, the diode is cooled down and the status LED will turn to green. The

Page 4 MTN025859_D02
SPDMA 3 Operating Instructions
status LED will return to red when the diode temperature is too high. If the LED is red, no
signal is sent to pulse output.
b. Green: Detector is ready for operation. The diode is at operating temperature and signal
arrives at the pulse output.
Note
The Status LED will turn red whenever the operating temperature is too high. Please ensure
sufficient air ventilation.
4. Push the cover back in front of the status LED to prevent LED light from disturbing the mea-
surement.
5. To increase the photon detection efficiency, turn the Gain Adjustment Screw with a slotted
screw driver (1.8 to 2.4 mm, 0.07" to 3/32"). For more information on the gain, please refer
to the chapter Operating Principle.
a. Use Minimum Gain when a low dark count rate is critical. This comes at the cost of low
photon detection efficiency.
b. Use Maximum Gain when it is desirable to collect a maximum number of photons. This
comes at the cost of a higher dark count rate.
c. Because the time between photon detection and signal output changes with the gain set-
ting, please reevaluate this parameter after changing the gain setting.
Note
"Trigger In" and "Pulse Out" are of a 50 W impedance. Make sure that the trigger pulse source
is capable to work on a 50 W load and that the device connected to "Pulse Out" operates at a
50 W input impedance.
3.4 Operating Principle
The Thorlabs SPDMA uses a silicon avalanche photo diode (Si APD), operated in reverse di-
rection and biased slightly beyond the breakdown threshold voltage VBR (see diagram below,
point A), also known as the avalanche voltage.
This operating mode is also known as "Geiger mode". An APD in Geiger mode will remain in a
metastable state until a photon arrives and generates free charge carriers in the PD's junction.
These free charge carriers trigger an avalanche (point B), leading to a significant current. An
active quenching circuit integrated into the APD limits the current through the APD in order to
avoid destruction and lowers the bias voltage below the breakdown voltage VBR (point C) im-
mediately after a photon released an avalanche. This enables high count rates with dead time
between counts down to the specified dead time at max gain. Afterwards the bias voltage is re-
stored.

Rev: 1.0, 08-Dec-2021 © 2021 Thorlabs Page 5
SPDMA 3 Operating Instructions
During the quenching time, which is known as the dead time of the diode, the APD is insensit-
ive 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. An integrated
TEC element stabilizes the diode’s temperature below the ambient temperature to reduce the
dark count rate. This eliminates the need for a fan and avoids mechanical vibrations.
In case the spontaneously triggered avalanches are correlated in time with a pulse caused by a
photon, it is called an afterpulse.
Note
Due to APD properties, not all single photons may be detected. Reasons are the APD's intrinsic
dead time during quenching and the APD's nonlinearity.
Gain Adjustment
Using the gain adjustment screw, an overvoltage beyond the breakdown voltage can be adjus-
ted to the SPDMA. This increases the photon detection efficiency but also the dark count rate.
Please be aware that the probability of afterpulsing slightly rises with higher gain settings and
that adjusting the gain also affects the time between photon detection and signal output.
The dead time increases with decreasing gain.
3.5 Block Diagram and Trigger IN
The current pulse generated by an incoming photon passes a pulse shaping circuit, which is
shortening the APD's output TTL pulse duration. On the "Pulse Out" terminal the signal from
the pulse shaper is applied so that counts can be viewed on an oscilloscope or registered by an
external counter. In the absence of a Trigger, the gate is closed and allows signal out.
The Gain changes the Bias (overvoltage) on the APD. The Bias is physically guided through the
active quenching element but does not impact the active quenching.
TTL Trigger:
The TTL Trigger allows for selective activation of the pulse output: At high Trigger Input (spe-
cified in the Technical Data) the signal arrives at Pulse Out. This is the default whenever no ex-
ternal TTL signal is applied as a trigger.

Page 6 MTN025859_D02
SPDMA 3 Operating Instructions
Whenever a TTL trigger input signal is used, the default TTL input needs to be "Low". Signal
from photon detection is sent to Pulse Out as the Trigger Input voltage switches to "High". High
and Low signal are specified in the section Technical Data.
Note
"Trigger In" and "Pulse Out" are of a 50 W impedance. Make sure that the trigger pulse source
is capable to work on a 50 W load and that the device connected to "Pulse Out" operates at a
50 W input impedance.