Photons, the fundamental particles of light, are essential to many scientific, industrial and medical applications. Detecting and counting photons with precision enables breakthroughs in fields ranging from quantum computing to biomedical imaging. But how do you detect photons, and what are the technologies that make this possible?
In this blog, we explore the world of photon detection, with a focus on single-photon detection, photon-counting techniques and the cutting-edge technology of Time-Correlated Single-Photon Counting (TCSPC) Single-Photon Avalanche Diode (SPAD) array cameras. We’ll also highlight our own innovative products and services that make photon detection more accessible and accurate than ever.
What Device Measures Photons?
The energy of a single photon of red light is about 3×10^(-19) J, which is about 540,000,000,000,000,000,000 times less than the energy stored in a small LR44 battery. Single photon detection requires highly sensitive devices capable of responding to even the tiniest traces of light. These devices are called photon detectors. Depending on the application, photon detectors can measure light intensity, count individual photons or determine the time at which photons arrive. Some of the most common types include:
1. Single-Photon Avalanche Diodes (SPADs)
SPADs are solid-state devices specifically designed for single-photon detection. They operate in Geiger mode, where even a single photon triggers a measurable avalanche of electrons. SPADs form the foundation of many modern photon-counting detectors.
2. Photomultiplier Tubes (PMTs)
PMTs are traditional photon detectors used in applications like spectroscopy and particle physics. They amplify the signal of incident photons through a cascade of electrons. While highly sensitive, they are bulky, fragile and require high voltages to operate.
3. Avalanche Photodiodes (APDs)
APDs operate by amplifying photon signals through avalanche multiplication, however, unlike SPADs, they are operated below the diode breakdown voltage and susceptible to excess noise, limiting the accuracy of photon counting. They are more compact than PMTs and can detect single photons under specific conditions, making them suitable for applications like LiDAR and fluorescence spectroscopy.
4. CMOS Image Sensors
CMOS image sensors are a popular choice in microelectronics manufacturing processes and, in fact, many SPAD image sensors are made using CMOS processes too. While able to detect single photons and potentially count them, a lack of temporal precision means that there can be no information about the photon arrival time when using CMOS photon detectors.
5. Superconducting Nanowire Single-Photon Detectors (SNSPDs)
SNSPDs are among the most sensitive photon detectors available. They operate at cryogenic temperatures, where a single photon striking a superconducting nanowire creates a temporary break in superconductivity. This disruption generates a measurable electrical signal, enabling single-photon detection with great efficiency and low noise. SNSPDs are used in applications such as quantum communication, optical quantum computing and deep-space optical communication. However, operating at very low temperatures means the use of SNSPDs in small, portable cameras and systems is challenging in comparison to SPADs, which operate at room temperature and don’t generally need to be cooled.
Single-Photon Detection and Counting
Single-photon detection is crucial in applications where every photon matters, such as quantum communication, single-molecule imaging and time-resolved measurements. Photon counters are devices designed to count individual photons, providing data with extraordinary precision.
Photon-counting detectors, such as SPADs, excel at this task. When coupled with time-correlated single-photon counting (TCSPC) techniques, they can measure the arrival times of photons with picosecond accuracy. This capability opens up a wealth of applications, from fluorescence lifetime imaging to high-resolution 3D LIDAR mapping.
How Does a Single-Photon Detector Work?
Single-photon detectors like SPADs rely on a principle called Geiger-mode operation. When a photon is absorbed in the detector, it generates an electron-hole pair. These initial carriers are accelerated by the high electric field inside the SPAD device. Very soon they start to collide with the crystal lattice of the semiconductor material and share their high kinetic energy with other carriers. These secondary carriers are released and contribute to the growth of the carrier avalanche, creating measurable electronic current. With the help of various pixel circuits, SPAD current resulting from the photon detection can be converted into a voltage pulse, which leading edge signals the precise time when the photon arrived.
TCSPC systems add an extra layer of sophistication by recording the time delay between the photon’s arrival and a reference signal. This timing information is vital for applications such as time-of-flight measurements and dynamic studies of molecular interactions.
TCSPC SPAD Array Cameras: Revolutionising Photon Detection
TCSPC combined with SPAD array cameras has transformed the way photons are detected and counted. Unlike single-element detectors, SPAD arrays consist of multiple SPAD pixels arranged in a grid. Each element acts as an independent photon counter, enabling high-resolution imaging with single-photon sensitivity.
Key Advantages of TCSPC SPAD Array Cameras:
- High Temporal Resolution: TCSPC enables precise measurement of photon arrival times, with resolutions in the picosecond range.
- Parallel Detection: SPAD arrays allow simultaneous photon detection across multiple channels, enabling real-time imaging and high-throughput data collection.
- Compact and Robust: SPAD arrays are compact, solid-state devices that are more durable and power-efficient than traditional PMTs.
Applications of TCSPC SPAD array cameras include fluorescence lifetime imaging (FLIM), quantum key distribution (QKD) and high-speed 3D imaging.
Photon Force: Innovating Photon Detection
At Photon Force, we specialise in advanced photon-counting solutions designed to meet the needs of cutting-edge research and commercial applications. Our flagship product range, the PF32 cameras, leverages TCSPC and SPAD array technology to deliver unparalleled performance in single-photon detection and counting.
The PF32 Camera Range
The PF32 cameras feature:
- High-resolution SPAD arrays for detailed photon-counting imaging.
- Integrated TCSPC capabilities for precise temporal measurements.
- Flexible configurations for a variety of applications, including time-of-flight imaging and fluorescence lifetime studies.
Custom Sensors for OEM Applications
In addition to our camera products, Photon Force offers custom module and sensor design and manufacturing services for OEM applications. Whether you need a tailored solution for underwater imaging, radiation detection, quantum communication or anything else, our team can help you develop and integrate cutting-edge photon-detection technology.
Why Choose Photon Force?
Photon Force combines deep expertise in photon detection with a commitment to innovation and customer success. Our products are designed to help researchers and engineers push the boundaries of what’s possible in photon science.
Whether you’re looking to understand more about how photons are detected, find the exact number of photons in your experimental set-up, or explore how photon detection can be integrated into your own production system, Photon Force has the tools and expertise you need.
Discover more about Photon Force’s PF32 cameras and custom sensor solutions on our website or by getting in touch.
