The main challenges in single photon detection include:

• Detection efficiency: The detection efficiency refers to the probability of a photon being detected by the detector. Achieving high detection efficiency is crucial in single photon detection applications. The efficiency depends on factors such as the detector technology, photon wavelength, and optical coupling efficiency. Maximizing detection efficiency is essential for capturing the highest possible number of photons.
• Timing resolution: Many applications involving single photon detection require precise timing information, such as in time-correlated single photon counting (TCSPC) or quantum cryptography. Achieving high timing resolution is challenging, as it requires fast electronics and detectors with short response times to accurately capture the arrival times of individual photons.
• Spatial resolution
• Spectral resolution
• Environmental and operating conditions
• Integration and scalability: In some applications, there is a need for miniaturized or integrated single photon detectors. Challenges arise in developing compact, robust, and efficient detector designs that can be integrated into complex systems or small-scale devices while maintaining high performance.

Vacuum tube-based single photon detectors offer several benefits for single photon detection applications compared to other technologies. Here are some of the main advantages:

• High sensitivity: Vacuum tube-based detectors are capable of detecting extremely low levels of light, down to the single photon level. This makes them well-suited for applications that require high sensitivity, such as quantum optics, fluorescence spectroscopy, and low-light imaging.
  Wide spectral range: Vacuum tube detectors have a wide spectral response range, spanning from ultraviolet (UV) to near-infrared (NIR) wavelengths. This versatility allows them to be used in a broad range of applications across different scientific disciplines.
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  Fast response time: MCP-PMTs have fast response times, typically in the sub-nanosecond range. This enables them to accurately capture fast events or rapidly changing light signals, making them suitable for time-resolved measurements and applications requiring high temporal resolution.
  Large active area: MCP-PMTs have relatively large active areas compared to other single photon detectors. This makes them capable of detecting photons over a larger spatial area, which is advantageous for applications such as imaging and light detection in broad fields of view.
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  Low noise: Vacuum tube-based detectors exhibit low noise characteristics, allowing for excellent signal-to-noise ratios. This is especially important for detecting weak light signals and enhancing the accuracy of measurements.
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  High gain: MCP-PMTs provide high gain amplification due to their electron multiplication stages. Each photon that enters the detector can generate a cascade of electrons, resulting in a significantly amplified output signal. This high gain makes it easier to detect and measure single photons with improved signal quality.
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  Versatility: Vacuum tube-based detectors can be used in a wide range of experimental setups and configurations, including single photon counting, photon correlation spectroscopy, fluorescence lifetime measurements, and many others. They are adaptable to different experimental requirements and can be integrated into various optical systems.

Vacuum tube-based Image Intensifier tubes consist of several essential components; a Photocathode, a Microchannel Plate (MCP) and an anode. These components work together to amplify input signal, creating a rich and dynamic output.

In the first step, existing ambient light passes through a photocathode, which converts the incoming photon signal into a photo-electron.

In the second step, photoelectrons are drawn by an electrical field into the MCP where they impinge multiple times on the inner walls and thereby multiply several thousands of times. In photon counting applications the multiplied electron signal is detected using an anode. In the instance of photon imaging applications, the anode converts the electron back into photons to produce an image.

Triaxial cables provide additional screening against unwanted sources of noise compared to coaxial cables- EMI/RFI interference and potential ground loops for small signals can be minimized, although this comes at a trade-off more difficult mechanical construction, lead-time, and cost. Typically, coaxial cables are sufficient for most nuclear applications but unusual, demanding, or unique applications may require the use of a triaxial cable solution. The Photonis Nuclear Instrumentation team has experience both working with our clients in determining the correct cable solution and qualifying the solution for use in industry.

Integrating a long mineral insulated cable with the body of the detector is ideal for the severe operating environments (high radiation level, humidity, vibration, high temperature) to maximize reliability and life of the instrument. Photonis recommend the use of integral cable for nuclear power applications to ensure trouble-free long-term operation. In mild environments, or in applications which otherwise do not permit integral cabling, Photonis is able to offer detectors with connection directly at the connector body.

Each detector type offers unique characteristics which suit it to a particular application. B-10 lined proportional counters offer excellent sensitivity to thermal neutrons, allowing them to achieve sufficient count rates in low neutron fluxes. For example, this feature makes the use of B-10 proportional counters attractive as monitors during initial reactor criticality, where the increased detector sensitivity ensures that smaller, less expensive, start-up sources can be installed in the reactor core. Fission chambers, in contrast, have lower sensitivity to thermal neutrons but have superior resistance to gamma ray interference and offer the capability to operate over many decades of neutron flux. This feature makes fission chambers the ideal choice as wide range monitors of reactor power. The Photonis technical team is happy to work with customers to determine which detector type makes the most sense in each customer application.

‘thermal’ and ‘fast’ refer to the energy level of the neutron incident on a detector. Thermal neutrons are typically defined as having energy <.025 eV. These lower energy neutrons are more likely to be absorbed by neutron sensitive materials, meaning thermal neutron detectors tend to have higher overall sensitivity. Thermal neutron detectors are designed to generate the majority of their usable signal from interactions with thermal neutrons, where fast neutron detectors are primarily capable of measuring high energy neutrons (>1 MeV). This has applications for research, where it may be important to use multiple detectors to differentiate between neutron energies, or in reactor applications where measurable neutron flux is primarily in high energy neutrons.

Detector operation can be significantly affected as the ambient temperature they are exposed to increases above 400 C, by several different mechanisms. The internal gases used to ensure linear operation of the detector must be carefully chosen to ensure they can remain chemically unchanged at these high temperatures. Further, as temperature rises above 400 C the internal resistance of the detector may decrease, causing a rise in leakage current which could limit the functional range or decrease the accuracy of the detector. For these concerns Photonis has designed high temperature detectors, utilizing the appropriate gases, materials, and guard ring construction to allow accurate and reliable operation up to 600 C.

A detector is usable so long as it remains sensitive to neutrons and capable of transmitting sufficient signal to be used by the electronics. The sensitivity of the detector will gradually decrease over time as it is exposed to thermal neutron flux, and the detector will remain viable as long as the electronics allow for the decrease in sensitivity. For B-10 lined proportional counters the gas internal to the detector is vital to linear performance of the detector and is subject to degradation during operation in high radiation environments. Photonis proportional counters may include an additional reservoir of proportional gas which extends detector life (up to ~5 x 1018 n/cm2) substantially, making total lifetime greater than the life of similar detectors without this reservoir and significantly longer than BF3 counters.

Auto-Gating provides a better reaction time when sudden bright light events occur, such as explosions or car headlights. The benefits can easily be seen not only during day-night-day transitions, but also under dynamic light conditions when rapidly changing from low light to high light conditions, such as sudden illumination of dark room or shooting at night (muzzleflash). 

The ATG maintains the optimum performance of the Image Intensifier Tube (IIT) while continuously revealing mission critical details, safeguarding the IIT from additional damage and protecting the user from temporary blindness.