NETD is one of the most important performance parameters for infrared imaging systems. It is a signal-to-noise figure which represents the temperature difference which would produce a signal equal to the camera’s temporal noise. In human language: NETD expresses the minimal resolvable temperature difference when the camera is used for relative imaging applications.

The thermal time constant τth of a bolometer is determined by the thermal mass C and by the thermal conductance G between the pixel and its environment. It expresses the physical time a bolometer needs to heat up and give an electrical output that equals or represents the input. Typical values for A-Si are between 7 and 10ms.

Researchers are exploring novel materials, device architectures, and fabrication techniques to address the technical challenges in single photon detection. This includes the development of new materials, such as 2D materials or perovskites, improved detector designs, advanced signal processing algorithms, and innovative cooling and shielding techniques. By pushing the boundaries of what is possible in single photon detection, researchers aim to unlock the full potential of this groundbreaking technology for a wide range of scientific and industrial applications.

Single photon detection has potential applications in a wide range of fields, including quantum communication and computing, biomedical imaging, LIDAR, astronomy, and remote sensing.
 

Current single photon detection technologies often struggle to achieve high performance across all relevant metrics, such as sensitivity, timing resolution, spatial resolution, and spectral resolution, without compromising on other aspects of detector performance.

Quantum Efficiency (QE) is a key objective in the development of single photon detectors, as it directly impacts the overall performance of the device.

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.
• 
  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.
• 
  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.
• 
  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.
• 
  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.