Live cell imaging in particular, like many other imaging tasks
, depends on making good use of the available fluorescence light. The detector is a critical component in the light path with regard to photon efficiency. This article explains the underlying detection technology that is hybrid and compares it to photomultiplier technology. The implications of this design for imaging and countingphoton are discussed.
What is Photon Counting?
This works by thresholding electrical pulses and treating them as binary events (photon or non-photon). The read-out photon is done sequentially. The arrival of photon pulse in relation to scanner internal clock signals determine which pixel, line and frame the photons are assigned to. In a photon counter or a scanning device like confocal microscopic this information is available by default.
What is Hybrid Detection?
Originally developed for particle physics the design goal for detection technology for hybrid was a short temporal response for high intensity singe photon counting. This is possible thanks to a very small transit time spread, meaning very sharp and defined pulses in response to incident photons. This is accomplished thanks to two-step architecture with one vacuum acceleration step followed by electron bombardment and avalanche gain.
How Does Hybrid Detection Technology Work?
Hybrid detector has a planar photocathode generates photoelectrons to be amplified. Planarity makes use of production technology from microchip manufacturing yielding higher quality photocathodes. The first amplification stage is the vacuum acceleration step over a high voltage about 8000V. The acceleration and simple geometry efficiently harvest all photoelectrons for downstream amplification. There is no loss at intermediate dynodes as in PMTs. Amplification is accomplished by electron bombardment in the range of 103times. Afterwards further amplification is achieved by an avalanche element similar to that used in avalanche photodiodes. The overall gain of this device is in the range of 105 times. Along with lower dark noise than typical PMTs this proves basis for efficient recovery of signal. The overall photon detection efficiency, meaning the effectively available information on detection of hybrid is thus higher than that of photomultipliers.
It is essential to get an effective detector for hybrid. The challenge is to integrate hybrid detection into a confocal scan head to provide both physical and optical connectivity. And along with this one has to also complement these basic prerequisites with electronics capable of providing high voltage approximately 8000V while maintaining time resolution of 108Hz range.