The luminous gain of a single stage with Af ( flux gain ) is, to a first approximation, given by the product of the photocathode sensitivity S ( amp / lumen ), the anode potential V ( volts ), and the phosphor conversion efficiency P ( lumen/watt ).

The second photocathode and both phosphor surfaces are deposited on the fiber plate substrates.

It is obvious that the careful choice of photocathode which maximizes Af for a given input E ( in the case of the second stage, for the first phosphor screen emission ) is very important.

Instead, a caesium iodide phosphor is deposited directly on the photocathode of the intensifier tube.

Also in 1936, a much improved photocathode, Cs < sub > 3 </ sub > Sb ( caesium-antimony ), was reported by P. Görlich.

Both the photocathode and the image plane of such an electrode configuration are curved concave as seen from the anode aperture.

Photomultipliers are constructed from a glass envelope with a high vacuum inside, which houses a photocathode, several dynodes, and an anode.

Finally, the electrons reach the anode, where the accumulation of charge results in a sharp current pulse indicating the arrival of a photon at the photocathode.

An image dissector is a camera tube that creates an " electron image " of a scene from photocathode emissions ( electrons ) which pass through a scanning aperture to an anode, which serves as an electron detector.

It consists of a photocathode, a microchannel plate, and an anode array.

Phototubes operate according to the photoelectric effect: Incoming photons strike a photocathode, generating electrons, which are attracted to an anode.

No suitable photoemissive surfaces have yet been reported to detect wavelengths longer than approximately 1700 nanometers, which can be approached by a special ( InP / InGaAs ( Cs )) photocathode.

The windows of the photomultipliers act as wavelength filters ; this may be irrelevant if the cutoff wavelengths are outside of the application range or outside of the photocathode sensitivity range, but special care has to be taken for uncommon wavelengths.

The long wavelength response can be extended to 930 nm by a special photocathode activation processing.

The entire electron image is deflected and a scanning aperture permits only those electrons emanating from a very small area of the photocathode to be captured by the detector at any given time.

Of note, the S1 photocathode had sensitivity peaks in both the infrared and ultraviolet spectrum and with sensitivity over 950 nm was the only photocathode material that could be used to view infrared light above 950 nm.

It was not until the development of the bialkali antimonide photocathodes ( potassium-cesium-antimony and sodium-potassium-antimony ) discovered by A. H. Sommer and his later multialkali photocathode ( sodium-potassium-antimony-cesium ) S20 photocathode discovered in 1956 by accident, that the tubes had both suitable infra-red sensitivity and visible spectrum amplification to be useful militarily.

To overcome the ion-poisoning problems, they improved scrubbing techniques during manufacture of the MCP ( the primary source of positive ions in a wafer tube ) and implemented autogating, discovering that a sufficient period of autogating would cause positive ions to be ejected from the photocathode before they could cause photocathode poisoning.

During the 1960s, in the PEEM, as well as TEM, the specimens were grounded and could be transferred in the UHV environment to several positions for photocathode formation, processing and observation.

The electron source for the ILC will use 2-nanosecond laser light pulses to eject electrons from a photocathode, a technique allowing for up to 80 % of the electrons to be polarized ; the electrons then will be accelerated to 5 GeV in a 250-meter linac stage.

The luminous efficiency Af of a photocathode depends on the maximum radiant sensitivity Af and on the spectral distribution of the incident light Af by the relation: Af where Af is normalized radiant photocathode sensitivity.

The photocathode contains combinations of materials such as caesium, rubidium and antimony specially selected to provide a low work function, so when illuminated even by very low levels of light, the photocathode readily releases electrons.

This is known as the electron affinity of the photocathode and is another barrier to photoemission other than the forbidden band, explained by the band gap model.

" The Soviet device used a magnetic field to confine the secondary electrons and relied on the Ag-O-Cs photocathode which had been demonstrated by General Electric in the 1920s.

The caesium-antimony photocathode had a dramatically improved quantum efficiency of 12 % at 400 nm, and was used in the first commercially successful photomultipliers manufactured by RCA ( i. e., the 931-type ) both as a photocathode and as a secondary-emitting material for the dynodes.

Besides the different photocathode materials, performance is also affected by the transmission of the window material that the light passes through, and by the arrangement of the dynodes.

Electrons are generated by a cold cathode, a hot cathode, a photocathode, or radio frequency ( RF ) ion sources.

Such an arrangement is able to amplify the tiny current emitted by the photocathode, typically by a factor of one million.

* by emission mechanism ( thermionic, photocathode, cold emission, plasmas source ),

The image dissector has no " charge storage " characteristic ; the vast majority of electrons emitted by the photocathode are excluded by the scanning aperture, and thus wasted rather than being stored on a photo-sensitive target, as in the iconoscope or image orthicon ( see below ), which largely accounts for its low light sensitivity.

On average, each image electron ejects several " splash " electrons ( thus adding amplification by secondary emission ), and these excess electrons are soaked up by the positive mesh effectively removing electrons from the target and causing a positive charge on it in relation to the incident light in the photocathode.

Using a simple lens, an image was focused on the photocathode and a potential difference of several thousand volts was maintained across the tube, causing electrons dislodged from the photocathode by photons to strike the fluorescent screen.

These devices used an S1 photocathode or " silver-oxygen-caesium " photocathode, discovered in 1930 which had a sensitivity of around 60 µA / lm ( Microampere per Lumen ) and a quantum efficiency of around 1 % in the ultraviolet region and around 0. 5 % in the infrared region.

A photographic comparison between a first generation cascade tube and a second generation wafer tube, both using electrostatic inversion, a 25mm photocathode of the same material and the same F2. 2 55mm lens.

There are two common photomultiplier orientations, the head-on or end-on ( transmission mode ) design, as shown above, where light enters the flat, circular top of the tube and passes the photocathode, and the side-on design ( reflection mode ), where light enters at a particular spot on the side of the tube, and impacts on an opaque photocathode.

In a photomultiplier tube, every photon striking the photocathode initiates an avalanche of electrons that produces a detectable current pulse.

These are extremely light-sensitive vacuum tubes with a photocathode coated onto part ( an end or side ) of the inside of the envelope.

The device consisted of a semi-cylindrical photocathode, a secondary emitter mounted on the axis, and a collector grid surrounding the secondary emitter.

The RCA prototype photomultipliers also used a Ag-O-Cs ( silver oxide-caesium ) photocathode.

Various combinations of photocathode and window materials were assigned " S-numbers " ( spectral numbers ) ranging from S-1 through S-40, which are still in use today.

For example, S-11 uses the caesium-antimony photocathode with a lime glass window, S-13 uses the same photocathode with a fused silica window, and S-25 uses a so-called " multialkali " photocathode ( Na-K-Sb-Cs, or sodium-potassium-antimony-caesium ) that provides extended response in the red portion of the visible light spectrum.