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.

Incident photons strike the photocathode material, which is present as a thin deposit on the entry window of the device, with electrons being produced as a consequence of the photoelectric effect.

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.

This was the first compound photocathode material, developed in 1929.

Since Ag-O-Cs has a higher dark current than more modern materials photomultiplier tubes with this photocathode material are nowadays used only in the infrared region with cooling.

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.

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.

It has a typical sensitivity of around 230 µA / lm and a higher quantum efficiency than S20 photocathode material.

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.

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.

The multialkali photocathode has a wide spectral response from the ultraviolet to near infrared region.

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.

Spectral response range similar to the Sb-Cs photocathode, but with higher sensitivity and lower dark current than Sb-Cs.

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

Second generation image intensifiers use the same multialkali photocathode that the first generation tubes used, however by using thicker layers of the same materials, the S25 photocathode was developed, which provides extended red response and reduced blue response, making it more suitable for military applications.

The high sensitivity of this photocathode, greater than 900 µA / lm, allows more effective low light response, though this was offset by the thin film, which typically blocked up to 50 % of electrons.

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.

Firstly, they used a GaAs / CsO / AlGaAs photocathode which is more sensitive in the 800 nm-900 nm range than second generation photocathodes.

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.

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 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.

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.

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.

In a photomultiplier tube, one or more electrons are emitted from a photocathode and accelerated towards a polished metal electrode ( called a dynode ).

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.

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.

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.

This makes the photocathode very efficient at creating photoelectrons from photons.

To protect the photocathode from positive ions and gases produced by the MCP, they introduced a thin film of sintered aluminium oxide attached to the MCP.

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.

In Thin Film image intensifiers, the thickness of the film is reduced from around 30 Angstrom ( standard ) to around 10 Angstrom and the photocathode voltage is lowered.

The Modulation Transfer Function on an image intensifier is a measure of the output amplitude of dark and light lines on the display for a given level of input from lines presented to the photocathode at different resolutions.

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.

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.

The wavelength of maximum emission is at 420 nm, well matched to the photocathode sensitivity of bialkali PMTs.

With special manufacturing techniques this photocathode can operate up to 1700 nm.

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

The photocathode sensitivities S, phosphor efficiencies P, and anode potentials V of the individual stages shall be distinguished by means of subscripts 1, and 2, in the text, where required.

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 ).

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.

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 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.

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

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

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