What does the photocathode do?

A photocathode is a negatively charged electrode in a light detection device such as the input screen in an image intensifier (II) that is coated with a photosensitive compound. When this is struck by light photons, the absorbed energy causes electron emission due to the photoelectric (PE) effect.

Is photocathode positive or negative?

Photocathodes are also commonly used as the negatively charged electrode in a light detection device such as a photomultiplier or phototube.

What is the photocathode composed of?

Photocathodes are typically made of alkali-metal films such as potassium bromide (KBr), cesium telluride (CsTe), cesium iodide (CsI), or rubidium telluride (RbTe).

What is radiant sensitivity?

Radiant sensitivity is the photoelectric current from the photocathode, divided by the incident radiant power at a given wavelength, expressed in A/W (amperes per watt). Quantum efficiency (QE) is the number of photoelectrons emitted from the photocathode divided by the number of incident photons.

What is a PMT detector?

PMT is the technology state of the art at present. The photomultiplier is an extremely sensitive light detector providing a current output proportional to light intensity. Photomultipliers are used to measure any process which directly or indirectly emits light.

How does a PMT work?

A photomultiplier tube, useful for light detection of very weak signals, is a photoemissive device in which the absorption of a photon results in the emission of an electron. These detectors work by amplifying the electrons generated by a photocathode exposed to a photon flux.

What is metal work function?

The work function (WF) of a metal can be defined as the minimum energy required to extract one electron from a metal. Obviously the WF is one of the fundamental electronic properties of bare and coated metallic surfaces.

What is the difference between photomultiplier and photodiode?

➨Photodiode convert one photon into one electron, while photomultiplier amplify electrons. Photomultiplier tube uses detector which changes photons into electrons so that they can be detected. Later photomultiplier tube uses dynodes to amplify the electrons.

What does the input phosphor do?

The input phosphor absorbs the x-ray photons and converts them into optical photons (a phenomenon called luminescence). These optical photons are converted to photoelectrons at the photocathode.

What is the meaning of sensitivity of photo diode?

Definition: The sensitivity of a photodiode is the ratio of amount of current flow with unit light irradiance. The dark current can be minimized in order to enhance the sensitivity of the photodiode.

What is quantum efficiency of photodetector?

In a photodiode (or some other photodetector), the quantum efficiency can be defined as the fraction of incident (or alternatively, of absorbed) photons which contribute to the external photocurrent.

Why is a PMT needed as a detector?

Therefore, from the preceding account, we can state that the PMT has a twofold purpose: (1) to convert any given scintillation of visible light emitted from the scintillation detector into a current pulse of secondary electrons and (2) to amplify the current pulse to a magnitude that can be handled by the counting and …

Which is the most sensitive photocathode in the world?

Multialkali (Na–K–Sb–Cs): wide spectral response from the ultraviolet to the near-infrared region. With special cathode processing, it can be extended to 930 nm. 8. Solar-blind (Cs–Te, Cs–I): highly sensitive to vacuum-UV and ultraviolet. However, it is insensitive to visible light and infrared.

How are photons detected in a photocathode device?

They detect light and multiply the current produced by the incident light by as much as 100 million times (160 dB), enabling individual photons to be detected when the incident flux of light is very low. Incident photons strike a photocathode material that is present as a thin deposit on the entry window of the device.

How is the efficiency of a photocathode expressed?

The effectiveness of a photocathode is commonly expressed as quantum efficiency, that being the ratio of emitted electrons vs. impinging quanta (of light). The efficiency varies with construction as well, as it can be improved with a stronger electric field.

Why does a photocathode have a dark current?

Photocathodes can exhibit some amount of dark current, which results from thermionic emission: electrons can receive sufficient energy from formal processes, so that they can leave the material without any incident light.