Hollow-cathode lamp

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The hollow-cathode (HCL) lamp is a type of cold cathode lamp used in physics and chemistry as a source of spectral lines (eg for atomic absorption spectrometers) and as frequency tuners for light sources such as lasers. An HCL takes advantage of the hollow cathode effect, which causes conduction at lower voltages and with more current than cold cathode lamps that do not have hollow cathodes.

HCL usually consists of a glass tube containing a cathode, an anode, and a buffer gas (usually a noble gas). The large voltage across the anode and cathode will cause the ionized buffer gas, creating the plasma. The gas buffer ions will then be accelerated to the cathode, removing the atoms from the cathode. Both the buffer gas and the staggered cathode atom will in turn be attracted by collisions with other atoms/particles in the plasma. As these excited atoms decay into the lower state, they will emit photons, which can then be detected and the spectrum determined. Neither the spectrum of the buffer gas or the stuttered cathode material itself, or both, may be of interest.

HCL can also be used to set the light source to a particular atomic transition by utilizing the optogalvanic effect, which is the result of direct or indirect photoionization. By illuminating the light source into the HCL, one can remove or even remove electrons (directly photoionize) from the atoms in the lamp, provided that the light source includes frequencies corresponding to the transition of the right atom. Indirect photoionisation can occur when the collision of electrons with excited atoms emits atomic electrons.

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The newly created ion causes an increase in current across the cathode/anode and produces a voltage change, which can then be measured.

To set the light source to a specific transition frequency, the tuning parameters (often the driving current) of the light source vary. By searching for resonance in the data plot of the voltage signal versus the source adjustment parameter, the light source can be set to the desired frequency. This is often aided by using a lock-in circuit.

Video Hollow-cathode lamp

See also

• List of light sources
• Electrodynamic Tether # Hollow Cathode

Maps Hollow-cathode lamp

References

Source of the article : Wikipedia