Hollow-cathode lamp

A hollow-cathode lamp (HCL) is type of cold cathode lamp used in physics and chemistry as a spectral line source (e.g. for atomic absorption spectrometers) and as a frequency tuner for light sources such as lasers.

A large voltage across the anode and cathode will cause the buffer gas to ionize, creating a plasma.

Both the buffer gas and the sputtered cathode atoms will in turn be excited by collisions with other atoms/particles in the plasma.

[2] An HCL can also be used to tune light sources to a specific atomic transition by making use of the optogalvanic effect, which is a result of direct or indirect photoionization.

= electron The newly created ions cause an increase in the current across the cathode/anode and a resulting change in the voltage, which can then be measured.