Hollow-cathode lamp

A hollow-cathode lamp (HCL) is type of 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.

An HCL usually consists of a glass tube containing a cathode, an anode, and a buffer gas (usually a noble gas). A large voltage across the anode and cathode will cause the buffer gas to ionize, creating a plasma. The buffer gas ions will then be accelerated into the cathode, sputtering off atoms from the cathode. Both the buffer gas and the sputtered cathode atoms will in turn be excited by collisions with other atoms/particles in the plasma. As these excited atoms decay to lower states, they will emit photons, which can then be detected and a spectrum can be determined. Either the spectrum from the buffer gas or the sputtered cathode material itself, or both, may be of interest. [1]