Hollow cathode lamp
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A hollow cathode lamp (HCL) is type of lamp used in physics and chemistry as a spectral line source and as a frequency tuner for light sources such as lasers.
An HCL usually consists of a glass tube containing a cathode made of the material of interest, 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. These ions will then be accelerated into the cathode, sputtering off atoms from the cathode. These 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.
An HCL can also be used to tune light sources by making use of the opto-galvanic effect, which is a result of direct or indirect photoionization. By shining the light source into the HCL, one can excite or even eject electrons (directly photoionize) in the atoms inside the lamp, so long as the light source includes frequencies corresponding to the right atomic transitions. Indirect photoionization can then occur when electron collisions with the excited atom eject an atomic electron.
- [A + \gamma \rightarrow A^*]
- [A^* + e \rightarrow A^+ + 2e]
See also
| L i g h t i n g and L a m p s | ||
|---|---|---|
| Incandescent: | Incandescent light bulb>Conventional - Halogen - Parabolic Aluminized Reflector (PAR) |
|
| Fluorescent: | Compact fluorescent lamp>Compact Fluorescent (CFL) - Linear fluorescent - Induction lamp | |
| Gas discharge: | High-intensity discharge lamp>High-Intensity Discharge (HID) - Mercury-vapor - Metal-halide - Neon - Sodium vapor | |
| Electric arc: | Arc lamp - Hydrargyrum medium-arc iodide>HMI - Xenon arc - Yablochkov candle | |
| Combustion: | Carbide lamp>Acetylene/Carbide - Candle - Gas lighting - Kerosene lamp - Limelight - Oil lamp - Safety lamp | |
| Other types: | Sulfur lamp - Light-emitting diode>Light-Emitting Diode (LED) - Optical fiber - Plasma | |
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