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.
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 . By tweeking your light source, you can then tune it to a specific transition frequency by looking for a resonance on the data plot of your signal vs. source tweaking parameter.
[edit] See also
| Lighting and Lamps
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|---|---|---|
| Incandescent: | Conventional - Halogen - Parabolic aluminized reflector (PAR) |  |
| Fluorescent: | Compact fluorescent (CFL) - Linear fluorescent - Induction lamp | |
| Gas discharge: | High-intensity discharge (HID) - Mercury-vapor - Metal-halide - Neon - Sodium vapor | |
| Electric arc: | Arc lamp - HMI - Xenon arc - Yablochkov candle | |
| Combustion: | Acetylene/Carbide - Candle - Gas lighting - Kerosene lamp - Limelight - Oil lamp - Safety lamp | |
| Other types: | Sulfur lamp - Light-emitting diode (LED) - Fiber optics - Plasma | |
