Optical frequency standards based on such technology with a high degree of sophistication are used for optical clocks, for example. Wavelength standards with far higher optical power and very much lower optical linewidth can be made based on wavelength-stabilized lasers.ĭue to the high spatial coherence, their radiance and of course also the spectral radiance are also higher by many orders of magnitudes. It may also be helpful to reach a somewhat higher lamp temperature that way. That can help by giving additional protection of the user against electric shocks, also protection for the lamp against short-circuits and touching.
That implies that the electrodes are relatively close together, and that the operation voltage is lower than for long-arc lamps.įrequently, the actual lamp envelope is integrated into another glass envelope, often of approximately cylindrical shape. The emitting volume in the lamp is often kept relatively small, because for many applications one can anyway only utilize light coming from a relatively small region. Operation currents are usually in the lower milliampere region, while high-power arc lamps are often operated with several amperes. However, they do not work with an arc discharge, but rather with a low temperature glow discharge. In principle, one can call such lamps arc lamps in the sense that they are used for continuous-wave operation. With that, one typically obtains light emission on several spectral lines. Spectral lamps are basically always gas discharge lamps with a low gas pressure, so that pressure broadening (spectral broadening based on frequent collisions during the emission of atoms or ions) is largely avoided. Table 1: Table of spectral lines which are frequently used in optics and can all be generated with spectral lamps. These are only some particularly common lines lamps are available for many others. The table below shows a list of wavelengths of standard spectral lines and indicates what kind of spectral lamps are used to generate them. That results in some degree of temporal coherence (but with a coherence length often well below 1 cm), while the spatial coherence is generally quite low.įor some applications, one isolates a specific line with an optical bandpass filter, usually with a monochromator or some type of interference filter. The radiation of each line can be considered as quasi- monochromatic, usually with a wavelength which is defined with a precision a tiny fraction of 1 nm.
In some cases, such species are mixed either in order to obtain more spectral lines or to improve performance via energy transfer processes. The light emission is nearly always from single atoms or ions, not from molecules. Typical emitting species are noble gases like helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe) as well as metal vapors like sodium (Na), cesium (Cs), mercury (Hg) and cadmium (Cd). The generated optical lines can be in the visible, infrared or ultraviolet spectral region. Such lamps are called spectral lamps or based on their application as calibration lamps. There are gas discharge lamps which emit light on certain standard spectral lines as required mostly for spectral calibration purposes.
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How to cite the article suggest additional literature Using our ad package, you can display your logo and further below your product description.ĭefinition: low pressure gas discharge lamps emitting light on one or more standard spectral lines
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