Vacuum Spectroscopy

the spectroscopy of the shortwave ultraviolet region and of soft X rays (wavelength from 200 to 0.4-0.6 nm [nanometers] or 2,000 to 4-6 Å [angstroms]).

The radiation in this range of wavelengths is highly absorbed in air; therefore, in vacuum spectroscopy the spectral instrument, receptor, and radiation source are installed in a hermetic chamber from which air is evacuated down to pressures of 10^-4-10^-5 mm of mercury (10^-2-10^-3 N/m²). The chamber is often filled with inert gases (for example, helium) that do not absorb radiation. The radiation source in vacuum spectroscopy is most often a high-voltage (or “hot”) spark operating at a voltage of 50 kV and a spark gap of about 1 mm. The unit that produces the spark is installed in a single chamber with the spectral instrument.

The instruments and methods that are used in vacuum spectroscopy have specific features because of the non-transparency of optical materials that are usually used for the shortwave region. For wavelengths less than 110 nm (1,100 Å), spectrographs with concave glass diffraction gratings or curved crystals (for example, mica) that act as diffraction gratings are used instead of instruments with ordinary prisms and lenses.

The investigation of the emission and absorption spectra in the ultraviolet region has great value for the study of the structure of the inner electron shells of the atom and the systematization of atomic and electronic molecular spectra and the interpretation of the spectra of stars and nebulas. Vacuum spectroscopy is particularly important in the physics of high-temperature plasma.