A GaN-based blue diode laser is employed for laser absorption spectroscopy in an aluminum hollow cathode glow discharge plasma. A Littrow grating stabilized external resonator is used for tuning the wavelength of laser emission. Scanning the wavelength of the laser probes the absorption profile of aluminum transitions yielding ground state aluminum densities. Hyperfine structure has to be taken into account in order to obtain correct temperatures. The diode laser is used to investigate both the temperature and the density of aluminum atoms sputtered from a cathode surface by ion bombardment from the cathode fall region. The blue diode laser allows quick and easy access to aluminum ground state atoms at low costs.

With an inlproved~~IAIER-LEIBSITZ collision chambar absolute values of the totalexcitation cross sections of the rare gases were msJsured. The half width of energy distribution in the beam of exciting electrons was approximately 0.7 eV. The results for He and Xe are in reasonable agreement with the excitation functions givzn by MAIER-LEIBSITZ, if some necessary corrections (especidly with regard to contact potentials) are made. Only the cross sections obtained by us are a little smaller. Furthermore the better fine structure yielded more favourable possibilitiss of comparison with other measurements pilblished so far. The error should not be greater than 30:;. *) Jetzt Institut fiir 1Cletallph\-sik und Reinstmetalle der DAW zu Berlin in Dresden, WinterberpstraBe.

Stepwise excitation cross sections of the rare gases helium, neon and argon were obtained by B n indirect method resting on the combination of experimentally determined excited species number densities of the rnre gns atoms in the positive column of a low pressure glow dischargt, with the results of the theory of the positive column and eleetron kineties. Furthermore a serniempirical expression of the excitation functions basing on the analysis of the Born-approximation and modifications as well as a formula of VAINSTEIY is offered.

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Radiative efficiency of resonance line emission of a dc glow discharge plasma is derived from experimentally determined profiles of atoms in resonant states. Spatial density profiles were determined by diode laser atomic absorption spectroscopy and laser induced fluorescence. Absorption measurements were used for absolute calibration. The influence of the shape of spatial density profiles was considered. Investigations show that power dissipation by resonance radiation transport remains nearly constant for the currents investigated (i = 1 ... 20 mA). Total power loss due to resonance radiation was found to be about 25% of electrical power input.