| Zugriffsnummer | 12992 |
| Dokumenttyp | Dissertation |
| Peer Review | unbekannt |
| Sprache | Deutsch |
| Titel | Messungen der Starkverbreiterung von Wasserstoff mittels Zwei-Photonen-Polarisationsspektroskopie und Dispersionsinterferometrie |
| Autor(in); Institution |
Steiger, Martina; 7.22, Hochtemperaturmetrologie, PTB-Berlin
|
| Quelle/Jahr | (2000), 1 - 101 |
| Dissertationsvermerk | Dissertation, Technische Universität Berlin, 2000 |
| Verlag | Berlin: Techn. Univ. |
| Zusammenfassung | The Stark-broadening of the first excited level of hydrogen was measured by means of Doppler-free two-photon-spectroscopy. The investigations were performed on axis of pure hydrogen arc-plasmas at pressures of 60 mbar to 100 mbar resulting in low electron densities of 1,1.10 ^ 20 m ^- 3 to 31.10 ^ 20 m ^- 3 and kinetic temperatures of the heavy particles of 5000 K to 9400 K. This electron density range, not accessible so far, is of special interest because Stark-broadening becomes comparable with the fine-structure splitting. Previous investigations at higher electron densities already demonstrated, that atomic fine-structure is causing a distinct asymmetry in the central part of the stark-profiles. Also theory predicts in the present electron density range the transition from complex ion-dynamic-broadening to simple ion-impact-broadening. A dispersion-interferometer was set-up and used for the precise measurement of the electron density. The detection limit of the interferometer is ne.l = 2.10 ^ 17 m ^- 2. Electron densities were determined with relative standard errors of 5 % to 7 %. The main contribution to this error was the uncertainty of 5 % of the effective plasma length. In order to excite the 1S-2S transition, a new UV-laser-spectrometer was developed. It consists only of solid state components and delivers the required radiation of the 243 nm in 2.5 ns pulses with 10 mJ and 10 Hz repetition rate. The relative spectral bandwidth of 2 . 10 ^- 7 of this tuneable laser was verified by resolving the 1S-2S hyperfine splitting of unperturbed hydrogen atoms. The stark-profiles were measured by two-photon-polarisation-spectroscopy. With the experimental set up a residual transmission of the crossed polariser analyser pair of 10^- 8 was achieved. Power-broadening was eliminated by measurements at different laser-intensities. Rest-Doppler-broadening and laser-bandwidth, which causes a correction of less than 0.5 %, can be neglected. With decreasing electron density the stark-profiles stay unshifted and the shape of the profiles becomes nearly lorentzian. This allows the comparison of experimental stark-profiles with theoretical predictions simply by the full width of half maximum (FWHM). In general, theories predict considerable lower broadening. The discrepancy increases with lower electron densities and reaches its maximum at electron densities around 5.10 ^ 20 m ^- 3 (30 % or 50%). Then the discrepancy decreases once more with decreasing electron density to about 22 % at ne = 1,1.10^ 20 m ^- 3. Experimentally verified by measurements performed at the same electron density but with different plasma pressures, these discrepancies are not caused by neutral broadening. Summarising, the experiment reveals a much sharper transition to ion-impact-broadening than theories predict and therefore, the new data of this experiments delivers information for further improvement of Stark-theories. |
