H atom plasma diagnostics: A sensitive probe of temperature and purity

Dunlop, James R.; Tserepi, Angeliki; Preppernau, Bryan L.; Cerny, Timothy M.; Miller, Terry A.

doi:10.1007/bf01447946

Cited by 29 publications

(25 citation statements)

References 20 publications

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“…When photodissociation by the UV laser occurs, a higher order dependence should be observed, since one extra photon is needed to first generate the atom to be detected. 16 We therefore conclude that in this plasma there is no contribution to the H LIF signal from photodissociation by the UV laser. Figure 5 gives the atomic hydrogen density in the expanding Ar-H plasma as a function of the distance z from the nozzle, i.e., along the symmetry axis of the plasma jet (rϭ0).…”

Section: Density Measurementsmentioning

confidence: 57%

“…This is commonly recognized and described in a number of papers. 16,21,23 The effect can even be turned into an advantage by using it to identify an impurity and measure its density via a careful analysis of the line profile in the excitation spectrum 16,21 ͑see also Sec. V͒.…”

Section: Density Measurementsmentioning

confidence: 99%

“…Observations of high atomic hydrogen temperatures in rf, microwave, and dc discharges have been associated with photolysis of NH 3 , H 2 S, C 2 H 2 , C 2 H 4 , and Si 2 H 6 . 16,21,23 In fact, ''the photolytically produced atoms bear a spectral profile signature characteristic of their precursor molecule,'' and the Doppler width can be used to determine the excess translational energy enabling an identification of the precursor molecule. 16 As already pointed out in Sec.…”

Section: Temperature Measurementsmentioning

confidence: 99%

“…16,21,23 In fact, ''the photolytically produced atoms bear a spectral profile signature characteristic of their precursor molecule,'' and the Doppler width can be used to determine the excess translational energy enabling an identification of the precursor molecule. 16 As already pointed out in Sec. IV, the contribution of photolytically produced atoms to the H LIF signal from the expanding Ar-H plasma is negligible.…”

Section: Temperature Measurementsmentioning

confidence: 99%

“…For light atoms in reactive environments ͑like H in plasmas͒ this is often the case, thus enabling a reasonably accurate determination of the kinetic temperature of these atoms. 16 Besides determining the velocity spread, and from that the temperature, of the particles from the Doppler width, the Doppler shift of the center frequency of the laser-induced transition can be used to determine the average velocity of these particles. The Doppler shift can be determined either in an absolute way, i.e., on an absolute frequency scale, in which case the laser frequency needs to be calibrated, or in a relative way by comparing the signal of the moving particles to that of a nonmoving reference.…”

Section: Introductionmentioning

confidence: 99%

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Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

Boogaarts

Mazouffre

Brinkman

et al. 2002

Review of Scientific Instruments

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We report on quantitative, spatially resolved density, temperature, and velocity measurements on ground-state atomic hydrogen in an expanding thermal Ar-H plasma using two-photon excitation laser-induced fluorescence ͑LIF͒. The method's diagnostic value for application in this plasma is assessed by identifying and evaluating the possibly disturbing factors on the interpretation of the LIF signal in terms of density, temperature, and velocity. In order to obtain quantitative density numbers, the LIF setup is calibrated for H measurements using two different methods. A commonly applied calibration method, in which the LIF signal from a, by titration, known amount of H generated by a flow-tube reactor is used as a reference, is compared to a rather new calibration method, in which the H density in the plasma jet is derived from a measurement of the two-photon LIF signal generated from krypton at a well-known pressure, using a known Kr to H detection sensitivity ratio. The two methods yield nearly the same result, which validates the new H density calibration. Gauging the new ''rare gas method'' by the ''flow-tube reactor method,'' we find a krypton to hydrogen two-photon excitation cross section ratio Kr ͑2͒ / H (2) of 0.56, close to the reported value of 0.62. Since the H density calibration via two-photon LIF of krypton is experimentally far more easy than the one using a flow-tube reactor, it is foreseen that the ''rare gas method'' will become the method of choice in two-photon LIF experiments. The current two-photon LIF detection limit for H in the Ar-H plasma jet is 10 15 m Ϫ3 . The accuracy of the density measurements depends on the accuracy of the calibration, which is currently limited to 33%. The reproducibility depends on the signal-to-noise ͑S/N͒ ratio in the LIF measurements and is orders of magnitude better. The accuracy in the temperature determination also depends on the S/N ratio of the LIF signal and on the ratio between the Doppler-width of the transition and the linewidth of the excitation laser. Due to the small H mass, the current linewidth of the UV laser radiation is never the accuracy limiting factor in the H temperature determination, even not at room temperature. Quantitative velocity numbers are obtained by measuring the Doppler shift in the H two-photon excitation spectrum. Both the radial and axial velocity components are obtained by applying a perpendicular and an antiparallel excitation configuration, respectively. The required laser frequency calibration is accomplished by simultaneously recording the I 2 absorption spectrum with the fundamental frequency component of the laser system. This method, which is well-established in spectroscopic applications, enables us to achieve a relative accuracy in the transition frequency measurement below 10 Ϫ6 , corresponding to an accuracy in the velocity of approximately 200 m/s. This accuracy is nearly laser linewidth limited.

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Section: Density Measurementsmentioning

confidence: 57%