Nonlinear optical processes in atoms and molecules using rare-gas halide lasers

Bischel, William K.; Bokor, Jeffrey; Kligler, Daniel J.; Rhodes, C. K.

doi:10.1109/jqe.1979.1070000

Cited by 87 publications

(2 citation statements)

References 65 publications

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“…In this case, one only needs to consider the processes caused by the laser pulse, such as the two-photon excitation and laser ionization. The rate equation of the density at n = 3 (N 3 ) state can be written as [18]…”

Section: Detectionmentioning

confidence: 99%

Absolute density distribution of H atoms in a large-scale microwave plasma reactor

Duan¹,

Lange²,

Meyer‐Plath³

2003

Plasma Sources Sci. Technol.

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Absolute number densities and the spatial distribution of atomic hydrogen in a large-scale microwave plasma reactor were measured by means of two-photon absorption laser-induced fluorescence (LIF) with laser radiation at 205 nm. The microwave discharge was operated at 2.45 GHz with a maximum power of 2 kW. Absolute number densities were obtained by calibrating the LIF detection system via NO 2 titration in a flow tube reactor and in the range from 0.5 × 10 15 to 2.5 × 10 15 cm −3 . Compared to small-scale reactors with a volume-to-surface ratio less than 3 cm, this reactor has a relatively homogeneous spatial distribution of atomic hydrogen. The mole fraction of atomic hydrogen in hydrogen plasmas ranges from 10% to 20%. The gas temperature-volume effect plays an important role in the spatial distribution of atomic hydrogen in this reactor.

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Section: Detectionmentioning

confidence: 99%

Absolute density distribution of H atoms in a large-scale microwave plasma reactor

Duan¹,

Lange²,

Meyer‐Plath³

2003

Plasma Sources Sci. Technol.

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“…The apparent I 1 dependence we observe for the (2+l)-photon process is due to the efficient photon absorption for the E ,F state. A rate equation analysis [9] shows that this should be the case if n > a*I, where r L is the laser pulse duration (-10 ~8 s) and cr* is the absorption cross section of the E ,F state (also see [22]). The number density of molecules excited to the E,F state, in turn, increases linearly with the laser intensity.…”

mentioning

confidence: 99%

H−formation in laser-excited molecular hydrogen

Pinnaduwage

Christophorou

1993

Phys. Rev. Lett.

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Experimental evidence is reported for the efficient H " formation in UV laser irradiated H2.PACS numbers: 34.80. Qb, 34.50.Rk, Only the lowest vibrational level (v=0) of the ground electronic state X 'z/ of H2 is populated at room temperature ( -300 K); for slow electrons, the electron attachment cross section for this state has a peak value of ~1.6xl0~2 1 cm 2 (rate constant -10~1 4 cm 3 s _1 ) at 3.75 eV electron energy [1]. However, the electron attachment cross section was shown to increase rapidly with increasing vibrational energy, and an enhancement of more than 4 orders of magnitude was observed for the v = 4 level [2,3]. Recent extended calculations [4,5] show that the maximum electron attachment rate constant approaches 10~8 cm 3 s _1 around v = 8. As for electron attachment to electronically excited states of H2, the only available study is a calculation [6] for the metastable c 3 n w state which predicts about 3 orders of magnitude enhancement for this state compared to the ground state A^Z+Cv-O).In this Letter, we report efficient H ~ formation in laser-irradiated H2. Free electrons produced via laser photoionization convert to H~ ions via attachment to electron attaching species produced by the same laser pulse; however, the identity of these electron attaching species remains unclear and we will discuss several possibilities.Besides its basic significance, the present observations could be significant for the development of a negative ion source for the generation of neutral beams for magnetic fusion research and other applications [7]. It is possible that the present scheme is more efficient compared to a low-pressure H2 discharge [8] as a H ~ source.The technique and the experimental apparatus have been described earlier [9,10]. Briefly, the gas under study (in the present case a few Torr of H2) is irradiated with a UV laser pulse; the attaching electrons are produced via (multiphoton) ionization, some of which are converted to negative ions. The negative ions and the unattached electrons are separated from positive ions resulting from photoionization using a three-electrode configuration [9]: The laser pulse propagates between two of the electrodes and the negative or positive charges produced in the interaction region are extracted to the adjoining detection region through a grid in the middle electrode by applying appropriately oriented electric fields in the two regions. In the "negative mode," the signal components due to the unattached electrons and the negative ions can be distinguished since they travel to the detection region with different (drift) velocities; a "break" in the signal wave form could easily be seen (see Fig. 5 of [10]) when the total pressure in the chamber exceeds -0.1 kPa.In the present experiments, transitions to energies above the ionization threshold of H2 were accomplished via three different schemes that have been employed in traditional resonance enhanced multiphoton ionization (REMPI) studies [a (m + n) REMPI process indicates the population of a resonant state w...

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Appendix C: Two‐Photon Absorption Cross Sections for Some Atoms and Molecules in the Ground State

Очкин

2009

Spectroscopy of Low Temperature Plasma

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Nonlinear optical processes in atoms and molecules using rare-gas halide lasers

Cited by 87 publications

References 65 publications

Absolute density distribution of H atoms in a large-scale microwave plasma reactor

Absolute density distribution of H atoms in a large-scale microwave plasma reactor

H−formation in laser-excited molecular hydrogen

Appendix C: Two‐Photon Absorption Cross Sections for Some Atoms and Molecules in the Ground State

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