Physical Review Letters

Ionization and Energy Pooling in Laser-Excited Na Vapor

Gregory H. Bearman, Jacob J. Leventhal

Published Oct 30, 1978• 63 citations

Abstract

We have observed ion formation (both ${\mathrm{Na}}^{+}$ and ${\mathrm{Na}}_{2}^{+}$) and radiation from high-lying Na states when low-density vapor (\ensuremath{\sim}${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) is irradiated with a cw dye laser tuned to one of the $D$ lines. The ${\mathrm{Na}}^{+}$ ions probably result from photodissociation of ${\mathrm{Na}}_{2}^{+}$ formed by $\mathrm{Na}(3p)\ensuremath{-}\mathrm{Na}(3p)$ associative ionization, while the high-lying radiating states are formed in energy-pooling reactions.

DOI: 10.1103/physrevlett.41.1227

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Energy pooling in Na 3p−Na 3p collisions

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Physical Review AJul 1, 198319 citations

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Physical Review Letters

Ionization and Energy Pooling in Laser-Excited Na Vapor

Gregory H. Bearman, Jacob J. Leventhal

Published Oct 30, 1978• 63 citations

Publisher

Abstract

We have observed ion formation (both

{\mathrm{Na}}^{+}

and

{\mathrm{Na}}_{2}^{+}

) and radiation from high-lying Na states when low-density vapor (\ensuremath{\sim}

{10}^{13}

{\mathrm{cm}}^{\ensuremath{-}3}

) is irradiated with a cw dye laser tuned to one of the

D

lines. The

{\mathrm{Na}}^{+}

ions probably result from photodissociation of

{\mathrm{Na}}_{2}^{+}

formed by

\mathrm{Na}(3p)\ensuremath{-}\mathrm{Na}(3p)

associative ionization, while the high-lying radiating states are formed in energy-pooling reactions.

DOI: 10.1103/physrevlett.41.1227

Related papers

Energy pooling in Na 3p−Na 3p collisions

Vikram S. Kushawaha, Jacob J. Leventhal

The formation of Na ( $\mathrm{nl}$ ) and $\mathrm{Na}_{2}^{}{}_{}{}^{+}$ in sodium vapor (\ensuremath{\sim} ${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) irradiated by a single-frequency (20-MHz bandwidth) cw dye laser tuned to one of the $D$ lines has been studied. The dependence of product signal on laser power density suggests that Na $3p$ -Na $3p$ energy pooling collisions are responsible for these species. Rate constants for specific reaction channels and temperature dependences of rate constants are also reported.The formation of Na ($\mathrm{nl}$) and $\mathrm{Na}_{2}^{}{}_{}{}^{+}$ in sodium vapor (\ensuremath{\sim}${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) irradiated by a single-frequency (20-MHz bandwidth) cw dye laser tuned to one of the $D$ lines has been studied. The dependence of product signal on laser power density suggests that Na $3p$-Na $3p$ energy pooling collisions are responsible for these species. Rate constants for specific reaction channels and temperature dependences of rate constants are also reported.

Physical Review ADec 1, 198045 citations

Ion formation in laser-irradiated sodium vapor

M. Allegrini, W. P. Garver, Vikram S. Kushawaha +1 more

The formation of ${\mathrm{Na}}^{+}$ and ${\mathrm{Na}}_{2}^{+}$ in laser-irradiated sodium vapor has been studied using a nitrogen-laser-pumped dye laser. The effects of irradiation by this pulsed laser are substantially different from those reported previously using a cw device, but otherwise identical experimental conditions. In contrast to the earlier experiments, in which ions were observed only when the cw laser was tuned to a $D$ line, relatively large "background" ion signals are observed at all excitation wavelengths, a result of multiphoton processes involving the ${\mathrm{Na}}_{2}$ component of the vapor. It is shown that the laser bandwidth and pulse duration are extremely important parameters; a wide bandwidth effectively magnifying the importance of the dimer component of the vapor and a short pulse duration minimizing the effects of interactions between excited atoms and molecules.The formation of ${\mathrm{Na}}^{+}$ and ${\mathrm{Na}}_{2}^{+}$ in laser-irradiated sodium vapor has been studied using a nitrogen-laser-pumped dye laser. The effects of irradiation by this pulsed laser are substantially different from those reported previously using a cw device, but otherwise identical experimental conditions. In contrast to the earlier experiments, in which ions were observed only when the cw laser was tuned to a $D$ line, relatively large "background" ion signals are observed at all excitation wavelengths, a result of multiphoton processes involving the ${\mathrm{Na}}_{2}$ component of the vapor. It is shown that the laser bandwidth and pulse duration are extremely important parameters; a wide bandwidth effectively magnifying the importance of the dimer component of the vapor and a short pulse duration minimizing the effects of interactions between excited atoms and molecules.

Physical Review AJul 1, 198319 citations

Associative ionisation of laser excited sodium in an atomic beam

A de Jong, F. van der Valk

Journal of Physics B Atomic and Molecular PhysicsSep 28, 197956 citations

Efficient collisional dissociation of Na{sub 2}{sup +} by laser-excited Na (3p)

Charles Tapalian, W. W. Smith

In studying ionization reactions in a single dense effusive beam of laser-excited Na(3p) atoms, we observe production of both Na{sub 2}{sup +} and Na{sup +} ions. The Na{sup +} results from the familiar associative ionization reaction of two Na(3p) atoms and the Na{sup +} ions under our conditions result mostly from the collisional dissociation of the Na{sub 2}{sup +} by reaction with a third excited Na(3p) atom, rather than from photo- dissociation or photoionization. A CW, single-frequency dye laser tuned to 589 nm resonantly excites the Na(3s) atoms to the 3p state. The atomic beam Na(3s) density is determined from low-intensity 589 absorption measurements. Na{sup +} ion yield depends on the cube of the Na beam density, suggesting successive collisions of three Na(3p) atoms: we believe the Na{sub 2}{sup +} ions polarize the third Na(3p) atom, resulting in a R{sup -4} orbiting collision interaction. A large collisional dissociation cross-section of approximately (4{plus_minus}2)x10{sup -13} cm{sup 2} results, for oven temperatures in the 500-600K range.In studying ionization reactions in a single dense effusive beam of laser-excited Na(3p) atoms, we observe production of both Na{sub 2}{sup +} and Na{sup +} ions. The Na{sup +} results from the familiar associative ionization reaction of two Na(3p) atoms and the Na{sup +} ions under our conditions result mostly from the collisional dissociation of the Na{sub 2}{sup +} by reaction with a third excited Na(3p) atom, rather than from photo- dissociation or photoionization. A CW, single-frequency dye laser tuned to 589 nm resonantly excites the Na(3s) atoms to the 3p state. The atomic beam Na(3s) density is determined from low-intensity 589 absorption measurements. Na{sup +} ion yield depends on the cube of the Na beam density, suggesting successive collisions of three Na(3p) atoms: we believe the Na{sub 2}{sup +} ions polarize the third Na(3p) atom, resulting in a R{sup -4} orbiting collision interaction. A large collisional dissociation cross-section of approximately (4{plus_minus}2)x10{sup -13} cm{sup 2} results, for oven temperatures in the 500-600K range.

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Efficient laser ionization of sodium vapor—A possible explanation based on superelastic collisions and reduced ionization potential

Raymond M. Measures

The recently observed efficient ionization of sodium vapor by a laser tuned to the sodium resonance line can be explained in terms of the large population of resonance-state atoms created by laser-induced radiative equilibrium. This large population of excited atoms represents (a) a reservoir of energy that can rapidly be transferred to the free electrons via superelastic collisions and (b) a source of pseudo-ground- state atoms possessing a much reduced ionization energy. Three-photon ionization is proposed as the mechanism for creation of the primary pool of free electrons.The recently observed efficient ionization of sodium vapor by a laser tuned to the sodium resonance line can be explained in terms of the large population of resonance-state atoms created by laser-induced radiative equilibrium. This large population of excited atoms represents (a) a reservoir of energy that can rapidly be transferred to the free electrons via superelastic collisions and (b) a source of pseudo-ground- state atoms possessing a much reduced ionization energy. Three-photon ionization is proposed as the mechanism for creation of the primary pool of free electrons.

Journal of Applied PhysicsJul 1, 197778 citations

Laser photodissociation of Na2+ions produced by laser resonant and non-resonant ionisation of Na vapour

F. Roussel, B. Carré, P. Breger +1 more

The authors report direct measurements of the photodissociation of Na 2 + ions created when a Na vapour in the density range 10 12 -10 13 cm -3 is irradiated by a pulsed laser with intensities in the 10 5 -10 6 W cm -2 range. The Na 2 + ions, accelerated by a weak electric field, are photodissociated in a second laser beam tuned to 6040 AA. In a preliminary experiment the Na 2 + ions are formed in the lowest vibrational levels and the measured photodissociation cross section is compared with existing calculations. When the Na vapour is irradiated at one of the 3S 1/2 -3P 1/2,3/2 resonances the photodissociation measurements show the existence of a distribution of rovibrational excited levels of the Na 2 + ions. A discussion is given in terms of associative ionisation in collisions of two Na(3p) atoms. The origin of the Na + ions produced simultaneously with the Na 2 + ions, in the vapour irradiated at resonance, is also discussed.The authors report direct measurements of the photodissociation of Na 2 + ions created when a Na vapour in the density range 10 12 -10 13 cm -3 is irradiated by a pulsed laser with intensities in the 10 5 -10 6 W cm -2 range. The Na 2 + ions, accelerated by a weak electric field, are photodissociated in a second laser beam tuned to 6040 AA. In a preliminary experiment the Na 2 + ions are formed in the lowest vibrational levels and the measured photodissociation cross section is compared with existing calculations. When the Na vapour is irradiated at one of the 3S 1/2 -3P 1/2,3/2 resonances the photodissociation measurements show the existence of a distribution of rovibrational excited levels of the Na 2 + ions. A discussion is given in terms of associative ionisation in collisions of two Na(3p) atoms. The origin of the Na + ions produced simultaneously with the Na 2 + ions, in the vapour irradiated at resonance, is also discussed.

Journal of Physics B Atomic and Molecular PhysicsMay 28, 19838 citations

We have observed ion formation (both

{\mathrm{Na}}^{+}

and

{\mathrm{Na}}_{2}^{+}

) and radiation from high-lying Na states when low-density vapor (\ensuremath{\sim}

{10}^{13}

{\mathrm{cm}}^{\ensuremath{-}3}

) is irradiated with a cw dye laser tuned to one of the

D

lines. The

{\mathrm{Na}}^{+}

ions probably result from photodissociation of

{\mathrm{Na}}_{2}^{+}

formed by

\mathrm{Na}(3p)\ensuremath{-}\mathrm{Na}(3p)

associative ionization, while the high-lying radiating states are formed in energy-pooling reactions.

The formation of Na (

\mathrm{nl}

) and

\mathrm{Na}_{2}^{}{}_{}{}^{+}

in sodium vapor (\ensuremath{\sim}

{10}^{13}

${\mathrm{cm}}^{\ensuremath{-}3}$) irradiated by a single-frequency (20-MHz bandwidth) cw dye laser tuned to one of the

D

lines has been studied. The dependence of product signal on laser power density suggests that Na

3p

-Na

3p

energy pooling collisions are responsible for these species. Rate constants for specific reaction channels and temperature dependences of rate constants are also reported.

The formation of

{\mathrm{Na}}^{+}

and

{\mathrm{Na}}_{2}^{+}

in laser-irradiated sodium vapor has been studied using a nitrogen-laser-pumped dye laser. The effects of irradiation by this pulsed laser are substantially different from those reported previously using a cw device, but otherwise identical experimental conditions. In contrast to the earlier experiments, in which ions were observed only when the cw laser was tuned to a

D

line, relatively large "background" ion signals are observed at all excitation wavelengths, a result of multiphoton processes involving the

{\mathrm{Na}}_{2}

component of the vapor. It is shown that the laser bandwidth and pulse duration are extremely important parameters; a wide bandwidth effectively magnifying the importance of the dimer component of the vapor and a short pulse duration minimizing the effects of interactions between excited atoms and molecules.