Plasma Dynamics in Capillary Discharge Soft X-Ray Lasers

Ben-Kish, A.; Shuker, Moshe; Nemirovsky, Ron A.; Fisher, A.; Ron, A.; Schwob, J. L.

doi:10.1103/physrevlett.87.015002

Cited by 80 publications

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“…The best reconstruction was achieved by displacing a 2cm long segment in the middle of the plasma column by 150µm from the axis. This instability obviously diminishes the amplification as the gain region diameter is of the order of 100µm [3]. Note that the magnitude of the instability has a large shot to shot variation and some shots display relatively stable collapse even with 5A pre-pulse current.…”

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“…The homogenous emission was achieved 6µs after the onset of the pre-pulse current. In order to further investigate the effect of the pre-pulse current on the stability of the plasma column collapse, an off-axis pinhole camera was used [3]. This camera consists of an array of four pinholes placed in front of the capillary, with each of the holes located slightly off the capillary axis.…”

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“…The two measurements discussed above indicated that minimal pre-pulse current must be used in order to insure instabilities free collapse of the plasma column. Indeed, appropriate pre-pulse conditions resulted in strong lasing at the 3S → 3P transition of the Ne-like Ar ion [3]. A Carbon X-ray diode was placed in front of the capillary to measure the temporal history of XUV radiation during the main current pulse.…”

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The effects of the prepulse on capillary discharge extreme ultraviolet laser

et al. 2006

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In the past few years collisionally pumped extreme ultraviolet (XUV) lasers utilizing a capillary discharge were demonstrated. An intense current pulse is applied to a gas filled capillary, inducing magnetic collapse (Z-pinch) and formation of a highly ionized plasma column. Usually, a small current pulse (pre-pulse) is applied to the gas in order to pre-ionize it prior to the onset of the main current pulse. In this paper we investigate the effects of the pre-pulse on a capillary discharge Ne-like Ar XUV laser (46.9nm). The importance of the pre-pulse in achieving suitable initial conditions of the gas column and preventing instabilities during the collapse is demonstrated. Furthermore, measurements of the amplified spontaneous emission (ASE) properties (intensity, duration) in different pre-pulse currents revealed unexpected sensitivity. Increasing the pre-pulse current by a factor of two caused the ASE intensity to decrease by an order of magnitude -and to nearly disappear. This effect is accompanied by a slight increase in the lasing duration. We attribute this effect to axial flow in the gas during the pre-pulse.PACS numbers: 42.55. Vc,42.60.Lh In the last decades the possibility of achieving Amplified Spontaneous Emission (ASE) in the soft X-ray and XUV regimes was extensively explored [1]. One of the realizations utilizes a homogenous column of highly ionized plasma created by a fast capillary discharge [2]. Specifically, a fast (∼ 50ns) and intense (∼ 50kA) current pulse is applied to a capillary filled with low pressure (∼ 1T orr) argon gas. The current induces magnetic forces that attract the gas towards the capillary axis. During the selfcollision of the gas on the axis a column of highly ionized Ar plasma is formed (this technique to create high temperature plasmas is called Z-Pinch). Careful design of the experimental parameters results in high abundance of Ne-like Ar ions in the plasma, and population inversion between the 3P and 3S electronic configurations. The population inversion is due to excitations by collisions with hot electrons in the plasma and spontaneous emission -i.e. the collisional excitation scheme [1]. Strong amplification was observed in the 3P → 3S transition at 46.9nm [2]- [5]. The timing of the amplification (that lasts about 1ns) is close to the pinch time (i.e. the collision of shock waves on the capillary axis). Obviously, for efficient amplification the plasma column must be relatively stable and homogenous (at least up to the amplification time). Several effects might cause instabilities or inhomogeneity in the Z-pinch process (see Ref.[6] and references therein). One of the possible reasons for inhomogeneity is the initial electrical breakdown through the gas column. At the onset of the main current pulse, high voltage across the capillary (hundreds of kV), may result in channel-like breakdown along the capillary walls (channel sparks) [7]. A technique to overcome this inhomogeneity is to pre-ionize the gas by a slow, low intensity current pulse ("pre-pulse"). In Refs...

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The effects of the prepulse on capillary discharge extreme ultraviolet laser

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“…Les calculs prédisent une densité électronique de l'ordre de quelques 1017 cum-3 au centre du plasma ; en outre cette valeur correspond au maximum dans tout le plasma, c'est-à-dire que la densité électronique présente un profil radial convexe. D'après [3] et [9], ces conditions ne sont pas favorables à une amplification de la raie d'Ar à 46, 9 nm : en effet, la densité d'électrons est d'un ordre de grandeur trop faible pour favoriser le schéma de pompage envisagé [9], et d'autre part un profil convexe de densité entraîne des effets de réfraction néfastes à l'amplification sans cavité [3]. Des mesures de spectroscopie ont montré par ailleurs qu'aucune raie d'Ar n'est émise durant la décharge, ce qui tend à confirmer ces résultats.…”

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“…L'objet de ce système est d'obtenir une émission cohérente de la raie à 46, 9 nm émise par l'ion Au8+ selon un schéma de pompage par excitation [l], en utilisant un procédé différent des dispositifs par décharge capillaire utilisés jusqu'à présent [2][3][4][5]. Ce système est compact et fonctionne avec une faible énergie injectée (10-30J) ; la forme des électrodes du capillaire a en outre été modifiée par rapport à une précédente configuration [6], afin de favoriser l'effet de cathode creuse [7] qui assure l'initiation du plasma.…”

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Étude théorique et expérimentale d'une source EUV par décharge capillaire

et al. 2003

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Role of the wall ablation in the operation of a 46.9 nmAr capillary discharge soft x‐ray laser

Ritucci¹,

Tomassetti

Reale

et al. 2003

Contrib. Plasma Phys.

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A capillary discharge pumped soft x-ray laser operating at 46.9 nm on the 3p−3s transition of the Ne-like Ar has been realized by pumping the active medium with a relatively slow current pulse (dI/dt ≈ 6·10 11 A/s). In order to study the role of the ablation in the production of the laser effect, the intensity of the amplified 46.9 nm line has been investigated using the same pumping current pulses in the plastic (polyacetal) and ceramic (Al2O3). We showed that the ablation of the capillary walls is unfavorable both for the compression and stability of the plasma and consequently for the soft x-ray laser production. The amplification and lasing effects are observed only in the ceramic channel. The measurements of the line intensity at 46.9 nm showed the lasing with a gain-length product of ≈ 9, a laser pulse energy of ≈ 5 µJ, a pulse duration of 1.3 ns and a beam divergence of ≈ 3.5 mrad. In addition, effect of the scaling of the time of lasing with the initial plasma diameter was demonstrated experimentally and compared with a one-dimensional MHD model.

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Plasma Dynamics in Capillary Discharge Soft X-Ray Lasers

Cited by 80 publications

References 9 publications

The effects of the prepulse on capillary discharge extreme ultraviolet laser

The effects of the prepulse on capillary discharge extreme ultraviolet laser

Étude théorique et expérimentale d'une source EUV par décharge capillaire

Role of the wall ablation in the operation of a 46.9 nmAr capillary discharge soft x‐ray laser

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