Observation of Solid-Density Laminar Plasma Transparency to Intense 30 Femtosecond Laser Pulses

Abstract

Near total transmission of 30 fs laser pulses through 0.1 mm plastic foil targets has been observed for the first time at an intensity of 3 3 10 18 W͞cm 2 in absence of precursor plasma. This level of transmittivity is far above the level predicted by current theoretical models or numerical simulations. The transmittivity was found to drop by 40 times at an intensity of 4 3 10 17 W͞cm 2 and was within the experimental background level at 5 3 10 16 W͞cm 2 . Our measurements strongly suggest a new mechanism of propagation of electromagnetic waves through overdense plasmas.[S0031-9007 (97)04356-1] PACS numbers: 52.40.NkThe interaction of intense optical radiation with plasmas characterized by solid-density and ultrasteep gradients can now be studied by using short pulse lasers capable of delivering up to joules of energy in few tens of femtoseconds. In principle, such laser systems open the possibility of investigating phenomena produced by high intensity radiation in experimentally unexplored conditions, including propagation in plasmas whose density is orders of magnitudes higher than the critical density n c m e v 2 0 ͞4pe 2 , v 0 being the laser frequency. Recently, penetration of ultraintense, short laser pulses into overdense plasmas has been extensively investigated both theoretically and experimentally also in view of its relevance to the implementation of the fast ignitor concept [1]. Several effects have been considered that predict enhanced propagation, including anomalous skin effect [2], self-induced transparency [3], and hole boring [4,5]. Hole boring and self-induced transparency have been mostly investigated in the interaction of relativistic laser pulses with moderately overdense plasmas. In particular, hole boring has been proposed as a possible mechanism for deep energy deposition in overdense plasma regions due to ponderomotive forces at relativistic intensities. The importance of relativistic effects is given by the value of the normalized relativistic momentum, a 0 p os ͞m o c Х 0.85l 0 p I 0 where p os is the momentum of the electrons oscillating in the laser field, m o is the electron mass, c is the velocity of light, and I 0 and l 0 are the laser intensity in units of 10 18 W͞cm 2 and the wavelength in microns, respectively. For these effects to give a nonmarginal increase of transmittivity through plasma slabs, either the plasma must be weakly overdense or the intensity must be very high (a 0 ¿ 1).At nonrelativistic intensity the propagation of the electromagnetic (e.m.) wave into an overdense plasma is expected to be limited to the skin depth d 0 . A deeper penetration (anomalous skin effect) is possible in very hot plasmas, where the electron velocity becomes larger than v 0 d 0 [6]. Recently the anomalous skin effect in solid-density plasmas has been considered both analytically [7] and numerically [8], with attention to the case of interaction with thin foils.From an experimental point of view, a serious problem that can prevent interaction of short pulses with solid-density plasmas may...

Flying mirror model for interaction of a super-intense nonadiabatic laser pulse with a thin plasma layer: Dynamics of electrons in a linearly polarized external field

“…Interaction of super-intense laser pulses with thin foils has been widely investigated during the past decade experimentally, [1][2][3][4] analytically, [5][6][7][8][9] and by computer simulations. [10][11][12][13][14] Many interesting physical phenomena have been predicted and observed experimentally in laser-foil interactions.…”

Intensity dependent anomalous transmittivity of thin plasma layers

“…If the intensity of the laser light is high enough (near the relativistic threshold) and the duration of the pulse is short (shorter than 1 nanosecond) the transmittivity of the plasma can be approximately 1. Anomalous transmission of laser light through thin slabs of plasma has been observed in several experiments [1,5]. The effect was observed in plasmas produced by relatively long (500 ps [5]) and short (30 fs [1]) laser pulses.…”

“…Anomalous transmission of laser light through thin slabs of plasma has been observed in several experiments [1,5]. The effect was observed in plasmas produced by relatively long (500 ps [5]) and short (30 fs [1]) laser pulses. Many authors attributed the optical transparency to the strong magnetic field induced by ionization or it has been supposed that this anomalous transparency is the result of mixing of two electromagnetic waves with appropriate frequencies.…”

“…Abstract: For some time now anomalous transparency induced by high intensity laser light interacting with thin solid foils has been found experimentally [1] and several theoretical models have been suggested to explain this phenomena [2,3]. In our present study based mostly on classical electrodynamics the increase of the transmittivity is the consequence of the more and more pronounced role of the frustrated total reflection in the plasma layer.…”

Flying mirror model for interaction of a super-intense laser pulse with a thin plasma layer: Transparency and shaping of linearly polarized laser pulses

“…1-11 These investigations were triggered both by the availability of the laser pulses with ultrarelativistic amplitudes 12 and by results of the experiments on the highintensity laser-pulse interaction with thin foils. [13][14][15][16][17] An exact analytical approach likely cannot be developed for a full description of a real plasma layer, and only numerical simulations are possible. However, the main features of the interaction of the laser pulse with the real plasma layer can be described by the approximate phenomenological models, particularly by models containing only one electron sheet.…”