R. Decoste

Laser‐plasma interaction and ablative acceleration of thin foils at 1012–1015 W/cm2

The interaction physics and hydrodynamic motion of thin‐foil targets irradiated by long, low‐flux Nd‐laser pulses (3 nsec, 1012–1015 W/cm2) are studied experimentally and compared with theoretical models. Laser light absorption is high (80%–90%) and thin‐foil targets are accelerated up to 107 cm/sec with good (20%) hydrodynamic efficiency in the 1012–1013 W/cm2 range. These results agree with a simple rocket ablation model. Details of thermal heat flow, both axially (related to ablation depth) and laterally (related to beam uniformity requirements), are also presented.

Characteristics of ablation plasma from planar, laser-driven targets

The momentum, energy, and velocity characteristics of plasma ablating from planar targets irradiated by long Nd‐laser pulses (4 ns,<1014 W/cm2) are measured and the dependence of ablation parameters upon absorbed irradiance is determined. Large laser spots are used in these experiments so that the results are not sensitive to boundary effects.

Laser‐produced‐plasma energy transport through plastic films

The transport of energy from a 1.06‐μm, 95‐psec laser pulse at an irradiance of 1015 W/cm2 through a thin layer of polystyrene into an Al substrate was studied by x‐ray, ion, and scattered‐light measurements. The intensities of the following quantities were measured as a function of polystyrene thickness: (1) x‐ray line radiation from the Al backing, (2) bremsstrahlung continuum from 3 to 88 keV, (3) ions of several keV energy, and (4) scattered laser light. The results indicate that a polystyrene thickness of no more than 0.5 μm is sufficient to inhibit substantial heating of the Al substrate.

Spectroscopic observation of fast ions from laser‐produced plasmas

Using a time‐of‐flight spectroscopic technique, measurements were made of the ion energy distributions of very fast ions and thermal ions produced when a 7–15‐J 100‐psec Nd : glass laser pulse (1.06 μm) strikes a (CH2)n slab target. Ion energies greater than 0.5 MeV have been observed for the first time with this technique of measurement. A simultaneous comparison is made between the signal of an ion charge collector placed 30 cm from the target and the intensity of the C VI 3434‐A ion line at 1 cm from the target.

Emission of energetic electrons from a Nd‐laser‐produced plasma

Absolute spectral measurements of 50–500‐keV electrons emitted from a Nd‐laser‐produced plasma are presented. For normally incident irradiation (1015–1016 W/cm2) onto polystyrene slab targets a total emitted energy of ∼1010 electrons is inferred with a total emitted energy of ∼0.2 mJ. The electron emission is observed to be almost the same both in and out of the plane of polarization. Properties of the emitted spectrum, such as spectral hardness and intensity, are observed to be dependent on the pulse shape and the target material.