Supplemental Information:
SI_1: Schematic of laser ion acceleration
File: SI_1_LaserIonAcceleration.WMV
Format: movie, wmv
Caption:
SI_1: Schematic of laser ion acceleration:
A multi-TW laser pulse is focused by an off-axis parabolic mirror onto a thin foil target
with an intensity I ~ 1019 W/cm2. Due to the finite contrast of the laser pulse (10-6 @ 2ns)
the prepulse intensity on target is strong enough (Iprepulse~1013 W/cm2) to create a plasma
about 2 ns before the arrival of the main pulse. The main pulse interacts with the
preplasma, ponderemotively pushing relativistic electrons through the target. This
electron sheath (red) sets up a quasistatic electric field, normal to the target rear surface,
which ionizes and accelerates the ions on the target rear surface (TNSA, Target Normal
Sheath Acceleration). Due to the ambient vacuum conditions these usually consist of
hydrocarbons. The ions are accelerated in the electric field, the higher charge states are
tighter collimated, accelerate faster and gain more energy. In the animation carbon charge
states 1+ (green), 2+ (dark blue), 3+ (light blue) and 4+ (magenta) are shown.
SI_2: Schematic of monoenergetic laser ion acceleration
File: SI_2_2005-08-09670A_CMYK_wText_res1k.pdf
Format: Adobe pdf
Caption:
SI_2: Schematic of monoenergetic laser ion acceleration:
Before the experiment, a 20 m palladium foil target (yellow)is heated up to ~1100K,
creating a monolayer thin graphite layer on the rear surface (purple). A 30 TW laser
pulse is focused onto this target with an intensity I ~ 1019 W/cm2. Due to the finite
contrast of the laser pulse (10-6 @ 2ns) the prepulse intensity on target is strong enough
(Iprepulse~1013 W/cm2) to create a plasma about 2 ns before the arrival of the main pulse.
The main pulse interacts with the preplasma, ponderemotively pushing relativistic
electrons through the target. This electron sheath sets up a quasistatic electric field,
normal to the target rear surface, which ionizes and accelerates the carbon ions out of the
graphite layer. The ions out of the thin source layer are accelerated quasi-instantaneous to
the same energy and form a tight bunch (magenta) running in front of the slower and
spread out Pd-substrate ions accelerated by a decaying electric field later in time.
SI_3: Photograph of an ion acceleration experiment
File: S_3_2005-08-09670A_PhotoIonAcceleration_CMYK.psd
Format: Adobe photoshop
Caption:
SI_3: Photograph of an ion acceleration experiment:
The target sits in its holder in the center of the picture, the laser comes from the left. The
green glow is due to a heating laser used to clean the target instead of the current passing
wires in earlier experiments. Plasma (ions and electrons) can be seen streaming away
from the target towards the right, hitting the RCF package. A fraction of the ion beam
passes through the hole in the film stack traveling on towards the Thomson parabola
spectrometers (not in picture). In the upper left corner the snout of an x-ray pinhole
camera is visible which is used to measure the focal spot size.
SI_4: Analysis of a W-target
File: SI_4_W target analysis.pdf
Format: Adobe pdf
Caption:
SI_4: Analysis of a W-target
After the target was heated to ~ 1000 °C, it was prepared for transmission electron
microscopy and analyzed. The left part shows a crossection image of the target. Three
different layers were identified:
1. The W-substrate (25 micron)
2. A 40 nm thick, crystalline Be-W alloy layer, formed from an imbedded 1nm Be-tracer
layer.
3. A 40 nm thick Tungsten Carbide layer formed from adhered hydrocarbon
contaminations.
The right part of the image shows an electron diffraction pattern, used to identify the
different materials.