e2v technologies has developed "Hi-Rho" devices manufactured on very high resistivity silicon. Special design features
have been included that enable extremely high gate to substrate potentials to be applied without significant current
leakage between back and front substrate connections. The approach taken allows the usual design rules for low noise
output amplifier circuitry to be followed. Thus low noise devices very sensitive to red and near infrared wavelengths can
be manufactured. This paper reports on the detailed characterisation of the large format "Hi-Rho" sensor designed for
astronomical applications and extends the data previously reported to include detailed assessment of the CTE, spatial
resolution, dark signal and cosmetic quality. The influence of the base material has also been investigated with devices
manufactured on silicon from two different manufacturers. Measurements of the quantum efficiency from devices
utilising a newly developed antireflection coating process are presented.
The demand for higher red wavelength sensitivity is being met by various technological developments of modern CCDs.
We discuss techniques for achieving higher red wavelength sensitivity by using thicker silicon to make backthinned
CCDs, which combines with very low read noise for enhanced sensitivity. Thicker devices requires higher resistivity
material including bulk (non epitaxial) silicon. An extended wavelength range also places more demand on the antireflection
coatings which benefit from corresponding optimisation.
e2v technologies have recently been developing large area (2k*4k), high resistivity (>8 kΩcm) silicon CCDs intended
for infrared astronomy. The use of high resistivity silicon allows for a greater device thickness, allowing deeper, or full,
depletion across the CCD that significantly improves the red wavelength sensitivity. The increased depletion in these
CCDs also improves the quantum efficiency for incident X-ray photons of energies above 5 keV, whilst maintaining
spectral resolution. The use of high resistivity silicon would therefore be advantageous for use in future X-ray
astronomy missions and other applications.
This paper presents the measured X-ray performance of the high resistivity CCD247 for X-ray photons of energies
between 5.4 keV to 17.4 keV. Here we describe the laboratory experiment and results obtained to determine the
responsivity, noise, effective depletion depth and quantum efficiency of the CCD247.
The rate of laser ablation at irradiances of ~2x1014 Wcm-2 of solid iron and aluminum has been measured using the
transmission of a neon-like zinc X-ray laser at 21.2 nm through thin iron and aluminum targets. It is shown that the
opacity of ablated material falls rapidly with increasing temperatures and decreasing density from the solid value. As
ablated plasma becomes transparent to the X-ray laser flux, the thickness of solid, unablated material and hence the rate
of ablation can be measured from time resolved X-ray laser transmission. A self-regulating model of laser ablation and
fluid code simulations with absorption to thermal plasma of 5-10% show agreement with our measured ablation rates.
The ablation of plain aluminium foil and aluminium foil with a thin (50 nm) iron coating was observed using a neon-like zinc x-ray laser. The 21.2 nm x-ray laser was produced by a double pass of a 3 cm long zinc target at the PALS centre in Prague. The x-ray laser was used to probe the sample targets as they were heated by a separate laser beam of 10 J, focussed to a 100 micron diameter spot. The data from the experiment are presented and compared with Ehybrid simulations and simple ablation rate calculations.
Evidence from experimental measurements of the temporal duration Δt of x-ray lasing and measurements or estimates of the frequency bandwidth Δν show that the Fourier transform limit ΔνΔt ~ 1 has been approached in several experiments. It is important to understand and quantify this fundamental limit. The temporal behaviour of x-ray laser pulses of short duration at the Fourier transform limit is examined in this paper. Using numerical methods to model ASE output, the behaviour of the electric field with time E(t) is determined from the Fourier transform of the electric field variation with frequency E(ν). The expected time-bandwidth product is then presented for different gain length products.
We give an overview of recent advances in development and applications of deeply saturated Ne like zinc soft X-ray laser at PALS, providing strongly saturated emission at 21.2 nm. Population inversion is produced in the regime of long scale-length density plasma, which is achieved by a very large time separation between the prepulse (<10 J) and the main pump pulse (~500 J), of up to 50 ns. This pumping regime is unique in the context of current x-ray laser research. An extremely bright and narrowly collimated double-pass x-ray laser beam is obtained, providing ~10 mJ pulses and ~100 MW of peak power, which is the most powerful soft X-ray laser yet demonstrated. The programme of applications recently undertaken includes precision measurements of the soft X-ray opacity of laser irradiated metals relevant to stellar astrophysics, soft X-ray interferometric probing of optical materials for laser damage studies, soft X-ray material ablation relevant to microfabrication technologies, and pilot radiobiology studies of DNA damage in the soft X-ray region. A concomitant topic is focusing the x-ray laser beam down to a narrow spot, with the final goal of achieving ~1013 Wcm-2.
Experimental measurements of the opacity of plasmas at densities close to solid state and temperatures ~ 60 - 300 eV using a probing X-ray laser are presented. Utilizing thin targets, opacities of iron have been measured using x-ray lasers of photon energy 89 eV created by pumping with the VULCAN RAL laser. The thin targets are separately heated by spot focus laser pulses. We have demonstrated that X-ray laser brightness is sufficient to overcome the self-emission of hot plasma so that useful opacity measurements can be made. Due to their high brightness, x-ray lasers can fulfill a useful niche in measuring opacity and other phenomena associated with laser-plasma interactions. Quantities such as opacity measured in laser-plasmas are useful elsewhere. For example, plasma opacity is important in understanding radiative transfer in the sun.
We present a detailed analysis of an experiment carried out recently in which the temporal coherence of the Ni-like silver transient X-laser at 13.9 nm was measured. Two main consequences of this measurement will be discussed and interpreted with numerical calculations. First we show that the high temporal coherence length measured corresponds to an extremely narrow spectral width of the X-ray laser line. Second we show that the high temporal coherence helps to explain the presence of small-scale structures observed in the cross-section of all transient X-ray laser beams.
Below saturation, X-ray laser output shows a reduction in pulse duration and frequency bandwidth as the gain-length product increases. Above saturation, both quantities can be expected to rebroaden. The duration of gain can be close to an order-of-magnitude longer than the output pulse duration. With gain-length products just below saturation, X-ray lasing at 13.9 nm in nickel-like silver has been measured with a pulse duration Δt of 3 - 4 ps and an estimated frequency bandwidth Δv of 5×1011 Hz. Such values imply that the pulses are close to transform limited with Δt Δv ≈ 1.5. Measurements of x-ray laser pulse-lengths and gain duration will described in this paper.