A schematic diagram of the experimental setup used for generation of the high order harmonic radiation from plasma plume and measurement of its spatial coherence.
The divergence of the 11th and 19th orders of the harmonic radiation generated from pre-formed plasma plume, when the laser was focused ∼6 mm away from the plasma plume centre (fs laser intensity ∼3 × 1015 W/cm2). The inset shows the size of the harmonics on the detector. The divergence of the 11th harmonic was ∼8 mrad, and that of the 19th harmonic was ∼6 mrad.
(a) The dispersed harmonic spectrum recorded by the XUV spectrograph; (b) The interference pattern of 11th harmonic order after inserting the double slit (slit width 30 μm and separation 100 μm); (c) The line profile of the interference fringes of the image b (solid line). The dashed line shows the calculated intensity profile from single slit.
The variation of the harmonic intensity and the fringe visibility with the laser focal spot position (negative distance means focus before the plasma plume) for the 11th harmonic, taken for a slit separation of 100 μm and slit width of 30 μm. The solid curves are to guide the eyes.
The dependence of the fringe visibility on the harmonic order when the laser beam is focused: (a) before the plume, (b) after the plume, at plasma plume position ∼6 mm away from the laser beam focus (in either case).
The variation of the fringe visibility with the slit separation, for 11th harmonic from carbon plume. The solid curve shows the Gaussian fit of the experimental data points. This curve gives an estimate of coherence radius (Rc).
The variation of the coherence area with the harmonic order, for the harmonics generated in plasma plume of carbon (graphite).
The calculated dependence of the fringe visibility on the electron density in plasma plume. At an electron density variation of ∼5×1016 cm−3, the fringe visibility matches with the experimental value.
The variation of the fringe visibility with the harmonic order, at an electron density variation of ∼5×1016 cm−3. The solid line shows the theoretical fringe visibility calculated using Eq. (6) , and the triangles are the experimental values.
Article metrics loading...
Full text loading...