Schematic overview of the complete TS setup, with the laser table shown on the left-hand side (see the top left for an enlargement of the leftmost part), and the TGS-II spectrograph at the top right. After passing through the plasma inside the vacuum chamber, the laser beam is collected by a beam dump. The scattered light is collected and imaged onto the entrance slit of the spectrograph by two achromatic lenses, of which the opening angle is matched to that of the spectrograph.
Schematic drawing of the laser path between the corner cubes in the optical delay line. The parts of the optical path inside the corner cubes have been omitted for clarity. Distances between the optical elements are not to scale; in particular, in the actual setup, the large corner cube is placed much further away from the other elements, to obtain a long path length.
Ray-trace simulated image spots in ZEMAX for four different cases: (a) , ; (b) , ; (c) , ; and (d) , , for a central wavelength of . Here, and represent shifts from the center of the image in the spatial and wavelength directions, respectively. The vertical bars represent sizes of for parts (a) and (c), and for parts (b) and (d).
Example of rotational Raman scattered spectrum from nitrogen gas. In this case, the signal was integrated over all spatial channels.
Example of a Thomson scattered signal recorded with the new setup. Top frame: a “raw” vertically polarized signal, showing strong plasma emission in spectral lines. Bottom frame: the same signal, after subtraction of the horizontally polarized part of the plasma background. This image was seven times digitally intensified compared to the top image. The feature between and is a part of the plasma background that remained after background subtraction, but this part of the spectrum could simply be ignored while fitting the TS signal to a theoretical curve. The curved shapes between roughly 2 and on either side of the spectrum represent the TS signal. The dark area in the center is due to the presence of the stray light filter.
Root mean squares of the distances of individual ray-trace points from each spot center, produced by ZEMAX for different horizontal positions inside the plasma and different wavelengths. and are defined as the shifts from the central position and the central wavelength, respectively, which is in this case. For evenly distributed points in a round image spot, the spot radius equals .
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