A schematic layout of the TRD optical system. Light emitted from the rear side of the target is magnified and relayed to a CCD camera. Filters and pinholes minimize background contributions. The right arm of the system is used only for preshot focusing on the rear surface.
A three-dimensional (3D) model of the TRD with the rear-side access panel removed. A detailed discussion of the device is found in the text.
The microscope objective is firmly held by the carriage, which glides in and out smoothly on rails attached to the inside of the outer case. The New Focus picomotor (not shown) is housed in the upper outer case and attached to the carriage via the mechanical buffer. It moves the objective in steps over a range of . Attached to the under side of the carriage is a glass slide encoded with a holographic ruler with graduations. The hologram is read out from below by a reader embedded in the lower outer case to provide closed-loop positioning control.
A 3D model of the MTW target chamber. An off-axis parabola (OAP) steers the MTW laser beam to focus at target chamber center (TCC). The TRD is housed in the port directly opposite the OAP. It images the rear-side optical emission from a normally illuminated target placed at TCC. The TRD optical system is folded through 90° so that the CCD camera lies in the -ray shadow of the TRD lead shielding.
Histogram of the number of gamma ray single hits from two shots conducted under almost identical conditions. The pixel values are shown in analog-to-digital units. The solid curve corresponds to a shot taken without lead shielding, the dashed curve to a shot with the lead shielding in place demonstrating the efficiency of TRD shielding in suppressing the number of gamma ray photons incident on the CCD.
The optical transmission curve for the TRD. The transmission efficiency at the laser second harmonic, , is . The transmission efficiency at the laser wavelength, , is orders of magnitude lower.
(a) The MTF of the TRD. The curves are produced by analyzing images obtained using the TRD fitted with a microscope objective. The solid line shows the theoretical MTF. The measured MTF at best focus is indicated by the dotted line; the contrast falls to at around corresponding to a spatial resolution of . The dashed line MTF expresses the effect of defocusing the collection optics. A defocus reduces the optical performance of the system. (b) A section of a SEM 400-resolution grid. The dotted line indicates the position from which the lineout shown in (c) was taken. (c) The lineout is normalized to it maximum value and used to calculate the MTF.
(a) Image of the rear-side optical CTR emission from a -thick aluminum foil. The scale is logarithmic and the intensity is expressed in arbitrary units. The emission region diameter is about . Contained within this region are a group of diameter structures. (b) Horizontal and vertical lineouts through the maximum-intensity filament.
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