SXR Technical Design Report - Stanford University

5.13 Optical Pump Laser Transport, collinear in-coupling
Optical femto second Laser pulses to excite or probe ultra fast dynamical processes have be guided from
the existing Near Experimental Hall optical laser facility (W. White) to the two sample interaction points,
transmission sample chamber and end station. The pump laser will be transported to optical table adjacent
to in-couple mirrors just up stream of each sample location. Focusing and pointing optics and feedback
will be located out-of-vacuum. This allows for flexibility in bringing the laser beam in coaxially or near
coaxially with the Hamburg in-coupling mirror system, described below, or though an off axis viewport.
The nominal set up will have the laser bean brought in though the Hamburg in-coupling mirror with a
~1mm spot size at the transmission sample position and ≥100μm spot at the end station.
The design is based on the Hamburg design used at the FLASH PG2 beam line. It has 2 inch diameter
dielectric plane mirrors with a central bore to transmit the X-ray beam. For different wavelengths specific
mirrors are mounted on a ball bearing stabilized manual translation stage. At 2 inch diameter and a central
bore diameter of 2 mm minimum distortion of the optical wave front is ensured. In the initial stage 800 nm
and 400 nm mirrors are used. The mirrors are in vacuum mounted in spring mounted holders, which allow
bake out of the UHV system without putting mechanical stress onto the mirror surfaces. On the back of the
mirrors matching fluorescence screens are mounted which allow rapid positioning of the X-ray beam
through the central bore.
In this implementation the mirror chamber is fixed with the pointing feed back done out of vacuum. In the
case of the transmission sample position, with the large spot size the pointing stability is not critical so the
in-coupling mirror and the pointing feed back loops are supported separately. At the end station with the
potentially small spot size the in-coupling mirror and the feedback loops and focusing optics will be
mounted on the same optical table.
Figure 5.5 The operational design at the PG2 beam line at the Free Electron Laser at Hamburg (FLASH)
facility.
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