CHEM: The Chemistry / Liquid Jet End Station

Overview

The Chemistry (CHEM) chamber is designed to introduce all sorts of dirt into the beam line! Ha. Ha.

Diagnotics Stage

The diagnostic stage is mounted downstream of the main chamber and houses a CeYAG screen and a pair of Si photodiodes for knife-edge scans of the optical and x-ray beams. One photodiode is fitted with and Al filter and other not.

The diodes are AXUV20 from Opto Diode Corporation, possibly via Digikey.

More details can be found in the elog: https://in.xfel.eu/elog/SCS+Instrument/2163

In-vacuum X-ray Photodiode

A silicon diode (AXUV20 from Opto Diode Corporation) with Al filter (custom from Luxel) is mounted in the chamber to detect x-ray fluorescene. Details are in the elog: https://in.xfel.eu/elog/SCS+Instrument/2990

We tried also a larger diode (AXUV100). It showed some signal, but seemed to be very noisy and saturated at 1.1 MHz operation. Bias at 4.6 V did not help. A Keithley picoameter also did not produce convincing results.

MCP

– An MCP (Surface Concept, same as TIM, in fact, from TIM) has been intalled at 90 degrees to the beam and elevated above the scattering plane.

– Another MCP (Hamamatsu) was installed on the in-vacuum breadboard close to the beam to enable XAS when the sample is close to normal incidence in the beam. Details can be found in elog: https://in.xfel.eu/elog/SCS+Instrument/3094

Laser In-coupling

Laser in-coupling is via a large, dedicated breadboard downstream of the LIN breadboard. The beam enters a DN100CF spherical cube chamber between the differential pumping section and the main CHEM chamber via a custom flange mounting a commercial 3” or 75mm diameter window with o-ring seals (as on LIN and FFT).

The laser window can be seen in elog: https://in.xfel.eu/elog/SCS+Instrument/2988

A 2” diameter mirror with a hole through the centre is mounted on a Smaract piezo mirror mount in the in-coupling chamber. It uses the LIN Smaract controller in the rack room.

Elog: https://in.xfel.eu/elog/SCS+Instrument/2999 Elog: https://in.xfel.eu/elog/SCS+Instrument/3089

The mirror mount can be translated vertically (Y) and perpendicular to the x-ray beam (X) with an external motorised manipulator. The range of motion along these axes is limited. It is intended to centre the hole in the mirror on the x-ray beam but is insufficient to move the mirror out of the beam.

Spatial Overlap at Liquid Jet

Spatial over between the FEL and PPL is critical and not so easy. Overlap at the pBN is not sufficient because the sample holder is slighly angled. A successful method to find overlap is described here: https://in.xfel.eu/elog/2866+Kuiken/76

Coarse Timing Antenna

See elog: https://in.xfel.eu/elog/SCS+Instrument/2987

An SMA connector is mounted on the sample manipulator as an antenna for coarse timing between the x-ray and optical pulses, in a similar way to FFT. It is connected to the fast oscilloscope in the control room via an in-vacuum coaxial cable and an 18GHz SMA feedthrough on top of the sample manipulator.

The SMA connector is mounted on a PEEK holder and retained by a clamp plate screwed to the PEEK. (This is different from FFT, where we forced the legs of the SMA connector into a copper holder to fix it.)

There are some details to consider. An eLog post about the details is here: https://in.xfel.eu/elog/2866+Kuiken/78

Fine Timing

Fine timing is done in the usual way by measureing transient reflectivity of a semiconduction (usually SiN) to visible or infrared light (ie the PP laser) afer pumping with x-rays. The reflected beam can be detected in vacuum or in air.

The first generation in-vacuum scheme is a Si PIN diode (Thorlabs FDS100) on a fixed mount. Details can be found in elog: https://in.xfel.eu/elog/SCS+Instrument/2989

Sample rotation information is at: https://in.xfel.eu/elog/SCS+Instrument/3028

Detection in air is easier bacause we can adjust the reflected intensity with ND filters.

Cabling of In-vacuum Detectors

The photodiodes in the chamber are connected via a 4-pin SMA feedthrough on a DN40CF flange on the wall side of the chamber. Details are given in the elog: https://in.xfel.eu/elog/SCS+Instrument/2991

Laser setup at LIN and CHEM breadboards

Details of the laser setup for 400nm operation can be seen here: https://in.xfel.eu/elog/2866+Kuiken/73