Versions Compared

Old Version 11

changes.mady.by.user Frederic P Poitevin

Saved on

compared with

New Version 12

changes.mady.by.user Frank Moss

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

Info

Check all diodes at the beginning of the shift (ideally this should also be done a few days before the experiment to give you time to fix things that don't work), by plugging them into Lecroy and visual check (with bias-T).

Toggle Cloak
Install a fast diode and mirror (roughly at 45 degrees with respect to the beam) on the SC1 post_sample_x stage (CXI:SC1:MMS:02.RBV) downstream on the interaction region. There is a danger of driving this stage into the Jungfrau or other components in SC1, so it might be disabled. It is also good practice to disable the motor when not in use.

Cloak

The fast diode has a small area and is therefore can be difficult to align. Ideally, a Y stage (PP-30 piezo) is used to allow remote motion of the diode to align to the laser and x-rays.

Due to the limited travel range of the long X-stage in SC1, the diode and mirror must be installed as far as reasonable towards the -X side, overhanging away from the carriage

Toggle Cloak
Roughly align the fast diode and mirror using the reference laser at the time tool.

Cloak

(-4 mm in position but this will soon be changed to 0 mm.   If the "out" position is 92 mm, then -4 mm, if 96 mm, then 0 mm).

Toggle Cloak
Install a regular diode connected to the Acqiris on the sample chamber door and align the reflected reference laser beam on the mirror onto that diode.

...

Toggle Cloak
Also install a fs laser diagnostic diode (OPC-TP) and connect it to the Acqiris. This is useful to confirm that the fs laser is firing during the experiment.

Cloak

Toggle Cloak
Insert a nozzle rod with both a clear YAG and a frosted YAG.

...

Toggle Cloak
Determine the position of the X-ray spot at the IP using the clear YAG and the beam with 1x10-4 Transmission (although the beam can be seen with less intensity). Mark the position of the beam with crosshairs (cyan and magenta in the example image below).

Cloak

Zoomed-in view:

Rough timing

...

Toggle Cloak
Move the fast diode into position (at this point should only need to move the SC1 sample_x stage) and move the IP YAGs out of the beam.

Cloak
  • Align the diode to the x-ray beam first since the x-ray beam cannot be moved. The laser will later be steered to the diode left int he fixed locaiton location of maximum x-ray signal
  • The focused x-ray beam may damage the diode. If the signal on the diode is too weak for 10^-4 transmission or less, it may be that the diode is improperly biased.
  • Increased x-ray signal may be achieved without damaging the diode by making the x-ray beam bigger suing using the DG2 Be lenses as described later in the fine timing section.
  • Make sure the Lecroy is triggered off the EVR.

Toggle Cloak
Measure the laser signal on the diode using the LeCroy scope to make sure there is overlap

Toggle Cloak
Turn off Shutter the fs laser and turn on unshutter the X-rays. Move the diode around in x and y to maximize the X-ray signal (if the steps are very large then the laser may need to be repointedre-pointed)

Toggle Cloak
Save Click Store on the Lecroy to save a trace of the X-rays on the scope

Toggle Cloak
Turn Shutter X-rays off and turn on unshutter fs laser.

Toggle Cloak
Temporally overlap the X-rays and the fs laser.

cloak
Cloak

If needed, align the fs laser to the diode (usually not needed). Move laser delay time (LAS:R52B:EVR:31:TRIG0:TDES) to bring laser within 100 picoseconds of the X-rays using the scope

...

. Alternatively, change the  Target Time in the fs laser window. Align the fs laser trace so that the leading edges of the traces line up. You can center the diode signal on the Lecroy by changing the Delay. Try to match the amplitude of the X-ray and fs laser signals. Type the time below the ns Offset in the fs laser window in the ns Offset box, which will reset the Target Time to 0.


Fine timing

Once the laser is roughly timed roughly, it is time to move onto the finer timing measurement using a cross-correlation measurement

...