To measure the UV laser pulse with cross-correlation ( XCorScan ) the IR and UV vectors must be overlaid on the crystal. There are some tips and tricks to achieving this
Step-by-step guide
- Insert the pinhole (should have a collar in place). Install perpendicular to beam vector (by eyeball)
- Using dichroic mirror, get IR through pinhole
- Can either use high sensitivity cards or orange cards + phone camera
- Steer the UV through the pinhole using downstream mirror
- Having a very sharp sliver of paper can help; once the beam is near the center it should start to visibly fluoresce
- Once the beam is through at all, continue to adjust mirrors to improve the "halo"
- The final refinement should result in a beam not too far from the center of the halo (won't actually be centered!) but the tuning should be done such that the halo is as circular as possible
- Next step is to check UV and IR upstream and downstream of iris
- There are a few ways to do this. Can use white and orange sections of a high sensitivity card.
- I've found that putting a 1.3 OD filter on the IR line reduces the amplitude of the IR enough that it doesn't wash out the UV on an orange card when viewed on a phone camera
- Adjust UV line ONLY to get overlap both upstream and downstream
- Replace pinhole with crystal
- Using white paper with a small hole in it (<mm), let the UV pass through the card onto the crystal then look on the paper for the reflection. Adjust the angle of the crystal such that the reflection is ~perpendicular
- Note the position of the manual delay stage
- Keeping pressure on the side of the stage without the screw (i.e. keeping the linear bearings in compression) adjust the position, looking for a peak on the oscilloscope
- If the signal is not found, more desperate measures might be necessary... time to break out the fast diode.
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