9. Experimental and procedure advice¶

Dear student, PhD, doctor, professor, and guests,

Here is some advice that you may find useful while performing SHG experiments. If you have any tricks or advice, please do not hesitate to contact the Alpaga maintainer to have them added to this list.

Perform a control experiment at the beginning of the day if possible.
Do not forget to remove your watch and jewellery in the optical room.

9.1. How to choose the parameters¶

Run an acquisition with several angles and a lot of iterations to choose the acquisition parameters wisely (see HYPERLINK).
It is better to have slightly longer acquisition times than too short.
Ensure there is enough signal for several angles: some configurations may require more time to obtain exploitable results.
If your spectra have a very high background, consider darkening the room and/or using a purer sample.
Be aware that increasing the laser power can have drawbacks (e.g., third-order effects, heating).

9.2. Before you launch the acquisition¶

Make sure the laser is mode-locked; check the fundamental power and the laser temperature.
Open the shutter.
Ensure the flip-mirrors are in the correct position.
Keep track of the room temperature.
Minimize parasitic light sources: room lights, lab computer screens, keyboard lights, etc.
Make sure the sample is correctly positioned.
If your room has a curtain, ensure it is in place.
Verify the analyser angle and the initial incoming polarization angle.
Check where the data are being saved and that the acquisition is actually recording.
Confirm the acquisition device is on and the correct entry/exit settings are used.
Ensure the DAM shutter is functioning correctly.

9.3. Between acquisitions¶

Before changing the sample, analyse your results in case any issues occurred (acquisition crash, laser mode-lock failure, shutter closed, etc.).
Make sure the laser does not shine on your sample when you remove it.

Release:: 1.2
Date:: Aug 26, 2025