How to get right intensity and what does it influence?
The light intensity can be tuned in several ways. The most straightforward is to tune the DAC of the laser. The % in the DAC setting (although the relevant number is mV written below) is inversely proportional to power the lower the % the larger the power. This is so because on the other hand the larger the % the narrower the light pulse which is what you want. So set the laser % to the level, where you still see the signal and get triggers (you may have to reduce also the trigger threshold on your oscilloscope/DRS). For the red light it may occur that this is still too much as the short penetration depth and focused beam result in density of free carriers orders of magnitude above Neff. In this case you can use NDF. One was already included in your shipment. To some extent you can also use iris to reduce the intensity, but that affects also the focusing performance.