For what reason can the laminar flow be dispersed?

It is necessary to develop a laminar flow installation 2-2. 5 meters high and 3 meters long. Looking through various materials from the Internet, I put together a laminar flow installation on my own, and achieved the desired effect. But, there is a problem: the jet starts to disperse from the top point of the arc. What can influence this?

I'm still relatively new to this, but my first inclination is that the exit point on your nozzle isn't clean enough. Based on my reading and a few experiments, the two things that seem to affect reliability of the laminar stream is the exit hole at the top of the nozzle, and a steady pump pressure (which is typically achieved through a low pass filter)

In the case of the exit hole, consider that small imperfections in the hole (and therefore small imperfections in the stream) have compounding effects down the stream, and cause it to break up the further they go.

Anecdotally- w/o seeing more details pictures and only from the pictures you've posted - I do not believe you have achieved a true laminar state. The stream has various twists visible in it before reaching the apex . . . . . I've constructed several laminar fountain heads and - if you can share specific details I could comment further.