William McGuigan, 17, forced the pilot to deviate the aircraft when he lit up the cockpit in a green laser attack above Cambuslang.
Experienced pilot Steve Kitchen moved away from the beam and the police officers on board, Ms Nelis and Nicholas Whyte, filmed the incident.
Officers on the ground then spotted McGuigan shining the laser from an open bedroom window, on October 31, 2012.
He later told police: "I wasn't shining it directly at the guy, I wasn't going to try and kill somebody."
McGuigan, from Whitlawburn, Cambuslang, pleaded guilty at Glasgow Sheriff Court to culpably and recklessly directing the laser beam towards the then Strathclyde Police helicopter, causing Captain Kitchen's vision to be impaired and him to take action.
The court was told that around 10pm the helicopter was sent to the Cambuslang area after reports were made to the police of an unrelated incident.
Procurator fiscal depute John Bedford told the court: "The police helicopter was put in to use to carry out airborne investigations.
"During that investigation, the pilot immediately was targeted by a high power green laser.
"That laser illuminated the cockpit of the aircraft. Captain Kitchen was fully aware of the risks of such laser attacks and he immediately, having control of the helicopter at that time, took evasive action.
"He piloted the helicopter away from this beam."
It was confirmed in court that PC Nelis lost her life in the tragic incident at the Clutha, when she was on board the helicopter that crashed.
Sheriff Andrew Normand deferred sentence on McGuigan until next month.