William McGuigan, 17, forced the pilot to deviate the aircraft when he aimed the green laser at the cockpit while it was in the air above the Cambuslang area of South Lanarkshire.
Experienced pilot Steve Kitchen moved away from the beam and the 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.
Ms Nelis was one of 10 people who died when the police helicopter crashed through the roof of the Clutha pub in Glasgow last November.
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.
The court was told that around 10pm the helicopter was sent to the Cambuslang area after reports were made to the police over an unrelated incident.
Procurator fiscal depute John Bedford said: "During that investigation the pilot immediately was targeted by a high power green laser.
"That laser illuminated the cockpit of the aircraft. Captain Kitchen piloted the helicopter away from this beam."
The court was told PC Nelis and her colleague then recorded the beam shining into the cockpit.
It was soon identified that the laser was coming from a property in Lorne Terrace in Cambuslang and police on the ground were sent to the house.
Mr Bedford added: "While outside in Lorne Terrace, two officers observed the accused, William McGuigan, at an open bedroom window. The accused was found to be holding a laser pen."
McGuigan's mother let the police into the house and while talking to her, the teenager told them: "It was me."
Sentence was deferred until next month for reports and bail was continued.