Dr. Freeman's glasses are level 1 special headgear wich were awarded to everyone who pre-purchased Shoot many robots through steam before april 6th along with the H.E.V. suit .
Dr. Freeman's glasses and the H.E.V. suit are from the Half-life series, worn by the main character: Dr. Gordon Freeman.
When Dr. Freeman's glasses are worn (boosted while worn in combination with H.E.V. suit), it makes the Portal turret appear.