Craig Gilroy, 23, of Ribble Road, central Blackpool, took cash, an iPhone and food from his victim when he pounced on the man in an alleyway at the back of a mini market on Palatine Road.
The thug pleaded guilty to robbery at Preston Crown Court yesterday, and was jailed for two years and eight months.
Louise Whaites, prosecuting, said Gilroy approached his victim on November 3 and was holding a glinting eight inch bladed knife by his waist.
Gilroy demanded money, but the lecturer, who was walking home from Blackpool and the Fylde College university campus on Palatine Road, said he did not have any.
Miss Whaites told the court: “The defendant pushed him against the alleyway wall, raised the hand holding the knife and held it to his neck and again requested money.”
The man gave him £10 cash and went on to give him his iPhone, worth £495, and a bag of food.
He waited in the alley until Gilroy had rejoined two other men and moved away from the area, and became extremely distressed when he arrived home.
Gilroy, who was wearing a hooded top at the time, with a scarf up to his nose, later sold the mobile for £20 and bought two bags of heroin.
The thief, who has 65 previous offences on his record, told his partner he had “jacked some guy”, but denied the offence when questioned by police.
Paul Humphries, defending, said his client accepted using the knife to threaten, but denied any intent to use it to cause harm. He also denied threatening to kill the man if he went to the police.
Mr Humphries said: “He tells me he is very sorry. He understands the pain and misery he has caused the male and his family.
“He wishes he could turn the clock back. He was at a low point in his life.
“There was also a food shortage in the house.”
Gilroy had also been on a methadone programme but was not attending at the time.
Judge Philip Butler said: “It must have been a terrifying experience for the man.
“That he suffered no physical injury is very little mitigation because one can imagine the psychological effect”.