Cochran, who was recently released by Yeovil Town, has signed a short term contract after impressing Jackett with an appearance in the reserves last week when he scored the winner while Karacan comes in on a month's loan from Premiership outfit Reading.
"Kenny Jackett was assistant manager when I was a young player at QPR," Cochrane told the club's official site when asked about The Lions interest in him. "He knows me well and asked me along for a trial a few days ago. I scored for the reserves at Watford last week and am delighted to be here. I am determined to earn a spot in the squad and hopefully the first team."
Both players go straight into the squad to face Oldham Athletic on Saturday.