Olsen was 1-4 with a 7.24 ERA before being placed on the DL on May 18 with left shoulder tendinitis. He will rejoin the starting rotation Monday, when he will attempt to earn his 20th career victory on the road against the Florida Marlins.
Martis was 5-3 with a 5.25 ERA in 15 games, all of them starts. His five wins was tied with John Lannan for most on the team.
"We do see him as a very valuable pitcher not only for now, but for many years to come," Washington manager Manny Acta said. "He's a big part of our future. He's going to be back here very soon."
Acta believes pitching every fifth day in the minor leagues will make Martis a better pitcher when he returns to the majors.
"Right now we just feel he just needs to go back to what got him here -- being more aggressive in the strike zone and working on making pitches," Acta said. "Right now he's got more walks  than strikeouts .
Morse, 27, will be assigned to Syracuse of the Triple-A International League. A third-round selection of the White Sox in 2000, Morse batted .300 with 18 doubles, three homers and 37 RBIs for Seattle from 2005-08.
The 29-year-old Langerhans hit .198 in 103 games with Washington in 2007 and batted .234 in 73 games last season.