Kenny Jackett, the Lions managaer. has transformed the club from relegation candidates to a top-six side inside 12 months.
The London side are assured of a play-off place, where they are likely to meet Leeds United in the semi-finals.
If they beat struggling Carlisle United on Saturday, they could claim third spot in the table and a semi-final against Scunthorpe or Tranmere.
Alexander said the Lions will be confident whoever they play, and expect to go into the games on a high.
"We want to get a good result at Carlisle," he told the club's official website.
"I've scored 13 goals from 29 starts this season, which isn't too bad a return of one goal every three games. But I want that figure to be better.
"This is a great club and we are all totally focused on trying to get to the Championship. The gaffer has been saying that the season starts here - and he is right. We know what we are aiming for and hopefully we will get there."