after a while意为“过了,一会儿、一段时间”.既然是“过了”当然是用于过去时了.
eg：1.After a while the police walked away.
过了不久警察就走开了.
2.After a while the road opened up and they traveled more quickly.
过了一会儿,路变宽了,他们也走得更快了.
3.After a while,I began to get bored with my job.
过了一段时间,我开始厌烦这份工作.
4.Mary and Joan quarreled,but made up after a while.
玛丽和琼吵架,但一会儿就和好了.