Is it permissible to raise the floor of the mosque's mihrab by about a handspan so that worshippers can see the imam, and is there any objection to that?

It is disliked, by consensus, for the Imam's position to be higher than that of the worshippers, except for the purpose of teaching them. Scholars differed on the extent of the elevation that is disliked. Some held that it is disliked if the elevation exceeds a cubit, and anything less than that is not disliked. Others maintained that the disliked elevation is one that exceeds a person's height. Accordingly, there is no objection to raising the floor level of the mosque's mihrab by the aforementioned amount.