Offset path appears

[Ongadi]

Hello guys. I have been trying to use offset path as shown in the image below. But I don't want it to show the white color path. I want it to be transparent but leaving the effect on the letter "a" how can I do that? If I leave it white it disappoints on black surfaces. 

[Monika Gause]

You could either punch it out using the pathfinder "Subtract" from the pathfinder panel.

Or you could use an opacity mask.

[Ongadi · Accepted solution]

Thanks very much for your answer.. It worked. I used Pathfinder >> trim and
the trick worked