Light guide for infra red emitter

Hi,

I have posted this on the optical engineering forum, but I realise that peole may had this problem or know the answer on this forum.

I am designing a hand held infra red transmitter, I need to produce a light guide to get the infra red out of the case into the environment, so that the infra red receiver can pick up the signal. I am fairly happy about the coupling of the infra red led's into the light guide and I intend to have highly polished surfaces on the inside of the light guide in the case in order to enable me to transmit as much light through the light guide. The thought I am having is the exit surface, I obviously want to exit as much light as I possibly can and therefore I assume I need to minimise the internal reflection as much as possible on the exit surface. Does this mean this surface should be diffused? or alternatively should it be a highly polished surface, because I am not interested in even light distribution, just simply getting my light signal out?

Any help or thought would be appreciated.

Andy