Der Duden meint dazu:

Nach Abkürzungen folgt ein Leerschritt. Das gilt auch für mehrere aufeinanderfolgende Wörter, die jeweils mit einem Punkt abgekürzt sind: Z. B., u. a. m.

Bei typografischen Fragen hat http://www.duden.de/service/download/textvera... fast immer eine Antwort.

To answer your question, there's generally no space after the period in English, so it's 'i.e.' 'B.C.', 'p.m.'. 'Q.E.D.' and so on.

But please note that this is more of a stylistic question than an orthographic one, so different institutions and individuals may differ and one really can't claim to have the "right" answer here, only a self-consistent one. I tend to leave the periods out entirely (ie, BC, ..)

My favorite AE usage guide (Garner's) says this:

"The question often arises whether to place periods after each letter in an acronym [nb: acronyms like NATO are not at issue here] or initialism [which is what you're talking about]. Searching for consistency on this point is futile. The trend nowadays is to omit the periods; including them is the more conservative and traditional approach... If an initialism is made up of lowercase letters, periods are preferable: 'rpm' looks odd as compared with r.p.m. and 'am' (as opposed to a.m.) looks like the verb."