suppose that infinite thin beam strikes the mirror through the gap between the mirror and the glass, also that the mirror and the glass block are made of the same material, then, there are two scenarios:www.ddhw.com
1. when the incident angle (defined as an angle from the norm) is larger than the critical angle (~83-86 degree), the total refelction occurs, and the reflection beam will be aligned with (or parallel to) the interface of the mirror and the glass block, and in the same plane with the incident beam.
2. when the incident angle (A) is smaller than the critical angle, the reflection beam will come into the glass block with a reflection angle smaller than A. When the beam continues, and comes out from the glass block (into air), it will have an outgoing reflection angle A.