how to detect ir beam
Did you try a video or still camera? Usual camera chips are sensitive for near IR as well. Available IR sensor cards are most likely not sensitive enough to detect the beam at that distance.
Do you use a complex optic system to concentrate the beam? If not, about any mobile phone with camera can "see" IR - it's portable and easy to use.
Frank are you proposing to detect the reflection of the transmitted IR from the background near the receiver (suppose the reciever is mounted on a wall)? That could work. May be, a temporary background could be placed behind the reciever during the alignment.
Another device that could work (similar approach) is a nigh-vision goggle - they are sensitive to IR. Civillian night vision tubes can be relatively inexpensive.
I'd also like to invite your question to a group dedicated to sensors: http://tech.groups.yahoo.com/group/sensorforum
