Everyone goes through this. 
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Raytracing only traces the diffuse light. So you could see a reflection of an object in a mirror, but what you are looking for is the specular light reflected off an object.
You have two options.
1. You can use "Caustics" in Mental Ray. I would look at some of the tutorials on www.edharriss.com. This is pretty CPU intensive, but gives "real" results.
- You can fake by using the projector shader on a spot light. This shader simulates shinning light through piece of film (bitmap) like a "projector". In this case your bitmap would be the "slide" you are trying to project. Just place a spot light, and then go to FxDirector in the Light pull down menu.
If you need to simulate the light beam you can do this with volumetric lights. You can also fake it pretty well by placing gemoetry the shape of the beams you want to see and then apply a material that is constant, transparent and turn on Blur. Playwith the material editor and you'll figure it out quickly.
Hope this helps,
Urp