About 1995 a company that makes laser sights for firearms developed something for pool called the "Laser Shark". It clamped to your own cue stick between the grip and the joint. It projected a vertical fan-shaped beam.
The best setup was shooting towards a white wall. The beam would show two stroke defects well: side-to-side motion and twisting motion. It was not particularly accurate for aiming since there was no good way to align the beam with the exact axis of the cue stick -- it might be useful for aiming short shots to get the concept of fractional ball aiming across. From an instructor's perspective, it was marginally useful for some students' problems.
A main downside was that the device weighed several ounces which changed the feel of the cue. Also, since it mounted above the stick, it tended to rotate the stick to the hang-down position.
Another problem is that it cost $100.
It would be possible to improve the product. The battery could be below the cue stick to eliminate the rotation problem. It could be a lot lighter if a different mounting system was used. I imagine it would be possible to sell a dedicated cue with the laser permanently mounted accurately and the battery inside the cue for about $100.
Some of the hobby laser pointers come with a variety of lenses including a fan-beam lens.