This could be done with a laser (and I'll give you one idea of how), but honestly you will probably be better off with an array of infrared LEDs instead of a laser. The infrared LEDs can be treated in much the same way over distances of a few meters. You would collimate each LED with a small lens and then put another lens in front of the receivers (i.e. photodiodes) on the other side## Heading ##.
If you want to do it with a laser, then you will likely want to use one or more laser diodes. They are cheap and reliable and well suited to a simple measurement like power detection. One feature of laser diodes is that the beam produced by them is elliptical. For many applications this is a disadvantage, but for yours it is useful. The beam coming out from the laser diode will be highly divergent and you will need to collimate it with two cylindrical lenses. 791
This will allow you to keep the beam narrow in one direction while allowing it to expand significantly in the other. Theoretically there isn't an upper limit to the ratio of the two beam sizes, but I suspect that a practical upper limit is ~100:1.
If a ratio of 100:1 isn't good enough for you, then you can use a series of beamsplitters such as I've tried to sketch below. In this case you would collimate the laser and send it in from the top of your transmitter bar and a series of evenly spaced beamsplitters would send part of the beam off toward the receiver bar. They could be made to essentially overlap, but you need to be careful not to have too much overlap lest you have significant interference effects (this is one reason that incoherent infrared light might be better). The beamsplitters would need to have properly chosen reflectivities to give the beams an equal amount of power.
Finally, there is the issue of detection. For this you would need an array of photodiodes on the receiver side. Photodiodes typically aren't that large, so you would need to focus the light down onto each one. This would require a pair of cylindrical lenses which are essentially the same as the ones you used to collimate the laser on the other side. 791