I need to emit a unidirectional infrared pattern, i.e. the emission cone should have small angle on one dimension and large angle on the other one (basically laser-like in one dimension and normal light on the other). I tried to illustrate this in the image below (alpha should be much bigger than beta, e.g. alpha = 90 degrees and beta = 4 degrees)
I looked into laser diode arrays, but majority of them are high power, which makes them hazardous and thus not suitable for my application.
Covering a normal LED with a mask is something I though about, but it is rather difficult to realize it with the tools that I have. It also reduces the intensity of the infrared, which I wish to avoid. Another approach is to mechanically sweep a low intensity laser diode, using an dc motor, but doesn't fit into my list of requirements (wrt size and cost)
So mainly, I need to find an LED which optically focuses the emitter light in one direction and not the other.
Do you know of such LED (manufacturer, part number, …), or any other solutions that can fulfill the following requirements: low cost, easy to reproduce in large quantities (i.e. 100s), and safe for usage without any protection glass and alike.
Best Answer
It's very difficult to collimate an LED output efficiently, and LED output is not coherent.
But, many laser diodes naturally emit a pattern like you drew. The reason is that the laser cavity is typically several microns across in the horizontal direction, but only a fraction of a micron tall in the vertical dimension. Due to diffraction, this results in an emitted beam with very large divergence vertically (like 40 degree full-angle) and much less divergence horizontally (10, 15, 20 degrees, maybe). For example, see these specs for a 10 mW laser from ThorLabs:
If a radially symetric output beam is needed, special output optics (like the cylindrical lenses mentioned in other answers) are used to correct for the problem.
So what you might really want is just an IR laser diode with no such corrective optics, or with corrective optics only to collimate the beam horizontally.
If you search "line-laser IR" you might also find some devices pre-packaged with suitable optics.
One more note, you expressed some concern about
Realize that the eye safety of a laser depends on how much power the laser can deliver to the roughly 1 mm2 aperture of a human eye. A laser emitting in a long line will only deliver a small fraction of its power to any particular 1 mm2 spot, so the danger is much reduced. Of course, while you're working on the system if you might get your face within a few inches of the laser, or look at it through magnifying optics, you will want to be very cautious to keep the laser off or reduce its output power at that time.