Laser and VCSEL
The main difference between laser diodes and LEDs is that the light generated in the pn junction is not emitted over the entire surface of the chip as for LEDs, but only in a very small window at the edge of the chip. This turns laser diodes into edge emitters and, due to the very small exit window, lasers are coherent light sources. In addition to the high energy density of the light, this coherence is an important property. The small exit window allows the light to be very strongly focused into an almost exactly parallel beam. With VCSEL (Vertical Cavity Surface Emitting Laser), the emitting surface is larger than with classic laser diodes and is located on the top face of the semiconductor chip. This makes the geometric design of a VCSEL simpler than that of laser diodes, where the chip generally has to be arranged vertically. Both components are suitable as light sources for optical measurement tasks, especially for long distances.