Under the Hood of Luminar’s Long-Reach Lidar – IEEE Spectrum

http://spectrum.ieee.org/cars-that-think/transportation/self-driving/under-the-hood-of-luminars-long-reach-lidar

Current automotive lidars scan their surroundings by firing pulses from semiconductor diode lasers emitting at 905 nanometers in the near infrared and recording reflected light to build up a point cloud mapping the car’s surroundings. 

But laser-safety rules in the U.S. and other countries restrict the power in the laser pulse, limiting the lidar’s range only to 30 to 40 meters for lidars that use 905-nm infrared light .
This spring, the U.S. startup Luminar Technology announced a lidar able to achieve that 200-meter range by using a 1550-nm laser.

The retina in eye does not respond to the 905-nm infrared light used in current car lidars, but the eye transmits 905 nm to the retina.

Essentially no light at wavelengths beyond 1400 nm reaches the retina, so laser safety standards allow higher output at longer wavelengths. Luminar’s lasers fire pulses 40 times more powerful at 1550 nm than 905-nm lasers are allowed to fire.

Developers of non-automotive lidars consider 1550 nm a “sweet spot,” Lasers and sensors for 1550 nm cost more than those for 905 nm.