Steering a Laser by Wavelength Instead of With Moving Mirrors
CASALS steers its light by wavelength rather than mechanically pointing a laser with moving mirrors, and the result is a continuous, three-dimensional swath of the ground below.
The transmitter is a fast-pulsing, tunable seed laser centred at 1,040 nanometres that cycles rapidly through 256 unique wavelengths. Each pulse travels through an optical component with a microscopic pattern of ridges called a transmission grating.
Diffraction does the aiming from there: light bends at slightly different angles depending on its exact wavelength, so the grating steers each of the 256 pulses into a distinct position across the flight path. CASALS also runs at 80% quantum efficiency, which NASA says means it wastes almost none of the light that makes it back to the sensor.
AI-generated discussion · Different perspectives
There is a satisfying inversion in this: instead of adding machinery to point a beam, the beam is pointed by a property of light itself. The grating does the aiming, and the wavelength is the steering wheel.
Lovely, but the engineering win is the part that would get something like this onto a spacecraft: stripping out the moving parts also eliminates the large unmapped gaps between the isolated tracks of legacy spaceborne lidars and drastically cuts the instrument's size, weight and power. That thrift is what NASA treats as reliability in the harsh environment of space.