Multi-spectral LIDAR using a 2-dimensional dynamic diffraction grating: how to get nanosecond resolution from a projector and a camera

The rapid angular sweep of mirrors in a micro-mirror array (digital micromirror device - DMD) creates a dynamic diffraction grating and when coupled with a camera produces a form of streak camera, which is able to give temporal dispersion as well as spectral dispersion. Three pulsed lasers of different wavelengths (red, green and blue) were combined into a single fibre and then focussed onto a target. Multiple collection heads were used to collect the reflected light and deliver it via separate fibres within an array to the DMD streak camera. Each fibre is imaged through the streak camera such that the temporal and spectral characteristics from each fibre channel are separate and distinguishable on the camera image. The lasers are fired via a delay triggered by the start of the micro mirror’s motion and the scale of the delay determines the distribution of intensity on the camera. Thus, the system is behaving as a multispectral and multichannel LIDAR, with temporal resolution at the level of 1nS, which is somewhat surprising considering that the DMD frame rate is limited to 10kHz.