Can a ToF distance sensor / LiDAR work when bounced off a mirror?

In theory, a ToF sensor or LiDAR can work with a mirror, but it depends on the setup.

A ToF sensor measures distance by sending light out and measuring the time it takes for the reflected light to return. A mirror does not reflect light back randomly like a normal surface; it follows the law of reflection, where the angle of incidence equals the angle of reflection.

If the mirror is positioned correctly so that the reflected light returns to the receiver, the sensor may measure the distance to the mirror (or the object reflected in the mirror). However, small changes in angle, vibration, or alignment can cause the reflected signal to miss the receiver completely.

This is why LiDAR systems usually work better with diffuse-reflective objects such as walls, floors, and most everyday objects. Highly reflective surfaces like mirrors, glass, or shiny metals can cause inaccurate readings or signal loss.

Modern DToF LiDARs using SPAD-based receivers can improve sensitivity, but they still follow the same optical principles.

For example, HM-LD1 uses SPAD-based direct ToF technology to detect reflected photons, so stable ranging depends on receiving enough returned photons from the target surface.