An optical device includes a light source, which is configured to emit a beam of light, and a sensor having a detection area. At least one scanning mirror is configured to scan the beam across a target scene. Light collection optics include a collection lens positioned to receive the light from the scene that is reflected from the at least one scanning mirror and to focus the collected light onto a focal plane, and a non-imaging optical element having a front surface positioned at the focal plane of the collection lens and a rear surface in proximity to the sensor and configured to spread the light focused by the collection lens over the detection area of the sensor.