Sensing apparatus includes a transparent window and a LiDAR assembly, including a beam source, which is configured to emit one or more beams of optical radiation along a beam axis, and which is configured to scan the one or more beams over an angular range about the beam axis. A diffractive structure is mounted approximately parallel to the transparent window and positioned to intercept the one or more beams emitted by the LiDAR assembly and turn the beam axis to pass through the transparent window at an angle greater than 30° relative to a normal to a surface of the transparent window.