In an embodiment, a slim imager is disclosed. The slim imager includes a substrate including an aperture, an image sensor, and an optics unit. The image sensor is on a bottom side of the substrate, spans the aperture, and has an aperture-facing top surface. The optics unit is on a top side of the substrate, spans the aperture, and includes a transmissive optical element having an aperture-facing bottom surface. A volume partially bound by the aperture-facing top surface and the aperture-facing bottom surface has a refractive index less than 1.01 at visible wavelengths.