An absorption spectroscopy apparatus including an elliptical mirror centered on the midpoint between a source/detector and a mirror. The cavity between the elliptical mirror and the source/bolometer and mirror defines an interior volume of a sample cell. Electromagnetic radiation from the source/detector travels along a multi-segment path starting from the source/bolometer toward the elliptical mirror, reflecting off of the elliptical mirror and traveling toward the mirror, reflecting off of the mirror and traveling back toward the elliptical mirror and finally reflecting off the elliptical mirror for a second time and returning toward the source/bolometer. The multiple reflections combined with the focusing effects of the elliptical mirrored surface result in an efficient sampling device. Among other aspects and advantages, the apparatus of the present disclosure is able to use incoherent, non-collimated light sources while maintaining high optical throughput efficiencies.