A sensor system having a multi-pass interaction region is disclosed. The system includes an input region, a multi-pass region, and an output region. The input region is configured to receive emitted light. The multi-pass region is coupled to the input region and is configured to absorb portions of the emitted light according to a specimen proximate the multi-pass region. The output region is coupled to the multi-pass region and is configured to provide interacted light from the multi-pass region.