@misc{fohrmann_freecarrier_detection_2019, 
author={Fohrmann, L.S.,Lotfi, N.,Alzein, B.,Gaafar, M.A.,Petrov, A.Y.U.,Eich, M.},
title={Free-carrier detection in a silicon slab via absorption measurement in 2D integrating cells},
year={2019},
howpublished = {journal article},
doi = {https://doi.org/10.1364/OL.44.000175},
abstract = {2D integrating cells provide long optical path lengths on a chip by multiple reflections at highly reflective mirrors similar to integrating spheres in free space. Therefore, they build a promising platform for integrated optical absorption sensing. Here, we present first absorption measurements of free carriers generated by a modulated pump laser inside a 2D integrating cell in a silicon slab. The results can be used to evaluate the lifetimes of free carriers in silicon slabs for integrated optics. Employing a silicon-on-insulator platform with a silicon thickness of 220 nm, we demonstrate measurements of the access free-carrier concentration on the order of 1−8·1015 cm−3 with lifetimes on the order of 0.1–1 μs governed by surface recombination at the silicon interfaces. The measured lifetimes are dependent on free-carrier concentration, which confirms previous observations. The presented free-carrier absorption experiment verifies the sensitivity of 2D integrating cells to changes in the absorption coefficient and thus demonstrates the potential of 2D integrating cells for absorption sensing.},
note = {Online available at: \url{https://doi.org/10.1364/OL.44.000175} (DOI). Fohrmann, L.; Lotfi, N.; Alzein, B.; Gaafar, M.; Petrov, A.; Eich, M.: Free-carrier detection in a silicon slab via absorption measurement in 2D integrating cells. Optics Letters. 2019. vol. 44, no. 1, 175-178. DOI: 10.1364/OL.44.000175}}