Mid-­Infrared Optical Coherence Tomography

Abstract

Optical coherence tomography (OCT) is implemented for a number of beneficial applications such as biomedical imaging, art conservation, and industrial process control. Previous attempts [3][4] to build a mid-infrared (mid-IR) OCT system have only been done using quantum cascade lasers (QCL) with discrete emission spectra and, thus, sidebands in the interferogram as well as a low signal to noise ratio (SNR) or with quantum cascade superluminescent (QCSL) light emitting diodes (LED) which do not generate enough optical power to penetrate deeply in water containing samples such as tissue. A recently developed high-power, low-coherence QCSL emitter eliminates all of these restrictions on performance. This thesis aims to develop a high performance OCT system with this emitter as the source. The OCT system was designed to imitate a Michelson interferometer where constructive interference leads to peaks in the interferogram that correspond to each interface within a sample. The following three samples were scanned successfully: a mirror, a KBr window, and conjoined KBr and ZnSe windows. The OCT measured distance between surfaces was within 0.05% of the actual width for the KBr window. In addition, a 1” diameter, 1” focal length Si lens was used to focus the beam onto a mirror sample resulting in a successful measurement of the location of the mirror surface, implying a symmetric emission and preparing the project for multidimensional imaging.