Polarization acquisition using a commercial Fourier transform spectrometer in the MWIR Michael W. Kudenov, Nathan A. Hagen, Haitao Luo, Eustace L. Dereniak, Shawn Robertson, Leonardo G. Montilla, Tom B. Vo, Justina Tam, Julia D. Nichols, College of Optical Sciences / The University of Arizona. Grant R. Gerhart, U.S. Army Tank-Automotive Research, Development and Engineering Ctr. ABSTRACT A spectropolarimeter utilizing an Oriel MIR8000 Fourier Transform Spectrometer in the MWIR is demonstrated. The use of the channeled spectral technique, originally developed by K. Oka, is created with the use of two AR coated Yttrium Vanadate (YVO 4 ) crystal retarders with a 2:1 thickness ratio. A basic mathematical model for the system is presented, showing that the Stokes parameters are directly present in the interferogram. Theoretical results are then compared with real data from the system, an improved model is provided to simulate the effects of absorption within the crystal, and error between reconstructions with phase-corrected and raw interferograms is analyzed. Keywords: Yttrium Vanadate, spectropolarimeter, Fourier transform spectrometer, channeled spectrum. 1. INTRODUCTION The use of a Fourier Transform Spectrometer (FTS) has many advantages over other forms of spectroscopic measurement, such as the use of a diffraction grating, in the MWIR. Predominantly, the FTS maintains the throughput (Jacquinot) and multiplex (Fellgett) advantages. 1,2 Yet aside from this, the FTS has another unique benefit for working with the channeled spectropolarimetric technique implemented by K. Oka 3 ; the FTS operates directly Fourier space through its interferometer. This is important because it provides a more direct method of acquiring the polarization data directly from the interferogram. Consequently, this provides another advantage for the FTS in terms of data processing, although it may not be so reliable to do without phase correcting the interferogram. Here, we describe some aspects of our proof of concept experiments. First, we will describe the theoretical model behind the spectropolarimetric technique with an FTS. This will be followed with our laboratory results by means of a commercial FTS in the MWIR using Yttrium Vanadate (YVO 4 ) crystal retarders. Detailed error analyses will be provided, and an improved system model will be discussed and simulated. Lastly, the effect of phase-correction on the reconstructions will be analyzed and compared to non phase-corrected results. 2. SYSTEM MODEL The basic setup of the Fourier Transform Spectropolarimeter (FTSP) can be seen in figure 1. It consists of two high- order retarders R 1 and R 2 with thicknesses d 1 and d 2 followed by an analyzer. The orientation of the retarders, with respect to their fast axes relative to the transmission axis of the analyzer, is 0° and 45° for R 1 and R 2 respectively. The output is then fed into an interferometer, where it is read and reconstructed on a computer. Figure 1. Basic FTSP block diagram. Infrared Detectors and Focal Plane Arrays VIII, edited by Eustace L. Dereniak, Robert E. Sampson, Proc. of SPIE Vol. 6295, 62950A, (2006) · 0277-786X/06/$15 · doi: 10.1117/12.688401 Proc. of SPIE Vol. 6295 62950A-1