Visible imaging Fourier transform spectrometer based on a beam-folding technique

A low-cost visible to Near-infrared Imaging Fourier Transform Spectrometer (IFTS) using a beam-folding technique instead of the spectral folding technique is presented. The retroreflectors are used to replace the plane mirrors to maintain the optical alignments without the adoption of complex active-alignment measures. Fast-scanning mechanism is adopted to avoid the high-cost precise-position control system. The interferogram images at sequential sampling points, spectral images at different wavenumbers and pixel interferograms and spectra of the multimode fiber ends illuminated by a He- Ne laser and a red LED source respectively, are given. The experimental results show that the IFTS based on the beamfolding technique can achieve a spectral resolution of ~15cm^-1 (~0.5nm) when measuring the bright coherent light source (the end of a 600 μm fiber coupled with the He-Ne laser). The resolution is mainly limited by the nonlinearity of the CCD output, the memory size of the PC and the data-transferring speed between the PC and the CCD camera PL-A741. Preliminary results showed that it is suited to the measurement of bright object sources. This restriction is only due to the poor performance of the CCD detector array used in the experiment. A fast-scanning visible-Near infrared IFTS for the objects of low light intensity is feasible when the high-sensitivity CCD camera is adopted.