All-mirror wavefront division interferometer for Fourier transform spectrometry across multiple spectral ranges

Abstract

We report on the design of an all-mirror wavefront-division interferometer capable of spectroscopic studies across multiple spectral ranges—from the plasma frequencies of metals to terahertz wavelengths and beyond. The proposed method leverages the properties of laser sources with high spatial coherence. A theoretical framework for the interferometer scheme is presented, along with an analytical solution for determining the far-field interference pattern, which is validated through both optical propagation simulations and experimental results. The practical implementation of the spectrometer, using cost-effective off-the-shelf components (knife-edge prisms for separation and recombination), is demonstrated. The system features ultra-broad optical bandwidth, high throughput, simple architecture, dispersion-free operation, and variable arm split ratio. These unique attributes make our approach a prospective alternative to standard Fourier transform spectrometer schemes, specifically tailored to laser-based scenarios. Further, the employed design inherently enables the measurement of the sample’s dispersion. In the experimental section, we demonstrate the feasibility of spectroscopic measurements by coupling the system with a supercontinuum source with more than an octave-spanning range (1.5 µm - 4.4 µm). As a proof-of-concept, an experimental demonstration is provided for various applied spectroscopic studies: transmission measurements of polymers (polypropylene) and gas (methane), as well as reflectance measurements of dried pharmaceuticals (insulin products on a metal surface).