All-mirror wavefront division interferometer for mid-infrared spectrometry

• DOI: 10.48550/arxiv.2405.18147
• Publication Date: 2024-01-01
• Authors: Zorin, Ivan; Gattinger, Paul; Ricchiuti, Giovanna; Lendl, Bernhard; Heise, Bettina; Brandstetter, Markus
• Keywords: Physics - Instrumentation and Detectors; FOS: Physical sciences; Instrumentation and Detectors (physics.ins-det); Physics - Optics; Optics (physics.optics)

We report on the design of an all-mirror wavefront-division interferometer capable of spectroscopic studies across multiple spectral ranges$\unicode{x2013}$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 $cm^{-1}$ - 4.4 $cm^{-1}$). 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).