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A novel micro optical diffusion sensor (MODS) has been developed that enables high-speed, on-site sensing with a small sample volume and without the use of additives. The diffusion coefficient can be measured by observing the mass diffusion process of the concentration distribution generated by laser-induced dielectrophoresis. In this paper, we propose a novel excitation system using a micro Fresnel mirror (MFM) that consists of two angled micromirrors and can provide interferometric excitation suitable for forming a sinusoidal concentration distribution. In this paper, MFM was successfully fabricated, and mirror angles were in good agreement with the design values calculated by the finite-element method. The contrast of the interference fringe induced by the fabricated MFM was sharp, and its visibility was 0.97. In addition, the diffusion phenomenon induced by MFM was successfully observed as the decay of the diffracted light intensity. As a result, the validity of MFM as an interferometric excitation device for MODS was confirmed.