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We propose and demonstrate the novel method that enables simultaneous measurements of physical thickness and refractive group index without any prior knowledge on samples. The system is based on the spectral-domain optical low coherence interferometry with two sample probes facing each other. Owing to both side measurements schemes, thickness and group refractive index could be measured with not only transparent but also highly absorptive samples. The average errors were ~0.06% in both the physical thickness and the group refractive index measurements.