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. 2018 May 9;8:7431. doi: 10.1038/s41598-018-25501-w

Figure 1.

Figure 1

Two possible schemes to estimate the absorption coefficient α. In the single-mode case (a) and (b) there is no correlation between probe and reference beam, i.e. 〈ΔNpΔNR〉 = 0 while in the two-mode case (c) and (d) 〈ΔNpΔNR〉 ≠ 0. Different possibilities of input states and absorption estimators for both the schemes are discussed in the text.