A very accurate measurement of the absorption coefficient of liquid water using a tunable diode laser double beam spectrometer is presented. The water absorption coefficient is 123 ± 1.8 cm−1 at 2590 cm−1 obtained by nonlinear least squares fitting to an exact transmittance formula including the effect of multiple reflections at all four window surfaces, using only the nominal values of the refractive indices of water and window of ZnSe.
