We report on the first, to the best of our knowledge, sub-second, - infrared (IR) spectroscopic measurements of thin organic films employing a laser-based phase-amplitude polarimeter in reflection geometry. The polarimeter uses a broadband mid-IR quantum cascade laser tunable between 1318   and 1765  , as well as a single-shot beam division scheme for simultaneous single-pulse phase and amplitude measurements. The instrument achieves 120 μm spatial and <0.5   spectral resolution, while providing unrivaled performance in terms of acquisition times. Spectral measurements within 100 ms and single-wavelength tracking at 16 μs are now possible. Investigating the vibrational properties accessible in the mid-IR, the polarimeter was applied for monitoring changes in molecular interactions of a 150 nm thin myristic acid film during its thermal phase transition around 55°C.