Interferometry-based downhole analysis tool

A downhole tool that comprises:

• a downhole light detector;
• a downhole interferometer on an optical path between a broadband light source and the light detector, wherein the interferometer produces, from light received along the optical path, a spectralized beam having a spectral composition with multiple frequency components measurable from time variations of the spectralized beam's intensity;
• a window on the optical path that enables light received along the optical path to illuminate a material to be analyzed, wherein the material is a borehole fluid or part of a borehole wall;
• and
• processing electronics coupled to the light detector to detect an electrical signal representing time variations of the spectralized beam's intensity and to determine therefrom the multiple frequency components and a parameter of the material,
• wherein the interferometer includes a spinning retroreflector having a position encoder coupled to the processing electronics.

A downhole analysis method that comprises:

• directing light from two downhole light sources along an optical path that includes a downhole interferometer and a window for downhole sample illumination, wherein the downhole sample is a borehole fluid or part of a borehole wall;
• modulating one arm length of the interferometer as a function of time to produce a spectralized beam before the light reaches a downhole detector, the spectralized beam having a spectral composition with multiple frequency components measurable from time variations of the spectralized beam's intensity;
• measuring time variations of the spectralized beam's intensity with the downhole detector;
• and
• using the measured time variations of the spectralized beam's intensity to determine the multiple frequency components and a property of the downhole sample.