Optical imaging of mineral species using hyperspectral modulation transfer techniques

A method of imaging a sample containing a target mineral species and other constituent species, the method comprising:

• a) generating a pump beam and a Stokes beam comprising of a train of short pulses and having a tunable optical frequency difference;
• b) imposing a modulation on one of the pump beam and Stokes beam;
• c) probing an array of probed regions of the sample with the pump beam and Stokes beam jointly, said probing comprising varying the optical frequency difference between the pump beam and Stokes beam over an optical frequency range encompassing at least one known Raman resonance of the target mineral species, said probing further comprising detecting, for each frequency of said optical frequency range for each of the probed regions of said array, an optical response of the sample resulting from a transfer of said modulation between the pump beam and the Stokes beam, thereby obtaining hyperspectral data of said optical response over said optical frequency range for each of the probed regions;
• d) identifying a first subset of the probed regions containing the target mineral species through a correlation of the hyperspectral data with the at least one known Raman resonance of the target mineral species;
• e) identifying a second subset of the probed regions containing one of the other constituent species through a correlation of the hyperspectral data with a non Raman-resonant contribution to said optical response;
• f) building an image of the sample by mapping the first and second subsets of the probed regions thereon.