Method for detecting a resonant nonlinear optical signal and device for implementing said method

Device according to any one of the previous claims, comprising a focusing lens (107) for focusing said excitation beam or beams in a common focal volume (45), to intercept an interface between the resonant medium and the non-resonant medium of a sample of the given type.

Device according to any one of the preceding claims, in which the optical detection module (106) comprises at least one shadow mask and at least one detector, enabling detection of the non-linear optical signal integrated into two complementary half-spaces, symmetrical about the optical axis, the difference being taken of the signals integrated into the two half-spaces.

Device according to any one of the preceding claims, also comprising a device for angular scanning of the excitation beam or beams, allowing the excitation beam or beams to intercept a sample of the given type at different positions of the interface between the resonant medium and the non-resonant medium.

Device according to any one of the preceding claims, in which the emission source emits at least one variable wavelength excitation beam, allowing a spectrum of vibrational or electronic resonances of the resonant medium of a sample of the given type to be obtained.

Method for detecting a resonant non-linear optical signal induced in a sample (105), the sample comprising a resonant medium (41) and a non-resonant medium (42) forming an interface (43), the method comprising:

• the emission of at least one first excitation light beam of the resonant medium, called a pump beam, at a first given angular frequency ωp, said pump beam being incident on the sample along an optical axis, and intercepting said interface between the resonant medium and the non-resonant medium,
• the detection of the nonlinear optical signal resulting from the interaction of said beam or beams with an axial interface between the resonant and non-resonant media of the sample, in at least two symmetrical directions ({right arrow over (k)}, {right arrow over (k)}′) about the optical axis, and
• the processing of the nonlinear optical signals thus detected along the at least two symmetrical directions, allowing the difference between said signals to be obtained, the resulting difference signal being characteristic of a vibrational or electronic resonance of the resonant medium of the sample.