System and method for high sensitivity vibrational imaging with frequency modulation coherent anti-stokes Raman scattering analyses

A system for detecting a nonlinear coherent field induced in a sample, said system comprising:

• a source system for generating a first electromagnetic field at a first frequency, a second electromagnetic field at a second frequency that is different from said first frequency, and a third electromagnetic field at a third frequency that is different from said first frequency and different from said second frequency;
• modulation means for providing a modulated electromagnetic field that is switched between said second and third frequencies at a modulation frequency;
• optics for directing said first electromagnetic field and said modulated electromagnetic field toward a common focal volume;
• and
• detector means for detecting a nonlinear coherent field that is generated responsive to said first and modulated electromagnetic fields in the focal volume.

A method of detecting a nonlinear coherent field induced in a sample, said method comprising the steps of:

• directing a first electromagnetic field at a first frequency ω1 and a second electromagnetic field at a second frequency ω2 toward a focal volume such that a difference frequency ω1–ω2 is resonant with a vibrational frequency of a sample in the focal volume;
• modulating the difference frequency ω1–ω2 such that the difference frequency ω1–ω2 is tuned in and out of the vibrational frequency of the sample at a modulation frequency;
• detecting an optical field that is generated through non-linear interaction of ω1 and ω2 and the sample responsive to the modulation frequency;
• and
• providing an output signal to a computer that is representative of the detected optical field that is generated through non-linear interaction of ω1 and ω2 such that coherent anti-Stokes Raman scattering analysis may be performed on the sample.