Interferometric Broadband Coherent Anti-Stokes Raman Scattering microscopy

Hongxia Zhao, Tak W. Kee, Marcus T. Cicerone

 Coherent Anti-Stokes Raman Scattering (CARS) microscopy has many attractive features for biological and materials imaging, including the fact that CARS signal is related to spontaneous Raman Scattering, but it is orders of magnitude more efficient, which is very important in imaging delicate biological specimens.  CARS is a nonlinear scattering technique in which a pump and a Stokes light overlap temporally and spatially to produce anti-Stokes light. The anti-Stokes signal is proportional to the third order polarizability c⁽³⁾, which has both resonant and nonresonant components.  The imaginary part of the resonant signal contains elements with the same lineshape as the spontaneous Raman signal which is of interest. The nonresonant scattered light interferes coherently with the resonant signal so as to distort the lineshapes. Many approaches have been established for reducing nonresonant background, such as heterodyne and interferometric methods. These methods can be used to selectively suppress the nonresonant background, while enhancing the resonant signal, and they allow separation of the real and imaginary parts of the resonant signal, as well as linearization of the resonant signal with respect to concentration of analyte in the sample. We present a new technique for interferometric suppression of the nonresonant background generated by CARS.

 In our application of the heterodyne CARS, a low spectral resolution broadband CARS signal and a high spectral resolution broadband CARS signal interfere with each other. The resultant interference signal contains separate components that are proportional to the real and imaginary parts of the resonant part of, which can be extracted from the overall signal. The nonresonant local oscillator and the resonant signal are generated in the same spot of the sample. As a result, there are no artifacts due to differential chirp between the signal and local oscillator, except in the case of sample birefringence.      

Author Information

            Name:                          Hongxia Zhao and Tak W. Kee

            Mentor’s name:            Marcus T. Cicerone

            Division:                       Polymer 854

            Laboratory:                  MSEL

            Room/Building: 118B/224

            Mail Stop:                    8543

            Telephone #:                 301-975-6782

            Fax #:                           301-975-4977

            Email:                           hongxia.zhao@nist.gov

            Sigma Xi:                      not a member

            Category:                     Materials