Nonlinear Interferometric Vibrational Imaging

Coherent anti-Stokes Raman scattering (CARS) processes are “coherent,” but the phase of the anti-Stokes radiation is lost by most incoherent spectroscopic CARS measurements. We propose a Raman microscopy imaging method called nonlinear interferometric vibrational imaging, which measures Raman spectra by obtaining the temporal anti-Stokes signal through nonlinear interferometry. With a more complete knowledge of the anti-Stokes signal, we show through simulations that a high-resolution Raman spectrum can be obtained of a molecule in a single pulse using broad band radiation. This could be useful for identifying the three-dimensional spatial distribution of molecular species in tissue.

Figure 1

Schematic of NIVI with a broad band continuum source, using the continuum for the reference pulse. The detection scheme is simplified, and in practice a single-shot detection scheme such as 13, 14 could be used.

Figure 2

NIVI input and output pulses, and the original and reconstructed Raman spectra in first simulation. (a) Temporal shape of amplitude of input pulse. (b) Power spectral density of input pulse. (c) Power spectral density of output pulse. (d) Power spectrum of beat frequencies of input pulse. (e) Magnitude of Raman susceptibility of hypothetical molecule. (f) Magnitude of least-squares reconstructed Raman susceptibility of hypothetical molecule.

Figure 3

Original and reconstructed Raman spectra in second simulation. (a) Power spectrum of beat frequencies of input pulse. (b) Magnitude of Raman susceptibility of hybrid DNA/RNA sample. (c) Magnitude of least-squares reconstructed Raman susceptibility of hybrid DNA/RNA sample.