Nonlinear Optical Microscope

Nonlinear confocal microscopy, such as two-photon fluorescence (TPF) and multi-photon fluorescence (MPF), second-harmonic generation (SHG) and third-harmonic generation (THG), Coherent anti-Stoke Raman Scattering (CARS) microscopy, has been demonstrated the potential applications in biomedicine, biology and material science et al. As a powerful optical imaging technique, nonlinear confocal microscopy intrinsically provides three-dimensional (3-D) imaging capability and potentially produces image contrast with chemical and physical specificity inside scattering samples. However, is it feasible to utilize Raman induced Kerr effect spectroscopy (RIKES) imaging? No person studies it systematically.In RIKES imaging, a strong circularly polarized pump beam at frequencyω₁ and a weak, y-polarized bean at frequencyω_s are employed. The pump beam modulated nonlinearly on the probe beam, i.e., the imaging beam. When the frequency differenceω_l-ω_s is tuned to match the frequency of a Raman modeω_R, i.e.,ω_l-ω_s=ω_R, the pump beam can induce an enhanced circular birefringence, which consequently causes a polarization rotation of the linearly polarized probe beam, termed Raman induced Kerr effect spectroscopy (RIKES). Beside the above advantages of nonlinear confocal microscopy, RIKES imaging is capable to characterize inherent structural features, such as vibration mode, vibration orientation, and optically-induced molecular reorientation et al. Considering that Raman spectrum is the fingerprint of the molecular structure, So RIKES imaging on the vibration mode can provide the basis for molecular identification, which is significant in molecular imaging and single molecular detection.If RIKES imaging is utilized instead of two-photon fluorescence, SHG and CARS imaging, it has potential to provide a novel sub-diffraction limit characteristic imaging method comparable to the existing imaging techniques based on other nonlinear optical processes, such as two-photon fluorescence, SHG and CARS.In this paper, a novel nonlinear confocal microscopy that utilizing Raman induced Kerr effect spectroscopy (RIKES) is presented. The imaging theory of RIKES confocal microscopy is derived. The imaging properties of RIKES confocal microscopy has been analyzed in detail. The main contents are as follows:Firstly, the physical mechanism of RIKES generation is discussed. A novel nonlinear imaging utilizing RIKES is presented. The characteristic of RIKES imaging is analyzed in detail.Secondly, according to Fourier imaging theory and nonlinear optical principle, the imaging theory of RIKES nonlinear confocal microscopy is derived. With the imaging theory, the impact of nonlinear property of RIKES on the spatial resolution and imaging properties of confocal microscopy has been analyzed in detail. Aditionally, the three-dimensional optical transfer function (OTF) of RIKES nonlinear confocal microscopy is calculated.Thirdly, considering the Gaussian distribution of source function, the three-dimensional point spread function of RIKES confocal microscopy is derived. The spatial modulation mechanism of pump beam on the probe beam is discussed.Finally, a novel differential confocal microscopy is developed based on a time-resolved technique and confocal scanning technique. The imaging theory of differential confocal microscopy is derived. The three-dimensional point spread function of differential confocal microscopy is derived. It is shown the differential confocal imaging technique can break through the classic diffraction limit and achieve high-resolution imaging.