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Due to unnoticeable changes in complex refractive index of tissue under varied pathological and physiological states, the traditional optical coherence tomography (OCT) is deficient in molecular characterization. In this paper, the stimulated-emission based optical coherence tomography is proposed, which provides both molecular contrast and scattering contrast OCT imaging simultaneously. Based on the established ultra-high resolution spectral domain OCT system, a pump-probe spectral domain OCT system with a single wide-bandwidth light source is developed through an added modulated pump beam via spectrum splitting. In addition, the theory about the stimulated-emission signal and the image formulation under the modulated pump beam is presented. The coherent detection of the transient stimulated emission is realized by the developed pump-probe spectral domain OCT system. With the stimulated-emission OCT signal and the traditional OCT signal obtained at the same time, molecular contrast OCT images of the samples consisting of nitride powder are reconstructed successfully.

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A full-field optical coherence tomography system using an achromatic phase shifter based on a rotating half-wave plate to implement phase shifting is developed. The phase shifter can achromatically introduce phase shift of eight times the rotating angle of the half-wave plate, and can rapidly provide various phase shifts for various algorithms. Real phase shift is measured and the result demonstrates that the system gives a phase shift of eight times the rotating angle of the half-wave plate, showing the achromatic phase shifter model is correct. Imaging experiment results of a mirror using Hariharan algorithm show that the system has high phase shift precision. A coin as the sample is imaged to demonstrate the performance of the system.

We report on our investigation of the spatial distribution and autofluorescence lifetime characterization of lipofuscin and oxidized melanin in the retinal pigment epithelium cells of the pig eye using a two-photon excitation fluorescence lifetime imaging microscopy (TPE-FLIM) system, which that is based on a time-correlated single photon counting technique. In particular, we analyzed the difference of autofluorescence lifetimes of these pigment granules in light-induced oxidizing environment. The experimental results showed that the fluorescence lifetime imaging can provide an effective differentiation of multi-component fluorophores, and fluorescence decay can be used to distinguish normal from abnormal fluorescence. TPE-FLIM has the potential to provide a high sensitive imaging instrument for the clinical diagnosis and pathological studies in ophthalmology, and is also of significance to the study of aging mechanism of cells in the fundus.