ABSTRACT
A new formulation of the lateral imaging process of point-scanning optical coherence tomography (OCT) and a new differential contrast method designed by using this formulation are presented. The formulation is based on a mathematical sample model called the dispersed scatterer model (DSM), in which the sample is represented as a material with a spatially slowly varying refractive index and randomly distributed scatterers embedded in the material. It is shown that the formulation represents a meaningful OCT image and speckle as two independent mathematical quantities. The new differential contrast method is based on complex signal processing of OCT images, and the physical and numerical imaging processes of this method are jointly formulated using the same theoretical strategy as in the case of OCT. The formula shows that the method provides a spatially differential image of the sample structure. This differential imaging method is validated by measuring in vivo and in vitro samples.
ABSTRACT
Optical resolution of far-field optical microscopy is limited by the diffraction of light, while diverse light-matter interactions are used to push the limit. The image resolution limit depends on the type of optical microscopy; however, the current theoretical frameworks provide oversimplified pictures of image formation and resolution that only address individual types of microscopy and light-matter interactions. To compare the fundamental optical resolutions of all types of microscopy and to codify a unified image-formation theory, a new method that describes the influence of light-matter interactions on the resolution limit is required. Here, we develop an intuitive technique using double-sided Feynman diagrams that depict light-matter interactions to provide a bird's-eye view of microscopy classification. This diagrammatic methodology also allows for the optical resolution calculation of all types of microscopy. We show a guidepost for understanding the potential resolution and limitation of all optical microscopy. This principle opens the door to study unexplored theoretical questions and lead to new applications.
ABSTRACT
Coherent Raman scattering microspectroscopy, which includes coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microspectroscopy, permits label-free hyperspectral imaging. We report the theoretical study of the phase-shift effect of the impulse response function on the spectral and image-forming properties of coherent Raman scattering microspectroscopy. We show that the spectrum and image are influenced by not only the NA of objective for excitation (NA(ex)) but also that for signal collection (NA(col)), in association with the phase-shift effect. We discuss that, under the condition NA(ex)≠NA(col), both the spectrum and the image become deformed by the phase-shift effect, which can be applied to the direct measurement of the imaginary part of the nonlinear susceptibility in CARS spectroscopy. We point out that, even in SRS microscopy, the nonresonant background can contribute to the image formation and cause the artifact in the image.
ABSTRACT
Third-order sum frequency generation (TSFG) is one of the third-order nonlinear optical processes, and has the generation mechanism analogous to third harmonic generation (THG). By using a white-light supercontinuum, we can obtain broadband multiplex TSFG spectra. In the present study, we developed an electronically resonant TSFG spectrometer, and applied it to obtain TSFG spectra of hemoproteins. Analyzed TSFG ratio spectra clearly showed the resonant enhancement attributable to the electronic state of hemoproteins. This is a promising method for the imaging of electronic states of molecules inside living cells or tissues.
ABSTRACT
We analyze the optical resolution of Fourier transform spectral interferometric-coherent anti-Stokes Raman scattering microscopy, which extracts the complex amplitude of an image by using a spectral interferometric effect. Image-formation formulas are presented that describe the properties of the image observed by the apparatus. The image-formation properties represented by the coherent transfer function are different depending on the mode (transmission, reflection, etc.) of the microscopy.
Subject(s)
Interferometry/methods , Optics and Photonics , Spectroscopy, Fourier Transform Infrared/methods , Spectrum Analysis, Raman/methods , Diagnostic Imaging/methods , Fourier Analysis , Image Processing, Computer-Assisted , Microscopy/methods , Models, Statistical , Scattering, RadiationABSTRACT
We analyze the resolution properties of nonlinear optical microscopy systems that use nonlinear optical effects, such as multiphoton-excited fluorescence, second- and third-harmonic generation, coherent anti-Stokes Raman scattering, and stimulated-emission depletion. Image formation formulas are presented that unitedly describe the properties of the image observed, wherein coherent, incoherent, or mixed-coherent phenomena are utilized. We develop the formalism for the optical resolution of all types of nonlinear systems. The properties of image formation represented by the transmission cross-coefficient are different depending on the type of nonlinear systems.
ABSTRACT
We propose a three-dimensional phase contrast digital holographic microscopy. The object to be observed is a low-contrast transparent refractive index distribution sample, such as biological tissue. Low contrast phase objects are converted to high contrast images through the microscopy we propose. In order to gain high three-dimensional resolution, the direction of pump plane wave is scanned, and separate holographic images produced at each angle are acquired and decoded into complex amplitude in Fourier space. The three-dimensional image is reconstructed in a computer from all information acquired through the system. The resolution in the direction of the optical axis is increased by utilizing a 4pi configuration of objective lenzes.
