Broadband interferometric microscopy (BIM) refers to microscopy techniques and methods that use the frequency of light and interferometric detection to infer the volumetric spatial structure of the scattering object. The goal is to achieve three-dimensional imaging with high resolution over large fields of view and extended depths. The interference of coherent signals in BIM is challenged by the separation of the conjugate signals and autocorrelation. The conjugate signal leads to a mirrored image of the object (coherent artifacts) that may foreshadow key features of the object and reduce the depth range of the reconstructed image. In addition, with the use of microscope systems with high numerical aperture, BIM is challenged to image objects with uniform high resolution over extended depths due to the short depth of the in-focus region. In consequence, object features of the imaged object located away from the focal plane become blurred (depth-dependent defocus), compromising the utility of the broadband illumination. Moreover, phase fluctuations in the interferometer due to mechanical vibrations may further degrade the quality of the final reconstructed image. This is especially critical for some metrology and biomedical applications where phase is of the utmost importance.
Researchers at the University of Rochester have invented a device that uses broadband/swept-source coherence confocal microscopy in combination with interference objectives and synthetic-phase modulation. This device achieves three-dimensional imaging with uniform high resolution over extended depths that is phase-sensitive and free of coherent artifacts. Researchers have also developed a coherent broadband backscattering model and inversion reconstruction algorithm, including the effect of the sinusoidal synthetic-phase modulation approach. The invention integrates an easily implemented, low-speed, low-amplitude phase modulation to encode detected image information. This effectively circumvents the caveat of a fixed reference arm in interference objectives. With this encoding, refocusing within the reconstructed object as well as suppression of artifacts from a single acquired image is possible.
This is the first time interference objectives can be used in broadband interferometry for three-dimensional imaging with extended depths. The encoding can be implemented in a variety of existing narrow-band and wide-band interferometric imaging platforms: optical coherence tomography, optical coherence microscopy and interferometric reflectance confocal microscopy. The invention also incorporates a window, which when applied over the sample being imaged provides information to both validate the system performance and optimize the reconstruction algorithm. Together the phase modulation, model, algorithm and window provide a complete solution to volumetric reconstruction.
Biomedical and metrology applications such as histopathology, surface profilometry, metrology inspection. Also, pre-existing imaging modalities such as optical coherence tomography, optical coherence elastography, and quantitative phase imaging.
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