Scattering and three-dimensional imaging in surface topography measuring interference microscopy

Simulation-driven machine learning approach for high-speed correction of slope-dependent error in coherence scanning interferometry

Slope-dependent error often occurs in the coherence scanning interferometry (CSI) measurement of functional engineering surfaces with complex geometries. Previous studies have shown that these errors can be corrected through the characterization and phase inversion of the instrument's three-dimensional (3D) surface transfer function. However, since CSI instrument is usually not completely shift-invariant, the 3D surface transfer function characterization and correction must be repeated for different regions of the full field of view, resulting in a long computational process and a reduction of measurement efficiency. In this work, we introduce a machine learning approach based on a deep neural network that is trainable for slope-dependent error correction in CSI. Our method leverages a deep neural network to directly learn errors characteristics from simulated surface measurements provided by a previously validated physics-based virtual CSI method. The experimental results demonstrate that the trained network is capable of correcting the surface height map with 1024 × 1024 sampling points within 0.1 seconds, covering a 178 µm field of view. The accuracy is comparable to the previous phase inversion approach while the new method is two orders of magnitude faster under the same computational condition.

Hyperspectral confocal microscopy in the short-wave infrared range

We demonstrate hyperspectral confocal microscopy in the short-wave infrared (SWIR) range of 1100-1600 nm using a wavelength-scanning laser in tandem with laser scanning confocal microscopy. Confocal microscopy in the SWIR range allows for high-resolution inspection of an integrated circuit (IC) chip, while hyperspectral imaging, together with a chemometric analysis, enables us to identify functional circuit block groups in the acquired image. With the extended capability, the developed instrument can be potentially used for inline inspection and non-invasive failure analysis of IC chips.

Advancing full-field metrology: rapid 3D imaging with geometric phase ferroelectric liquid crystal technology in full-field optical coherence microscopy

Optical coherence microscopy (OCM) is a variant of OCT in which a high-numerical aperture lens is used. Full-field OCM (FF-OCM) is an emerging non-invasive, label-free, interferometric technique for imaging of surface structures or semi-transparent biomedical subjects with micron-scale resolutions. Different approaches to three dimensional full-field optical metrology are reviewed. The usual method for the phase-shifting technique in FF-OCM involves mechanically moving a mirror to change the optical path difference for obtaining en-face OCM images. However, with the use of a broadband source in FF-OCM, the phase shifts of different spectral components are not the same, resulting in the ambiguities in 3D image reconstruction. In this study, we demonstrate, by imaging tissues and cells, a unique geometric phase-shifter based on ferroelectric liquid crystal technology, to realize achromatic phase-shifting for rapid three-dimensional imaging in a FF-OCM system.

Modeling nonlinear optical microscopy in scattering media, part II. Radiation from focal volume to far-field: tutorial

The development and application of nonlinear optical (NLO) microscopy methods in biomedical research has experienced rapid growth over the past three decades. Despite the compelling power of these methods, optical scattering limits their practical use in biological tissues. This tutorial offers a model-based approach illustrating how analytical methods from classical electromagnetism can be employed to comprehensively model NLO microscopy in scattering media. In Part I, we quantitatively model focused beam propagation in non-scattering and scattering media from the lens to focal volume. In Part II, we model signal generation, radiation, and far-field detection. Moreover, we detail modeling approaches for major optical microscopy modalities including classical fluorescence, multi-photon fluorescence, second harmonic generation, and coherent anti-Stokes Raman microscopy.

Modeling nonlinear optical microscopy in scattering media, part I. Propagation from lens to focal volume: tutorial

The development and application of nonlinear optical (NLO) microscopy methods in biomedical research have experienced rapid growth over the past three decades. Despite the compelling power of these methods, optical scattering limits their practical use in biological tissues. This tutorial offers a model-based approach illustrating how analytical methods from classical electromagnetism can be employed to comprehensively model NLO microscopy in scattering media. In Part I, we quantitatively model focused beam propagation in non-scattering and scattering media from the lens to focal volume. In Part II, we model signal generation, radiation, and far-field detection. Moreover, we detail modeling approaches for major optical microscopy modalities including classical fluorescence, multi-photon fluorescence, second harmonic generation, and coherent anti-Stokes Raman microscopy.

Surface topographic characterization of optical storage devices by Digital Holographic Microscopy

In this study, we have used Digital Holographic Microscopy (DHM) for surface topographic characterization of the optical storage devices. Optical storage devices like Compact Discs (CDs) and Digital Versatile discs (DVDs) are used worldwide for memory storage, grating, sensing and spectroscopy applications. These devices can store the information in binary form on a spiral track in the data recording layer. We demonstrate that these data tracks can be characterized through DHM and one can decode the binary data in transmission mode. The experimental results are shown for blank (without data) and burned (with data) areas of CDs and DVDs. The average width of the CD and DVD data track is experimentally found to be 600 ± 30 nm & 230 ± 20 nm, respectively and the thickness of the data recording track is obtained as 80 ± 10 nm. The obtained results are verified by Field Emission Scanning Electron Microscopy (FESEM) measurements and found a very close agreement between the two results. In addition, the proposed method can also be used for manufacturing defect identification and measurement.

Surface measuring coherence scanning interferometry beyond the specular reflection limit

The capability of optical surface topography measurement methods for measurement of steep and tilted surfaces is investigated through modelling of a coherence scanning interferometer. Of particular interest is the effect on the interference signal and measured topography when tilting the object at angles larger than the numerical aperture slope limit (i.e. the specular reflection limit) of the instrument. Here we use theoretical modelling to predict the results across a range of tilt angles for a blazed diffraction grating. The theoretically predicted interference patterns and surface height measurements are then verified directly with experimental measurements. Results illustrate the capabilities, limitations and modelling methods for interferometers to measure beyond the specular reflection limit.

Three-dimensional transfer function of optical microscopes in reflection mode

Three-dimensional (3D) transfer functions build the basis for a comprehensive characterization of optical imaging systems in the spatial frequency domain. Utilizing the projection-slice theorem, the 2D modulation transfer function of an incoherent imaging system can be derived from a 3D transfer function by integration with respect to the axial spatial frequency. For a diffraction limited microscope with homogeneous incoherent pupil illumination, the modulation transfer function equals the 2D autocorrelation function of a circular disc. However, until now to the best of our knowledge no 3D transfer function has been published, which exactly leads to the 2D modulation transfer function of a diffraction limited microscope in reflection mode. In this article, we derive a formula, which after integration with respect to the axial spatial frequency coordinate perfectly fits to the diffraction limited 2D modulation transfer function. The inverse three-dimensional Fourier transform of the 3D transfer function results in a complex-valued 3D point spread function, from which the depth of field, the lateral resolution and, in addition, the corresponding 3D point spread function of both, a conventional and an interference microscope, can be obtained.