Fresnel incoherent correlation holography (FINCH) was a milestone in incoherent holography. In this roadmap, two pathways, namely the development of FINCH and applications of FINCH explored by many prominent research groups, are discussed. The current state-of-the-art FINCH technology, challenges, and future perspectives of FINCH technology as recognized by a diverse group of researchers contributing to different facets of research in FINCH have been presented.
The key information about any nanoscale system relates to the orientations and conformations of its parts. Unfortunately, these details are often hidden below the diffraction limit, and elaborate techniques must be used to optically probe them. Here we present imaging of the 3D rotation motion of metal nanorods, restoring the distinct nanorod orientations in the full extent of azimuthal and polar angles. The nanorods imprint their 3D orientation onto the geometric phase and space-variant polarization of the light they scatter. We manipulate the light angular momentum and generate optical vortices that create self-interference images providing the nanorods' angles via digital processing. After calibration by scanning electron microscopy, we demonstrated time-resolved 3D orientation imaging of sub-100 nm nanorods under Brownian motion (frame rate up to 500 fps). We also succeeded in imaging nanorods as nanoprobes in live-cell imaging and reconstructed their 3D rotational movement during interaction with the cell membrane (100 fps).
Gold , Nanotubes , Motion
The phase of monochromatic light directly relates to the optical path difference (OPD), but finding this connection for spectrally broadband light is challenging. Due to a missing concept of the compatibility between the phase of randomly fluctuating fields and the OPD, demanding scanning is the only proven way for a highly accurate OPD measurement in white light. Here, we use the self-coherence function (SCF) of the spatially incoherent light to reveal the connection between the white-light phase and the OPD. Our method uses an associated field assigned to the SCF to mimic the intensity oscillation of a correlation pattern. The associated field allows restoring a cumulative OPD integrated into the SCF across all spectral constituents. The method is essential for quantitative phase microscopy, in which the SCF is available even in white light, but its processing beyond the quasi-monochromatic approach is still lacking. Improper assessment of the white-light phase may result in a loss of measurement accuracy, as we demonstrate theoretically and experimentally. Deploying our method in coherence-controlled holographic microscopy, we measured the cumulative OPD in the broadband light with a strongly asymmetric spectrum (bandwidth of 150â nm), achieving accuracy better than 5â nm in the measuring depth range of 2â µm.
Measuring rough surfaces is challenging because the proven topographic methods are impaired by the adverse effects of diffuse light. In our method, the measured surface is marked by fluorescent nanobeads allowing a complete suppression of diffuse light by bandpass filtering. Light emitted by each fluorescent bead is shaped to a double-helix point spread function used for three-dimensional bead localization on the surface. This non-interferometric measurement of rough surface topography is implemented in a vibration resistant setup. The comparison of our method with vertical scanning interferometry shows that a commercial profiler is surpassed when ground glass surfaces with steep slopes are measured.
We present geometric-phase microscopy allowing a multipurpose quantitative phase imaging in which the ground-truth phase is restored by quantifying the phase retardance. The method uses broadband spatially incoherent light that is polarization sensitively controlled through the geometric (Pancharatnam-Berry) phase. The assessed retardance possibly originates either in dynamic or geometric phase and measurements are customized for quantitative mapping of isotropic and birefringent samples or multi-functional geometric-phase elements. The phase restoration is based on the self-interference of polarization distinguished waves carrying sample information and providing pure reference phase, while passing through an inherently stable common-path setup. The experimental configuration allows an instantaneous (single-shot) phase restoration with guaranteed subnanometer precision and excellent ground-truth accuracy (well below 5 nm). The optical performance is demonstrated in advanced yet routinely feasible noninvasive biophotonic imaging executed in the automated manner and predestined for supervised machine learning. The experiments demonstrate measurement of cell dry mass density, cell classification based on the morphological parameters and visualization of dynamic dry mass changes. The multipurpose use of the method was demonstrated by restoring variations in the dynamic phase originating from the electrically induced birefringence of liquid crystals and by mapping the geometric phase of a space-variant polarization directed lens.
Optical metasurfaces have emerged as a new generation of building blocks for multifunctional optics. Design and realization of metasurface elements place ever-increasing demands on accurate assessment of phase alterations introduced by complex nanoantenna arrays, a process referred to as quantitative phase imaging. Despite considerable effort, the widefield (nonscanning) phase imaging that would approach resolution limits of optical microscopy and indicate the response of a single nanoantenna still remains a challenge. Here, we report on a new strategy in incoherent holographic imaging of metasurfaces, in which unprecedented spatial resolution and light sensitivity are achieved by taking full advantage of the polarization selective control of light through the geometric (Pancharatnam-Berry) phase. The measurement is carried out in an inherently stable common-path setup composed of a standard optical microscope and an add-on imaging module. Phase information is acquired from the mutual coherence function attainable in records created in broadband spatially incoherent light by the self-interference of scattered and leakage light coming from the metasurface. In calibration measurements, the phase was mapped with the precision and spatial background noise better than 0.01 and 0.05 rad, respectively. The imaging excels at the high spatial resolution that was demonstrated experimentally by the precise amplitude and phase restoration of vortex metalenses and a metasurface grating with 833 lines/mm. Thanks to superior light sensitivity of the method, we demonstrated for the first time to our knowledge the widefield measurement of the phase altered by a single nanoantenna while maintaining the precision well below 0.15 rad.
The knowledge of the phase distribution of the near electromagnetic field has become very important for many applications. However, its experimental observation is still technologically a very demanding task. In this work, we propose a novel method for the measurement of the phase distribution of the near electric field based on the principles of phase-shifting digital holography. In contrast to previous methods the holographic interference occurs already in the near field and the phase distribution can be determined purely from the scanning near-field optical microscopy measurements without the need for additional far-field interferometric methods. This opens a way towards on-chip phase imaging. We demonstrate the capabilities of the proposed method by reconstruction of the phase difference between interfering surface plasmon waves and by imaging the phase of a single surface plasmon wave. We also demonstrate a selectivity of the method towards individual components of the field.
A new concept of dual-polarization spatial light interference microscopy (DPSLIM) is proposed and demonstrated experimentally. The method works with two orthogonally polarized modes in which signal and reference waves are combined to realize the polarization-sensitive phase-shifting, thus allowing advanced reconstruction of the phase associated with the image field. The image phase is reconstructed directly from four polarization encoded interference records by a single step processing. This is a progress compared with common methods, in which the phase of the image field is reconstructed using the optical path difference and the amplitudes of interfering waves, which are calculated in multiple-step processing of the records. The DPSLIM is implemented in a common-path configuration using a spatial light modulator, which is connected to a commercial microscope Nikon E200. The optical performance of the method is demonstrated in experiments using both polystyrene microspheres and live LW13K2 cells.
Light vortices carry orbital angular momentum and have a variety of applications in optical manipulation, high-capacity communications or microscopy. Here we propose a new concept of full-field vortex topographic microscopy enabling a reference-free displacement and shape measurement of reflective samples. The sample surface is mapped by an array of light spots enabling quantitative reconstruction of the local depths from defocused wavefronts. Light from the spots is converted to a lattice of mutually uncorrelated double-helix point spread functions (PSFs) whose angular rotation enables depth estimation. The PSFs are created by self-interference of optical vortices that originate from the same wavefront and are shaped by a spiral phase mask (SPM). The method benefits from the isoplanatic PSFs whose shape and size remain unchanged under defocusing, ensuring high precision in a wide range of measured depths. The technique was tested using a microscope Nikon Eclipse E600 working with a micro-hole plate providing structured illumination and the SPM placed in the imaging path. The depth measurement was demonstrated in the range of 11 µm exceeding the depth of field of the microscope objective up to 19 times. Throughout this range, the surface depth was mapped with the precision better than 30 nm at the lateral positions given with the precision better than 10 nm. Application potential of the method was demonstrated by profiling the top surface of a bearing ball and reconstructing the three-dimensional relief of a reflection phase grating.
We present all-optical motionless arrangement for polarization sensitive phase-shifting (P-S) interferometry, where the phase shifts are accurately implemented by a liquid crystal variable retarder (LCVR). The LCVR is used as a polarization selective device capable of introducing a computer-controlled phase retardance between signal and reference waves with orthogonal linear polarizations. The proposed optical P-S is deployed in a polarization adapted common-path Mirau interferometer. Application of the method to a setup using the Michelson interference objective or Linnik interference module is also outlined. The accuracy of the quantitative phase reconstruction is examined theoretically, and a possibility to reduce the optical path difference error below 1/200 wavelength is demonstrated experimentally. Benefits and application potential of the polarization P-S interferometry supported by versatile liquid crystal devices are also discussed.
The vortex self-imaging (SI) implemented in optical imaging systems and its usage for a robust axial localization of point-like objects are presented. The vortex SI is used to generate a double-helix point spread function (DH PSF) maintaining its shape and size unchanged in a large working area. The robustness of the axial localization is demonstrated by a resistance against the spherical aberration. Using a thorough analysis, the experiments are optimized to achieve the highest localization sensitivity and to find a trade-off between the aberration stability of the DH PSF, the length of the localization range and the energy efficiency. The benefits of the method are achieved by applying the SI of nondiffracting vortices prepared by a spatial light modulator (SLM). The feasibility of the proposed technique is demonstrated by a defocusing induced rotation of the fixed and moving 1µm polystyrene beads, carried out in the transmitted light illumination.
In contemporary optics, the spatial light modulator (SLM) is effectively used as a flexible optoelectronic device playing the key role in a number of experiments of science and technology. Its operation is optimal when using almost monochromatic light but an extremely strong diffractive dispersion occurs when white light is applied. In this paper, the design concepts are proposed resulting in optimization and implementation of a refractive corrector cooperating with the SLM. The corrector maintains the operation of the SLM unchanged for the central wavelength of light and ensures an achromatic dispersion compensation throughout the visible region in applications based on a lens-pattern formation. A significant improvement of the imaging performance of the achromatic SLM was proved by the computer simulation and measurement of the chromatic focal shift and the image contrast of the resolution target.
We present a novel technique of digital holography using digitally implemented diffraction-free vortices for a precise three-dimensional (3D) localization of point-like objects. The localization is realized by the processing of the holographic image reconstructed at arbitrarily selected plane. Separating a single radial component of the spatial spectrum and modulating its phase by a virtual spiral mask, the holographic images of individual object points are transformed to the image structures analogous to the diffraction-free vortex beams. The real part of the complex amplitude of the digital vortices creates the shape-invariant patterns rotating due to a defocusing. Determining the angular rotation, the axial positions of the individual point objects are specified over a wide axial range. In the proposed method, a single in-line hologram is processed without phase shifting and multiplane reconstruction, so that a dynamic localization and tracking of particles becomes possible. The principle of the method is presented in a unified computational model valid for both coherent and incoherent techniques of digital holography. The functionality of the method has been verified in experiments of the Fresnel incoherent correlation holography (FINCH) and its flexibility presented by controlled variations of the localization sensitivity. The application potential has been demonstrated by the defocusing image rotation of fixed fluorescent microspheres and the 3D localization and tracking of moving polystyrene beads resulting in the trajectory reconstruction of a selected particle.
Holography/methods , Optical Phenomena , Rotation , Fluorescence , Imaging, Three-Dimensional , Microspheres , Models, Theoretical , Polystyrenes/chemistry
We demonstrate a new imaging method enabling a selective edge contrast enhancement of three-dimensional amplitude objects with spatially incoherent light. The imaging process is achieved in a spiral modification of Fresnel incoherent correlation holography and uses a vortex impulse response function. The correlation recordings of the object are acquired in a one-way interferometer with the wavefront division carried out by a spatial light modulator. Two different methods based on applying a helical reference wave in the hologram recording and a digital spiral phase modulation in image reconstruction are proposed for edge enhancement of amplitude objects. Results of both isotropic and anisotropic spiral imaging are demonstrated in experiments using an LED as an incoherent source of light.
In this paper we show how to advantageously combine two effects to enhance the sensitivity with depth in Fourier domain (FD) optical coherence tomography (OCT): Talbot bands (TB) and Gabor-based fusion (GF) technique. TB operation is achieved by routing the two beams, from the object arm and from the reference arm in the OCT interferometer, along parallel separate paths towards the spectrometer. By adjusting the lateral gap between the two beams in their way towards the spectrometer, the position for the maximum of contrast variation of spectral modulation versus the optical path difference in the interferometer is adjusted. For five values of the focus position, the gap between the two beams is readjusted to reach maximum sensitivity. Then, similar to the procedure employed in the GF technique, a compound image is formed by stitching together the parts of the five images that exhibited maximum brightness. The smaller the diameters of the two beams, the narrower the visibility profile versus depth in Talbot bands, which brings advantages in terms of mirror terms attenuation. However, this leads to a larger spot on the linear camera, which introduces losses, therefore the combined procedure, TB/GF is investigated for four different values of the beam diameters of the two beams. Future cameras with larger pixel size may take full advantage of the TB/GF procedure proposed here.
Algorithms , Image Enhancement/instrumentation , Image Interpretation, Computer-Assisted/instrumentation , Interferometry/instrumentation , Subtraction Technique , Tomography, Optical Coherence/instrumentation , Equipment Design , Equipment Failure Analysis , Reproducibility of Results , Sensitivity and Specificity
Fresnel Incoherent Correlation Holography (FINCH) allows digital reconstruction of incoherently illuminated objects from intensity records acquired by a Spatial Light Modulator (SLM). The article presents wave optics model of FINCH, which allows analytical calculation of the Point Spread Function (PSF) for both the optical and digital part of imaging and takes into account Gaussian aperture for a spatial bounding of light waves. The 3D PSF is used to determine diffraction limits of the lateral and longitudinal size of a point image created in the FINCH set-up. Lateral and longitudinal resolution is investigated both theoretically and experimentally using quantitative measures introduced for two-point imaging. Dependence of the resolving power on the system parameters is studied and optimal geometry of the set-up is designed with regard to the best lateral and longitudinal resolution. Theoretical results are confirmed by experiments in which the light emitting diode (LED) is used as a spatially incoherent source to create object holograms using the SLM.
Holography/methods , Optics and Photonics/methods , Algorithms , Computer Simulation , Equipment Design , Imaging, Three-Dimensional/methods , Lenses , Light , Liquid Crystals , Models, Statistical , Normal Distribution
