Soilless cultivation systems in controlled environment agriculture create varying rootzone oxygen conditions, which can impact biomass production. The present study investigates the effect of mild hypoxia and its effect on shoot biomass production, root anatomy and architecture of basil (Ocimum basilicum L.) in ebb-flood, deep-water, and aeroponic systems in a greenhouse. After 4–5 weeks, aeroponically grown plants produced greater shoot biomass than those in the ebb-flood system, although root dry weights did not differ significantly. Using optical coherence tomography (OCT), we non-destructively quantified aerenchyma formation, confirming the suitability of OCT for imaging living root tissues. Aerenchyma developed 14–21 days after transplanting and were more extensive in unaerated deep-water systems than in aerated or aeroponic systems. Ethylene emission 20 days after transplanting did not differ between treatments. Thus, basil shows adaptative responses at mild hypoxia, which can lead to yield losses. This emphasises the need to define rootzone oxygen thresholds.

Lensless single-shot dual-wavelength digital holography is resolution limited by the pixel-size of the camera and often has an insufficient depth range. We present a novel dual-wavelength holographic configuration with expanding wavefront illumination that breaks the pixel-limited resolution barrier and achieves diffraction-limited spatial resolution. By implementing expanding wavefront illumination with dual-wavelength digital holography based on a wavelength-tunable laser, we achieve a high-resolution centimeter-scale depth range. A quantitative precision analysis demonstrates that single-shot acquisition reaches the shot-noise-limited depth detection. The proposed holographic scheme provides a robust 3D optical inspection solution for high-throughput, micro-scale resolution industrial inline metrology.

High-accurate unwrapped phases are demanded in various research fields such as optical imaging optical holography, optical diffraction tomography, and magnetic resonance imaging. However, the ground-truth phase is not accessible due to 2 ambiguity which arises from phase jumps in the wrapped phase. In this study, we propose to improve the accuracy of unwrapping process by increasing the sampling frequency to reconstruct the unwrapped phase with high accuracy for the application of optical imaging. The simulation results show increasing the optical magnification from 4X to 8X enables improvement of the phase estimation accuracy by 51% for a highly refractive object. Experimental results validate the sensitivity of phase estimation on the sampling size. Our approach demonstrates significant achievement in obtaining ground-truth phases for highly refractive objects.

We quantify the precision and bias of dynamic light scattering optical coherence tomography (DLS-OCT) measurements of the diffusion coefficient and flow speed for first and second-order normalized autocovariance functions. For both diffusion and flow, the measurement precision and accuracy are severely limited by correlations between the errors in the normalized autocovariance function. We demonstrate a method of mixing statistically independent normalized autocovariance functions at every time delay for removing these correlations. The mixing method reduces the uncertainty in the obtained parameters by a factor of two but has no effect on the standard error of the mean. We find that the precision in DLS-OCT is identical for different averaging techniques but that the lowest bias is obtained by averaging the measured correlation functions before fitting the model parameters. With our correlation mixing method, it is possible to quantify the precision in DLS-OCT and verify whether the Cramer-Rao bound is reached.

We demonstrate wavenumber-dependent DLS-OCT measurements of collective and self-diffusion coefficients in concentrated silica suspensions across a broad q-range, utilizing a custom home-built OCT system. Depending on the sample polydispersity, either the collective or self-diffusion is measured. The measured collective-diffusion coefficient shows excellent agreement with hard-sphere theory and serves as an effective tool for accurately determining particle sizes. We employ the decoupling approximation for simultaneously measuring collective and self-diffusion coefficients, even in sufficiently monodisperse suspensions, using a high-speed Thorlabs OCT system. This enables particle size and volume fraction determination without the necessity of wavenumber-dependent measurements. We derive a relationship between the particle number-based polydispersity index and the ratio of self and collective mode amplitudes in the autocorrelation function and utilize it to measure the particle number-based polydispersity index. Notably, the polydispersity determined in this manner demonstrates improved sensitivity to smaller particle sizes compared to the standard intensity-based DLS cumulant analysis performed on dilute samples.

The complex refractive index is analyzed by measuring its scattering attenuation µ_s, group index n_g, and group velocity dispersion (GVD) for 100 nm diameter silica nanoparticles dispersed in water. The experiments were performed for wavelengths between 410 nm and 930 nm. The experimental results were compared with different mixing models for the complex refractive index of colloidal suspensions. The group index linearly scaled with the volume fraction both in experiment and for all tested models. It was found that the GVD has a nonlinear dependence on volume fraction in agreement with the coupled dipole model of Parola et al. [J. Chem. Phys. 141, 124902 (2014)] The scattering attenuation is in good agreement with both the coupled dipole model and the low frequency quasi-crystalline approximation [J. Electromagn. Waves Appl. 2, 757 (1988)] that take particle correlations into account. With an iterative fitting procedure of all the data based on both the coupled dipole model and the quasi-crystalline approximation, the refractive index, porosity, and size of the nanoparticles were determined. We determined that the coupled dipole model is in best agreement with the data.

We show number fluctuations dynamic light scattering optical coherence tomography (OCT) for measuring extremely slow, sub-diffusion flows of dilute particle suspensions. Our method removes the minimum measurable velocity limitation of conventional correlation-based or phase-resolved Doppler OCT, set by flowing particles’ Brownian motion. Our technique works for any Doppler angle, is applicable to 2D flow imaging with scanning OCT systems and can be used to determine concentration of particles under flow.

The group index, n_g , group velocity dispersion (GVD), and scattering attenuation coefficient, µ_s, were measured for dilutions of glycerol, ethanol, and Intralipid 20% with water. Experiments were performed with a supercontinuum laser based Mach–Zehnder spectroscopic interferometry setup for wavelengths between 400 and 930 nm. All optical properties could be retrieved from a single calibrated measurement of the interference spectrum. Scattering attenuation was determined from the envelope of the interference. The group index and GVD were retrieved from the unwrapped spectral phase. It was found that the group indices of glycerol and ethanol dilutions are in accordance with the Lorentz–Lorenz mixing formula. The scattering attenuation matches well to a semi-empirical model based on the Twerksy effective packing fraction.

Phase sensitive optical coherence tomography (OCT) is able to measure small axial motion at the level of ten nanometer. However, when interfaces are located close to each other, the phase of one interface may influence the phase of the other interface. This spectral leakage hampers the ability to see relative motion between structures within the sample, especially when the separation is below the axial resolution. Spectral estimation OCT (SE-OCT) based on IAA can not only improve the axial resolution beyond the conventional bandwidth limitation, but also reduce this spectral leakage. Here we show accurate reconstruction of the vibration of an interface at sub-resolution distance from a high-intensity interface with a different vibration frequency. Phase preserved IAA successfully reduces spectral leakage and outperforms conventional DFT-based reconstruction methods.

We show number fluctuations dynamic light scattering optical coherence tomography (OCT) for measuring extremely slow, sub-diffusion flows of dilute particle suspensions. Our method removes the minimum measurable velocity limitation of conventional correlation-based or phase-resolved Doppler OCT, set by flowing particles’ Brownian motion. Our technique works for any Doppler angle, is applicable to 2D flow imaging with scanning OCT systems and can be used to determine concentration of particles under flow.

Phase-preserving spectral estimation optical coherence tomography (SE-OCT) enables combining axial resolution improvement with computational depth of field (DOF) extension. We show that the combination of SE-OCT with interferometric synthetic aperture microscopy (ISAM) and computational adaptive optics (CAO) results in high 3D resolution over a large depth range for an OCT system with a narrow bandwidth visible light super-luminescent diode (SLD). SE-OCT results in up to five times axial resolution improvement from 8 µm to 1.5 µm. The combination with ISAM gives a sub-micron lateral resolution over a 400 µm axial range, which is at least 16 times the conventional depth of field. CAO can be successfully applied after SE and ISAM and removes residual aberrations, resulting in high quality images. The results show that phase-preserving SE-OCT is sufficiently accurate for coherent post-processing, enabling the use of cost-effective SLDs in the visible light range for high spatial resolution OCT.

Phase-preserving spectral estimation optical coherence tomography (SE-OCT) enables combining axial resolution improvement with computational depth of focus (DOF) extension. We combine SE-OCT with interferometric synthetic aperture microscopy (ISAM) to obtain a high 3D resolution over a large depth range with a narrow bandwidth visible light super-luminescent diode (SLD). SE-OCT gives a five times axial resolution improvement to 1.5 micrometer. The combination with ISAM gives a sub-micron lateral resolution over a 300 micrometer axial range, 12 times the conventional DOF. The results show that phase-preserving SE-OCT is sufficiently accurate for coherent post-processing, enabling the use of cost-effective SLDs in the visible light range for high spatial resolution OCT.