Keding Yan

Smartphone based hand-held quantitative phase microscope using the transport of intensity equation method

In order to realize high contrast imaging with portable devices for potential mobile healthcare, we demonstrate a hand-held smartphone based quantitative phase microscope using the transport of intensity equation method. With a cost-effective illumination source and compact microscope system, multi-focal images of samples can be captured by the smartphones camera via manual focusing. Phase retrieval is performed using a self-developed Android application, which calculates sample phases from multi-plane intensities via solving the Poisson equation. We test the portable microscope using a random phase plate with known phases, and to further demonstrate its performance, a red blood cell smear, a Pap smear and monocot root and broad bean epidermis sections are also successfully imaged. Considering its advantages as an accurate, high-contrast, cost-effective and field-portable device, the smartphone based hand-held quantitative phase microscope is a promising tool which can be adopted in the future in remote healthcare and medical diagnosis.

Phase measurements of erythrocytes affected by metal ions with quantitative interferometric microscopy

Abstract. Erythrocyte morphology is an important factor in disease diagnosis, however, traditional setups as microscopes and cytometers cannot provide enough quantitative information of cellular morphology for in-depth statistics and analysis. In order to capture variations of erythrocytes affected by metal ions, quantitative interferometric microscopy (QIM) is applied to monitor their morphology changes. Combined with phase retrieval and cell recognition, erythrocyte phase images, as well as phase area and volume, can be accurately and automatically obtained. The research proves that QIM is an effective tool in cellular observation and measurement.

Fast pixel shifting phase unwrapping algorithm in quantitative interferometric microscopy

Quantitative interferometric microscopy is an important method for observing biological samples such as cells and tissues. In order to obtain continuous phase distribution of the sample from the interferogram, phase extracting and phase unwrapping are both needed in quantitative interferometric microscopy. Phase extracting includes fast Fourier transform method and Hilbert transform method, etc., almost all of them are rapid methods. However, traditional unwrapping methods such as least squares algorithm, minimum network flow method, etc. are time-consuming to locate the phase discontinuities which lead to low processing efficiency. Other proposed high-speed phase unwrapping methods always need at least two interferograms to recover final phase distributions which cannot realize real time processing. Therefore, high-speed phase unwrapping algorithm for single interferogram is required to improve the calculation efficiency. Here, we propose a fast phase unwrapping algorithm to realize high-speed quantitative interferometric microscopy, by shifting mod 2π wrapped phase map for one pixel, then multiplying the original phase map and the shifted one, then the phase discontinuities location can be easily determined. Both numerical simulation and experiments confirm that the algorithm features fast, precise and reliable.

Quantitative interferometric microscopy with improved full-field phase aberration compensation

Abstract. Single-shot quantitative interferometric microscopy (QIM) needs a high-accuracy and rapid phase retrieval algorithm. Retrieved phase distributions are often influenced by phase aberration background caused by both imaging system and phase retrieval algorithms. Here, we propose an improved phase aberration compensation (PAC) approach in order to eliminate the phase aberrations inherent in the data. With this method, sample-free parts are identified and used to calculate the background phase, reducing phase errors induced in samples and providing high-quality phase images. We now demonstrate that QIM based on this PAC approach realizes high-quality phase imaging from a single interferogram. This is of great potential for a real-time speedy diagnosis.

Unwrapping free Hilbert transform-based phase retrieval method in quantitative interferometric microscopy

Abstract. In order to obtain quantitative phase distributions from interferograms, phase retrieval composed of phase extracting and unwrapping is adopted in quantitative interferometric microscopy. However, phase unwrapping often requires a long time, limiting applications such as high-speed phase observations and measurements. In order to accelerate the processing speed, a phase unwrapping free Hilbert transform (HT)-based phase retrieval method is proposed. Though another background interferogram without a sample is needed, phase unwrapping can be omitted, saving a large amount of time for phase recovery. Additionally, the proposed HT-based method can maintain more sample details, thus providing high-accurate quantitative phase imaging. Considering its fast speed and high accuracy in phase retrieval, it is believed that the unwrapping free HT-based phase retrieval method can be potentially applied in high throughput cellular observations and measurements.

Full angular Stokes vectors of light scattering from two-dimensional randomly rough surfaces by Kirchhoff approximation method

Light scattering from rough surfaces remains an important area of interest as it has great potential in a wide variety of fields such as polarized imaging and target identification. Compared to existing simulative methods, the Kirchhoff approximation method offers a much higher calculation efficiency and easy polarization setting that is especially fit for polarized scattering research. In this paper, by studying full angular Stokes vectors via the Kirchhoff approximation from two-dimensional (2D) randomly rough surfaces with various materials, the difference between Stokes vectors of metals and dielectrics is discovered. Moreover, we have successfully explained the distinction between metals and dielectrics by the phase difference between the incident and scattered waves using theoretical analysis. We believe the research could provide an easy and robust criterion for distinguishing metals and dielectrics in various fields such as laser radar and remote sensing.

Cellular phase observations and measurements on red blood cells affected by lithium and lead ions with quantitative interferometric microscopy

As an important marker in disease diagnosis, red blood cell morphology measurement is necessary in biological and medical fields. However, traditional setups as microscopes and cytometers cannot provide enough quantitative information in morphology detections. In order to capture tiny variations of red blood cells affected by metal ions in external environment, quantitative interferometric microscopy is applied: combining with phase retrieval and cell recognition, cellular phases as well as additional quantitative cellular parameters can be acquired automatically and accurately. The research proves that quantitative interferometric microscopy can be potentially applied in cellular observations and measurements for both biological and medical applications.

Dielectric and metal target identification based on polarized light scattering analysis: a numerical study

In order to quantitatively analyze scattering from two dimensional randomly rough Gaussian surfaces, Kirchhoff approximation method is adopted in numerical calculation for analyzing full angular Stokes vectors of light scattering. With studying both the p- and s-polarized scattering fields from various materials such as metals and dielectrics, it is found that V components of scattering light from metals and dielectrics are different. Via analytical calculation according to slope probability density, the V component difference is attributed to refractive index of materials. Both numerical and analytical calculations prove the V component difference in light scattering can act as a criterion for metal and dielectric identification.

Random laser scattering pulse signal analysis in laser particle counter with lognormal distribution

The statistical distribution of natural phenomena is of great significance in studying the laws of nature. Here, in this paper, based on laser scattering particle counter, a simple random pulse signal generating and testing system is designed for studying the counting distributions of three typical objects including particles suspended in the air, standard particles, and background noises. Moreover, in order to have a deep understanding of the experimental results from laser scattering particle counter, a random process model is also proposed theoretically to study the random law of measured results. Both normal and lognormal distribution fittings are applied to analyze the experimental results, and we have proved that statistical amplitude and width distributions of particles suspended in the air, standard particles, and background noise match well with lognormal distribution when natural numbers are used as the variables. This study is an important reference for statistical data processing for laser scattering particle counter, moreover, it will also be a useful guide for designing laser scattering particle counter with high accuracy and processing speed.

High quality underwater imaging platform with laser range gated technique combining with image denoising and restoration

Underwater laser imaging is of great significance in underwater search and marine science, etc. However, traditional underwater laser imaging is often of poor quality with noises and blurs, moreover, the resolution of the image is also low. In order to obtain clear underwater images with high resolution and quality, here, we have designed a range gated imaging underwater imaging system and realized an image restoration approach. In this paper, based on the introduction to the imaging system and image restoration algorithm, the experiment is established by setting the imaging system under water in the lake to capture the underwater targets. With the proposed underwater image restoration approach, images of high quality could be retrieved which proves that the method is able to identify the target ~10 meters away underwater.