To realize portable device with high contrast imaging capability, we designed a quantitative phase microscope using transport of intensity equation method based on a smartphone. The whole system employs an objective and an eyepiece as imaging system and a cost-effective LED as illumination source. A 3-D printed cradle is used to align these components. Images of different focal planes are captured by manual focusing, followed by calculation of sample phase via a self-developed Android application. To validate its accuracy, we first tested the device by measuring a random phase plate with known phases, and then red blood cell smear, Pap smear, broad bean epidermis sections and monocot root were also measured to show its performance. Owing to its advantages as accuracy, high-contrast, cost-effective and portability, the portable smartphone based quantitative phase microscope is a promising tool which can be future adopted in remote healthcare and medical diagnosis.
Massive image acquisition is required along the optical axis in the classical image-analysis-based autofocus method, which significantly decreases autofocus efficiency. A wavefront-sensing-based autofocus technique is proposed to increase the speed of autofocusing and obtain high localization accuracy. Intensities at different planes along the optical axis can be computed numerically after extracting the wavefront at defocus position with the help of the transport-of-intensity equation method. According to the focus criterion, the focal plane can then be determined, and after sample shifting to this plane, the in-focus image can be recorded. The proposed approach allows for fast, precise focus detection with fewer image acquisitions compared to classical image-analysis-based autofocus techniques, and it can be applied in commercial microscopes only with an extra illumination filter.
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.