Common-path Digital Holographic Microscopy Research Articles

Common-path digital holographic microscopy based on a volume holographic grating for quantitative phase imaging.

Digital holographic microscopy (DHM) is a powerful quantitative phase imaging (QPI) technique that is capable of recording sample's phase information to enhance image contrast. In off-axis DHM, high-quality QPI images can be generated within a single recorded hologram, and the system stability can be enhanced by common-path configuration. Diffraction gratings are widely used components in common-path DHM systems; however, the presence of multiple diffraction beams leads to system power loss. Here, we propose and demonstrate implementation of a volume holographic grating (VHG) in common-path DHM, which provides single diffraction order. VHG in common-path DHM (i.e., VHG-DHM) helps in improving signal-to-noise ratio as compared to the conventional DHM. In addition, VHG, with inherently high angular selectivity, reduces image noise caused by stray light. With a simple fabrication process, it is convenient to utilize VHG to control the beam separation angle of DHM. Further, by using Bragg-matched wavelength degeneracy to avoid potential cell damaging effect in blue light, the VHG is designed for recording at a maximum sensitive wavelength of ∼488 nm, while our VHG-DHM is operated at the longer wavelength of red 632.8 nm for cell observation. Experimental results, measured by the VHG-DHM, show the measurement of target thickness ranging from 100 nm to 350 nm. In addition, stability of the system is quantitatively measured. High-contrast QPI images of human lung cancer cells are demonstrated.

Functionally integrated waveguide illuminator for common-path digital holographic microscopy through random media.

We designed and fabricated a functionally integrated optical waveguide illuminator specially for common-path digital holographic microscopy through random media. The waveguide illuminator creates two point sources with desired phase shifts, which are located close to one another so that the common-path condition of the object and reference illumination is satisfied. Thereby, the proposed device permits phase-shift digital holographic microscopy free from bulky optical elements such as a beam splitter, an objective lens, and a piezoelectric transducer for phase shifting. Using the proposed device, microscopic 3D imaging through a highly heterogeneous double-composite random medium was experimentally demonstrated by means of common-path phase-shift digital holography.

Single capture bright field and off-axis digital holographic microscopy.

We report on a single capture approach for simultaneous incoherent bright field (BF) and laser-based quantitative phase imaging (QPI). Common-path digital holographic microscopy (DHM) is implemented in parallel with BF imaging within the optical path of a commercial optical microscope to achieve spatially multiplexed recording of white light images and digital off-axis holograms, which are subsequently numerically demultiplexed. The performance of the proposed multimodal concept is firstly determined by investigations on microspheres. Then, the application for label-free dual-mode QPI and BF imaging of living pancreatic tumor cells is demonstrated.

A common-path digital holographic microscope with a rotatable birefringent prism for synthesizing high-quality quantitative phase images from multi-angle interferograms

We propose a simple common-path off-axis interferometric system to perform high-quality quantitative phase imaging based on a rotatable birefringent prism that is placed at the output port of a conventional transmission or reflection microscope. The proposed system effectively eliminates the zero-order term of holographic data and increases the phase image reconstruction bandwidth by compounding multi-angle holograms, thereby obtaining high-quality quantitative phase images without zero-order artifacts. In addition, the proposed multi-angle phase image compounding method can eliminate the repetitive object phases caused by self-reference interferometry, thereby alleviating the problem of field-of-view reduction. Furthermore, we realize high-quality quantitative phase imaging based on multi-angle phase images without sacrificing the imaging frame rate. The concept is demonstrated by performing high-quality quantitative phase imaging of polystyrene microspheres and a freshwater alga, Pinnularia. Experimental results show that the noise level of the quantitative phase images synthesized using the proposed rotatable common-path digital holographic microscopy system is lower than that of conventional single-shot digital holographic microscope reconstruction quantitative images, and a more detailed cell internal structure can be observed.

Low-pass filtering compensation in common-path digital holographic microscopy

A low-pass filtering compensation (LPFC) method is proposed to compensate for phase aberrations in point diffraction-based common-path digital holographic microscopy. This method estimates the phase aberration from the object hologram by Fourier transform and low-pass spatial filtering. The estimated phase aberration is subtracted from the object phase image to achieve single-hologram phase compensation. The accuracy and capability of LPFC for phase compensation were demonstrated by experiments on a Ronchi grating and a human blood smear. LPFC provides phase compensation for both smooth objects and objects containing abrupt edges, in the special case of a system with relatively high-frequency objects and low-frequency slight phase aberrations. LPFC operates without the need for fitting procedures, iterative steps, or prior knowledge of the optical parameters, which substantially simplifies the process of phase compensation in quantitative phase imaging.

Wavelength-Tuning Common-Path Digital Holographic Microscopy for Quantitative Phase Imaging of Functional Micro-Optics Components

This study proposes a novel wavelength-tuning common-path digital holographic microscopy technique for quantitative phase imaging of functional micro-optics components. The proposed technique is immune to vibration and can reduce system error. In the proposed configuration, a parallel glass plate was inserted into the light path to create two identical test beams, which passed through a specially designed window filter. In this process, one beam serves as the object beam, while the other is diffracted to produce an ideal spherical wave front (the reference beam). A wavelength tunable laser was used as the light source to generate phase-shifting digital holograms. Structural information for the functional micro-optics components was then extracted using a classical four-step phase-shift algorithm. The viability of the proposed technique was assessed by measuring a micro-optics array.

Speckle-free common-path quantitative phase imaging with high temporal phase stability using a partially spatially coherent multi-spectral light source

Quantitative phase imaging (QPI) has been an important technique for the determination of various biophysical parameters, such as the refractive index and morphology of biological cells and tissues. The technique has been implemented using off-axis and common path digital holographic microscopy (DHM). Off-axis DHM, though being ideal for QPI, offers lower temporal phase stability compared to common path techniques. Common path DHM offers a higher temporal phase stability but, being a coherent imaging technique, suffers from speckle artefacts and spurious interference fringes due to the high coherence of the light source. Both artefacts not only degrade the image quality, but also affect the phase measurement results. In this paper, we report the implementation of common path QPI set-up using a partially spatially coherent multi-spectral light source. The spatial coherence of the red and green color lasers is reduced by using a rotating diffuser. Also, a speckle free QPI was implemented using common path Fresnel biprism interferometer. A Fresnel biprism is used in the self-referencing mode, thus offering the advantage of no optical power loss in addition to high temporal stability and the least speckle artefacts. Furthermore, it is very easy to implement, as the system completely replaces the need for spatial filtering at the source end as well as for the reference beam generation. The experiments have been carried out on industrial and biological samples to prove the effect.

卤素灯照明光栅衍射共路数字全息显微定量相位成像

卤素灯照明光栅衍射共路数字全息显微定量相位成像

Off-axis tilt compensation in common-path digital holographic microscopy based on hologram rotation.

We present a simple and effective compensation method for the off-axis tilt in common-path digital holographic microscopy (CPDHM) by introducing a rotating operation on the hologram. The proposed method mainly requires a digital reference hologram (DRH), which is a rotated version of the original one; it is assumed to be easy to obtain by rotating the specimen's hologram 180°. In this way, the off-axis tilt could be removed by subtracting the retrieved phase of DRH from the retrieved phase of the original hologram, but without any complex spectrum centering judgment, fitting procedures, or prior knowledge of the system. This highly automatic and efficient performance makes our approach available for real-time quantitative phase imaging (QPI), although it limits the field of view (FOV) of the specimen. Some experimental results of microlens array and phase plate demonstrate the feasibility and effectiveness of the proposed method.

Depth-filtering in common-path digital holographic microscopy.

We demonstrate a method to select different layers in a sample using a low coherent gating approach combined with a stable common-path quantitative phase imaging microscopy setup. The depth-filtering technique allows us to suppress the negative effects generated by multiple interference patterns of overlaying optical interfaces in the sample. It maintains the compact and stable common-path setup, while enabling images with a high phase sensitivity and acquisition speed. We use a holographic microscope in reflective geometry with a non-tunable low coherence light source. First results of this technique are shown by imaging the hardware layer of a standard micro-controller through its thinned substrate.

Dual-wavelength common-path digital holographic microscopy for quantitative phase imaging of biological cells

Biological cells are usually transparent with a small refractive index gradient. Digital holographic interferometry can be used in the measurement of biological cells. We propose a dual-wavelength common-path digital holographic microscopy for the quantitative phase imaging of biological cells. In the proposed configuration, a parallel glass plate is inserted in the light path to create the lateral shearing, and two lasers with different wavelengths are used as the light source to form the dual-wavelength composite digital hologram. The information of biological cells for different wavelengths is separated and extracted in the Fourier domain of the hologram, and then combined to a shorter wavelength in the measurement process. This method could improve the system’s temporal stability and reduce speckle noises simultaneously. Mouse osteoblastic cells and peony pollens are measured to show the feasibility of this method.

Lateral shearing common-path digital holographic microscopy based on a slightly trapezoid Sagnac interferometer.

We propose a compact and easy-to-align lateral shearing common-path digital holographic microscopy, which is based on a slightly trapezoid Sagnac interferometer to create two laterally sheared beams and form off-axis geometry. In this interferometer, the two beams pass through a set of identical optical elements in opposite directions and have nearly the same optical path difference. Without any vibration isolation, the temporal stability of the setup is found to be around 0.011 rad. Compared with highly simple lateral shearing interferometer, the off-axis angle of the setup can be easily adjusted and quantitatively controlled, meanwhile the image quality is not degraded. The experiments for measuring the static and dynamic specimens are performed to demonstrate the capability and applicability.

Tunable time-resolved tick-tock pulsed digital holographic microscopy for ultrafast events.

This study presents a time-resolved imaging technique for detecting ultrafast events in the sample with tunable tick-tock pulses in common-path digital holographic microscopy. The tick-tock pulses are generated from the same single femtosecond pulse source and manipulated through a spatial-multiplexing encoding/decoding scheme with two complementary binary codes for digital hologram recording and reconstruction. The spatial-multiplexing encoding/decoding scheme with compressive sensing on the Fresnel digital hologram is used to recover missing data and achieve high-fidelity wavefront reconstruction. The elapsed time of tick-tock pulses can be adjusted by changing the optical path difference between the pulse pair arms for dynamic observation at various timescales. The proposed method is applied to explore the ultrafast physical phenomenon by quantitative phase imaging with a stopwatch-like tunable timescale ranging from nanoseconds to femtoseconds.

Synthetic aperture common-path digital holographic microscopy with spiral phase filter

This paper describes a synthetic aperture common-path digital holographic microscopy through phase-shifting in a rotating spiral phase filter (SPF) to strengthen axial phase accuracy and fully utilize frequency coverage to improve of the spatial resolution. A phase-type liquid crystal on a silicon spatial light modulator was employed to generate an SPF on the Fourier plane of the digital holographic microscopy system. Subsequently, the scattering wave passing through the spiral phase plate and the reference wave generated through the center of phase plate as a spatial filter were used for the interference process, thereby completing the recording of the on-axis digital hologram. The common-path digital holographic microscopy system integrated with synthetic aperture imaging can be applied for Fresnel hologram recording and numerical focusing on objects without being affected by environmental vibration and coherence, thereby improving the spatial resolution and axial phase accuracy.

Common-path digital holographic microscopy for near-field phase imaging based on surface plasmon resonance.

We develop a common-path digital holographic microscopy based on prism-coupling surface plasmon resonance (SPR) for near-field phase imaging. A single beam splitter with specific configuration is introduced in an SPR imaging system to realize off-axis holographic recording. By measuring the phase shift difference of the reflected light at SPR exploiting the proposed holographic microscopy with high temporal stability, near-field characteristic measurement can be realized. With its simplicity, vibration isolation, and inherent capability of phase curvature compensation, the recommended system shows advanced performance in monitoring tiny refractive index variations and imaging biological tissues.

Microsphere-assisted super-resolved Mirau digital holographic microscopy for cell identification.

In this paper, we use a glass microsphere incorporated into a digital holographic microscope to increase the effective resolution of the system, aiming at precise cell identification. A Mirau interferometric objective is employed in the experiments, which can be used for a common-path digital holographic microscopy (DHMicroscopy) arrangement. High-magnification Mirau objectives are expensive and suffer from low working distances, yet the commonly used low-magnification Mirau objectives do not have high lateral resolutions. We show that by placing a glass microsphere within the working distance of a low-magnification Mirau objective, its effective numerical aperture can be increased, leading to super-resolved three-dimensional images. The improvement in the lateral resolution depends on the size and vertical position of microsphere, and by varying these parameters, the lateral resolution and magnification may be adjusted. We used the information from the super-resolution DHMicroscopy to identify thalassemia minor red blood cells (tRBCs). Identification is done by comparing the volumetric measurements with those of healthy RBCs. Our results show that microsphere-assisted super-resolved Mirau DHMicroscopy, being common path and off-axis in nature, has the potential to serve as a benchtop device for cell identification and biomedical measurements.

Dual-wavelength common-path digital holographic microscopy for quantitative phase imaging based on lateral shearing interferometry.

A dual-wavelength common-path digital holographic microscopy based on a single parallel glass plate is presented to achieve quantitative phase imaging, which combines the dual-wavelength technique with lateral shearing interferometry. Two illumination laser beams with different wavelengths (λ1=532 nm and λ2=632.8 nm) are reflected by the front and back surfaces of the parallel glass plate to create the lateral shear and form the digital hologram, and then the hologram is reconstructed to obtain the phase distribution with a synthetic wavelength Λ=3339.8 nm. The experimental configuration is very compact, with the advantages of vibration resistance and measurement range extension. The experimental results of the laser-ablated pit, groove, and staircase specimens show the feasibility of the proposed configuration.

Three-dimensional quantitative phase measurement by Common-path Digital Holographic Microscopy

Common-path Digital Holographic Microscopy (CP-DHM) is a new technique which can physically compensate the phase curvature introduced by the microscope objective. We designed a compact CP-DHM system for quantitative phase measurement of transparant microscopic samples. The system incorporates a special fiber-connected condenser system which makes adjustment easy when using different microscope objectives. We present the results for the system calibration and analysis of a micro-lens array to demonstrate the performance of the system.