3D shape reconstruction of normal and cancerous red blood cells using digital holographic tomography: Combination of angular spectrum method and multiplicative technique.

Since the red blood cell shape affects the oxygen transport, so a robust method to reconstruct the 3D shape of an RBC from different projections is presented. A robust one-piece polarizing holographic microscope setup is used to record inline holograms of normal and cancerous red blood cells (RBCs) with high stability. The inline holograms are corrected by flat fielding and windowed Fourier filtering methods to mitigate the zero-order and the defocused twin image due to the inline recording configuration to the least measure. The corrected inline holograms are then reconstructed by the angular spectrum method to extract the 2D wrapping phase-contrast images. The 2D wrapping phase-contrast images are then unwrapped using the graph cuts algorithm to extract the continuous 2D phase-contrast images. The continuous 2D phase-contrast images are reconstructed at different projections by the multiplicative technique to extract the 3D shape of the normal and the cancerous RBCs. Experimental results show that any deformation in the shape of the normal and the cancerous RBCs can be seen clearly at any rotational angle in 3D. This method, which is based on the degree of deformation from the best fitting, can be used as an alternative method of counting method for discrimination between normal and cancerous cells and hence diagnoses the disease easily.

Estimation of an uncertainty budget and performance measurement for a dual-wavelength Twyman-Green interferometer.

In this paper, the uncertainty budget from 10 sources we claim they have direct impact on measurement is estimated. The measurement has been applied to nominal step heights of 1.34 and 1.50 µm using a dual-wavelength Twyman-Green interferometer. Experimental results show that the measured step heights match with their nominal values with expanded uncertainty in the range of 5% from the object being measured. The performance of the measurement process over time has been estimated at different confidence levels and the obtained results show that the process is maintained in a state of statistical control. To the best of our knowledge, this is the first report for estimation of uncertainty budget from a synthetic wavelength.

Improving the intensity-contrast image of a noisy digital hologram by convolution of Chebyshev type 2 and elliptic filters.

In this paper, a new, to the best of our knowledge, technique convolves the windowed Fourier filtering (WFF) of the Fresnel transform with the transfer functions of both Chebyshev type 2 and elliptic filters to enhance the intensity-contrast image of a noisy digital hologram. The recorded digital hologram is reconstructed by the Fresnel approach, the reconstructed intensity-contrast image is transformed by WFF, and the obtained spectrum is convolved in frequency domain with the transfer functions of Chebyshev type 2 and elliptic filters. The result of convolution is transformed by inverse WFF to produce a speckle-free image with a sharp roll-off and no ripples in both pass- and stop-bands. The experimental results with a die in the presence and absence of a rotating ground glass diffuser are shown and demonstrate that the resolution can be effectively enhanced with simple setup and procedure. The proposed technique can improve the capabilities of digital holography in three-dimensional (3D) microscopy.

Common-path phase-shift microscope based on measurement of Stokes parameters S2 and S3 for 3D phase extraction.

In this paper, we report a common-path, phase-shift optical microscope based on measurement of Stokes parameters S2 and S3 to extract the three-dimensional (3D) phase map of transparent objects with high precision. The microscope employs three polarizers and two identical quarter-wave plates to extract S2 and S3. The reference phase in the absence of the object is subtracted from the total phase in the presence of the object to extract the 3D phase of the object. The microscope is tested on imaging a USAF resolution test target and a reticle test pattern with excellent results. To the best of our knowledge, this is the first report of a common-path phase-shift optical microscope for 3D phase extraction based on measurement of Stokes parameters S2 and S3.

Simultaneous dual-wavelength digital holographic microscopy with compensation of chromatic aberration for accurate surface characterization.

In this paper, a simultaneous dual-wavelength digital holographic microscope with compensation of chromatic aberration is presented. The microscope has been used to calibrate two standard step heights of 1340 and 1000 nm. The extracted results have been compared with those extracted by the single-shot, dual-wavelength digital holographic microscope, and the comparison has shown that measurements by the proposed microscope are more accurate by around 40 nm. We claim that the high accuracy in measurement is due to the fact that the proposed system works in real time with very low chromatic aberration. Judging the performance of the measurement process over time is explained by the control charts. Evidence from the control measurements sets a probable limit on precision for this process at about 3σ=3.5 nm.

Multicascade-linked synthetic wavelength digital holography using an optical-comb-referenced frequency synthesizer.

Digital holography (DH) is a promising method for non-contact surface topography because the reconstructed phase image can visualize the nanometer unevenness in a sample. However, the axial range of this method is limited to the range of the optical wavelength due to the phase wrapping ambiguity. Although the use of two different wavelengths of light and the resulting synthetic wavelength, i.e., synthetic wavelength DH, can expand the axial range up to several hundreds of millimeters, its axial precision does not reach sub-micrometer. In this article, we constructed a tunable external cavity laser diode phase-locked to an optical frequency comb, namely, an optical-comb-referenced frequency synthesizer, enabling us to generate multiple synthetic wavelengths within the range of 32 µm to 1.20 m. A multiple cascade link of the phase images among an optical wavelength ( = 1.520 µm) and 5 different synthetic wavelengths ( = 32.39 µm, 99.98 µm, 400.0 µm, 1003 µm, and 4021 µm) enables the shape measurement of a reflective millimeter-sized stepped surface with the axial resolution of 34 nm. The axial dynamic range, defined as the ratio of the axial range ( = 2.0 mm) to the axial resolution ( = 34 nm), achieves 5.9 × 105, which is larger than that of previous synthetic wavelength DH. Such a wide axial dynamic range capability will further expand the application field of DH for large objects with meter dimensions.

Steep large film thickness measurement with off-axis terahertz digital holography reconstructed by a direct Fourier and Hermite polynomial.

In this paper, we enhance the steepness of film thickness edge in terahertz off-axis digital holography by employing a reconstruction method based on a direct Fourier and Hermite polynomial function. The method is applied to samples of 110 µm and 80 µm step heights to extract the phase images in real time. Use of this method reduces the resolution factor by around one half, representing around a 50% decrease in critical dimension as compared with conventional measurements. The method is very promising and opens the route to potential applications in the fields of microlithography.