Linear phase microscopy

Shearing interference microscope for step-height measurements

A shearing interference microscope using a Savart prism as the shear plate is proposed for inspecting step-heights. Where the light beam propagates through the Savart prism and microscopic system to illuminate the sample, it then turns back to re-pass through the Savart prism and microscopic system to generate a shearing interference pattern on the camera. Two measurement modes, phase-shifting and phase-scanning, can be utilized to determine the depths of the step-heights on the sample. The first mode, which employs a narrowband source, is based on the five-step phase-shifting algorithm and has a measurement range of a quarter-wavelength. The second mode, which adopts a broadband source, is based on peak-intensity identification technology and has a measurement range up to a few micrometres. This paper is to introduce the configuration and measurement theory of this microscope, perform a setup used to implement it, and present the experimental results from the uses of the setup. The results not only verify the validity but also confirm the high measurement repeatability of the proposed microscope.

Ptychographic phase microscope based on high-speed modulation on the illumination beam

A type of ptychography-based phase microscope was developed by integrating a spatial light modulator (SLM) into a commercial wide-field light microscope. By displaying a moving pattern on the SLM to change the sample illumination and record the diffraction intensities formed, both the modulus and phase of the transmission function of the sample could be accurately reconstructed with formulas similar to those of common ptychography. Compared with other kinds of phase microscopes, the developed microscope has several advantages, including its simple structure, high immunity to coherent noise, and low requirement for quality optics. In addition, defects in the illumination beam are also removed from the reconstructed image. Further, this microscope’s fast data acquisition ability makes it highly suitable for many applications where highly accurate quantitative phase imaging is important, such as in living cells or other fragile biological samples that cannot sustain continuous imaging over a long period of time.

Lensless phase microscopy using phase retrieval with multiple illumination wavelengths

A phase retrieval method for microscopy using multiple illumination wavelengths is proposed. A fast algorithm suitable for calculations with high numerical aperture is used for the iterative retrieval of the object wavefront. The advantages and limitations of the technique are systematically analyzed and demonstrated by both simulation and experimental results.

Quantitative measurement of a phase object by fringe scanning interference microscopy

A simple interference microscope based on a fringe scanning technique is described. This interference microscope can provide quantitative phase information of a phase object. The theory and experimental results are presented.

Scanning differential phase contrast optical microscope: application to surface studies

The characteristics and theory of operation of a new scanning differential phase contrast optical microscope are described, and a number of results are presented. High-contrast micrographs of a polished stainless steel sample are included, showing clearly the grain boundaries as well as some fine structure within the grains. Micrographs are also presented of natural diamonds both in polished and unpolished forms. In the former many polishing lines are visible, and in the latter one can clearly see a large number of stacking faults. Results on the study of monolayers of Langmuir-Blodgett films are also presented. The micrographs clearly show the boundaries as well as nonuniformities within the films. The ability of our system to image objects showing refractive-index variation is demonstrated by producing micrographs of an exposed but undeveloped photoresist film and a partially doped Si sample. In each case a qualitative comparison is made with the differential interference (Nomarski) micrograph of the same field of view.

Recording of phase-amplitude images

An interferometer comprising three diffraction gratings and an imaging system is used with spatially and spectrally noncoherent light to produce high fidelity low noise recording of phase- and -amplitude objects.

Phase image differentiation with linear intensity output

A heuristic development of the operation of a square root filter (one whose amplitude transmittance is proportional to the square root of position in frequency space) is presented. The output of a coherent optical processor utilizing this filter for phase image inputs is shown to be an intensity which is directly proportional to the derivative of the input phase function. The results of a digital filtering experiment which confirms this linear relationship are presented. The use of this filter in phase image visualization systems is also discussed.

Noncontact optical profilometer

The optical profilometer is a measuring instrument that utilizes a laser beam reflected from a surface to generate a profile of the reflecting surface. The device has been configured in such a manner as to allow stabilization of the measured profile with respect to laser intensity fluctuations and the reflectivity of the tested object. Measurements can be made quickly and without damaging the surface.