White light interferometry is an extremely powerful tool for optical measurements. This paper discusses the advantages and disadvantages of white light interferometry compared to laser light interferometry. Three different white light interferometers are discussed: 1) diffraction gratin interferometers; 2) vertical scanning or coherence probe interferometers, and 3) white light scatterplate interferometers.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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White light interferometry

The possibility of compensating for the aberrations of an imaging lens in digital holography is outlined theoretically. The principle is demonstrated with a Mach–Zehnder arrangement and transilluminated objects. Diffraction-limited resolution can be obtained with a plano–convex lens. Amplitude and phase objects were imaged.

Compensation of lens aberrations in digital holography.

We discuss how the stain left after evaporation of a suspension evolves with heating of the glass or plastic on which the liquid has been deposited. Upon increasing the substrate temperature, it is found that the stain gradually changes from the usually observed ring to an “eye” shape, that is, a combination of the thick central stain and the thin outer ring. Both the size and the relative volume of the central stain increase with the substrate temperature. The main mechanism for this phenomenon is proposed to be an enhanced Marangoni recirculation flow on hot substrates. These findings can be exploited to continuously tune the morphology of coffee stains, with potential applications in self-assembly and ink-jet printing.

From coffee rings to coffee eyes

Researchers in Israel have developed a method for doubling the field of view in single-exposure depth-resolved holographic imaging. Pinhas Girshovitz and Natan Shaked from Tel Aviv University based their technique on digital interferometric microscopy, which uses interference effects to extract quantitative information on the thickness or height profile of the imaged object. Such information is useful, for example, in imaging of biological samples without labeling, or for optically profiling elements for non-destructive testing with sub-nanometer accuracy. Unfortunately, to enable capturing the entire quantitative image in a single exposure, a reduction in the field of view occurs. Girshovitz and Shaked proposed a way to optically compress more information into the same camera frame without loss in the imaging details or the magnification. A compact and portable interferometric module, positioned only in the output of the imaging system, splits the image beam into two components that are then superimposed at different angles on the imaging camera. This multiplexing approach increases the information in the image and doubles the field of view over previous techniques. Therefore, they were able to image wider samples or acquire the samples in faster frame rates. The main experimental demonstrations include fast high-magnification quantitative imaging of a swimming sperm cell, and non-destructive profiling of a thin element during rapid lithography process.

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Doubling the field of view in off-axis low-coherence interferometric imaging

Coherence-controlled holographic microscope (CCHM) combines off-axis holography and an achromatic grating interferometer allowing for the use of light sources of arbitrary degree of temporal and spatial coherence. This results in coherence gating and strong suppression of coherent noise and parasitic interferences enabling CCHM to reach high phase measurement accuracy and imaging quality. The achievable lateral resolution reaches performance of conventional widefield microscopes, which allows resolving up to twice smaller details when compared to typical off-axis setups. Imaging characteristics can be controlled arbitrarily by coherence between two extremes: fully coherent holography and confocal-like incoherent holography. The basic setup parameters are derived and described in detail and experimental validations of imaging characteristics are demonstrated.

Off-axis setup taking full advantage of incoherent illumination in coherence-controlled holographic microscope

Achromatic interferometers are developed that perform optical processing operations and record both the phase and amplitude of the output by means of a coherent reference beam. The interferometers simultaneously carry out the data processing tasks and form fringes with white light extended sources.

Achromatic interferometers for white light optical processing and holography.

Low noise diffraction gratings are constructed with the aid of a circular grating interferometer illuminated with a polychromatic or extended source.

Interferometric construction of circular gratings

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.

Recording of phase-amplitude images.

An interferometer capable of producing high-quality off-axis zone plates in spatially incoherent light is described. An example is shown that demonstrates the noise-suppressing ability of the spatially incoherent process.

Interferometric recording of high-quality zone plates in spatially incoherent illumination.

The aberration-compensation method of passing the conjugate beam from a hologram through the same optical system used in making the hologram is combined with broad-source interferometer techniques to give, along with the aberration compensation, considerable noise reduction. As with conventional photography, the image is two dimensional.

Gary J. Swanson

Papers

Achromatic interferometers for white light optical processing and holography.

Interferometric construction of circular gratings

Recording of phase-amplitude images.

Interferometric recording of high-quality zone plates in spatially incoherent illumination.

Holographic aberration compensation with partially coherent light.