Abstract
We present a simple-to-align, highly-portable interferometer, which is able to capture wide-field, off-axis interference patterns from transparent samples under low-coherence illumination. This small-dimensions and low-cost device can be connected to the output of a transmission microscope illuminated by a low-coherence source and measure sub-nanometric optical thickness changes in a label-free manner. In contrast to our previously published design, the τ interferometer, the new design is able to fully operate in an off-axis holographic geometry, where the interference fringes have high spatial frequency, and the interference area is limited only by the coherence length of the source, and thus it enables to easily obtain high-quality quantitative images of static and dynamic samples. We present several applications for the new design including nondestructive optical testing of transparent microscopic elements with nanometric thickness and live-cell imaging.
Highlights
Wide-field interferometric phase microscopy (IPM), known as digital holographic microscopy, is a label-free powerful tool that can be utilized for a wide range of applications including biological cell investigations [1,2,3,4,5], surface measurements [6], biometry [7], and others
Many IPM setups were presented over the years, and they can be divided into various groups, such as setups that use common-path geometry [8,9,10] or separated reference and sample beam geometry [1,2,5,11], setups that use high-coherence source [1,2,3,4,5,6,7] or lowcoherence source [12,13,14], setups that use on-axis geometry [11,15] or off-axis geometry [1,2,5,12,13,14,16,17,18,19], etc
These results show that the off-axis τ interferometer can be used to perform inexpensive quality checks and imaging during or after the manufacturing of transparent optical elements, as long as the lateral dimensions of the smallest element that needs to be examined is larger than the diffraction-limit spot of the microscope
Summary
Wide-field interferometric phase microscopy (IPM), known as digital holographic microscopy, is a label-free powerful tool that can be utilized for a wide range of applications including biological cell investigations [1,2,3,4,5], surface measurements [6], biometry [7], and others. In contrast to regular interferometers, since there is only one sample beam till the output of the inverted microscope, the user does not need to take into consideration the thickness of the constant sample elements such as the coverslip in order to create beam path matching for achieving interference with a low-coherence source Due to these advantages, this setup achieved a low temporal and spatial noise levels, with standard deviations of 0.18 nm and 0.42 nm, respectively. The proposed setup can operate in full off-axis geometry, obtain interference on a large field of view (limited only by the coherence length of the source) and use the full frame rate of the camera, while still retaining the advantages of the device portability, low cost, and easy alignment, even with a low-coherence source
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