Partially coherent light-emitting diode illumination for video-rate in-line holographic microscopy

Abstract

The light of a light-emitting diode or a common thermal source, such as a tungsten filament lamp, is known to be quasi-incoherent. We generated partially coherent light of these sources with a volume of coherence in the micrometer range of $5–100{\mathrm{\mu m}}^3$ by spatial and spectral filtering. The corresponding degree of partial coherence was adapted for microscopic interference setups, such as a digital in-line holographic microscope. The practicability of the sources was determined by the spectral emittance and the resulting signal-to-noise ratio (SNR) of the detector. The microscale coherence in correlation with the SNR and its resolution for microscopy were analyzed. We demonstrate how low-light-level, non-laser sources enable holographic imaging with a video frame rate ($25\text{frames}/\mathrm{s}$), an intermediate SNR of 8 dB, and a volume of coherence of $3.4\times {10}^4{\mathrm{\mu m}}^3$. Holograms of objects with a lateral resolution of 1 μm were achieved using a microscope lens ($50\times /\mathrm{NA}=0.7$) and a CCD camera featuring a 4–12 bit dynamic range.

© 2012 Optical Society of America

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