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

摘要

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 (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 frames/s), an intermediate SNR of 8 dB, and a volume of coherence of 3.4 X 10~(4) (mu)m~(3). Holograms of objects with a lateral resolution of 1 (mu)m were achieved using a microscope lens (50 X /NA velence 0.7) and a CCD camera featuring a 4-12 bit dynamic range.