Wan Yuhong

Effect of Wavefront Properties on Numerical Aperture of Fresnel Hologram in Incoherent Holographic Microscopy

Fresnel incoherent correlation holographic (FINCH) microscopy is a recently developed new technique, which employs a spatial light modulator (SLM) as the beam splitter. Light originating from the same object point is split into two beams by the wavefront-division phase mask displayed on SLM, and a Fresnel-zone plate-like hologram is formed by the interference of the two beams. The numerical aperture NAH of the recorded Fresnel hologram is introduced as a comprehensive parameter for evaluating the imaging characteristics in the FINCH scheme. The effect of wavefront properties on NAH of the hologram is investigated theoretically in the sense of optimizing imaging resolution. The variation trends of NAH are described and an optimal NAH is achieved by implementing an appropriate phase mask for a given recording distance between SLM and CCD; thus optimized imaging resolution and signal-to-noise ratio are demonstrated experimentally.

Holographic and Thermal-Fixing Characteristics of Doubly Doped Zn:Fe:LiNbO3 Crystals

We perform a comprehensive experimental study on holographic and thermal-fixing characteristics of Zn:Fe:LiNbO3. The measured hologram decay time constants, respectively caused by optical readout and under dark condition, with thermal fixing are 15 times and 75 times longer than that obtained without thermal fixing. This suggests that Zn:Fe:LiNbO3 crystals are suitable for thermal fixing. Multiplexed recordings of 300 holograms using different thermal fixing schemes verify that a proper multiplexing scheme such as track-division thermal-fixing scheme for disc-type holographic storage can effectively compensate for the negative effect of zinc-doping on the dynamic range, thus the storage density is enhanced.

The resolution characteristics of volume holographic lens

We introduce two kinds of typical volume holographic gratings into the imaging system respectively, and discuss their resolution characteristics in lateral and longitudinal defocus condition to improve the image quality.