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Dual-wavelength holography has a better axial range than single-wavelength holography, allowing unambiguous phase imaging. Partial coherence sources reduce coherent noise, resulting in improved reconstructed images. We measured a ball-grid array using dual-wavelength holography with partial coherence sources. This holography method is useful for measurement samples that exhibit coherence noise and have a step height larger than the single wavelength used in holography.

In this paper we have applied self-reference hologram to DHM (digital holography microscopy) to remove phase aberration. We have constructed an off-axis reflection- type digital holography microscope. We have extracted a low spatial frequency hologram from the conjugated hologram and used it as a reference hologram. Experimentally we show that distortion of image and aberration of phase in a measurement system are removed using the self-reference hologram.

A simple method has been developed to suppress the DC term in in-line digital holographic microscope images. The technique is based on the use of the average intensity of a variable number of pixels rather than a fixed number of pixels. The DC-suppression ratio is similar to that associated with the averaging method proposed by Kreis and Juptner, while the image quality resulting from the new method is higher. This method can potentially yield significant improvements in the quality of reconstructed images.

Three-Dimensional Information and Two-Dimensional Refractive Index Measurements Using a Combined Digital Holographic Microscope Hyungjun Cho, Jingwoong Lim, Doocheol Kim and Younghun Yu Department of Physics, Cheju National University, Jeju 690-756 Sanghoon Shin AP & Tec, Seoul 135-539 Wongun Jang Micro-Optics Team, Korea Optical Photonics Technology Institute, Gwangju 500-460 (Received 12 December 2007, in nal form 10 March 2008) We developed a combined digital holographic microscope that can measure the refractive index of a sample. This system provides highly precise three-dimensional (3-D) information on the sample. We also propose theoretical and experimental methods for the combined holography microscope. The measured data were reasonable although the data error was large. This error was attributable to alignment issues in the experiment. By improving the experimental method, we can measure the refractive index more precisely and obtain more accurate 3-D information on the samples. PACS numbers: 42.40.My, 42.30.W, 42.25.F

A fundamental problem in digital holography is the presence of zero-order noise in the reconstruction process, which decreases the signal to noise ratio(SNR). For many applications, that reduction of SNR makes digital holography impractical, so a great number of approaches have been tested in order to overcome such a problem. In this paper we use the scanning method to suppress the zero-order diffraction noise and the interference noise between object beams. We demonstrate that it is possible to increase the image quality with the scanning method.

A novel method is employed to eliminate the twin-images in the so called 'in-line' digital holographic microscope. We could achieve digital holographic microscope which solve the problems of overlapping of real and imaginary images and eliminating one of them by padding and removing DC term by averaging method. The entire process needs only one digital hologram.

We could distinguish the virtual image and real image by controlling the distance between the hologram plan to object lens in in-line holography microscope.