Daesuk Kim

Three-dimensional-object recognition by use of single-exposure on-axis digital holography

On-axis phase-shifting digital holography requires recording of multiple holograms. We describe a novel real-time three-dimensional- (3-D-) object recognition system that uses single-exposure on-axis digital holography. In contrast to 3-D-object recognition by means of a conventional phase-shifting scheme that requires multiple exposures, our proposed method requires only a single digital hologram to be synthesized and used to recognize 3-D objects. A benefit of the proposed 3-D recognition method is enhanced practicality of digital holography for 3-D recognition in terms of its simplicity and greater robustness to external scene parameters such as moving targets and environmental noise factors. We show experimentally the utility of the single-exposure on-axis digital holography-based 3-D-object recognition method.

Single-shot, dual-wavelength digital holography based on polarizing separation.

We describe what we believe to be a new digital holographic configuration that can be utilized for both single-shot, dual-wavelength, off-axis geometry and imaging polarimetry. To get the feasibility of the single-shot, dual-wavelength, off-axis geometry, a sample with a nominal step height of 1.34 μm is used. Undesirable noises that strongly affect the measurement have been suppressed successfully by using a modified flat fielding method for the dual-wavelength scheme. And also, the experiment is conducted on a nanopattern sample on the basis of a single image acquisition to show the imaging polarimetry capability. The proposed scheme can provide a real-time solution for measuring three-dimensional objects having a high abrupt height difference with moderate accuracy. Furthermore, it can be used as a fast polarization imaging measurement tool.

Distortion-tolerant 3-D object recognition by using single exposure on-axis digital holography

We present a distortion-tolerant 3-D object recognition system using single exposure on-axis digital holography. In contrast to distortion-tolerant 3-D object recognition employing conventional phase shifting scheme which requires multiple exposures, our proposed method requires only one single digital hologram to be synthesized and used for distortion-tolerant 3-D object recognition. A benefit of the single exposure based on-axis approach is enhanced practicality of digital holography for distortion-tolerant 3-D object recognition in terms of its simplicity and high tolerance to external scene parameters such as moving targets. This paper shows experimentally, that single exposure on-axis digital holography is capable of providing a distortion-tolerant 3-D object recognition capability.

Two-wavelength in-line phase-shifting interferometry based on polarizing separation for accurate surface profiling

We describe a configuration that can be used for two-wavelength phase-shifting in-line interferometry based on polarizing separation. The experiment is conducted on a sample with a step height of 1.34 μm nominally. In this paper, five- and seven-phase step algorithms have been compared for their effectiveness in reducing the noise in the phase maps. The noise is further reduced by the application of the flat fielding method. The recorded interferograms are processed using seven-phase step algorithm to obtain the phase map for each wavelength separately. The independent phase maps are subtracted and a phase map for the beat-wavelength is obtained and converted to height map. The results extracted from the seven-phase step algorithm have been compared with the results extracted from the single shot off-axis geometry and the results are in agreement.

3-D Surface Profile Measurement Using An Acousto-optic Tunable Filter Based Spectral Phase Shifting Technique

An acousto-optic tunable filter based 3-D micro surface profile measurement using an equally spaced 5 spectral phase shifting is described. The 5-bucket spectral phase shifting method is compared with a Fourier-transform method in the spectral domain. It can provide a fast measurement capability while maintaining high accuracy since it needs only 5 pieces of spectrally phase shifted imaging data and a simple calculation in comparison with the Fourier transform method that requires full wavelength scanning data and relatively complicated computation. The 3-D profile data of micro objects can be obtained in a few seconds with an accuracy of

High speed volumetric thickness profile measurement based on full-field wavelength scanning interferometer

{\sim}10nm

Surface Form Measurement Using Single Shot Off-axis Fizeau Interferometry

. The 3-D profile method also has an inherent benefit in terms of being speckle-free in measuring diffuse micro objects by employing an incoherent light source. Those simplicity and practical applicability is expected to have diverse applications in 3-D micro profilometry such as semiconductors and micro-biology.

Two Step on-axis Digital Holography Using Dual-channel Mach-Zehnder Interferometer and Matched Filter Algorithm

A novel high speed volumetric thickness profilometry based on a wavelength scanning full-field interferometer and its signal processing algorithm is described for a thin film deposited on pattern structures. A specially designed Michelson interferometer with a blocking plate in the reference path enables us to measure the volumetric thickness profile by decoupling two variables, thickness and profile, which affect the total phase function phi(k). We show experimentally that the proposed method provides a much faster solution in obtaining the volumetric thickness profile data while maintaining the similar level of accurate measurement capability as that of the least square fitting method.

Coherent noise suppression in digital holography based on flat fielding with apodized apertures

This paper describes the surface form measurement of a spherical smooth surface by using single shot off-axis Fizeau interferometry. The demodulated phase map is obtained and unwrapped to remove the

Snapshot phase sensitive scatterometry based on double-channel spectral carrier frequency concept.

2\pi