Smoothing of inter-layer edge artifacts in depth-map computer-generated holograms.

In the depth-map computer-generated hologram (CGH), inter-layer edge artifacts are observed in the discontinuous edges of section-wise depth-map objects. CGH synthesis, utilizing the hybrid smoothing method of silhouette masking and edge-apodization, alleviates unwanted inter-layer edge artifacts. The proposed method achieves improved de-artifact filtering that generates holographic images closer to the ground truth image of the depth-map object unattainable by the conventional CGH synthesis method.

Motion-free TSOM using a deformable mirror.

Through-focus scanning optical microscopy (TSOM) is a model-based optical metrology method that involves the scanning of a target through the focus of an optical microscope. Unlike a conventional optical microscope that directly extracts the diffraction-limited optical information from a single in-focus image, the TSOM method extracts nanometer scale sensitive information by matching the target TSOM data/image to reference TSOM data/images that are either experimentally or computationally collected. Therefore, the sensitivity and accuracy of the TSOM method strongly depends on the similarities between the conditions in which the target and reference TSOM images are taken or simulated, especially the lateral instability during through-focus scanning. As a remedy to the lateral instability, we proposed the application of adaptive optics to the through-focus scanning operation and initially developed a closed-loop system with a tip/tilt mirror and a Shack-Hartmann sensor, with which we were able to keep the plane position within peak-to-valley (PV) 33 nm. We then further developed a motion-free TSOM tool reducing the instability down to practically zero by the replacement of the tip/tilt mirror with a deformable mirror that performs through-focus scanning by deforming its mirror surface. The motion-free TSOM tool with a × 50 (NA 0.55) objective lens could provide a scanning range of up to ± 25 µm with a minimum step of 25 nm at a maximum update rate of 4 kHz. The tool was demonstrated to have a recognition accuracy of < 4 nm for critical dimension (CD) values in the range of 60 ∼ 120 nm with a reference TSOM image library generated by a Fourier modal method matching various observations conditions.

Metrological sensitivity improvement of through-focus scanning optical microscopy by controlling illumination coherence.

We investigate the influence of the degree of illumination coherence on through-focus scanning optical microscopy (TSOM) in terms of metrological sensitivity. The investigation reveals that the local periodicity of the target object is a key structural parameter to consider when determining the optimal degree of illumination coherence for improved metrological sensitivity. The optimal coherence conditions for the TSOM inspection of several target objects are analyzed through numerical simulation.

Through-focus scanning optical microscopy with the Fourier modal method.

We propose a Fourier modal method (FMM) based through-focus scanning optical microscopy (TSOM) featuring sub-nano scale measurement tolerance. TSOM is very recently conceptualized non-destructive optical metrology technique just at the beginning stage of research. Nowadays the reliability and feasibility of TSOM concept is subject to controversy. We experimentally demonstrate stable nano-scale metrology of the FMM-based TSOM for the verification of the TSOM metrology and provide a numerical tool for true nano-meter scale TSOM through devising the FMM based TSOM scheme. By considering the illumination light parameters of incidence angle, polarization, degree of coherence, illumination numerical aperture, and collection numerical apertures in the FMM modeling of TSOM image acquisition, we reach precise agreement between the calculated and experimentally measured TSOM images. The essential elements of the FMM based TSOM for achieving high-level consistency are elucidated.

DC-free on-axis holographic display using a phase-only spatial light modulator.

A DC-noise-free on-axis holographic display scheme using a phase-only spatial light modulator (SLM) is proposed. The origin of DC noise in the on-axis holographic display using a phase-only SLM is analyzed, and a DC noise rejection filter is optimized for a phase-only SLM is designed. A novel two-step iterative Fourier transform algorithm for the optimal synthesis of a phase-only computer-generated hologram using the proposed scheme is devised. The proposed scheme and algorithm are validated with numerical simulations and experiments.

Characteristics of complex light modulation through an amplitude-phase double-layer spatial light modulator.

The complex modulation characteristics of a light field through an amplitude-phase double-layer spatial light modulator are analyzed based on the wave-optic numerical model, and the structural conditions for the optimal double-layer complex modulation structure are investigated. The relationships of interlayer distance, pixel size, and complex light modulation performance are analyzed. The main finding of this study is that the optimal interlayer distance for the double-layer structure can be found at the Talbot effect condition. For validating the practical usefulness of our findings, a high quality reconstruction of the complex computer-generated holograms and the robustness of the angular tolerance of the complex modulation at the Talbot interlayer distance are numerically demonstrated.

Quasi-retroreflection from corner cubes with refractive free-form surfaces.

Quasi-retroreflection from corner-cube structures with a refractive free-form surface is studied. It is shown that adjustment of the structural parameters of the free-form surface allows control of quasi-retroreflection. Quasi-retroreflection corner-cube array sheets with specified quasi-retroreflection angle are modeled, and their quasi-retroreflection characteristics are analyzed.

Truncated corner cubes with near-perfect retroreflection efficiency.

By isolating a finite effective volume from a conventional triangular pyramid corner cube, we obtained truncated corner cube structures with greatly enhanced retroreflection efficiency. We explore an optimal truncated corner cube with near 100% retroreflection efficiency based on the expectation that the traveling paths of the optical rays can be localized in the finite effective volume of the structure, and, as a result, truncated corner cubes with perfect efficiency can be produced. As a case study, the retroreflection efficiency of a commercialized 3M truncated corner cube sample is evaluated. Furthermore, it is shown with numerical verification that a truncated corner cube array sheet with near-perfect retroreflection efficiency can be produced.

Transmission-type photonic crystal structures for color filters.

A transmission-type structure based on woodpile photonic crystal layers is proposed for use in color filters. Selective bandpass filters for red, green, and blue wavelength bands are constructed using optimally designed multilayered woodpile photonic crystals. The R/G/B color filtering for a wide range of incidence angles of light is demonstrated numerically, and the operation principle and design method are described.

Iterative method for optimal design of flat-spectral-response arrayed waveguide gratings.

A novel iterative projection-type optimal design algorithm of arrayed waveguide gratings (AWGs) with a flat spectral response is proposed based on the Fourier optics model of AWG. The enhancement of the spectral-response flatness of the AWG is demonstrated, with an analysis on the trade-off relationship between band flatness and crosstalk.

Polycyclic aromatic hydrocarbon levels and risk assessment for food from service facilities in Korea.

In this study, levels of benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene (BaP), dibenzo[a,h]anthracene, benzo[g,h,i]perylene and indeno[1,2,3-c,d]pyrene in 412 food items collected from food service facilities in Korea were analysed. The concentrations of the eight polycyclic aromatic hydrocarbons (PAHs) ranged 0.13-0.48 µg/kg. The concentrations of benzo[a]pyrene in all food samples were <1 µg/kg, which is the lowest maximum limit in foods regulated by European Union legislation. PAH contents were employed to conduct exposure and risk assessment. The chronic daily intake of PAHs from 412 food samples was 5.48 × 10-6-4.70 ×x 10-4 µg-TEQBaP/kg/day with margins of exposure of 1.04 × 109-1.16 × 1011.

Noise performance of readout electronics for photodetector.

A 16 channel integrated circuit charge sensitive preamplifier (CSA) has been developed for an X-ray detector module that uses a 16 linear arrays of photodetector. The photodiode is made of 280 um thickness, 30 M Omega shunt resistivity, the measured junction capacitance 200 pF. The main performances of the CSA for photodetector are the following: the input equivalent noise charge is 300 e(-)rms at peaking time 200 ns, the highest gain is 10 mV/fC, the peaking time is adjustable between 50 ns and 300 us by external passive components. The noise simulation yield ENC values of 50 e(-) and 250 e(-) for thermal and 1/f noise, respectively. The design was fabricated in standard 0.35 um CMOS technology and the circuit occupies an area of 4 x 4 mm2 and dissipates 2 mW per channel from a 3.3 V single power supply.

Design and evaluation of a 2D array PIN photodiode bump bonded to readout IC for the low energy x-ray detector.

A 2D array radiation sensor, consisting of an array of PIN photodiodes bump bonded to readout integrated circuit (IC), has been developed for operation with low energy X-rays. The PIN photodiode array and readout IC for this system have been fabricated. The main performance measurements are the following: a few pA-scale leakage current, 350 pF junction capacitance, 30 microm-depth depletion layer and a 250 microm intrinsic layer at zero bias. This PIN photodiode array and readout IC were fabricated using a PIN photodiode process and standard 0.35 microm CMOS technology, respectively. The readout circuit is operated from a 3.3 V single power supply. Finally, a 2D array radiation sensor has been developed using bump bonding between the PIN photodiode and the readout electronics.

Polycrystalline CdZnTe thick films for low energy x-ray: system evaluation.

The X-ray response of polycrystalline-CdZnTe was measured by signal-to-noise (S/N) analysis. The CdZnTe material has optimal properties in a solid-state X-ray detector, and much research has focused on single crystal CdZnTe with a small-sized, silicon readout device. However, it would be difficult to apply CdTe or CdZnTe single crystal to large area, flat panel detectors, such as those used for radiography and mammography. As an alternative of single crystal CdZnTe, we have grown thick, polycrystalline CdZnTe films of high resistivity (>5 x 10(9) Ohm cm) using the thermal evaporation method on carbon substrate. A high signal-to-noise value has a direct impact on the performance of CdZnTe X-ray detectors. Important image parameters, such as dynamic range and detective quantum efficiency, rely on the signal and noise characteristics of the system. In this paper, we analyzed the properties of the X-ray detector and obtained images of the X-ray detector using the data acquisition system. The X-ray detector used the Cd1-xZnxTe (x=0.04), which used carbon substrate and gold as the electrode. The detector design is planar and 32 mm x 10 mm in size, and it has a 1.75mm x 1mm pixel electrode size and a detector thickness of 150 microm.