Inter-pixel Gaps Research Articles

Low-crosstalk 3D display without color moiré patterns based on a color light source array.

A low-crosstalk 3D display without color moiré patterns based on color light source array is proposed. The proposed 3D display consists of a color light source array, a transparent liquid crystal display (T-LCD) panel, a scattering layer, and a parallax barrier from back to front. The color light source array consists of three primary color light sources that correspond to the sub-pixels on the T-LCD panel. These light sources project the sub-pixels with matching color to the same location on the scattering layer to form new pixels without color moiré patterns. The new pixels have inter-pixel gaps that enhance signal bandwidth and decrease crosstalk. The parallax barrier projects the new pixels of parallax images to different viewpoints, creating a 3D effect. A prototype is developed and evaluated.

Photon counting Detectors: Concept, technical Challenges, and clinical outlook

Photon counting detectors in Computed Tomography overcome several drawbacks of classical detectors used in Computed Tomography.Classical detectors measure X-rays by converting them into visible light during the initial absorption inside a pixel (individual scintillator cube which is separated mechanically from neighboring pixels) and then collecting the emitted visible light per pixel with a photo diode. High resolution imaging with scintillator-based detector experiences a limit due to the dose usage capabilities, low dose applications suffer from classical electronic noise and true material separation inside the scan object can only be performed, if the data acquisition was selected prior the scan examination (dual energy protocols).Photon counting detectors made of a semiconductor crystal which allows the detection of the incoming photons individually using a direct conversion process. The spatial resolution is defined electrically and only limited by the charge distribution inside the semiconductor. This enables sharper images without the dose penalty of interpixel gaps or post patient collimation. The contrast to noise ratio is increased by detecting each photon individually with respect to its energy. This additional energy information can be used during any diagnostic procedure to gain further detailed insights into the morphology and functionality of the scanned object. And finally, no classical noise is deteriorating the signal as the digitization of the signal is done during the initial detection.Photon counting detectors lead the way to higher contrasts, higher resolution, and lower doses which may help elevating the potential of computed tomography. Upcoming studies will evaluate the true potential of this technology and point to the variety of clinical fields which may profit from this imaging modality to make all humans lives healthier.

Incomplete Charge Collection at Inter-Pixel Gap in Low- and High-Flux Cadmium Zinc Telluride Pixel Detectors.

The success of cadmium zinc telluride (CZT) detectors in room-temperature spectroscopic X-ray imaging is now widely accepted. The most common CZT detectors are characterized by enhanced-charge transport properties of electrons, with mobility-lifetime products μeτe > 10−2 cm2/V and μhτh > 10−5 cm2/V. These materials, typically termed low-flux LF-CZT, are successfully used for thick electron-sensing detectors and in low-flux conditions. Recently, new CZT materials with hole mobility-lifetime product enhancements (μhτh > 10−4 cm2/V and μeτe > 10−3 cm2/V) have been fabricated for high-flux measurements (high-flux HF-CZT detectors). In this work, we will present the performance and charge-sharing properties of sub-millimeter CZT pixel detectors based on LF-CZT and HF-CZT crystals. Experimental results from the measurement of energy spectra after charge-sharing addition (CSA) and from 2D X-ray mapping highlight the better charge-collection properties of HF-CZT detectors near the inter-pixel gaps. The successful mitigation of the effects of incomplete charge collection after CSA was also performed through original charge-sharing correction techniques. These activities exist in the framework of international collaboration on the development of energy-resolved X-ray scanners for medical applications and non-destructive testing in the food industry.

An opto-thermal study of high brightness 280 nm emission AlGaN micropixel light-emitting diode arrays

We present a study of the light output power and the thermal impedance of 281 nm emission AlGaN based micropixel LEDs. A modular interconnected micropixel array design is presented which enables dense packing with area and power scalability. We study 5–15 μm diameter stand-alone devices and parallel-connected micropixel arrays with 5 μm interpixel gaps. A standalone 5 μm pixel emits 291 W cm−2 at 10.2 kA cm−2 DC-drive. A power as high as 23 mW (361 W cm−2) was measured at a pulsed-pump current of 800 mA (∼15 kA cm−2) for an interconnected array. These are the smallest and brightest DUV LEDs to date.

The Mid-Infrared Instrument for the James Webb Space Telescope, VII: The MIRI Detectors

The MIRI Si:As IBC detector arrays extend the heritage technology from the Spitzer IRAC arrays to a 1024 × 1024 pixel format. We provide a short discussion of the principles of operation, design, and performance of the individual MIRI detectors, in support of a description of their operation in arrays provided in an accompanying paper. We then describe modeling of their response. We find that electron diffusion is an important component of their performance, although it was omitted in previous models. Our new model will let us optimize the bias voltage while avoiding avalanche gain. It also predicts the fraction of the IR-active layer that is depleted (and thus contributes to the quantum efficiency) as signal is accumulated on the array amplifier. Another set of models accurately predicts the nonlinearity of the detector-amplifier unit and has guided determination of the corrections for nonlinearity. Finally, we discuss how diffraction at the interpixel gaps and total internal reflection can produce the extended cross-like artifacts around images with these arrays at short wavelengths, ∼5 μm. The modeling of the behavior of these devices is helping optimize how we operate them and also providing inputs to the development of the data pipeline.

Development of PET Detectors Using Monolithic Scintillation Crystals Processed With Sub-Surface Laser Engraving Technique

New monolithic scintillation detectors for PET have been developed, where the crystals are processed using an internally focused laser processing technique called sub-surface laser engraving (SSLE). When high intensity light pulses of short duration from a laser are focused into a scintillation crystal, they induce multi-photon absorption at the focal point and result in refractive index changes or micro-cracks inside the crystal. By applying the SSLE technique to a monolithic scintillation block, fine segmentation in the crystal can be formed without inter-pixel gaps. We have fabricated 2D segmented arrays by using a Nd:YAG laser to engrave various patterns of micro-cracks inside monolithic LYSO crystal blocks. The processed crystal array, segmented to 12 × 12 with 1.67 mm pitch, has been evaluated by coupling to a position-sensitive photomultiplier tube (PS-PMT). The 2D position histograms were measured for uniform irradiation of gamma rays, and each crystal segment was clearly separated. The average energy resolution was 9.7%, similar to that of the conventional arrays, so the laser-processed LYSO crystals have kept their primary scintillation properties. We have also evaluated the laser-processed crystals by using multi-pixel photon counters (MPPCs) to investigate their possibility as a future PET detector. The results suggest that it is possible to fabricate high performance PET detectors using the SSLE technique.

Improvement of the sensitivity and spatial resolution of pixelated CsI:Tl scintillator with reflective coating

Abstract Pixelated-scintillator films used for X-ray image sensors were developed and tested. The air gap between scintillator pixels reduces the transport of visible light photons generated by X-rays into the neighboring pixels so it will maximize the overall spatial resolution as well as the light collection efficiency of an X-ray imager. For further improvement, the inter-pixel gaps and surface are filled and coated with a reflective or a lower refractive material than an CsI(Tl) scintillator. The scintillator films of 30–40 μm thickness were made with thallium-doped CsI by the conventional physical vapour deposition process on glass substrates with a photo resist layer patterned by UV lithography. In this work, the effects on light collection efficiency and spatial resolution of the pixelated-scintillator films before and after reflective coating were evaluated using a CCD sensor and X-rays within the medical diagnostic energy range.

A high efficiency pixelated detector for small animal PET

We report on the development of a new high efficiency detector for small animal PET. The detector is based on a monolithic block of LSO pixelated using laser ablation technique. The laser processing allows pixelation with very narrow, 70 /spl mu/m wide, inter-pixel gaps resulting in a substantially enhanced sensitivity when the detectors are operated in coincidence mode. This paper presents the first results of a detector module fabricated using this approach. Preliminary imaging data at 511 keV obtained by coupling the pixelated LSO to a position sensitive photomultiplier tube (PSPMT) and a position sensitive avalanche photodiode (PSAPD) are presented.

Demonstration of a linear optical true-time delay device by use of a microelectromechanical mirror array.

We present the design and proof-of-concept demonstration of an optical device capable of producing true-time delay(s) (TTD)(s) for phased array antennas. This TTD device uses a free-space approach consisting of a single microelectromechanical systems (MEMS) mirror array in a multiple reflection spherical mirror configuration based on the White cell. Divergence is avoided by periodic refocusing by the mirrors. By using the MEMS mirror to switch between paths of different lengths, time delays are generated. Six different delays in 1-ns increments were demonstrated by using the Texas Instruments Digital Micromirror Device as the switching element. Losses of 1.6 to 5.2 dB per bounce and crosstalk of -27 dB were also measured, both resulting primarily from diffraction from holes in each pixel and the inter-pixel gaps of the MEMS.

Modified femtosecond pulse shaper using microlens arrays

We discuss a modified femtosecond pulse shaper that uses microlens arrays to convert the continuous band of frequencies normally obtained in the mask plane of a pulse shaper into a series of discrete spots. Our experiments demonstrate that this modification can improve pulse-shaping quality when modulator arrays with large interpixel gaps are used for Fourier-plane filtering.

A femtosecond pulse-shaping apparatus containing microlens arrays for use with pixellated spatial light modulators

We discuss a modified femtosecond pulse shaper that uses microlens arrays to convert the continuous band of frequencies normally obtained at the mask plane of a pulse shaper to a series of discrete spots. Two possible modified pulse-shaping geometries are described and the optimum geometry is chosen. Our experiments demonstrate that this modification can improve pulse-shaping quality when modulator arrays with large interpixel gaps are used for Fourier-plane filtering.