Abstract--Electron avalanching in liquid argon is being studied as a function of voltage, pressure, radiation intensity, and the concentrations of certain additives, especially xenon. The avalanches produced in an intense electric field at the tip of a tungsten needle are initiated by ionization from a moveable americium ( 241 Am) gamma ray source. Photons from xenon excimers are detected as photomultiplier signals in coincidence with the current pulse from the needle. In pure liquid argon the avalanche behavior is erratic, but the addition of even a small amount of xenon (≤100ppm) stabilizes the performance. Similar attempts with neon (30%) as an additive to argon have been unsuccessful. Tests with higher energy gamma rays ( 57 Co) yield spectra and other performance characteristics quite similar to those using the 241 Am source. Two types of signal pulses are commonly observed: a set of pulses that are sensitive to ambient pressure, and a set of somewhat smaller pulses that are not pressure dependent.

Abstract-Gas electron multipliers (GEMS) have been made by a deep X-ray lithography technique (LIGA process) using synchrotron radiation on polymethylmethacrylate (PMMA) and by UV processes using a UV etchable glass. Gain, stability and rate capability for these detectors are described.The LIGA detectors described consist of PMMA sheets of various thicknesses, 125µm to 350µm, and have 150µm × 150µm square holes spaced with a pitch of 300µm. Thin copper electrodes are plated on the top and bottom surfaces using a Damascene method, followed by electroless plating of the copper onto a palladium-tin base layer. For various thicknesses of PMMA measurements have been made of absolute gain vs. voltage, time stability of gain, and rate capability. The operating gas mixture was usually Ar/CO 2 (70/30) gas, but some tests were also done using P10 gas. We also made GEM-like detectors using the UV etchable glass called Foturan, patterned by exposure to UV light and subsequent etching. A few measurements using these detectors will be reported, including avalanche gain and time stability. I. INTRODUCTIONINCE the group of Sauli introduced in 1996 the gas electron multiplier (GEM) [1] as a pre-amplification foil, there has been a considerable effort devoted to the investigation of its characteristics, and to the improvement of its performance. Other methods of fabrication have been investigated, including dry etching and laser drilling [2].We have made GEM-like detectors [3] by the LIGA process [4], using X-rays from an electron synchrotron (the ALS) for exposing the PMMA, and by exposure of Foturan glass [5,6] and subsequent etching. In this paper, we describe fabrication techniques and a new method for placing copper electrodes on the top and bottom GEM surfaces. We also present new measurements of GEM-like detectors made by the LIGA process, including absolute gain, time stability and rate capability, and preliminary results from the Foturan detectors. , in which low-energy X-rays are used to expose patterns on polymethylmethacrylate (PMMA) sheets. Our LIGA-fabricated detectors described here consist of thin PMMA sheets (125µm -350µm thickness) with arrays of 150µm × 150µm square holes having steep wall sides and a pitch of 300µm. These patterns are made on PMMA sheets exposed to X-rays of about 10keV energy through patterned gold masks. GEM-like detectors have also been made using Foturan glass of 300µm thickness. These have arrays of 130µm × 130µm square holes, and also have steep wall sides and a pitch of 250µm. The cross sectional dimensions of the detector sensitive region are approximately 30mm × 30mm for the PMMA and 10mm × 10mm for the Foturan. A. Fabrication of LIGA DetectorsThe fabrication process begins with the creation of a chromium-on-quartz photomask using an electron beam Nanowriter. The photomask is then used as a template to generate a LIGA mask: a 20µm thick gold pattern on a silicon wafer using photolithography of a spin-cast photoresist layer. The function of the LIGA mask is to produce a high differenti...

Previously [1] we showed how small admixtures of xenon (Xe) stabilize electron avalanches in liquid Argon (LAr). In the present work, we have measured the positive charge carrier mobility in LAr with small admixtures of Xe to be 6.4 x 10 -3 cm 2 /Vsec, in approximate agreement with the mobility measured in pure LAr, and consistent with holes as charge carriers. We have measured the concentration of Xe actually dissolved in the liquid and compared the results with expectations based on the amount of Xe gas added to the LAr. We also have tested LAr doped with krypton to investigate the mechanism of avalanche stabilization.

We demonstrate a photonic integrated circuit using a novel monolithic integration platform combining InGaAsP gain elements and index matched amorphous silicon waveguide devices. The AWG based multi-frequency laser emits eight 100-GHz-spaced wavelengths near 1550 nm.OCIS codes: (250.5300) Photonic integrated circuits 1. Introduction Integration of photonic circuits is required to satisfy growing bandwidth demands in cost sensitive communication networks at affordable cost. Monolithic photonic circuits containing both active and passive components have been demonstrated using various integration techniques. Typically, the materials used for active as well as passive components in monolithic systems are InP and lattice matched epitaxially grown semiconductor compounds InGaAsP, GaInAlAs [1][2][3][4][5]. Most integrated devices require very low reflections and low loss at active-passive transitions. This makes materials that are popular for passive optical components such as SiO2/SiN/SiON and polymers less attractive for monolithic integration due to refractive indices much lower than those of the III/V compounds. Amorphous silicon alloys, transparent at telecommunication wavelengths (1310, 1550 nm), can be made with refractive indices matching those of III/V semiconductors but do not require lattice matched epitaxy. Optical waveguides made of amorphous silicon alloys deposited on silicon substrates have been explored in [6][7][8]. Low temperature PECVD deposition of amorphous silicon alloys makes this material system compatible with III/V components and substrates. In this paper we demonstrate the first monolithically integrated device combining amorphous silicon and III/V components. We have designed and fabricated a multi-frequency laser, which consists of InGaAsP/InP gain elements, and amorphous silicon waveguides, an amorphous silicon arrayed waveguide grating (AWG) and an amorphous silicon multimode interference (MMI) splitter monolithically integrated on an InP substrate.