Paolo Bergamini

Performance evaluation of a photon-counting intensified CCD

The performance of a prototype photon counting imaging detector, being developed for the international UV space mission spectrum-UV, is presented. The detector is based on a 4-cm diameter, Z stack, high gain microchannel plate (MCP) intensifier endowed with a RbTe photocathode. The electron cascade generated by the MCP intensifier is transduced, via a phosphor screen and a 1:3.6 fiber optics reducer, into a 5 by 5 pixel2, quasi-Gaussian charge distribution on a 15 micrometer, 512 by 512 pixel2 format CCD matrix read out in the frame-transfer mode at 20 MHz, corresponding to 60 frame sec-1 in the full frame mode and to 220 frame sec-1 in the window (128 by 512 pixel2) mode. The data flow is acquired serially as to generate a 5 by 5 pixel2 event sash that sweeps dynamically the CCD matrix at the 50 ns place of the readout clock. Each and every event sash is searched for the presence of events whose charge distribution lie within set thresholds and satisfy given morphological rules, i.e. a peaked charge profile. The centroid coordinates of identified events are subsequently determined with sub-pixel accuracy and stored in an external, high resolution memory. The data acquisition and processing system, based on field programmable gate array technology, is well able to resolve the front MCP pore geometry (10 micrometer diameter pores at 12 micrometer pitch).

Performance characteristics of the MAMA detectors for the SUMER instrument on the SOHO Mission

We have initiated the characterizations of the Multi-Anode Microchannel Array (MAMA) detector systems for the European Space Agency/NASA Solar and Heliospheric Observatory (SOHO) mission. In this paper we briefly review the configurations of the SOHO MAMA detectors and describe their expected performance characteristics based on the results of characterizations of the curved-channel microchannel plates and of the initial characterization of the first engineering model detector system for the Solar Ultraviolet Measurements of Emitted Radiation instrument.

Characterization of a photon-counting intensified active pixel sensor (PC-IAPS): preliminary results

We report about preliminary results of the characterization of a new kind of MCP-based detector: a Photon Counting Intensified Active Pixel Sensor (APS). PC-IAPS appears as the natural evolution of the Intensified CCD, maintaining the basic characteristics, but with improved performance in terms of dynamic range, along with some other appealing properties: higher radiation hardness, more compact design, lower requirements on the external electronics, low power consumption. The prototype we realized is currently in an early stage of development. Nevertheless, it allows us to demonstrate the feasibility of the photon counter and to measure some of the basic parameters. Some of the characteristics of the APS, relevant to the use in intensified systems, are analyzed and compared with the CCD ones, demonstrating the potentiality of the new device and allowing us to set the basis of future development.

Preliminary results from the MAMA detectors for the SOHO mission

Multi-Anode Microchannel Array (MAMA) detector systems are being fabricated and tested for use in the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) and the Ultraviolet Coronagraph Spectrometer (UVCS) instruments on the ESA/NASA Solar and Heliospheric Observatory (SOHO) mission. The SOHO MAMA detector systems have formats of 360 x 1024 pixels and pixel dimensions of 25 x 25 sq microns and are optimized for operation at Extreme Ultraviolet (EUV) wavelengths between 40 and 160 nm. In this paper we report on the initial results of measurements of the performance characteristics of the first flight-configuration detector system employing the new custom Application Specific Integrated Circuits (ASICs) which are designed to improve both the dynamic range and the uniformity of response. The performance characteristics of this detector system are compared with those of earlier breadboard systems employing discrete-component electronics circuits.

Characterization of a photon-counting ICCD prototype

The result obtained in the course of the characterization of a photon-counting ICCD prototype. The detector consists of a 40 mm diameter, Z stack, high gain microchannel plate intensifier, endowed with a RbTe photocathode. The intensifier electron cascade is transduced, via a phosphor screen and a 1:3.6 fiber optics reducer, into a 3 by 3 pixel, quasi-gaussian charge distribution on a 512 by 512 pixel format CCD matrix with square pixels of 15 micrometers . The CCD is read out, in the frame-transfer mode, through a single output amplifier at a frequency of 20 MHz. The data flow is acquired serially and fed to a virtual shift- register system, as to generate a 3 by 3 pixel even sash that sweeps dynamically the CCD matrix at the 50 ns clock pace. Each and every events has is searched for the presence of events whose integral charge distribution lie within set threshold levels, and satisfy given morphological rules, i.e. a single-peaked charge profile. The centroid coordinates of identified events are then determined with sub-pixel accuracy and subsequently stored in an external, high resolution memory. Detective quantum efficiency, spatial resolution and dynamic range obtained for the prototype system in the 150-600 nm spectral domain, are given and discussed, together with the up-graded performance expected for a second-generation prototype, presently being assembled.

HiRES: the High-Resolution EUV Spectroheliometer

The high-resolution EUV spectroheliometer (HiRES) is our first step towards the 0.1 arc sec angular resolution goal at EUV wavelengths. The HiRES instrument consists of a Gregory telescope with a 45-cm-diameter primary mirror, and an imaging EUV spectrometer, employing a single-reflection toric diffraction grating in a Rowland circle mounting and an imaging pulse-counting multi-anode microchannel array (MAMA) detector system. The MAMA detector covers the spectral range from 560 to 631 angstrom with a spectral resolution of 70 mAngstrom. A Pt/Ne lamp impresses a wavelength calibration spectrum on the upper part of the detector while the solar spectrum is recorded simultaneously on the lower part. The times-of-arrival and addresses of the detected photons are transmitted directly to the ground to allow correction of the SPARCS pointing jitter. The HiRES spectrometer slit is pointed to a specific location using real-time control of the SPARCS, and SPARCS can be commanded to execute a linear (push broom) scan across the sun. Two EUV photodiodes are used to measure the absolute sola irradiances and the atmospheric extinction profiles in wavelength bands centered at 304 angstrom and 584 angstrom respectively.

HiRES - High Resolution Extreme Ultraviolet Spectroheliometer toroidal diffraction grating performance evaluation

The HiRES sounding rocket payload has been described in detail in previous SPIE Proceedings. Here, optical design of the toroidal grating spectrograph is presented and discussed. Ray tracing results are presented which outline the extreme ultraviolet (EUV) performance theoretically attainable with the HiRES instrument. Effects of optical system misalignment on the spectrograph image quality are investigated. Laboratory test results of two f/15 toroidal diffraction gratings using a 1 meter vacuum spectrograph and a multi-anode microchannel array detector are presented and discussed. The test toroidal gratings are fabricated using the elastic substrate replication technique from a ruled master grating with either a 3600 lines/mm or 1800 lines/mm density. EUV images of 10 25 micrometers pinholes with 250 micrometers center-to-center spacing taken with a hollow cathode discharge lamp are presented. Interferometric studies of toroidal figure accuracy as well as optical and electron microscopy investigations into surface quality are presented and discussed. It is found that the current toroidal gratings exhibit good imaging characteristics across a wide wavelength range but suffer from excessive EUV scatter and spectral ghosting.

Stanford MAMA detector characterization facility

We have designed and fabricated a high-vacuum facility for the detailed characterization of the Multi-Anode Microchannel Array (MAMA) detector systems at Extreme Ultraviolet and Far Ultraviolet wavelengths between about 300 angstroms and 3000 angstroms. The first task for this facility is the characterization of the MAMA detectors for the European Space Agency/NASA Solar and Heliosphere Observatory (SOHO) mission. This paper describes the different configurations of the characterization facility and outlines the SOHO MAMA characterization procedures.

Spectroscopic characterization of the EUV toroidal grating for the HiRES rocket

The evaluation of the performances of a toroidal grating for the high-resolution EUV spectroheliometer (HiRES) has been realized. This is a holographically ruled grating operating in a normal incidence Rowland configuration at the 510 - 630 angstroms spectral range. An analysis of the grating resolution performances has been realized by means of a scintillator- intensifier-CCD detector showing very good results. Also a measurement of the grating diffraction efficiency has been performed, showing on the contrary a value lower than the predicted one.

Interferometric methods for assessment of toroidal diffraction grating performance

The measurement of the shape and optical performance of toroidal mirrors has always presented a challenge to the manufacturer and user of these types of optical elements. This report presents a technique for evaluating the complex shape and optical performance of long radius toroidal mirrors that are to be used in the EUV. The measurement techniques will be discussed and examples given. Interferometric analysis will be presented. Performance spot diagrams and MTF analysis will be discussed. Manufacturing techniques will be evaluated with respect to the application of more definitive measurement technology.