E. Ables

Tabletop x-ray microscope using 8 keV zone plates

We describe the implementation of an 8 keV microscope that operates with a conventional x-ray source in our lab. Samples are scanned pixel-by-pixel through a focused x-ray spot produced by a phase-modulating zone plate fabricated with the sputtered-sliced technique. The micro- focused x-ray source uses a Cu target and produces 8 keV photons that are detected with a Si(Li) spectroscopy system. The microscope currently achieves 10 µm resolution.

Real-Time Optical Flux Limits from Gamma-Ray Bursts Measured by the Gamma-Ray Optical Counterpart Search Experiment

The Gamma-Ray Optical Counterpart Search Experiment presents new experimental upper limits on the optical flux from gamma-ray bursts (GRBs). Our experiment consisted of a fully automated very wide-field opto-electronic detection system that imaged locations of GRBs within a few seconds of receiving trigger signals provided by BATSEs real-time burst coordinate distribution network. The experiment acquired 3800 observing hours, recording 22 gamma-ray burst triggers within ~30 s of the start of the burst event. Some of these bursts were imaged while gamma-ray radiation was being detected by BATSE. We identified no optical counterparts associated with gamma-ray bursts among these events at the mV ~ 7.0-8.3 sensitivity level. We find the ratio of the upper limit to the V-band optical flux, Fν, to the gamma-ray fluence, Φγ, from these data to be 1 × 10-18 < Fν/Φγ < 2 × 10-16.

RadSensor: Xray Detection by Direct Modulation of an Optical Probe Beam

We present a new x-ray detection technique based on optical measurement of the effects of x-ray absorption and electron hole pair creation in a direct band-gap semiconductor. The electron-hole pairs create a frequency dependent shift in optical refractive index and absorption. This is sensed by simultaneously directing an optical carrier beam through the same volume of semiconducting medium that has experienced an xray induced modulation in the electron-hole population. If the operating wavelength of the optical carrier beam is chosen to be close to the semiconductor band-edge, the optical carrier will be modulated significantly in phase and amplitude. This approach should be simultaneously capable of very high sensitivity and excellent temporal response, even in the difficult high-energy xray regime. At xray photon energies near 10 keV and higher, we believe that sub-picosecond temporal responses are possible with near single xray photon sensitivity. The approach also allows for the convenient and EMI robust transport of high-bandwidth information via fiber optics. Furthermore, the technology can be scaled to imaging applications. The basic physics of the detector, implementation considerations, and preliminary experimental data are presented and discussed.

New Constraints on Simultaneous Optical Emission from Gamma-Ray Bursts Measured by the Livermore Optical Transient Imaging System Experiment

LOTIS is a gamma-ray burst optical counterpart search experiment located near Lawrence Livermore National Laboratory in California. Since operations began in 1996 October, LOTIS has responded to five triggers as of 1997 July 30, which occurred during good weather conditions. GRB 970223 (BATSE trigger 6100) was an exceptionally strong burst, lasting ~30 s with a peak at ~8 s. LOTIS began imaging the error box ~11 s after the burst began and achieved simultaneous optical coverage of 100% of the region enclosed by the BATSE 3 σ error circle and the interplanetary network annulus. No optical transients were observed brighter than the mV~11 completeness limit of the resulting images, providing a new upper limit on the ratio of simultaneous optical to gamma-ray fluence of RL<1.1×10−4 and on the ratio of simultaneous optical (at 700 nm) to gamma-ray (at 100 keV) flux density of RF<305 for a B-type spectrum and RF<475 for an M-type spectrum.

8 Kev X-Ray Zone Plates

Sputtered-sliced transmissive x-ray zone plates consisting of concentric rings of Al and Cu have been fabricated and tested using the 8.04 keV k-a line from Cu. Due to the need for high aspect ratios for this 1.54 A radiation, magnetron sputtering onto a rotating opaque central wire was chosen as the fabrication method. Both the fabrication technology and initial results are presented.

Beam control and diagnostic functions in the NIF transport spatial filter

Beam control and diagnostic systems are required to align the National Ignition Facility laser prior to a shot as well as to provide diagnostics on 192 beam lines at shot time. A design that allows each beams large spatial filter lenses to also serve as objective lenses for beam control and diagnostic sensor packages helps to accomplish the task at a reasonable cost. However, this approach also causes a high concentration of small optics near the pinhole plane of the transport spatial filter (TSF) at the output of each beam. This paper describes the optomechanical design in and near the central vacuum vessel of the TSF.

Fabrication of Cryogenic Manganite Bolometers to Measure the Total Energy at the LCLS Free Electron X-Ray Laser

We are developing cryogenic bolometers to measure the total energy of the Linac Coherent Light Source (LCLS) free electron X-ray laser that is currently being built at the Stanford Linear Accelerator Center. LCLS will produce ultrashort ~ 200 fs X-ray laser pulses with ~ 1013 photons at 0.8 keV up to ~ 1012 photons at 8 keV per pulse at a repeat interval as short as 8 ms, and will be accompanied by a halo of spontaneous undulator radiation. Our bolometer consists of a 375 mu m thick Si absorber and a Nd0.67 Sr0.33 MnO3 sensor operated at its metal-insulator transition. It will measure the total energy of each pulse with a precision of < 1%, and is designed to meet the conflicting requirements of radiation hardness, sensitivity, linearity over a dynamic range of three orders of magnitude, and readout speed compatible with the LCLS pulse rate. Here we discuss bolometer design and fabrication, and the photoresponse of prototype devices to pulsed optical lasers.

Results from GROCSE, a real-time search for the Optical Counterparts of Gamma-Ray bursts

The GROCSE Collaboration (Gamma-Ray Optical Counterpart Search Experiment) has been operating a rapid response camera since January 1994 in an attempt to capture optical images of GRB events. This detector has a response time of 15 seconds and a limiting magnitude of 8. A second generation detector is now under construction which is expected to eventually reach mv ≃ 15 with a 5 second exposure.

Observation of drift chamber signals using a Mach-Zehnder electro-optic modulator

Abstract A Mach-Zehnder electro-optic modulator has been used to read out the charge collected on drift chamber sense wires. The modulator sensitivity is sufficient to allow measurement of the pulse waveform without preamplification of any kind. We report here initial results and discuss ongoing research and potential applications projected performance improvements as we continue to optimize the system for drift chamber readout.

Instrumentation of LOTIS: Livermore Optical Transient Imaging System; a fully automated wide field of view telescope system searching for simultaneous optical counterparts of gamma ray bursts

LOTIS is a rapidly slewing wide-field-of-viewtelescope which was designed and constructed to search for simultaneous gamma- ray burst (GRB) optical counterparts. This experiment requires a rapidly slewing (less than 10 sec), wide-field-of-view (greater than 15 degrees celsius), automatic and dedicated telescope. LOTIS utilizes commercial tele-photo lenses and custom 2048 X 2048 CCD cameras to view a 17.6 X 17.6 degree field of view. It can point to any part of the sky within 5 sec and is fully automated. It is connected via Internet socket to the GRB coordinate distribution network which analyzes telemetry from the satellite and delivers GRB coordinate information in real-time. LOTIS started routine operation in Oct. 1996. In the idle time between GRB triggers, LOTIS systematically surveys the entire available sky every night for new optical transients. This paper will describe the system design and performance.