Eiji Inuzuka

Photon-Counting Imaging and its Application

Publisher Summary Photon-counting imaging systems incorporate three important features: the ability to detect individual photons or particles, spatial resolution, and the capability of real-time imaging and subsequent image analysis. Various types of photon-counting systems have been reported and applied in fields such as astronomy, high-energy physics, and spectroscopy. The chapter describes the design, operation, and performance of a photon-counting image acquisition system (PIAS) and discusses the results of basic experiments and application of a PIAS. A PIAS is developed to detect and display individual photons or particles in real time and to carry out subsequent image processing or analysis; it consists of a photon-counting imager, a position analyzer, and an image processor. The imager incorporates a photocathode, a three-stage microchannel plate (MCP), and a position-sensitive device (PSD). Various types of imagers have also been developed to detect X-ray, extreme ultraviolet (XUV), vacuum UV (VUV), UV, and visible photons, as well as charged particles. A PIAS allows real-time imaging and subsequent analysis of a very faint object whose intensity is only few counts per second for the entire image.

Universal Streak Camera

A universal streak camera which works in synchroscan and single-shot modes with 3 plug-ins (synchroscan, fast and slow) has been developed utilizing a microchannel plate-incorporated streak tube. The synchroscan plug-in features low jitter of less than 4 ps, and high-speed sine-wave deflection from 80 to 160 MHz, achieving a limiting temporal resolution of 5 ps. The fast plug-in offers temporal resolution of better than 2 ps with triggering jitter of less than t20 ps. The slow plug-in provides longer time windows from 10 ns to 1 ms/15 mm in 16 ranges. Shutter operation down to 100 ns in duration is available with a maximum repetition rate of 1 - 10 KHz for the 3 plug-ins. An on-off ratio of more than 1:106 has been achieved by using double gate operation at photocathode and built-in microchannel plate.

Performance Analysis Of The Photon-Counting Image Acquisition System

We have developed a photon-counting image acquisition system (PIAS), which can detect a two-dimensional object in a very low-light-level condition. The improvement of the system performance has been accomplished in an image distortion and gain drift owing to the improvement of the silicon PSD (position sensitive detector). The geometric shape of the electrode on the PSD has been redesigned, resulting in the small image distortion of less than 3%. The gain degradation of the electron-bombarded silicon PSD had been a biggest problem in the stable operation of the system. It has been successfully overcome by irradiating the electrons from back side of the PSD instead of front side as formerly. The spatial resolution of the system has been measured to be better than 16 1p/mm typically at the center. Its maximum data is 18 1p/mm or better. Experiments and a theoretical analysis has also been carried out to clarify the limiting parts of the spatial resolution. We have exprimented on system applications in astronomy, spectroscopes and microscopes. In astronomical observation, several kind of stars and galaxies were observed. And also using PIAS combined with the spectroscopy, we measured three spectrums nearby 365nm of Hg-lamp. Further in microscope application, we observed the fibroblast cell of rat by fluorescent microscope using PIAS.

Demountable Photocathode X-Ray Streak Camera

Demountable photocathode X-ray streak camera developed for X-ray diagnostics in ICLF experiments is described. The system can be installed to the experimental chamber via gate valve furnished at one end of the front end chamber, the other end of which is connected to the streak tube. Remarkable features of the system are demountable photocathode scheme which enables to change the photocathode very easily and quickly, demountable accelerating mesh electrode, gate valve which enables the system to operate independently from the experimental chamber, differential pumping scheme which keeps the_vacuum_in the streak tube better than 10 6 torr while the front end is evacuated down to 10 ~ 4 % 10 05 torr through the gate valve and data taking scheme such as a film back or SIT TV camera combined with a temporalanalyzer. Typical performances of the system are characterized by the sensitivity of the photocathode to the soft X;ray ranging from 100 eV to 10 keV because of a 300 Å Au photocathode deposited on a 1000 Å Parylene film, the streak sweep rate of 1 ns/15 mm to 10 ns/15 mm, the streak trigger delay time of 20 ns to 30 ns and the excellent low trigger jitter less than ±20 ps. Simultaneous gating of the photocathode of the streak tube and the MCP in image intensifier gives low back ground output image. Preliminary test of the system showed that the system has a temporal resolution of 17 ps and a limiting dynamic spatial resolution of 20 1p/mm along the 10 mm useful photocathode slit at the fastest sweep rate of 1 ns/15 mm.

Direct Readout System For Streak Cameras

To analyze the streak image directly, we have developed a new image processing system. The system consists of a high sensitive television camera and a microprocessor-based video image analyzer. The streak image can be observed easily on the TV monitor screen,and at the same time the video signal is digitized, then displayed with an intensity profile of 256 channels. The y factor Houtput)nu(input() is within 1% of unity over an input light range of better than 200:1 for a single video frame. By integration of 256 frames, the linear dynamic range can be extended to 1000:1 or greater. The system provides many features for the precise analysis of an intensity profile. The output is available to a chart recorder or to a host computer.

Superlinear emission of light-emitting diodes at very low current excitation

Light-emitting diode emission behaviors at a very weak injection current level are studied using the photon-counting method. It is observed that the emission is superlinearly dependent on the injection current irrespective of the emitting wavelength. The bending point of the L:I plot is different from that of the V:I plot. The bimolecular emission nature is interpreted to be a nonradiative transition mechanism due to some deep level trapping.

Development Of A Subpicoseconci Streak Camera

Better than 500fs(femtosecond) Temporal resolution for optical phenomena has been obtained using a newly developed subpicosecond streak camera. The temporal resolution has been measured with CPM ring dye laser system which can generate shorter than 300 fs laser pulse at 113MHz repetition rate. Another characteristics of the streak camera are also discussed.

Designing And Performance Of VUV, XUV And X-Ray Streak Cameras With Improved Time Resolutions

Three kinds of x-ray streak cameras in wavelength regions ranging from several Å to 2000 It are developed. A time resolution in the shorter wavelength region is successfully improved to about 10 ps by adopting most desirable parameters, especially high electric field and by minimizing velocity distributions of electrons emitted from a photo-cathode. The design and the performance of these streak cameras are described. Plasma experiments are performed by a YAG laser with 30 ps of pulse-width and 100 mJ of output energies. Both time and spatial resolutions are investigated by using higher harmonics of a YAG laser and soft x-rays from laser-produced plasmas.

Theoretical And Experimental Studies Of Picosecond Time Resolved X-Ray Spectra Generated From Laser-Produced Plasmas

Dynamical behaviour of picosecond soft x-rays generated from laser-produced plasmas were studied both theoretically and experimentally. A grazing incident suctrometer with a flat field focal plane is developed and time resolved spectra near 100 A are obtained by using a newly designed XUV streak camera with 10 ps time resolutions. Temporal changes of intensities of soft x-rays from laser produced plasmas is investigated for various targets. Decay times are about 100 ps and decrease as targets are changed from low Z to high Z materials. Computationally, temporal changes of x-ray intensities is predicted in the framework of the simplified model. A qualitative agreement between experimental and computational results is obtained.

Picosecond High Power Laser Systems And Picosecond Diagnostic Technique In Laser Produced Plasma

Highly repetitive, high power YAG and Glass laser systems have been developed and been successfully used for the studies of laser-plasma interactions. Various picosecond diagnostic techniques have been developed for sudh purposes in the regions from optical to X-ray frequency. Recently highly sensitive X-ray (1 - 10KeV) streak camera for highly repetitive operations have been developed. Preliminary experiment shows the achievement of 28ps temporal resolution (100μm slit) and good sensitivety with detectable minimum number of 10E3-1KeVphotons/shot/slit area.