H. M. Epstein

Laser‐generated plasmas as a source of x rays for medical applications

High‐resolution medical radiographs have been produced with a laser‐generated plasma x‐ray source. The nanosecond pulse width is capable of arresting biological motion. In addition, the soft x rays from this source have been transmitted through a new type of x‐ray beam handling device, the x‐ray pipe, which is an x‐ray analogue of the conventional light pipe. This may allow new medical applications such as channeling soft x rays to internal locations of the body without damaging intervening tissue.

Laser-EXAFS: Fast Extended X-ray Absorption Fine Structure Spectroscopy with a Single Pulse of Laser-Produced X-rays

The extended x-ray absorption fine structure (EXAFS) spectrum of aluminum has been measured with a nanosecond pulse of soft x-rays generated by a laser-produced plasma. This technique provides a practical alternative to synchrotorn radiation for the acquisition of EXAFS data. It also provides a unique capability for the analysis of molecular structure in highly transient chemical species.

Nd-glass burst laser with kW average power output

Demonstrations of operation of a compact neodymium glass laser with average output powers greater than 1 kW for several seconds are reported. The laser is based on the thermal inertia laser (TIL) concept wherein a neodymium-doped glass rod is pumped uniformly without cooling during a burst mode of laser operation. Design principles for TIL devices and scaling to 100 kW class lasers are discussed. Experimental results for a low repetition-rate proof-of-concept pulsed device (30 J, 0.2 Hz) and a high repetition-rate pulsed prototype (40 J, 36 Hz) are presented and compared to numerical solutions for the laser rate equations with temperature dependent cross-sections. >

Laser Plasma X-Ray Source Optimization For Lithography

The laser-plasma X-ray source has been evaluated for submicrometer X-ray lithography exposure machines. X-ray lithography systems based on commercially available lasers of reasonable cost appear to be feasible. Such machines would make full wafer exposures of silicon slices with a throughput consistent with current manufacturing requirements.

Amplified−spontaneous−emission suppressor for Q−switched lasers

A passive device for suppressing amplified spontaneous emission in Q−switched lasers has been developed. The technique is applicable to lasers of any aperture.

APPLICATIONS OF X-RAYS FROM LASER PRODUCED PLASMAS

Progress in the development of high power lasers during the past decade has opened the door to many new areas of applications. The best known, of course, is the possibility of achieving controlled thermonuclear fusion by means of laser heated plasma. However, several applications of laser plasma x-rays have more attractive current prospects. There are many points of similarity between the x-ray and fusion problem. Both, for example, require laser heating of plasmas to the kilovolt regime. But there are significant differences. The x-ray work usually involves heating of high Z materials, while the fusionable materials are low Z. Most of the x-ray applications do not require target compressions, and can use simple planar targets. Additionally, neither the plasma temperature nor the laser efficiency requirements are as severe. The main effect of these differences is that the lasers for x-ray production can be much smaller and less expensive than lasers for fusion. We have recently demonstrated that x-rays can be efficiently generated with mode locked laser pulses of several hundred mj1. The characteristics that differentiate a laser plasma x-ray source from conventional sources are: (1) The x-ray spectrum comes from highly stripped species and is predominantly L line radiation or continuum in the kilovolt regime. Heliumlike K lines are also obtainable. (2) The pulse width is very short in the ~0.1 to 10 ns range. (3) The source size is very small, ~10–200 µm diameter.

Laser‐EXAFS: Laboratory EXAFS with a nanosecond pulse of laser‐produced X‐rays

Laser‐produced x‐rays are a promising alternative to synchrotron radiation for the measurement of EXAFS spectra. Experiments to date indicate that the K‐edge EXAFS spectra of elements with atomic numbers up to about Z = 20, and L‐edge spectra of elements with atomic numbers up to about Z = 40, can be obtained with a single nanosecond pulse of x‐rays emitted by a laser‐produced plasma. The technique shows promise of providing single‐shot EXAFS spectra for the remaining elements as well, with the use of advanced laser systems that are available today. The x‐ray pulse can be synchronized easily with an external optical or electrical perturbation of the sample, thereby providing a unique capability for recording EXAFS spectra of highly transient species having lifetimes the order of a nanosecond.

Real-Time Diagnostics for a Laser Fusion System

An automated diagnostic system has been developed and installed on a multibeam laser for fusion research. Laser-beam phase and intensity profile, focal-spot profile, pulse width, beam energy, and other laser parameters are measured at a number of points in the system. Data from the optical and voltage sensing elements are processed by an on-line mini-computer and the information is presented in graphic, pictorial, and tabular form. The processed information is used

Current status of laser fusion research at Battelle.

The central research discussed is the analysis and control of laser-produced high-Z plasmas. Research consisting mainly of laser development, model and code development, and target irradiations is described. Some medical applications of the research are also mentioned. (MOW)

A New Method for Isolating Q‐Switched Lasers

A laser‐isolator device capable of protecting Q‐switched lasers from target backscatter has been designed and tested. The technique is readily applicable to lasers of any aperture.