We demonstrate a simple and practical single-stage ultrafast laser amplifier system that operates at a repetition frequency from 1 to 10 kHz, with millijoule pulse energy and as much as 13 W of average power. The repetition rate can be adjusted continuously from 1 to 10 kHz by new all-solid-state pump laser technology. This is to our knowledge the highest average power ever obtained from a single-stage ultrafast laser amplifier system. This laser will significantly increase the average power and the repetition rate that is easily accessible for high-field experiments such as coherent x-ray generation or for laser-synchrotron studies. © 2001 Optical Society of America OCIS codes: 140.7090, 140.6810, 140.3590, 140.3280. The development of compact, high-intensity, ultrafast lasers has facilitated many new experiments in high field science. Many applications of these sources, including laser-synchrotron experiments, coherent x-ray generation, time-resolved holography, ultrafast surface science, and metrology for extreme-ultraviolet (EUV) optical systems, are limited by the average f lux available for experiments rather than by the available peak power or pulse energy. High-harmonic generation (HHG), for example, can be successfully driven by ഠ200-mJ pulse energies, provided that the laser pulse width is sufficiently short ͑ഠ20 fs͒. The recent development of techniques for phase-matched HHG by use of hollow waveguides, 1 -4 demonstrating the use of temporally shaped pulses for optimizing the conversion eff iciency to a single harmonic order, 5 has significantly advanced the utility of this source. Phase-matched frequency conversion in a hollow-core waveguide also makes it practical to develop coherent EUV sources with extremely high repetition rates. The waveguide geometry eliminates the need for pulsed-valve gas sources to implement HHG, which were limited at an ϳ1-kHz repetition rate. The hollow waveguide can be maintained at a relatively high gas pressure, where the hollow waveguide limits the gas f low into the vacuum system by serving as a differential pumping aperture of diameter ഠ150 mm. Laser-synchrotron experiments can also take advantage of the extremely high repetition rates of synchrotrons ͑.500 kHz͒ only if the laser repetition rate is increased. These and other considerations have motivated the development of simple, high-repetition-rate ͑$1-kHz͒ laser systems capable of generating .1-mJ pulse energies with good ͑M 2 , 2͒ beam quality. The ability to vary the repetition rate of the laser continuously, such that initial alignment of an experiment can be performed at modest average powers, is also desirable.Past research has demonstrated ultrafast laser systems that operate at terawatt peak powers for 1-kHz repetition-rate systems and at average powers of as much as 25 W for 5 -10-kHz repetition-rate systems. 6 -14 However, high-average-power systems that have been demonstrated to date have been large (requiring two or more optical tables), complex, and expensive, typically requiring several stages...

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An automated, low-cost programmable instrumentation system which solves many of the problems associated with the data acquisition and control of high repetition rate experiments is described. The system can monitor and control experiments on a pulse-by-pulse basis while digitally storing consecutive pulses which occur in the train. The system compares well with manual test equipment and commercial transient diagnostic systems which cannot provide the high-speed control and data acquisition available here. The oscilloscope used to store the train of pulses can digitize at a maximum rate of 100 MHz, and has 32 kbytes of acquisition memory that can be subdivided into a sequence of as many as 250 separate segments. In order to reduce the system software reinitialization time to acquire each successive sequence within the total train, a novel IEEE-488 compatible microprocessor system is used in conjunction with a host personal computer. The microprocessor controls triggering of the experimental equipment based on digitally acquired waveform information. This information is also used to coordinate the reinitialization of the oscilloscope by the host computer. The system can acquire each and every pulse at repetition rates up to 40 Hz. Above this rate, the probability of acquiring a particular pulse in the train falls slightly below unity due to the finite time required to reinitialize the oscilloscope. The maximum synchronously controllable pulse repetition rate of the microprocessor is 20 000 Hz. Minimum performance specifications are provided which are significantly better than other approaches. The system is employed in high-voltage, dielectric breakdown experiments. For the example given, there are 62 segments in the acquired sequence, with a 100-MHz digitizing rate during the 5-μs acquisition time for each segment. The breakdown pulse in the train and as many as 61 pulses preceding it are obtained.

A simple method of pretreating carbon black has been developed which permits measurements to be made on the dry carbon black which reflect on the basic property called “structure.” Correlation between these measurements and extrusion shrinkage of raw stocks is demonstrated. With a small surface area adjustment, this correlation is believed to be as reliable as extrusion shrinkage values.