Clinical data shows that short pulse duration lasers used in laser induced shock wave lithotripsy severely damage optical fibers on both the proximal and distal ends which is unsuitable for clinical use. An Alexandrite laser system has been developed that uses dynamic pulse stretching of the Q-switched laser pulse and improved optical fiber coupling to eliminate the fiber damage. The method of pulse stretching presented controls the laser output pulse energy from 50 to 150 millijoules and temporal shape from 0.5 to 1.5 microseconds. This yields effective fragmentation of calculi without damage to the optical fiber.
The method of achieving a high energy discharge in a controlled manner with relative ease is to use a pulse forming network. The design of such networks generally uses a single inductor and capacitor. Although easy to design and implement, this practice does not provide optimum performance in all cases. For example, most laser welding applications require a uniform energy discharge within the pulse to produce a high quality weld. Analysis has shown that when the pulse forming network approximates a lumped constant transmission line a maximum flat pulse is produced with minimal degradation of the pulse rise time. This paper shows that a low pass filter ladder network composed of equal capacitors and inductors provides a flat pulse whose energy discharge becomes more uniform as the filter's order increases. This is highly favorable in achieving a producible design since all the capacitors and inductors will be of equal value. An algorithm is generated and used to calculate the coefficients for the Laplace transform of the networks. Design equations are derived for calculating the network's components for use with flashlamps. Then a computer's simulation of a network is compared to actual performance.
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