Two cases involving Erbium:YAG laser incision of proximal bulbar urethral strictures are described. Erbium:YAG
laser radiation with a wavelength of 2.94 &mgr;m, pulse energy of 10 mJ, and a pulse repetition rate of 15 Hz, was
delivered through a 2-m-long, 250-&mgr;m-core sapphire optical fiber in contact with tissue. Total laser irradiation time
was 5 min. The first patient suffering from a virgin urethral stricture was treated and is stricture-free. The second
patient suffering from a recurrent urethral stricture required further treatment. This case report describes the first
clinical application of the Er:YAG laser in urology.
Laser-induced surface breakdown in fused silica has been studied as a function of pulse width in the
nanosecond regime. The third harmonic of a Nd:YAG laser was used to produce 7.5 ns duration pulses
(FWHM) at 355 nm. A novel system using optical delay lines was used to extend these pulses to variable
widths between 7.5 and 400 ns. At each pulse width, the beam was focused onto the surface of a
commercially available fused silica flat and the breakdown fluence was determined. The breakdown fluence
threshold was found to scale as the pulse width to the 0.8 power, significantly higher than the 0.5 power
reported elsewhere for similar cases. Experiments were also performed on 200 jim core fused silica optical
fibers and the results Obtained were consistent with a 0.8 power scaling law. This strong scaling law led to
a dramatic increase in the amount of 355 nm light that could be transmitted through 200 p.m core fibers -
from 1-2 mJ at 7.5 ns up to over 30 mJ at 400 ns. An experiment was also performed to probe the
recovery time of fused silica (the time separation between pulses such that their effects are independent).
This time was determined to be less than 25 ns.
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