Submitted on: 16 January 1998.
Revised on: 03 April 1998.
Accepted on: 14 April 1998.
___________________JOURNAL OF LASER APPLICATIONS---AIP PUBLISHING
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Submitted on: 16 April 1998.
Revised on: 18 July 1998.
Accepted on: 20 August 1998.
___________________JOURNAL OF LASER APPLICATIONS---AIP PUBLISHING
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