Minor corrections as suggested by referees on SAIP website -Acknowlegements has been moved before References -Affiliation of authors superscript has been removed -The micro µ symbol has been used instead of u (e.g. 1.3 um laser) -Small language corrections to page 3 -Reference to figure 3 corrected to figure 2 -Laser amplitude label added to figure 3 -Reference 6 corrected