Enhancement of optical emission signal in double-pulse laser ablation of titanium in vacuum Nikša Krstulović, Marijan Bišćan and Slobodan Milošević Eur. Phys. J. D, 69 4 (2015) 98 Published online: 07 April 2015 DOI: 10.1140/epjd/e2015-50904-3