In 1997 Tropper worked with Ursula Keller on the first passively mode-locked Vertical External-Cavity Surface-Emitting Laser (VECSEL). Tropper leads the VECSEL group at the University of Southampton and coordinates the annual SPIE conference on VECSELs. She was awarded a Personal Chair in 2000 and made Head of Department in 2002. She has investigated semiconductor lasers that emit femtosecond optical pulses.