For the time-resolved imaging, latent fingerprints depos-ited on fluorescing substrates were used. The fluorescent powders used were ultra azure-blue and ultra white powders along with transparent PMMA substrates that show fluor-escence in the violet-blue region of visible spectrum. Fluor-escence lifetime study of these substrates was conducted prior to TR imaging experiments.
The experimental setup is shown in Fig. 3. Light from the argon-ion laser (Coherent, Innova 90 8C) was square wave modulated at frequency 1 MHz with the help of an electro-optic modulator (EOM, Conoptics, model 350–210) through function generator 1(Agilent, Model-33250A) that operates at 20% duty cycle. Laser is capable of operating in multiline UV mode with predominant line at 361 nm. A similar square wave at same frequency and duty cycle was used to trigger the gating of the detecting device, an Intensified Charge Couple Device Camera, (ICCD, La Vision, PicoStar HR).