For the time-resolved imaging, latent fingerprints deposited on fluorescing substrates were used. The fluorescent powders used were ultra azure-blue and ultra white powders along with transparent PMMA substrates that show fluorescence in the violet-blue region of visible spectrum. Fluorescence lifetime study of these substrates was conducted prior to TR imaging experiments.
The experimental setup is shown in Fig. 3. Light from the argonion laser (Coherent, Innova 90 8C) was square wave modulated at frequency 1 MHz with the help of an electrooptic 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).