A time-gated fluorescence detector using a tuning fork chopper

Time-Gated Luminescence Microscopy Allowing Direct Visual Inspection of Lanthanide-Stained Microorganisms in Background-Free Condition

“…We have tested liquid crystal shutters (e.g., Oriel ferroelectric liquid crystal shutter, model 50075, ), but these suffer from high optical transmission loss (typically up to 75%) and slow switching time (∼80 μs) and are fragile to UV light. Vibrating choppers, such as tuning fork choppers, have been considered, but their switching times are still relatively long (>50 μs), and cycle rates are low (<1 kHz) . Though mechanical choppers generally also have slow switching time, ∼ 100−200 μs, ,,,,, they have a number of advantages for the present application including 100% transparency when open and 100% blocking when closed, they provide an automatic synchronization signal (using internal optical diodes monitoring the chopper directly), and in compact forms, they can be fairly easily incorporated into microscopes.…”

“…Vibrating choppers, such as tuning fork choppers, have been considered, 39 but their switching times are still relatively long (>50 μs), and cycle rates are low (<1 kHz). 39 Though mechanical choppers generally also have slow switching time, ∼ 100-200 μs, 7,19,21,35,40,41 they have a number of advantages for the present application including 100% transparency when open and 100% blocking when closed, they provide an automatic synchronization signal (using internal optical diodes monitoring the chopper directly), and in compact forms, they can be fairly easily incorporated into microscopes. For the present demonstration, we have adopted a latest-generation compact fast chopper and a new optical configuration to achieve as short as 11 μs switching time and 2.5 kHz cycle rate, an on-off duty ratio of 3:1 (that is, 75%:25%).…”