JULY 2, 2008--Recording simultaneous, ultrafast two-dimensional (2-D) and time-resolved images is of significant interest to scientists in a growing number of fields. Traditionally such measurements have been accomplished by the use of two independent imaging systems looking at the event at slightly different angles of view or through external imaging beam splitting optical configurations that can limit light collecting efficiency. More recently, cameras with built-in imaging beamsplitters allowed for streak tubes and their electronics to be fitted into the same camera body as the framing electronics. These systems limited the versatility, primarily of the streak functions, as the designs required that they used small streak tubes with small photocathodes and output screens and had closed fixed relay optics between the objective lens and the slit input to the streak tube.
For many years, the department of radiology at the University of Michigan (Ann Arbor, MI, USA;www.umich.edu) has been studying the cycles of contraction and expansion of micro droplets and bubbles in a liquid medium when hit with an acoustic shock wave. The size and speeds at which these events take place make imaging such events a challenge. The acoustic wave in liquid travels at ~1500 m/s. Transition time through micro droplets is on the order of tens of nanoseconds. Cyclical events in the droplet occur in submicroseconds and longer, thus the need for framing speeds of 1 million frames/s and faster and exposure time resolution of less than 1 μs are needed to stop and record the motion.
New research carried out by the University of Michigan using a dual-camera system made up of a SIM8-02 ultrafast framing camera from Specialised Imaging (Tring, UK;www.specialised-imaging.com) and an Optoscope SC-10 streak camera from Optronis (Kehl, Germany; www.optronis.com) has reached performance levels never before achieved with a dual-camera system. Framing data images show extremely detailed 2-D information of the full field of view. By comparison the recorded streak images give a continuous record of time looking at a slit image of the diameter of droplets. Both cameras together give a unique insight into the visualization of biomedical micro- and nanoscale events.
Incorporating a supplementary optical port that uses a beamsplitter to deliver 50% of the primary image to an image plane, the SIM8-02 framing camera allows secondary instruments such as streak cameras, high-speed video, or time-resolved spectrometers to share the same optical axis as the framing channels. The simultaneous framing and streak imaging system was able to deliver a distortion-free image of the primary image to eight separate output ports where ICCDs are used to capture eight individual frames of the event at framing rates up to 2 billion frames/s and exposures as short as 500 ps. Using the SC Optoscope streak camera fitted with the slow streak electronics unit, the simultaneous framing and streak imaging system can give streak speeds from 330 ps/mm to 5 ms/mm.