Simultaneous Ultra Fast Framing and Streak Imaging
- Saturday, 01 November 2008
The ability to record simultaneous framing images and streak images has long been a requirement in the research fields of detonation, electrical discharge, biomedical and many other applications. Early systems incorporating both framing and streak cameras used external beam splitting optics with light gathering limitations that required critical alignment of the external splitting optics. Later systems incorporated framing cameras and streak cameras, built into one mainframe, using available beam splitters. This allowed for simultaneous framing and streak, however, this type of beam splitter limited access to streak optics, and primarily limited the performance of the streak camera due to the smaller format streak tubes.
A new system recently configured for a proof of principle demonstration incorporated a SIM8 Ultra Fast Framing Camera manufactured by Specialised Imaging, Ltd. of Tring, Hertfordshire, England and an Optoscope SC-10 Streak Camera manufactured by Optronis, GmbH of Kehl, Germany as a single package and attained performance levels never before achieved with a dual camera system.
An Ultra Fast Framing Camera built around a newly designed beam splitter optimized for spatial resolution with no geometric distortions and configured for up to 16 output ports was the primary imaging system. The system used for this test was configured with 9 ports, eight of which were used for 8 channels of ICCDs for framing operation. The 9th optical port allowed a full sized Ultra Fast Streak Camera to be coupled to the system. Having the streak camera external to the framing camera allowed the use of a large format streak camera with a fullsized 8-35mm photocathode and a large 20-40mm output screen ensuring long time windows. It also offered full access to the input streak optics. The adjustable slit and efficient lens coupling also allowed 88 filters and spectrographs to be inserted if needed. The beam splitter maintains an optical spatial resolution >70 lp/mm (line pairs per millimeter) to ensure maximum image quality for both framing and streak modes.
This system was configured as a proof of principle in February 2007 at the Optronis GmbH laboratory in Kehl Germany. The two cameras were optically coupled as described above. As a virtual image plane is present 46 mm from the output port, setup and alignment was easily performed using the real time focus modes of both the framing camera and the streak camera with the same optical axis.
SIM8 Framing Camera: The camera was fitted with 8 ICCDs and with 1360 × 1040 pixels and 12 bit digitization. This particular camera is programmable for framing speeds from 100 fps (frames per second) to 200 Million fps and exposure times are programmable from 10msec to 5nsec. Each frame has independently adjustable gain from unity to ≈10,000X. Other options allow for multiple exposures in each frame if required.
The framing camera offers output pulses which are user programmable to allow for synchronization of other devices such as pulsed lasers or flash lamps. They can also be used to verify critical timing of the actual exposure with respect to other events of the experiment using oscilloscopes and time interval counters. The framing camera also has the ability to output an additional pulse prior to the framing sequence to pre-trigger devices that need to be synchronized such as flash lamps. This pre-pulse option was used to trigger the event.