Short exposure times enable images to capture extremely high-speed motion. Two illumination systems that support imaging with short exposure times are discussed in this paper. The MegaSun plasma discharge illumination system for ultrahigh-speed imaging (approximately 1 million frames per second (fps)) was described at the previous Congress. It provides a single "long" pulse of broadband light sufficient to replace argon candles; the pulse duration can be adjusted to provide uniform illumination for the required number of frames (typically 30 μs to 60 μs) and rapidly extinguishes thereafter. This paper presents the optical and electrical features of a larger energy version of the system, the Super MegaSun, powering new lamp configurations. It provides a full width half maximum (FWHM) pulse of 90 μs. Short exposure times that freeze fast motion are also useful for high-speed framing cameras imaging fast events at rates from 500 fps to several thousand fps. A repetitively pulsed strobe was previously demonstrated that provided short pulses (a few microseconds) at up to 1850 fps synchronized with a film camera for a special test scenario. Some variations of this system that may have more general application are also discussed in this paper.
The MegaSun high intensity illumination system has been developed for ultrahigh-speed imaging applications that previously required argon candles (argon bombs) for adequate illumination. This plasma discharge system has produced excellent color images of explosive tests taken by various Cordin cameras operating up to two million frames per second with small stops (125 ns exposure). Exposure times of 10 ns to 50 ns were easily achieved with a variety of intensified electronic cameras. For tests involving explosives, the non-destructive nature of the lamps facilitates new test arrangements -- for example, the large standoff distances associated with destructive argon candles are no longer necessary. For the wider test community that does not use explosives, this benign, yet intense, light source generates the illumination necessary to use these ultrahigh-speed cameras to acquire superb color images. This paper will briefly review the mechanical, electrical, and optical characteristics of the MegaSun system, and then illustrate its capabilities with a variety of images from live tests.
The MegaSun illumination system, designed to replace argon candles for ultra high speed photography, has be used routinely to support live tests at Eglin AFB for the past two years. It has exposed detailed color images of fragmenting plates at framing rates of 1 million frames per second (1 Mfs) with a Cordin 330A. A longer 200 mus pulse version illuminated explosively formed penetrators in flight both for framing images taken by an Imacon 468, and for color synchro-ballistic images captured with a Cordin 132A streak camera. In addition, a demonstration version of the MegaSun was used for exposure tests performed at Lawrence Livermore National Laboratory (LLNL) Site 300 with Cordin 121 and 140 cameras. It provided enough illumination for proper exposure of 400 ASA film processed on time at 1 Mfs. These results confirm that the MegaSun can replace argon candles for most ultra high speed photography applications.
This paper reports on the progress made in developing a practical illumination system to replace argon candles. The basic concept--inexpensive, disposable, modular, surface discharge lamps that provide a flexible illumination geometry and which can be sized to match the impedance of the pulse forming network (PFN)--was described in the previous paper. Since then, the pulse shape and energy output have been measured for the complete system for the three different 19 kJ PFNs, having characteristics times of 70 microsecond(s) , 200 microsecond(s) , and 1 ms. Exposure tests confirmed that the illumination level is sufficient for color photography at 2 Mfps with a Cordin 330A and for 10 ns exposures with an IMACON 468. As the illumination source for plate fragmentation tests using live explosives, the system created `high quality images' and proved to be a useful tool that was easily integrated into the test procedure. The laboratory demonstration system has since been converted into a production model that has been installed in an instrumentation van at Eglin AFB to provide illumination at various ranges.
A repetitively pulsed broad band visible illumination system has been developed that is suitable for capturing images of high speed motion over sizable areas. At full pulse energy, a two lamp system can illuminate 60 square feet for movies at f/4 with 400 ASA color film and framing rates as high as 1700 fps. At reduced energy, for smaller area applications, the framing rate can be doubled. The short pulse length (4.5 microsecond(s) at full energy, 1.5 microsecond(s) at reduced energy) produces sharp images of high speed objects. This paper reports developments since the last presentation, including: (1) higher pulse repetition rates (a few kilohertz), (2) synchronization with high speed camera, (3) full scale burst of several thousand pulses, (4) characteristics of a compact demonstration system, and (5) demonstration of the ability of the short pulse to freeze motion.
High speed photography for range testing often requires intense disposable illumination sources. A low cost surface discharge source is being developed to replace argon candles for many range tests. Since the test environment will likely destroy the lamp, it is fabricated from inexpensive materials and does not require machining of any components. A series of tests were performed to determine the radiative output in the visible of candidate surface discharge lamps, and to clarify the illumination requirements. Tests using a range camera and a short pulse 100 cm2 planar surface discharge determined that an irradiance of 600 W/cm2 on target is sufficient for black and white photography at 2 million fps whereas color photography requires approximately 3 kW/cm2. The results of the subscale tests have been used to guide development of a full scale pulse forming network (PFN) matched to a set of surface discharge lamps. The PFN delivers 12 kJ to the lamps in pulses that can range from 40 microseconds to 1 ms. The matching lamps have been developed and tested for pulse lengths as long as 200 microseconds.
The acoustic environment created by turbulence in aircraft flight tests demands that illumination sources for high speed photography of munitions drops be extremely rugged. A repetitive pulsed surface discharge system has been developed to provide wide angle illumination in a bomb bay for photography at 250 - 500 Hertz. The lamp has a simple construction suitable for adverse environments and produces 100 mJ of visible light per pulse. The discharge parameters were selected to minimize the size and complexity of the power supply. The system is also capable of operating at high repetition rates; preliminary tests demonstrated 1000 pulses at 1 kHz, 200 pulses at 1.5 kHz, and 13 pulses at 2 kHz. A simple power supply capable of providing several amperes at 450 V is being completed; it will be used to extend the run times and to explore extensions to higher repetition rate.
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