High quality imaging is a key parameter in many scientific applications. CCD and ICCD cameras have proven to be powerful tools and are consequently used in a wide range of fields such as engineering research and physical or biological sciences. The very new Electron Multiplying CCD technology seems now to provide the most sensitive detection capabilities. Here we compare analytically the signal-to-noise performance of the three systems and identify the most influencing parameters. The SNR provided by CCDs is strongly influenced by the readout noise and is also a significant function of the pixel rate. ICCD cameras are practically not at all affected by the CCD chip temperature and are shown to be mostly shot-noise-limited because readout and dark current noises are negligible. Therefore no cooling is needed for ICCDs. Although EMCCDs unite the quantum efficiency of CCDs and the gain of ICCDs, their performance is constricted by charge transfer and dark current noises which will be multiplied up along with the signal by the gain register. Therefore, EMCCDs must be strongly cooled (down to -70°C) and slowly read out in order to get rid of any unwanted "pseudo signal". In addition, their properties limit exposure times to milliseconds time scales and longer. We conclude that ICCD cameras remain the most efficient systems in all gated experiments and perform very well in extreme low light situations. They still keep great advantages over standard CCDs and the new incoming generation of EMCCDs.
High repetition rate intensified cameras having interframe times in the microsecond(s) range are needed for flow analysis measurements such as Particle Imaging Velocimetry (PIV) or Molecular Tagging Velocimetry (MTV). For these applications, the lower efficiency, fast decay P46 and P47 phosphors must then be used instead of the higher efficiency P20 and P43 phosphors. Previous literature provides only the time-resolved phosphor response. For very short interframe time imaging applications, a significant fraction of the previous frame's intensity can appear as a 'ghost image' in the trailing frame. Fast phosphors minimize this energy transfer into a second frame. Previous data show a dependence of decay time on exposure time for the P46. The P47 has been reported to decay a factor of 3 to 30 faster than the P46. The transferred total intensity as a function of the shutter repetition rate is measured for these two fast phosphors. They are compared with data published in previous papers. Neither phosphor under investigation behaves fully in accordance with these prior characterizations.
New flow analysis applications of MCP image intensifier tubes require faster image repetition rates. When coupled to CCD readout chips their time-integrated behavior determines the overall system's response concerning the intensity of unwanted ghost images. Previously published experimental data as well as manufacturer's literature provide only time resolved response information. New data for the widely used high-efficiency, slow-decay P20 and P43 phosphors are determined as functions of both exposure (excitation) time and interframe time. Previously reported dependency of decay time being determined solely by the preceding exposure time is not supported by new data. Data herein show an increase of decay time by more than a factor of 100, especially for short excitation times. This is caused by intensity integration on the CCD chip. The P20 shows a very long non-exponential decay. Though being faster during the initial 200 to 500 microsecond(s) , the P20's decay extends over a substantially longer time as compared to the P43 phosphor. This is in clear contradiction to earlier results, which could lead to the expectation of the P20 being more than an order of magnitude faster than P43 for very short exposure times.
Proximity focused microchannel plate image intensifiers (MCPIIs) with a mesh underlay photocathode are analyzed for their irising time. It is found to be of the order of 650 ps for early prototypes. This is much longer than previously reported but is finally explained by the mesh thickness. Increased metal layer thickness provides highly nonlinear increase of mesh conductivity. Modified tubes show irising below 100 ps. It is expected to be only limited by its theoretical 40 ps minimum time caused by the propagation speed of the electrical field strength's change. A newly introduced impedance match has real broadband characteristics, and the irising is fully caused by other effects. The minimum gate time observable was clearly below 1 ns. The earlier investigated prototype mesh underlay MCPIIs did not open to its full diameter at the shortest applied times. Ni underlay photocathodes were analyzed for comparison. They also provide irising times down to 200 ps. The long laser diode pulse and a too flat voltage slope of the driving generator prevented exact results for subnanosecond gate timing. Continued development of the system is underway.
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