Intensified CCD

Special CCD cameras are used to acquire high-resolution images for scientific work. They are also called HCCD cameras. They belong to the two following classes cooled CCD cameras or intensified CCD cameras. Intensified cameras have been mostly used to follow spectroscopic fast events but they are now used in imaging to offer very high sensitivity. Cooled CCD cameras, however, offer better spatial resolution for luminescence work in the field of analysis and a broader combination of spectral ranges and sensitivity. 

In this case, a particularly sensitive spectrometer and an intensified CCD were used, so the images were obtained quite rapidly (8 sec to 2 min). 

The incident probe pulse was the 532 nm second harmonic beam from a Coherent Infinity Nd YAG laser. The 3 nanosecond laser pulse was oriented 60 degrees from the water surface normal direction. The 6 millimetre diameter laser beam was not focussed, and the beam energy was 85 mJ per pulse. The imaging detection system described in Part 1 was used in this experiment it consisted of a dichroic image splitter, quartz Nikon camera lens, and a pulsed gated, intensified CCD camera (Roper Scientific formerly Princeton Instruments). 

The above discussion is presented merely to give an idea of the types of EUV detectors and their applications in use on present fusion plasma experiments. It is by no means an exhaustive list of possibilities. Indeed, several different detectors are in use or being planned in future experiments. Resistive anode encoders will probably see more use in fusion experiments as they become commercially available. However, the low count rates available ( 10 to 10 sec-1) will result in these detectors being used mostly for line profile studies (e.g., ion temperature measurements via Doppler broadening measurements). Intensified CCD arrays (back-illuminated or otherwise), vidicon or CID systems, lens-coupled intensifiers, and anode detectors have all seen some use on tokamak experiments or are planned for the near future, but have not been widely used as yet. However, in terms of availability, pixel format, dynamic range, insensitivity to magnetic fields, compact package, and moderate cost, the IPDA remains the most versatile multichannel EUV detector for plasma spectroscopy. 

Direct observation of phosphorescence from conjugated polymers has been achieved by the application of gated detection techniques. In these techniques the detection window of an intensified CCD is delayed with respect to the excitation laser pulse. Therefore the detector is blocked during the intense prompt fluorescence caused by the conjugated polymer and able to detect the delayed emission that is usually orders of magnitude lower than prompt fluorescence. Spectrally resolved detection allows for the observation of the shape and energetic position of the delayed emission. By varying the width of the detection window... 

Schlatterer and Schaloske (35) used a low-light SIT camera (Heimann, Wiesbaden, Germany). However, to increase the sensitivity Sonnemann et al. (4) used an intensified CCD camera (model HLA, Proxitronic, Bensheim, Germany) to capture images of the cells. Use of the CCD camera increases the sensitivity of the image captured by a factor of 10. This allows more accurate measurements of cells that have incorporated low amounts of the indicator therefore are only weakly fluorescent. Levels of less than 10 pM of the indicator were able to be detected (4). 

There are two practical choices for a multichannel detector, namely, PDAs and CCDs. Different detectors use different methods to transfer the photon signals into the detectable current. The CCD detector has a relatively low dark current and high quantum efficiency, especially for the intensified CCD (ICCD). 

The different sensitive techniques of Doppler-limited laser spectroscopy discussed in the previous sections supplement each other in an ideal way. In the visible and ultraviolet range, where electronic states of atoms or molecules are excited by absorption of laser photons, excitation spectroscopy is generally the most suitable technique, particularly at low molecular densities. Because of the short spontaneous lifetimes of most excited electronic states the quantum efficiency rjk reaches 100% in many cases. For the detection of the laser-excited fluorescence, sensitive photomultipliers or intensified CCD cameras are available that allow, together with photon-counting electronics (Sect. 4.5), the detection of single fluorescence photons with an overall efficiency of 10 —10 including the collection efficiency 5 0.01—0.3 (Sect.6.3.1). 

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