Abstract
A photon event counting imaging detector, originallydeveloped for astronomical applications, has been adapted for use on alow light level fluorescencemicroscope. It is based on a 40 mm diameter, three-microchannel plate imageintensifier with a photon gain of 107 when operating in the photon eventcounting mode. The intensifier's output screen is lens coupled to a fullframe progressive scan CCD camera which transfers the photonevent data into a PC via a framegrabber.The image is built up from the photon events in the frames usingsoftware-based event processing. The high sensitivity of the photon countingapproach means that low excitation light levels and/or a low probeconcentration can be used. Moreover, the inherent linearity betweenincident intensity and thenumber of detected events provides intrinsic photometricaccuracy independent of camera gain and offset.To demonstrate the viability of photon event counting imaging appliedto fluorescence studies, we have imaged4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran-(DCM-) and rhodamine 6G-doped thin films produced bythe sol-gel technique using tetraethylorthosilicate (TEOS) as aprecursor.We show that fluorescence imaging is a feasible tool for finding cracks,streaks or other defects and for assessing the uniform thickness of thefinished films. In addition, we image the fluorescence in responseto an excitation beam illuminating rhodamine 6G-doped bulk monolithsol-gel samples. The results are analysed using the Lambert-Beer law.
Published Version
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