A Position-Sensitive Photon Event Counting Detector Applied to Fluorescence Imaging of Dyes in Sol-Gel Matrices

A photon event counting imaging detector, originally developed for astronomical applications, has been adapted for use on a low light level fluorescence microscope. It is based on a 40 mm diameter, three-microchannel plate image intensifier with a photon gain of 10(7) when operating in the photon event counting mode. The intensifier's output screen is lens coupled to a full frame progressive scan CCD camera which transfers the photon event data into a PC via a framegrabber, The image is built up from the photon events in the frames using software-based event processing. The high sensitivity of the photon counting approach means that low excitation light levels and/or a low probe concentration can be used. Moreover, the inherent linearity between incident intensity and the number of detected events provides intrinsic photometric accuracy independent of camera gain and offset.To demonstrate the viability of photon event counting imaging applied to fluorescence studies, we have imaged 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran(DCM-) and rhodamine 6G-doped thin films produced by the sol-gel technique using tetraethylorthosilicate (TEOS) as a precursor. We show that fluorescence imaging is a feasible tool for finding cracks, streaks or other defects and for assessing the uniform thickness of the finished films. In addition, we image the fluorescence in response to an excitation beam illuminating rhodamine 6G-doped bulk monolith sol-gel samples. The results are analysed using the Lambert-Beer law.