Multiwavelength operation

Multiwavelength operation of a TCSPC device can be achieved by using a system of dichroic mirrors and a corresponding number of individual detectors (see Sect. 3.1, page 29). The general optical setup is shown in Fig. 5.23. 

Light of interna) (He - Ne) and external (Ar ion or UV) lasers passes the scanner unit swilchable mirrors and barrier fillers permit multiwavelength operation. Additional barrier filters are located between the confocal variable pinhole and the beam splitter adjacent to the photomultipliers. 

The operation and application of streak cameras in fluorescence lifetime spectroscopy has been reviewed previously (see, e.g., Refs. 91 and 92). Streak cameras are useful in 2-D time-resolved imaging applications such as microscopy or multiwavelength array fluorometry. The operating principle is based on converting an optical pulse into a photoelectron pulse and spatially dispersing the electron image on a phosphor by means of a synchronized deflection voltage across two plates. 

A multiwavelength, dual beam optical system with 256 detectors operating in a free spectral range of 200 to 800 nm has been designed and implemented for use with a liquid chromatograph. 

As discussed earlier, the PEM is, in many ways, an ideal modulation device for polarization-selective measurements. Thus, the optimum simultaneous multiwavelength CD instrument should incorporate both the PEM and CCD, and at the same time allow the PEM to operate at its resonant frequency. One way to overcome the basic incompatibility of the PEM and CCD is to use an optical demodulation scheme in which the two oppositely polarized components would be directed by a polarizing beamsplitter, to either different areas of the same CCD, or to different CCDs [14]. Since two distinct detector areas would be accessed by the oppositely polarized light, pixel-to-pixel sensitivity variations may be a significant source of noise. 

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