Scanning illumination mode

Fluorescence Measurement Fluorescence spectra were measured on a Spex Fluorolog 212 spectrofluorometer equipped with a 450 W xenon arc lamp and a Spex DM1B data acquisition station. Spectra were recorded in the front-face illumination mode using 343 nm as the excitation wavelength. Single scans were performed using a slit width of 1.0 mm. PDA fluorescence emission spectra were recorded from 360 to 600 nm, with the monomer and excimer fluorescence measured at 376.5 and 485 nm, respectively. Monomer and excimer peak heights were used in the calculation of the ratio of excimer to monomer emission intensities (Ie/Im). Excitation spectra were recorded from 300 nm to 360 nm and monitored at 376.5 and 500 nm for the monomer and excimer excitation, respectively. 

Figure 19. Micrographs of a tapered fiber probe for illumination mode scanning near-field optical microscopy. The upper two panels are optical micrographs with light emeig-ing from the aperture. The electron micrograph in die lower panel shows the apex of the tip with the aluminum coating.

When the diffusion is very slow and high spatial resolution is more important than high frame rates, such as in a polymer film, illumination mode scanning near-field optical microscopy can be used to image the diffusion of individual fluorophores. This application will be discussed in the Section V.B. 

Figure 7.9. Types of the SNOM configurations, (a) Transmission coiiection mode. The tip is generaiiy metaiiized except for its nano-sized end. (b) Transmission iiiu-mination mode, (c) Refiection coiiection mode, (d) Photon scanning tunnei mode. The iiiumination beam is totaiiy refiected inside a substrate, (e) Duai iiiumination coiiection mode. It is a combination of (a) and (b). (f) Refiection illumination mode, it is an inverted photon tunnel mode (d) [53].

Mechanically registering two scanning systems would be difficult, so commercial LCSMs are reflection microscopes, where (as shown in Fig. 6.1) the beam passes through the same scanner twice. The beam is scanned On the specimen, then de-scanned onto a fixed confocal pinhole. Con-focal microscopes may have a transmission mode, but currently this will not be confocal. It may use a separate regular illumination system, or the scanned illumination. In the latter case the... 

Imura, K and Okamoto, H. (2006) Redprodty in scanning near-field optical microscopy illumination and collection modes of transmission measurements. Opt. Lett., 31, 1474-1476. 

The scanning transmission electron microscope (STEM) combines the two modes of operation. Here, the scanning coils are used to illuminate a small area of... 

The Zeiss PMQ 3 chromatogram analyzer is probably the most versatile thin-film scanner available (Fig.3.13). The system can be used for reflectance, transmission, simultaneous reflectance and transmission and fluorescence quenching. It has two direct fluorescence modes, one with filter emission and surface illumination at a direction of 90° to the surface of the plate, and the other with 45° illumination and monochromatic emission. The instrument can be used for scanning thin-layer chromatograms, paper... 

Fig. 3. Typical setup of a scanning near-field optical microscope. Excitation light is coupled into a single-mode fiber with a metal coated taper at its far end. The light emitted by the aperture illuminates a region of the samples whose size is determined by the aperture diameter and the distance between probe and sample. Light from the interaction region is collect using a conventional optical microscope.

Current-potential measurements, in the dark and under illumination of the semiconductor working electrode, are extremely useful for first defining the charge-transfer behavior across the interface before more sophisticated experiments are undertaken. The irradiation can be either continuous or intermittent (chopped) the latter mode has the distinct advantage that both the dark and light behavior can be examined in the same scan [55, 58]. Even some dynamic information can thus be extracted under the nominally steady-state conditions typical of a cyclic or linear potential sweep experiment. Another useful steady-state experiment is photocurrent spectroscopy (performed at a fixed DC potential) [55], although this can also be dynamically performed via IMPS (see below). Such measurements not only yield the so-called photoaction spectrum of the semiconductor electrode, but also afford information on surface recombination and surface state activity at the interface as discussed below. 

Fig. 25. Schematic diagrams of (A) conventional and (B) diode array scanning spec-trophometers operated in the dispersion mode. (A) The spectrum is dispersed by a grating or prism (the dispersing element) and scanned across an exit slit. A single-element detector (usually a photomultiplier tube) is used to measure the intensity of a monochromatic beam after it passes through the sample. (B) The sample is illuminated with white light prior to dispersion. The dispersed spectrum is imaged on a linear array detector, and the signals from individual elements provide the information necessary to generate spectral information. [Redrawn from Santini et al. (134) with permission.]...

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