Excitation source and measured

In Table I, well-known techniques are listed by excitation source and measured emission. Although mentioned there, x-ray fluorescence (XRF), electron microprobes (EMP), and scanning electron microscopes (SEM) will be excluded here because they are not sensitive to the surface, which is generally considered to be 2.5-5.0 nm deep. 

Table I. Better-Known Spectroscopic Techniques According to the Excitation Source and Measured Emission0...

Electro-evaporated soot was purchased from the MER Corporation. The toluene-soluble portion of the soot was separated and purified by the method of ref. 7. The measuring apparatus has previously been described. We use temporally smooth, spatially uniform, optical pulses from a mode-locked, frequency-doubled Nd-YAG laser as the excitation source, and measure the incident and transmitted energy for each pulse. The output from the laser is collimated. The incident fluence is first increased and then decreased to check for evidence of photodegradation. 

In FD fluorometry the excitation source and measurements are rather different than for TD measurements. The pulsed... 

Although CL does not require a lamp as excitation source and thus allows measurements against a zero background, some basic requirements have to be... 

The measurement of the growth and decay of fluorescence requires essentially two items (a) modulated excitation source and (b) a detector. The modulation of an excitation source may be accomplished in various ways. These range from simple mechanical choppers to highly sophisticated electronic pulsers. Detectors may be phototubes or semiconducting devices, or even the human eye. The detector itself, in some instances, may be modulated. Of course, the detector chosen must depend upon the spectral range to be studied and the response time desired. 

Zarowin (68) has made use of a multiple-sampling technique in the measurement of decay times. This method uses a periodically pulsed- or chopped-excitation source and a continuously operating photomultiplier detector. The fluorescent signal is displayed on an oscilloscope. The response of the photomultiplier tube must be fast enough to resolve individual photoelectron pulses, and the time density of pulses is then proportional to the light intensity. 

A Raman spectrum is obtained by exposure of a sample to a monochromatic source of exciting photons and measurement of the frequencies of the scattered light. Because the intensity of the Raman scattered component is much lower than the Rayleigh scattered component, a highly selective monochromator and a very sensitive detector are required. 

Figure 3-17 Block diagram of a typical spectrofiuorometer XS Is the xenon source PS is the power supply Mi is the excitation monochromator C is the sample cell M is the emission monochromator. D) and D2 are detectors D monitors the variation in excitation intensity and measures fluorescence emission intensity. A and A2 are excitation signal and emission signal amplifiers, respectively.

Laser lUman spectroscopy (LRS). The spectra were recorded on a Nicolet 950 FT-Raman spectrometer instrument, equipped with a nitrogen cooled Ge detector. A Nd YAG laser (1064 nm) was used as excitation source. The measurements were performed with a power at the sample of 100-200 mW in order to avoid decomposition and thermal effects. The samples were rotated to provide a noncontinuous irradiation of any given spot on the samples. The spectral slit width was typically 4 cm". ... 

Steady-state and time-resolved luminescence measurements were carried out at room temperature. A nitrogen laser was used as an excitation source in measurements of luminescence decays. Time-resolved luminescence spectrally selected at 613 2 nm by a custom-made interference filter was detected using a FEU-83 photomultiplier tube and digitized by an ADC computer board. 

Visible and UV light sources, which excite electronic transitions, can be used also for PD spectroscopy. By scanning the frequencies of the radiation emitted from the UV/vis light source and measuring PD or electron photodetachment as a function of excitation wavelength, an electronic action spectrum can be constructed in the same way as a vibrational action spectrum is constructed using an IR source. 

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