Broadband continuous source

Sources of pulsed incoherent radiation are so-called flash lamps, which produce short light pulses of broadband continuous-wave characteristic. Commonly, an intense pulse of short duration is used to generate sufficient concentration of a transient species suitable for spectroscopic observation. 

The flash lamps used in archetypal time-resolved techniques produced an intense pulse of short duration and broadband continuous-wave characteristic, and provided information in a millisecond timescale. Gradual improvements, and especially use of laser sources, allow decrease of resolution times to micro-, nano- and femtoseconds [2,10-12],... 

Figure 13.1 shows the typical layout of a grating-based PA-IR spectrograph. In contrast with the set-up of Heilweil et al. [5], an inexpensive continuous-wave broadband IR source is used, thus decreasing the cost and complexity of the... 

In conclusion, when a WGM is excited in a dielectric microresonator, its evanescent component provides a convenient probe of the microresonator s surroundings. Various ways to implement evanescent-wave sensing have been devised, but the emphasis of this chapter has been on microcavity-enhanced absorption spectroscopy. The techniques described here have broad applicability, can even be used with broadband sources, and lend themselves well to further enhancement methods. We are looking forward to continuing our development of these sensors. 

More recently, comprehensive studies of typical areas of exposure of samples from synthesis, through manufacturing, packaging and in-use have been performed and reported by McGreer (39), Reed et al. (40) and Baertschi et al. (41). The results of these studies show the variety of sources samples are exposed to during their lifetime. A source that is broadband and continuous from about 300 to 700 nm will cover the spectrum of all natural light except for the infrared, and meet the guidelines objectives. 

Conventional CARS spectroscopy is carried out using the two-color CARS process induced by continuous-wave or narrowband pulsed laser sources. On the basis of the progress in the broadband pulsed laser technology, broadband CARS methods are now drawing much attention [29-31]. One of most remarkable examples is... 

Perhaps the most important elements in THz systems are sources and detectors. Sources are vaguely classified into two categories pulsed broadband and continuous narrowband. The most common approaches for generating broadband THz pulses are photoconductive antenna and optical rectification, while voltage controlled oscillators or dielectric resonators are the two widely used sources for generating low power narrowband continuous THz waves [5]. 

A commercial high-resolution FTS is depicted in Fig. 4.2. The output of the broadband source is focused on a circular aperture (entrance iris). As in the dispersive set-up, the optical beam is made parallel by a collimating mirror, and it intercepts a beam splitter at a non-normal incidence (usually 45 or 60°). One part of the beam is transmitted towards a fixed plane mirror while the other part towards a plane mirror, which can be translated continuously or in steps at a given distance (scan mirror). The beams reflected back by... 

Photometers can be of the broadband type (broad spectral band light source-r filter) or the narrow-band type (line spectrum light source-i-filter) [41], [42], In more expensive equipment, continuous radiation sources (broadband) are used, and the filter is replaced by a monochromator, so that a complete spectrum can be observed point by point. Only a very good monochromator can give resolution (monochromaticity) as good as that from a combination of a line source and filter since in the latter system, the very small width of the... 

No commercial electron magnetic resonance spectrometer presently operates continuously over one or more frequency octaves, but instead utilizes a narrow band source that is mechanically or electrically tunable over a 500-MHz range. Despite past arguments against their use, wideband solid-state devices perform competitively with traditional narrow band devices, and numerous synthesized frequency sources are continuously tunable from 2-26 GHz. The phase noise, rated at <-80 dBc at 10 kHz offset for many systems, is excellent, and comparable to narrow band reflex klystrons. Similarly, many components can be made broadband or at least octave spanning, and therefore the experimental capability is available. One approach that is economical relies on the VXIbus instrumentation architecture, which enables one to assemble a modular instrument on a common computer-controlled mainframe that allows experimental flexibility, and further details of a broadband EMR instrument may be found in Volume 21 of this series (Bender, 2004). 

With the continuous developments, IR spectroscopy became the most widely used characterization technique in industry and in many technological processes, e.g. in food sciences. However, modern applications such as IR microspectroscopy require intense, brilliant and broadband sources, so that research has been oriented towards new IR sources. Actually, Fourier transform spectroscopy strongly benefits from a broadband non-thermal source such as SR that not only fulfils these requirements but also exhibits well-defined polarization properties and time structure. 

A more detailed discussion of phase correction is given in Chapter 4. At this point it is sufficient to say that if the phase angle 0 in an interferogram measured with a continuous broadband source varies only slowly with wavenumber (as is... 

The advantages of Fourier transform spectrometry over the use of a scanning monochromator (often referred to as dispersive spectrometry) is fully valid only when the detector noise is independent of the power of the radiation incident on the detector. When the detector is photon shot-noise limited [as it generally is for a photomultiplier tube (PMT), and often is for other sensitive detectors used in the near-infrared, visible, and ultraviolet spectral regions], the noise level is proportional to the square root of the incident power. For a boxcar spectrum, this means that shot noise is proportional to the square root of the number of resolution elements in the spectrum, This disadvantage therefore precisely offsets Fellgett s advantage when continuous broadband sources are employed. It should also be... 

The time resolution of the measuring system using a conventional infrared source of continuous broadband radiation is determined by the response speed of the detector and its preamplifier. If a conventional MCT detector is used, the highest time resolution is about 100 ns. However, if pulsed infrared radiation could be used, the time resolution would be determined by the pulse width, and it would become higher [1, 16]... 

Noise artifacts that appear on X and/or Y but not Z are horizontal and often represent the seismometer tilting in some manner. There are many potential causes and sources of tilt, and so it is useful to further characterize the noise. Sudden isolated transitions are suggestive of rapid discrete tilt events, oscillations can indicate rocking behavior, and broadband horizontal noise may indicate continual random tilting. Steps that occur with a consistent polarity suggest a series of tilts in the same direction, as may happen if the seismometer is slumping in discrete steps to one side. Steps that alternate polarity may indicate a back-and-forth tipping action. The direction of the tilt is indicated by the proportion of X-to-Y noise, and some combination of X and Y (with very little Z) noise is a further confirmation of probable tilt actimi. 

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