Broadband radiation

When the SRI is equal to the cladding one, the cladding layer becomes an infinitely extended medium and thus supports no discrete cladding modes. In this case, a broadband radiation mode coupling occurs with no distinct attenuation bands8. 

The Broadband Radiation Thermometer (Total Radiation Pyrometer)... 

Performing an FTIR experiment requires some specialized equipment. First, a broadband radiation source is needed. Typically a SiC globar is used that reaches temperatures of 1200-1500 K. When studying species that are weak absorbers or are in low concentration a brighter source is needed and high temperature sources (>2500 K) for such experiments have been developed [75]. These devices are nearly... 

Prom a spectroscopic standpoint, the main difference between a synchrotron and an FEE is that a synchrotron emits broadband radiation, while the FEL emits monochromatic radiation with several orders of magnitude higher brUUance than a synchrotron. Thus, radiation from a synchrotron can be expanded and passed into a FT-IR spectrometer, for which the interferometer and aU the subsequent optics are no different from those in a conventional FT-IR spectrometer (or microspectrometer.) When a FEL is used for spectroscopy, the monochromatic radiation generated can be modulated in any appropriate manner (e.g., by a tuning fork chopper) before being passed onto the sample and detector. In principle, FELs can... 

J. Rodriguez, D.L. Andrews, Inter-particle interaction induced by broadband radiation. Opt. Comm. 282 (2009) 2267. 

One of the most significant implications of the result is that an absorption spectrum measured with intense white light may be significantly different from the spectrum that would be observed using tunable monochromatic radiation. In particular, there should be a decrease in the apparent width of many lines in any absorption spectrum measured with broadband radiation. This is because, for any sample transition of frequency coq, photons of appreciably off-resonant frequency (oiq + fi) can be cooperatively absorbed and result in the excitation of two separate molecules, provided selection rules permit. In fact the Lorentzian linewidth of the concerted absorption process is readily shown to be approximately 0.64 x the ordinary absorption linewidth, if the probe radiation is assumed to be of nearly constant intensity in the frequency region of interest. Nonetheless, the observed linewidth would not be reduced to quite this extent, because of the additional and invariably stronger response associated with normal single-photon absorption. 

In conclusion, it is worth reiterating that the anomalous absorption effects described here may be manifest in any experiments that employ sufficiently high-intensity broadband radiation. To this extent, anomalies may be observable in experiments not specifically involving USES light. In particular, the continued advances in techniques of laser pulse compression have now resulted in the production of femtosecond pulses only a few optical cycles in duration (Knox et al. 1985 Brito Cruz et al. 1987 Fork et al. 1987) which necessarily have a very broad frequency spread, as the time/energy uncertainty principle shows. Thus, mean-frequency absorption may have a wider role to play in the absorption of femtosecond pulses. If this is correct, it raises further questions over the suitablity of absorption-based techniques for their characterization. 

The increased availability of synchrotron radialion in recent years has given XPS experimenters another useful source. The synchrotron produces broadband radiation that is highly collimated and polarized. Such sources when used with a monochromator can provide a source of X-rays that is tunable for photoelectron experiments. 

In contact printing [see Fig. 13.24(a)] the mask and the photoresist-coated substrate are in direct contact during exposure, with the mask held chrome-side down on the resist film. Patterns on the mask are transferred to the entire wafer hy broadband radiation. The theoretical resolution hmit of contact printing is given by ... 

Broadband radiation which covers a bandwidth ao- can be considered to be a composite of many spectrally non-overlapping monochromatic sources of width do-, possibly with different intensities. It is this variation in intensity which constitutes the spectral information of the radiation. The resulting fringe pattern from this broadband radiation is the summation of each of the individual monochromatic contributors. That is. 

We can now generalize (2.71) to include the interaction of broadband radiation with our two-level system by integrating (2.71) over all frequencies co of the radiation field. This yields the total transition probability 3 ab(0 within the time r, if Dab II 0 ... 

In the previous sections we assumed weak-field conditions where the probability of finding the atom in the initial state was not essentially changed by the interaction with the field. This means that the population in the initial state remains approximately constant during the interaction time. In the case of broadband radiation, this approximation results in a time-independent transition probability. Also the inclusion of weak-damping terms with yab coba did not affect the assumption of a constant population in the initial state. 

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