Spectral brightness

Fs-laser-induced ps X-ray generation has also been demonstrated in the laboratory by exploiting the high spatial and spectral brightness of plasmas that, once created, emit X-ray pulses on a time scale of order ps and typically with a kHz rate of repetition [60, 61]. The development of these instrumental advances for affording laboratory-based, quantitative X-ray-diffraction results would prove highly beneficial to this area of structural endeavour. 

The obtainable spectral brightness in photons s-1 mrad-2 (1% bandwidth)-1 is given by... 

Figure 6. The evolution of spectral brightness (brilliance in our terminology) of -ray sources through time. [Used by permission of the editor, World Scientific, from Winick (1994), Fig. 1.4, p. 6]...

Plasma Sources of Radiation with High Spectral Brightness... 

Thermal plasma sources are based on the radiation of quasi-equilibrium plasma (see Fridman Kennedy, 2004) heated to very high temperatmes. Taking into account their wide area of application, let s consider these high-spectral-brightness radiation sources in more detail. 

Protasov, Yu.S. (2000), Plasma Sources of Radiation with High Spectral Brightness, in Encyclopedia of Low-Temperature Plasma, Fortov, VE. (ed.), vol. 4, p. 232, Nauka (Science), Moscow. 

The detector is the most important part of a MMW spectrometer. The photon energy at MMW frequencies is similar to kT (Equation 1.15) and so the noise naturally occurring in the semiconductor diode detectors is significant at these frequencies. The sources are spectrally bright and their close-in sideband noise... 

Originally called sampling synthesis in the music industry, any synthesis using stored PCM waveforms has now become commonly known as wavetable synthesis. Filters are usually added to high-quality wavetable synthesis, allowing control of spectral brightness as a function of intensity, and to achieve more variety of sounds from a given set of samples. 

As indicated by this equation, the multiplex gain at the frequency a- offered by Fourier transform spectroscopy in the presence of photon shot noise is a function of the spectral brightness at that frequency and of the overall structure in the total spectrum. This is completely different from the situation presented earlier where detector noise was assumed to dominate. 

Recently, a XeCl laser (308 nm) with high spectral brightness has been used by Maeda and Takahashi [lO] to excite up to the 11th AS component at 128.3 nm in H2 gas at 10 atm. This source and therefore the AS Raman emission is tunable over the bandwidth of the XeCl laser ( V IOA). The potential for emission at much shorter wavelengths now exists with excitation of stimulated Raman scattering with an E-beam pumped Ar2 ex-cimer laser operating at 124 to 127.5 nm with 2 MW output power. In preliminary experiments, Sasaki et al. [ll] have generated X IOO kW power in the first and second order Stokes emission (at 134 and 141 nm) of H2 at 8 atm pressure. 

Figure 10. A high spectral brightness laser system for use in generating VUV radiation [29].

The principles of the laser-excited atomic fluorescence (LEAF) technique are very simple. A liquid or solid sample is atomized in an appropriate device. The atomic vapor is illuminated by laser radiation tuned to a strong resonance transition of an analyte atom. The excited analyte atoms spontaneously radiate fluorescence photons and a recording. system registers the intensity of fluorescence (or total number of fluorescent photons). The extremely high spectral brightness of lasers makes it possible to saturate a resonance transition of an analyte atom. Therefore, the maximum fluorescence intensity of the free analyte atoms can be achieved while the effect of intensity fluctuations of the excitation source are minimized. Both factors provide the main advantage of LEAF— extremely high sensitivity. The best absolute detection limits achieved in direct analysis by LEAF... 

To determine the signal-to-noise ratio (SNR) obtainable in any measurement, we must know not only the noise power but also the power of the signal. The spectral brightness i.e., the power flow per unit area per wavenumber per steradian at wavenumber v from a blackbody source at temperature T is given by the Planck equation ... 

Although the technique of photoacoustic spectroscopy has existed for more than a century it is particularly the advent of lasers as radiation sources with high spectral brightness that has initiated a renaissance of the PA effect. In the meantime a great variety of experimental schemes have been developed which render the PA method a very versatile spectroscopic tool. 

Perhaps even more than other fields of application in laser spectroscopy, ion physics is likely to benefit rapidly from progress in the U.V. range. Frequency doubled CW gas and dye lasers are now able to provide on a routine basis the few milliwatts of monomode laser power which have been necessary for the N20" photodissociation experiment. Further in the U.V., the Doppler tuning method could take advantage with much benefit of the high spectral brightness of injected excimer amplifiers operated at high repetition rate. 

Lasers for LIF should correspond to the following main requirements to have a possibility of tuning of the radiation line, to possess a narrow spectral width of the generation line, a short pulse duration, and a high spectral brightness. The repetition frequency of pulses should be rather high to perform the procedure of accumulation of fluorescence signals. 

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