Excited state Filter

This direct filter teclnrique is very powerfiil [, 59] in extracting highly excited states, since only the propagation of a wavepacket is required. However, it is inefficient when there are closely-lying eigenvalues T... 

The fluorescence spectra measured just upon ablation are given in Figure 2A as a function of laser fluence. The contribution below 370 nm was suppressed, as a Hoya L37 filter was used in order to cut off the laser pulse. Fluorescence spectra of this polymer film consist of sandwich (max. 420 nm, lifetime 35 ns) and partial overlap (max. 370 nm, lifetime 16 ns) excimers (20). The latter excimer is produced from the initially excited monomer state, while the sandwich excimer from the partial overlap excimer and the monomer excited states. Since these processes compete with efficient interactions between identical and different excimers (Si - Si annihilation) (12), the sandwich excimer is quenched to a greater extent compared to the partial overlap one under a high excitation. Actually the fluence-dependent spectral change around the threshold can be interpreted in terms of Si - Si annihilation. 

Platinum and palladium porphyrins in silicon rubber resins are typical oxygen sensors and carriers, respectively. An analysis of the characteristics of these types of polymer films to sense oxygen is given in Ref. 34. For the sake of simplicity the luminescence decay of most phosphorescence sensors may be fitted to a double exponential function. The first component gives the excited state lifetime of the sensor phosphorescence while the second component, with a zero lifetime, yields the excitation backscatter seen by the detector. The excitation backscatter is usually about three orders of magnitude more intense in small optical fibers (100 than the sensor luminescence. The use of interference filters reduce the excitation substantially but does not eliminate it. The sine and cosine Fourier transforms of/(f) yield the following results ... 

In most cases two different additives are used, one acting as an internal filter or excited state quencher and the other one being a scavenger of free radicals. These two additives have a synergic effect, that is they are much more effective together than either of them separately. 

Sonobe and Rosenfeld (48,49) have measured the 4.7 pm infrared emission of CO. The extent of the CO vibrational excitation can be estimated using a cold gas filter containing CO and a 4.7 pm filter. If CO is vibrationally excited there is a smaller amount of attenuation of 4.7 pm fluorescence by the cold gas filter. When ketene is photolyzed at 193 nm, they estimate from their data that the rotational and vibrational temperatures are about 6700 and 3700 K, respectively. A high rotational temperature suggests that the C-C-0 angle is bent in the excited state. The CO vibrational excitation becomes less for longer excitation wavelengths. 

Krause et a/.123-125 have recently reported a series of measurements of the spin-orbit relaxation of the alkali metals in their first excited states (2P). The technique, for example for atomic caesium with AE = 554 cm-1, consists of irradiating the metal vapour with light from a monochromator to excite only one of the 2P states. The vapour pressure of the metal is controlled at 10-6 torr to avoid imprisonment of the resonance radiation. The components of the fluorescence light are measured with a photomultiplier by isolating the 2P - 2S lines with interference filters. In the presence of added gases which cause the transitions... 

Generally there are two different methods for measuring excited state spectra in the ms time regime. Typically, IR PIA spectra are not recorded with the lock-in technique but by referencing several hundred accumulated single beam spectra (by FTIR spectrometer) under illumination and in the dark, while UV/VIS PIA uses a lock-in detector to filter out signal changes due to photoexcitation. 

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