Pulsed dye laser

After condensation, the clusters are transported by the He-flow through a nozzle and a differential pumping stage into a high vacuum chamber. For ionization of the clusters, we used excimer and dye laser pulses at various wavelengths. The ions were then mass analyzed by a time-of-flight mass spectrometer, having... 

Figure 10-5. Transient transmission changes AV/Po in PPV for different lime delays between the pump and probe pulse. The pump pulse is a 100 fs laser pulse at 325 nm obtained by frequency doubling ol amplified dye laser pulses, (a) and (b) correspond to different sides of a PPV-film. The spectra in (a) were obtained lor the unoxidized side of the sample while the set of spectra in (b) was measured for the oxidized side of the same sample. The main differences observed are a much lower stimulated emission effect for the oxidized side. The two bottom spectra depict the PL-spectra for comparison. The dashed line indicates the optical absorption (according to Kef. (281).

Triplet quantum yields for eosin and some other dyes have been determinded by Soep et al. The system to be studied is exposed to a dye laser pulse (with tunable wavelength) and the transient absorb-tion changes in the system due to triplet population are recorded with the light from a dc xenon lamp. 

The results of the hole-opening measurements are presented in the series of oscilloscope traces shown in Figure 16. Traces 16a and b are the results obtained on a sample fabricated with polystyrene of molecular weight 4 K. From trace a it can be seen that under the action of the 8 nsec dye laser pulse, the holes or pits develop fully in —30 nsec. Furthermore, from the measurements taken at 100 nsec/div (b), it can be seen that the pit, once fully developed, maintains its dimensions. Similar conclusions can be drawn from oscilloscope traces c, d and e which show measurements taken on samples... 

As shown by Fig. 8.14, in most Stark spectra above the classical ionization limit there is never one isolated resonance but, more often, an irregular jumble of them. For example, in Fig. 8.15 we show the observed22 and calculated23 Na spectra near the ionization limit in a field E = 3.59 kV/cm.22 The experimental spectrum of Fig. 8.15(a) was obtained by Luk et al.22 by exciting a Na beam with two simultaneous dye laser pulses from the 3s1/2 to 3p3/2 state and then to the ionization limit. Both lasers were polarized parallel to the field, and the ions... 

Equation 31 is plotted in Figure 5 for typical combustion conditions and with the combined uncertainty in k. > ft and V as a parameter. The sample time is 1 Usee, typical of flash-lamp pumped dye laser pulses, and thus remarkably low detectability limits are achievable with single pulse sampling. 

The statistical nature of the turbulent flame required the analysis of many temperature and density data points from separate pulses for accurate results. Thus, an overall computer system was used to control the various components of the combustion probe apparatus, and to collect and interpret the resultant data in an accurate and timely fashion. This system produced a block of data for each laser shot that included information about the Raman signals, LV readings, and ancillary data such as an identifying shot number and corresponding dye laser pulse energy. Typical current operation permits about twenty experimental run conditions daily, with up to several hundred shots per run. 

The output is thus a continuous train of pulses separated by the dye cavity round-trip time. Even though the pump laser pulses may be of the order of 200 ps long, dye laser pulses of less than 10 ps can be achieved by synchronous pumping. This is because the dye molecules have extremely large stimulated emission cross-sections and the dye laser pulse passing through the dye stream immediately de-excites the dye molecule, in a few picoseconds, by stimulated emission [13]. 

Hirata Y, Mataga N. (1990) Solvation dynamics of electrons ejected by picosecond dye laser pulse excitation of p-phenylenediamine in several alcoholic solutions. J Phys Chem 94 8503-8505. 

The experiments are done by exciting Na atoms in an atomic beam to the 17s state, by the route 3s —> Sp —> 17s, using two 5 ns dye laser pulses. The atoms are allowed to collide for 3 ps, and then the final states are analyzed by selective field ionization. In particular, atoms in the 17p state are detected as the tuning electric field is slowly swept over many shots of the laser. In Fig. 2 we show the resonances observed in this way. There are four resonances corresponding to the two possible rni values of the up states, mi = 0 and 1. It is convenient to label the four resonances by the m values of the upper and lower p states, e.g., (0,0) has m = 0 in both. 

These experiments are slightly more difficult in that both the 29s and 27d states must be excited. In this case the atoms are allowed to collide for a few microseconds after pulsed laser excitation, and the 29p atoms are detected as the tuning field is slowly swept over many shots of the laser. The important difference from the Na experiment is that the K atoms can be velocity selected. As shown in Fig. 5, there is a slotted disc in front of the oven, and if the disc is turning, a burst of the atoms passes through the slit, and only those within a narrow velocity range are excited by the 5 ns dye laser pulse 200 /xs after the burst of atoms passes through the slit. 

The nitrogen pump lasers are triggered by a common master control unit with delay lines arranged so that each laser fires at predetermined and well-controlled times with respect to the others. The dye laser pulses were monitored by a fast vacuum photodiode and oscilloscope. The dye lasers provided 5-10 ns pulses having 0.5-2.0 cm spectral linewidths with less than 5 ns jitter. A boxcar integrated the signal received from the particle multiplier. 

Figure 1 The effect of i.r. radiation on the phosphorescence (upper trace, ) and fluorescence (lower trace, b) signals from biacetyl. Time zero corresponds to optical excitation at 405 nm from a dye laser pulse, and the time of introduction of the 9.6 pm COj laser pulse is indicated by the arrow...

Conductometric methods have been used to follow the reactions of the transient species formed by flash photolysis (X 200 nm) of nitrate ions in aqueous solution. The initial excited state produced was shown to decay by two routes either to give HOONO or to give a lower energy excited state. Other reactions observed, and also those described previously by other workers, are summarized in Figure 1. A study of the photolysis of HN3 induced by 290 nm dye-laser pulses has been reported. The isomerization of NjFj in the presence of fluorine and oxygen has been initiated photochemically. ... 

---