Effective laser intensity

Fig. 2.8. Left Ratio of doubly to singly charged (7, = 2, , ) and triply to doubly charged (Z = 3, o, ) molecular ions are plotted as a function of effective laser intensity. Circles and squares indicate them by circularly and linearly polarized lights, respectively. Right figure Ratio of the sum of molecular ions of all charge states (JO Mz+) to the total ions (Total). Signals by circularly polarized light are indicated by (o) and for linearly polarized light by ( )...

The peak of the intensity of the circularly polarized light is half of that of the linearly polarized light. But this is not sufficient for the effective laser intensity in the ionization experiments. A factor of 0.65 has been estimated on the basis of the ADK calculation of Xe ionization rates [27]. The factor, 0.75 was experimentally obtained here by comparing the Isat of Xe for linearly polarized light to that for circularly polarized light [12]. 

Fig. 2 Effect of the laser intensity on the quantum yield of formation of oxidized bases (j)ox) and pyrimidine dimeric photoproducts (0dim)...

Fig. 3 Effect of UV laser intensity on the distribution of oxidation products. DNA was solubilized in 1 mM pH 7 TRIS buffer in order to stabilize the duplex... 

Photothermal sensitization has been mentioned briefly with regard to nickel(II) octabutoxy-naphthalocyanine (Section 9.22.10.1). A similar phenomenon has been observed with copper(II) haematoporphyrin ((1), Cu for 2H).196 This substance is accumulated by amelanotic melanoma cells. When the impregnated cells were subjected to light from a quartz-halogen lamp cell survival was not affected (i.e., no PDT effect), but intense pulsed laser irradiation (532 nm, Q-switched... 

Surprisingly, transparency to the laser light was observed in a 0.5 im thick plasma slab (much thicker than the skin depth) obtained by ultra-fast ionization of a plastic foil at a density orders of magnitude higher than nc [4]. The effect was observed at laser intensities corresponding to ao 1. Figure 8.1 shows the measurements of plasma transmittivity in that experiment vs. the intensity on target of a focused Ti Sa laser pulse (30 fs, 800 nm). 

The study confirmed that the action of the precursors of the main pulse has to be carefully considered in the ultrashort intense laser pulse interactions. Nevertheless, a regime of rather stable propagation [34] of a laser pulse of tens of femtoseconds was found in a broad window of the laser intensity/medium density diagram, in which (1) the ionization occurs in one or a few optical cycles, avoiding effects of self-phase modulation and defocusing for most of the... 

This situation corresponds to the well-known saturation effect in the emission of most gas laser transitions, where, for the same reason, fewer upper-state molecules can contribute to the gain of the laser transition at the center of the doppler-broadened fluorescence line than nearby. When tuning the laser frequency across the doppler-line profile, the laser intensity therefore shows a dip at the centerfrequen-cy, called the Bennet hole or Lamb dip after W.R. Bennet who discovered and explained this phenomen, and W.E. Lamb 2) who predicted it in his general theory of a laser. 

A cooperative model for isomerization was proposed to explain the effect of intense laser irradiation. In this model, the formation of excited or transient states in close proximity can transiently provide enough free volume for isomerization to occur. This work with NOSH has been complemented by studies using 6-nitro-BIPS and NIPS [109,110]. This cooperative model is shown in Figure 12. 

S2 - Sq fluorescence in condensed media has so far been found in several types of molecules. However, metalloporphyrins are contrasted with these compounds by another arresting feature such that the S2 fluorescence can be observed even upon photoexcitation to the state. Stelmakh and Tsvirko have first noticed the anomalous S2 - Sq fluorescence in metalloporphyrins (15,16). Figure 1(a) shows the fluorescence spectra of ZnTPP in EPA taken by the 540 nm excitation of a nitrogen pumped dye laser. The fluorescence band at around 430 nm observed by visible excitation is safely assigned to the S2 state fluorescence. The laser power dependence of the fluorescence intensity is quadratic at low power density of excitation (<5 x 10 photons cm"2 pulse ) but shows typical saturation effect with increasing the laser intensity. It should be emphasized here that the S2 fluorescence of ZnTPP can be observed without focusing of the laser beeim. 

In this contribution recent results [13] on the control of the quantum mechanical phase of an atomic state in strong laser fields studied using the Autler-Townes (AT) effect [14] in the photoionization of the K (4p) state are discussed. We demonstrate quantum control beyond (i) population control and (ii) spectral interference, (i) We show, that for suitable combinations of the laser intensity of the first pulse and the time delay the second resonant intense laser pulse leaves the excited state population unchanged. However, the knowledge of the... 

Finally, we want to emphasize an interesting result of the numerical calculation that has been proven experimentally. As shown in Fig. 6, there exist two pulse sequences (b, c) leading to a small population of level 2. In case (c) most of the population is transferred to level 3 while in case (b) nearly all of the population remains in the initial level. In coherent ion dip experiments case (b) is used as it provides deeper dips due to the more effective suppression of ionization. Using higher laser intensities would allow us to achieve nearly 100% ion dips also in case (c) however, for off-resonant conditions the ion current would be smaller by an order of magnitude than in the pulse sequence of case (b) and dips are more difficult to detect. 

V. S. Letokhov My answer to Prof. Quack is that it is indeed difficult to predict theoretically the effect of intense femtosecond IR pulses on the IVR rate of polyatomic molecules, which is important for the transfer of vibrationally excited molecules from low-lying states to the vibrational quasi-continuum. We are developing the relevant theoretical mechanisms of IR MP E/D of polyatomics since the discovery of this effect for isotopic molecules BC13 and SF6 in 1974-1975.1 hope that it will become more realistic to study experimentally the influence of intense IR pulses on IVR due to the great progress of femtosecond laser technology. 

Table 3 summarizes our results obtained with Eosin lactone using different exposures and incident laser intensities. These results indicate that the rate of growth of the spike increases linearly with the incident intensity. The data show that the polymerization depth depends on the total incident energy and not on the rate at which the energy is delivered. The system is said to obey reciprocity since irradiation with a high intensity for a short period of time produces the same effect as irradiation with a low intensity for a long time, provided the total energy delivered is the same in both cases. 

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