Laser pulse duration effect

A serious problem in LA-ICP-MS described in the literature on many occasions is the time-dependent elemental fraction (so-called ablation fractionation ) occurring during laser ablation and the transport process of ablated material, or during atomization and ionization processes in the inductively coupled plasma.20-22 Numerous papers focus on the study of fraction effects in LA-ICP-MS as a function of experimental parameters applied during laser ablation (such as laser energy, laser power density, laser pulse duration, wave length of laser beam, ablation spot size,... 

Unlike a few hundreds of femtosecond laser pulses, when the laser pulse duration is a few tens of femtoseconds, the damage threshold fluence does not decrease rather than 1 J/cm or less. This limit seems to be persisted even with decreasing pulse width. However, the damage threshold may increase as the laser pulse decreases when the MPI effect is negligible. 

Fourth remark There is an independent method of determining the drift velocity. The cuts can be sufficiently close that carriers made during the 10 ns laser pulse transit between the cuts in the duration of the pulse. The current detector is not fast enough to resolve these time effects however they also reduce the current magnitude and can be so detected. The reduction of current is by a factor d/vT, where T is the laser pulse duration for this is the fraction of otherwise free carriers that have not hit the walls. Thus... 

The photochemical decomposition process occurs exclusively at UV wavelengths with excimer lasers, such as XeCl (308 nm), KrF (248 nm), and ArF (193 nm). The laser pulse duration has much less effect on ablation. Long pulses of laser irradiation of the order of microseconds can still cause polymer ablation. However, there is a threshold fluence (mJ/cm ) above which the ablation oeexus. The threshold fluence is different for different polymers, for different photon wavelengths, and for different pulse durations [5]. 

The laser pulse parameters used in our ARPA simulations are optimized [17] for a 100 p,K thermal ensemble of Rb atoms. The pump and dump overlap time is chosen to match the average coherence time of a colliding atom pair at 100 p,K, and the spectral widths of the pulses are chosen as the energy spread of the thermal ensemble. The laser pulse durations define their intensities because the area under the pulse envelope must be sufficiently large to ensure adiabaticity and efficient population transfer. (Note, the pulse intensities in this work are higher than those in Ref. [17], our main interest being the study of interference effects rather than searching for the lowest acceptable values of laser power.)... 

To realize effective multistep excitation of an atom by multiple-frequency radiation to the final bound state, the laser pulse duration must be shorter than the population relaxation times of the intermediate quantum states. In addition the laser pulse fiuence (photons/cm ) at the transition frequency ijJkn must ensure absorption... 

From Equation (8.61) we can see that 0(Xp) is appreciable only if is appreciable. In other words, if the laser pulse duration is short (e.g., nanosecond), it has to be very intense in order to induce an appreciable reorientation effect. In this respect and because the surface elastic torque is not involved, the dynamical response of a nematic liquid crystal is quite similar to its isotropic phase counterpart. However, the dependence on the geometric factor sin 2p is a reminder that the nematic phase is, nevertheless, an (ordered) aligned phase, and its overall response is dependent on the direction of incidence and the polarization of the laser. 

Besides these material parameters, perhaps the single most important factor governing the magnitude of the effective optical nonlinearities is the laser pulse duration relative to the material response time. If the laser pulse is too short, the material response time will be minimal, and the corresponding nonhnearity as seen by the laser will be small. This could be cast in more quantitative terms as follows. 

The final form for Acl) (f), as well as the output intensity distribution on the observation plane P, depends on the form of and the response time tf versus the laser pulse duration tp. If the response time tf is longer than tp, the self-limiting effect is... 

Typical mass resolution values measured on the LIMA 2A range from 250 to 750 at a mass-to-charge ratio M/ Z= 100. The parameter that appears to have the most influence on the measured mass resolving power is the duration of the ionization event, which may be longer than the duration of the laser pulse (5—10 ns), along with probable time broadening effects associated with the l6-ns time resolution of the transient recorder. ... 

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