Laser pulse duration

The quantities in this fomuila are defined as in equation Bl.5,32. but with the laser parameters translated into more convenient tenns is the average power at the indicated frequency is the laser pulse duration ... 

The transversely excited atmospheric-pressure (TEA) laser, inherently a pulsed device rather than a continuous laser, is another common variety of carbon dioxide laser (33,34). Carbon dioxide—TEA lasers are an important class of high-power pulsed lasers. Pulse durations are in the submicrosecond regime peak powers exceed 10 MW. 

This sequence of events is quite rapid. If we take typical instrumental conditions of the LIMA 2A, where the UV laser pulse duration is 5-10 ns, the fight path is "2 m, and the accelerating potential is 3 kV, then an ion arrives at the detector i n approximately 3 ps, and a ion arrives at the detector in approximately 40 ps. Since the time width of an individual signal can be as short as several tens of nanoseconds, a high speed detection and digitizing system must be employed. 

Excitation conditions and threshold vulues for lasing in different conjugated polymers. Different resonator structures are used to achieve real lasing. Note that it is in some cases difficult to compare the values due to the different laser pulse duration used in the experiments. indicates the wavelength for excitation, r(,u< is the pulse duration of the exciting laser pulse atu A the urea of the spot on the sample. 

In our tip-enhanced near-field CARS microscopy, two mode-locked pulsed lasers (pulse duration 5ps, spectral width 4cm ) were used for excitation of CARS polarization [21]. The sample was a DNA network nanostructure of poly(dA-dT)-poly(dA-dT) [24]. The frequency difference of the two excitation lasers (cOi — CO2) was set at 1337 cm, corresponding to the ring stretching mode of diazole. After the on-resonant imaging, CO2 was changed such that the frequency difference corresponded to none of the Raman-active vibration of the sample ( off-resonant ). The CARS images at the on- and off- resonant frequencies are illustrated in Figure 2.8a and b, respectively. 

From the discussion presented in previous sections, vibrational relaxation (Appendix II) plays a very important role in the initial ET in photosynthetic RCs. This problem was first studied by Martin and co-workers [4] using Rb. capsulatas Dll. In this mutant, the ultrafast initial ET is suppressed and the ultrafast process taking place in the ps range is mainly due to vibrational relaxation. They have used the pumping laser at Xpump = 870 nm and probed at A.probe = 812 nm at 10 K. The laser pulse duration in this case is 80 fs. Their experimental results are shown in Fig. 16, where one can observe that the fs time-resolved spectra exhibit an oscillatory build-up. To analyze these results, we use the relation... 

Note The fluence is defined as energy per unit area in MALDI typical flu-ences are in the range of 10-100 mJ cnT. The irradiance is fluence divided by the laser pulse duration in MALDI the irradiances are in the range of 10 -... 

Menzel, C. Dreisewerd, K. Berkenkamp, S. Hillenkamp, F. The Role of the Laser Pulse Duration in Infrared MALDI-MS. J. 

Figure 10.10 shows the experimental system of TE-CARS microscopy (Ichimura et al. 2004a). As similar to the TERS system (Hayazawa et al. 2000), the system mainly consists of an excitation laser, an inverted microscope, an AFM using a silver-coated probe, and a monochromator. Two mode-locked Ti sapphire lasers (pulse duration 5 picoseconds [ps] spectral band width 4 cm- repetition rate 80 MHz) are used for the excitation of CARS. The (o and (O2 beams are collinearly combined in time and space, and introduced into the microscope with an oil-immersion objective lens (NA = 1.4) focused onto the sample surface. As the z-polarized component of the... 

Fig. 11. Calculated energy transmission Tj versus peak laser intensity Jo for several values of the laser pulse durations At, and the dye parameters Tq = 0,173, a = 1,84 -10-16cm2, and Tf = 9.1 psec. (From Ref. 44>)...

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,... 

An important parameter in order to avoid elemental fractionation in laser ablation ICP-MS is the laser power density ( ) which is a function of laser energy, of laser pulse duration and focusing conditions, as described in the following equation ... 

The character of reflection of electrons from the evanescent wave strongly depends on the relationship between the duration r of the laser pulse and the time of flight of an electron through the laser wave, rtr. It may be shown that when the laser pulse duration is much longer than the characteristic transit time rtr, the character of reflection of the electrons is close to the mirror. Where the relationship between these times is reversed, the mirrorlike character of reflection is disturbed. Let us make some simple estimates of the laser field and electron beam parameters with which the reflection of electrons is possible. 

At a laser pulse duration r = 10 12 s (all the other parameters remaining the same) the corresponding velocity iw = 6x 107 cm/s that is, as one would expect, it is lower than in the case r rtr. 

Figure 2. Threshold energy fluence for the appearance of the tripeptide mass spectrum with distinct chromophore R+ photoion as a function of the UV laser pulse duration (from Ref. 8).

Deconvolution. When the luminescence lifetime is close to the laser pulse duration, the kinetics can still be obtained by a process known as deconvolution, so long as the luminescence decay is exponential. The deconvolution program is a computer simulation of the shape of the laser pulse modified for various luminescence lifetimes. An example is given in Figure 7.33. The kinetics of fluorescence decay could not be resolved directly, but it is clear that the emission pulse shape differs from the laser pulse shape... 

To help completely understand the ultrafast interface ET between dye molecules and semiconductor nanoparticles, it is desirable to experimentally measure the femtosecond time-resolved spectra (i.e., probing signal in the pump-probe experiment) at various pumping wavelengths. Changing laser pulse-durations will also be useful. 

---