Photonics laser addressable

In this chapter we review some of the most important developments in recent years in connection with the use of optical teclmiques for the characterization of surfaces. We start with an overview of the different approaches available to tire use of IR spectroscopy. Next, we briefly introduce some new optical characterization methods that rely on the use of lasers, including nonlinear spectroscopies. The following section addresses the use of x-rays for diffraction studies aimed at structural detenninations. Lastly, passing reference is made to other optical teclmiques such as ellipsometry and NMR, and to spectroscopies that only partly depend on photons. 

Abstract. We address the question of the importance of relativity in selected non-linear radiative processes to be observed when an atomic system is submitted to an intense radiation field. To this end, we report on recent results obtained in the theoretical analysis of the following processes i) two-photon transitions in high-Z hydrogenic systems, ii) laser-assisted Mott scattering of fast electrons, and iii) two-colour photoionisation spectra of atoms in the simultaneous presence of two ultra-intense laser fields. In each case, the signature of relativistic effects is evidenced. 

The first volume contained nine state-of-the-art chapters on fundamental aspects, on formalism, and on a variety of applications. The various discussions employ both stationary and time-dependent frameworks, with Hermitian and non-Hermitian Hamiltonian constructions. A variety of formal and computational results address themes from quantum and statistical mechanics to the detailed analysis of time evolution of material or photon wave packets, from the difficult problem of combining advanced many-electron methods with properties of field-free and field-induced resonances to the dynamics of molecular processes and coherence effects in strong electromagnetic fields and strong laser pulses, from portrayals of novel phase space approaches of quantum reactive scattering to aspects of recent developments related to quantum information processing. 

Therefore, heterogeneous catalysts present a greater potential for the application of HT and Combinatorial methods, because they involve diverse compositional phases that are usually formed by interfacial reactions during their synthesis, which in turn produce a variety of structural and textural properties, often too vast to prepare and test by traditional methods. In this respect the HT and Combinatorial methods extend the capabilities of the R D cycle, which comprises the synthesis, the characterization of physicochemical properties and the evaluation of catalytic properties. The primary screening HT method gives the possibility of performing a rapid test of hundreds or thousands of compounds using infrared detection methods [27-29]. Alternatively, a detection method called REMPI (Resonance Enhanced Multi Photon Ionization) has been used, which consists of the in situ ionization of reaction products by UV lasers, followed by the detection of the photoions or electrons by spatially addressable microelectrodes placed in the vicinity of the laser beam [30, 31]. 

We now address the question how much atomic physics needs to be included in order to account for ATI In fig. 9.6, we show experimental data for ATI from [493], obtained at several laser intensities. One of the important properties of ATI peaks, referred to as peak suppression, is that the relative intensity of the first ATI peaks above threshold does not increase uniformly with laser field strength, but actually begins to decrease in intensity relative to higher energy peaks as the laser field strength increases. Such behaviour cannot be explained in a perturbative scheme, in which interactions must decrease monotonically order by order as the number of photons involved increases, but can be accounted for in terms of the AC Stark shift of the ionisation potential in the presence of the laser field. In ATI experiments, the ionisation potential appears to shift by an average amount nearly equal to the ponderomotive potential, so that prominent, discrete ATI peaks are seen despite the many different intensities present during the laser pulse. However, ATI peaks closest to the ionisation limit become suppressed as the amplitude of the laser field oscillations increases and the ionisation threshold sweeps past them (a different effect which also suppresses ionisation near threshold is discussed in section 9.24.1). 

Laser ionization of atomic or molecular neutrals in the gas phase offers an unsurpassed potential with respect to analytical specificity and sensitivity. Unlike other ionization methods, photon absorption imparts to the analyte a well-defined amount of energy. Addressing the transitions between specific energy levels allows one species in a complex environment to be analyzed with isotopic selectivity. Because lasers deliver sufficiently high fluxes to saturate the population of an excited state, virtually each neutral in the irradiated volume is ionized. Hence, the ionization efficiency, 1, exceeds that of current methods by a factor of 10 -10". ... 

As was already suggested in the introduction, once the mechanism as well as the experimental parameters of laser induced multiple photon ionization have been investigated these ions may be used in spectroscopic and ion-molecule interaction studies. For two cases such an application has now been demonstrated in this laboratory by Proch, Trickl and Sha /II,12/. For practical experimental reasons the two diatomic molecules N and CO were chosen to address questions of cold- eam formation and E to E energy transfer. Nitrogen molecular ions N X were made in selected vibrational states by going through the folfowii sequence of excitation steps. 

Note that stimulated emission, ultimately responsible for laser amplification, does indeed take place in the two-level photon-matter interaction addressed here however, stimulated emission is less important than the other processes, under such conditions. 

To conclude this section we address the phenomenon of the stimulated Raman effect and its application to molecular spectroscopy. Stimulated Raman scattering is experimentally different from normal Raman scattering, in that it is observed in the forward direction (the stimulated Raman photon emerges into a very narrow cone to the propagation direction of the laser beam propagation direction). But the effect is normally only observed for high-power laser radiation. 

Given the fact that rotational levels are spaced in the GHz range and thus only low-frequency photons are required, this scheme is suitable for both the superconducting wire architectures and the optical lattice (in this case, at least one higher-frequency addressing laser might be necessary) for a dipole moment ji = 10 D, r = 10 [im, and /i = 0.1 p,m, the necessary interaction time is of the order of 3 t.sec. With a coherence time of the order of 100 msec to 1 sec, this setup would thus allow for 10 -10 operations. 

The high time resolution that is achievable with pulsed or mode-locked lasers (Chap. 11) opens the possibility for studying the dynamics of collision processes and relaxation phenomena. The interesting questions of how and how fast the excitation energy that is selectively pumped into a polyatomic molecule by absorption of laser photons, is redistributed among the various degrees of freedom by intermolecular or intramolecular energy transfer can be addressed by femtosecond laser spectroscopy. 

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