Nonresonant profiling

When reaction cross sections are suflSciently large over an extended energy range, the entire depth profile may be obtained using a single incident beam energy. This is referred to as nonresonant profiling. 

In nonresonant profiling, the silicon surface barrier detectors that detect the products of the nuclear reaction may also detect signals from incident ions that have been backscattered from the sample. Figure 4 shows an a particle spectrum from the reaction (p, a) along with the signal produced by backscattered... 

Figure 4 Spectrum of diffusion in the mineral olivine ((Mg, Fe)2 SiO ) taken using nonresonant profiling technique with the reaction (p, a) Both the a particles resulting from the nuclear reaction and backscattered protons are collected. Inset shows expanded region of the spectrum, where a yield indicates diffusion of into the material.

This article discusses why one would choose nonresonant multiphoton ionization for mass spectrometry of solid surfaces. Examples are given for depth profiling by this method along with thermal desorption studies. 

FIGURE 9.12 (a) Calculated FE-CARS radiation profile when a HGOl excitation field overlaps with a lateral interface between a resonant and a nonresonant material. Note that the intensity along the optical axis is no longer zero due to partial lifting of the phase step by the interface. The inset shows the excitation field relative to the orientation of the interface, (b) Comparison of the calculated spectral dependence of CARS in a bulk material with a weak resonance and FE-CARS measured at an interface similar to the one considered in (a). Note the Raman-like spectral dependence of the FE-CARS signal. 

Fig. 6.11. Temporally and spatially resolved CARS signal from a l- lm polystyrene sphere embedded in water at a Raman shift centered at 3054 cm 1 where aromatic C-H stretching vibrations reside. A Measured and simulated decay curves when focused on the bead and into bulk water. B RFID images and the lateral intensity profiles along the lines indicated by the arrows at time 0 and r 370 fs, demonstrating the complete removal of nonresonant background contributions from both the object and the solvent to the image contrast at r w 370fs (Adapted from [64])...

Spectroscopic observables can be categorized in several ways. We can follow a temporal profile or a frequency resolved spectrum we may distinguish between observables that reflect linear or nonlinear response to the probe beam we can study different energy domains and different timescales and we can look at resonant and nonresonant response. This chapter discusses some concepts, issues, and methodologies that pertain to the effect of a condensed phase environment on these observables. For an in-depth look at these issues the reader may consult many texts that focus on particular spectroscopies. ... 

In contrast to nonresonant two-photon excitation, the cross-section for resonant two-photon excitations is relative large if the atoms are excited via a strong resonance transition. To achieve resonant two-photon excitation, however, two tunable lasers are necessary with sufficiently narrow spectral bandwidths. The laser beams intersect the absorbing volume in CO- or counter-propagating direction. If the first laser is tuned to the Doppler profile of the lower transition, atoms are excited with a well-defined velocity component in beam direction, whereas the second laser probes the population density of the excited atoms within this velocity group (Figure 4). The basic arrangement for isotope-selective analysis makes use of two absorption volumes, which are intersected by... 

Minor actinides present in some nuclear waste produce large quantities of helium when they decay. When considering materials for storage of this waste, it is necessary to have some knowledge of helium diffusion in the material matrix. Helium diffusion into possible materials has been simulated by exposing them to a He ion beam (i.e., implantation). The implanted helium has then been profiled using the He(D,p)" He nonresonant nuclear reaction enabling diffusion coefficients to be determined. 

There are a few potential future developments. The possibility of combining the position scanned He microbeam NRA technique and the D-( He,p)" He nonresonant nuclear reaction technique to produce three-dimensional profiles has been discussed in the literature. 

The temporal evolution of the OKE signals in solutions and films of the linear conjugated polynitriles with different m values was observed. As an example, the time-resolved transient optical Kerr signals of PBN with m = 11.8 are presented (Fig. 24). The signal profiles of all samples are approximately symmetric with respect to the delay time, which indicates a primarily pulse width-limited response. To obtain the relaxation time of the Kerr medium we can fit the experimental curve with an exponential function [45,57]. Because the time constants of all samples are all less than the pulse duration, we can only roughly determine that the relaxation time of all samples is shorter than the laser pulse width (165 fs). The ultrafast optical response may be caused by distortion of the ir-electron cloud occurring with the nonresonant excitation [58]. 

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