Laser fast accelerated atom

The velocity of a fast accelerated atom is typically 1 mm/ns compared to an average thermal velocity of lO mm/s. Thus the kinematics becomes important the first-order Doppler shift can be as large as 100 A and the second-order shift several GHz. Thus resonant three-level spectroscopy, using only one laser field can be carried out by Doppler tuning the energy levels appropriate. A simplified three-level system is shown in Fig.2. The excited velocity classes determined by... 

Figure 14.4 Generation of ions by desorption methods. The sample is placed on a target and then hit either by accelerated electrons (secondary ion mass spectrometry), accelerated atoms (fast atom bombardment) or laser light (laser desorption/ ionization, matrix-assisted laser desorption/ionization). In the case of FAB and MALDl, the analyte is additionally embedded in a matrix, which also is desorbed during these processes.

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

Here the time-dependent "acceleration" is a(t) = h t)/C, Uo = Ej, m = C and 2kl = 27r/T>o. We shall assume abrupt (step-like) changes of the tilt, causing the acceleration to periodically alternate between a I h(< I). within time intervals of length n, and d (e = 0), within time intervals of length ro — T. This time dependence is realizable in a JJ by rapid (< 0.1 ns) up-down ramping of the bias current. For atomic Bose condensates trapped in optical lattices [Smerzi 1997 Anderson 1998 (a)] we can turn the coupling and tilt between adjacent wells up and down by fast (< 10 ps) modulation of the laser intensity. 

For a molecular compound, the full molecular formula can be established from the empirical formula and the molecular mass (RMM). Various physical properties, including the vapour density of a gas, and so-called colligative properties (such as freezing point depression) in solution, can be used to determine the RMM. However the most important technique in modem research is mass spectrometry (MS) where molecular ions are accelerated in an electric field, and then pass through a magnetic field where their paths are bent to an extent that depends on the mass/charge ratio. The traditional MS method requires a volatile sample, ionized by electron bombardment, but methods are now available that overcome the limitations of that method. Direct desorption from solids by a laser beam or by fast atom bombardment (FAB) allow measurement of involatile compounds. Solutions may also be sprayed directly into the spectrometer inlet and the spectrum measured after the solvent has evaporated. 

If fast atoms generated in exothermic processes react before Maxwellization, they are able to perturb translational distribution and accelerate the following reactions. A laser-chemical... 

This method, which is a modernized version of the old Wien method, uses fast atomic, molecular, or ion beams with kinetic energies in the keV to MeV range. The atoms which move into the x direction are excited at a well-defined small interval ax around x = 0. The excitation source may be a laser or collisions with other atoms in foils or gas chambers. The subsequent fluorescence Ip- (x) is measured as a function of the distance x from the point of excitation (see Fig.11.17). The transformation to a time scale Ip (t) uses the relation x = vt where the velocity v=(2e U/m) of the ions is determined by the acceleration voltage U and the mass m of the ions. Neutral atoms or molecules can be produced from ions by charge exchange. 

The development of fast ion beam laser spectroscopy techniques (for short FIBLAS) is not so unusual a case of simultaneous but independent technical evolution both in atomic and molecular physics. Although the concepts involved in both cases were quite similar, the apparatus used in the pioneering experiments were widely different, ranging from the table top mass spectrometer for the early molecular physics work to the largest tandem Van de Graaff accelerators for some of the atomic physics experiments. ... 

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