VUV Spectroscopy of Atoms, Molecules and Surfaces

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14 VUV light generation: possibilities and limitations rower than stated in table 1.1. In the low-energy part of the 40 eV region it is likely that the bandwidth may be decreased significantly below the stated value of 5×10−3 by increasing the pulse duration from the femtosecond to the picosecond regime as is currently being investigated [86]. As stated in section 1.3, it is at present uncertain how long the pulses can be made while still being able to reach a given harmonic order and synchrotron radiation should thus be considered the superior spectral source at present. Obviously, for high-resolution frequency measurements where the time structure of the radiation is irrelevant, the high photon flux implied by the high repetition rate of synchrotron-radiation sources can be fully exploited, making them advantageous in this respect also. Narrow-bandwidth laser radiation is commercially available only down to 157 nm, provided by a non-tunable F2 laser. Proceeding to shorter wavelengths becomes difficult because of the lack of neutral atoms and molecules with electronic transition frequencies that are large enough for the required population inversion. One has to resort to stimulated emission from excited states of multiply charged ions in laser-produced plasmas, or from the recombination of electron-ion pairs in such plasmas [87]. X-ray lasers are favourable in terms of the (Doppler-limited) bandwidth and the number of photons per shot but the lack of tunability and the very low repetition rate imposed by the power demands to the plasma-producing laser make them useless for most applications at the present stage of development. For studies of structural dynamics where a pump-probe configuration is desired, the high repetition rate of the synchrotron-radiation sources cannot be exploited and in addition, the pulse duration is limited to ∼100 ps [88] by the electronic bunch length. The bunch length is difficult to reduce further due to Coulomb scattering among the electrons, causing a momentum redistribution and subsequent time broadening and loss of confinement in the storage ring [89]. For the same reason electron diffraction experiments are limited to the picosecond regime [90, 91] with the current record being 1 ps [90]. Further compression to the femtosecond regime is, though, possible by acceleration through a very long (∼km) linac, and terminating with a ∼100 m undulator results in a mirror-less X-ray free-electron laser (X-FEL). The operation is based on the coherent amplification of spontaneously emitted synchrotron radiation which interacts with the electrons wiggling along the undulator [92, 93, 94]. Such a device, superior in all respects to other sources, is planned to become operational at DESY in Hamburg as well as at the SSRL in Stanford by ∼2010 [95]. The DESY project is divided into three parts, of which phase I—a FEL operating at 109 nm—was completed in the fall of 2000 [96]. The parameters for the VUV-FEL and X-FEL listed in table 1.2 are referring to the subsequent phases II and III.
1.4 Comparison with other methods ... 15 Table 1.1: A comparison of parameters for existing VUV light sources with the highest available freqency resolution. Bandwidth refers to the relative bandwidth. Source
Page 1: VUV Spectroscopy of Atoms, Molecule
Page 4 and 5: ii CONTENTS 4 .6 Conclusion . . . .
Page 6 and 7: iv Experimental and theoretical stu
Page 8 and 9: vi me to the principle of negative-
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Page 12 and 13: 2 VUV light generation: possibiliti
Page 20 and 21: 10 VUV light generation: possibilit
Page 28 and 29: 18 REFERENCES [14 ] C. R. Vidal, in
Page 30 and 31: 20 REFERENCES [55] C. J. G. Uiterwa
Page 32 and 33: 22 REFERENCES [98] Parameters from
Page 34 and 35: 24 Negative ions ing the binding en
Page 36 and 37: 26 Negative ions located energetica
Page 38 and 39: 28 Negative ions available has been
Page 40 and 41: 30 Negative ions assignment will th
Page 42 and 43: 32 Negative ions feel the repulsion
Page 44 and 45: 34 Negative ions Figure 2.1: Adiaba
Page 46 and 47: 36 Negative ions
Page 48 and 49: 38 REFERENCES [16] E. Kopp, Adv. Sp
Page 50 and 51: 40 REFERENCES [63] P. Balling et al
Page 52 and 53: 42 REFERENCES
Page 54 and 55: 44 High-resolution VUV spectroscopy
Page 70 and 71: 60 REFERENCES [19] J. S. Nielsen an
Page 72 and 73: 62 Lifetimes of molecular negative
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64 Lifetimes of molecular negative
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76 REFERENCES [19] V. V. Petrunin e
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78 REFERENCES [66] F. Robicheaux, P
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80 Chapter 5. Femtosecond VUV core-
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100 Chapter 5. Femtosecond VUV core
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120 REFERENCES [17] A. Cavalleri et
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122 REFERENCES [61] R. J. Finlay et
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124 REFERENCES [104]R.W.Joyner,inTh
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126 REFERENCES [152] T.-C. Chiang,
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128 Chapter 6. Two-colour pump-prob
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144 REFERENCES [16] Information ava
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146 REFERENCES [62] S. Baier et al.
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148 The following three chapters ar
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VUV Spectroscopy of Atoms, Molecules and Surfaces

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