Using electron beam lithography fine Au<SUB>60</SUB>Pd<SUB>40</SUB> wire samples have been made, which were then used to investigate size effects in disordered systems. The wires made had widths from 140nm to 36nm, and lengths from 125nm to 100μm. The thickness was varied from 10nm to 50nm. Using gas etching techniques it was possible to make these wires free-standing with lengths of over 100μm and thicknesses of 10nm. At first some of the important electrical and mechanical properties of the free-standing wires were investigated. The tensile strength was found to be much larger than that found in bulk gold, and a simple model was developed to predict at what voltage the wires would melt. At low temperatures localisation and interaction contributions to the resistance were seen both in wires on a substrate and when free-standing. Electric field heating of the wires on a substrate was used to find the electron-phonon scattering time, which was seen to be proportional to T<SUP>-2</SUP>. The resistance rise for the free-standing wires was less than for the same wires on a substrate. Magnetoresistance measurements revealed this to be due to an increased negative localisation term in the presence of strong spin orbit scattering. The inelastic lengths were consistent with strong magnetic scattering which was reduced on being made free-standing. Electric field heating of the free-standing wires revealed that the thermal conduction of the wire is dominated by the electron contribution. At 1K the phonons in the wires should be one dimensional, but no contribution to the heat conduction was observed from these phonons. Below 800mK conductance fluctuations were observed in the magnetoresistance of the short samples. Below 125 K the amplitude of the fluctuations saturated which is consistent with both the interaction and the inelastic lengths being longer than the wire.

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The free-electron laser (FEL) is a device for converting kinetic energy in a relativistic electron beam directly into laser light. A classical theory of the FEL is discussed. This theory uses the Boltzmann distribution to describe the electrons and Maxwell equation to describe the evolution of the laser field. The harmonic expansion of the Boltzmann equation leads to a set of "quasi-Bloch" equations describing the electron distribution. The behavior of the momentum distribution is discussed theoretically in the small-signal regime of the FEL. The distribution function changes in nontrivial ways. The electron distribution does not only experience a recoil, but is also subject to spread through the amplification process. The recoil plays a relatively minor role compared to the spread. This behavior of the electron distribution may play an important role in the efficiency of the FEL. Free-electron lasers, except for those using helical wigglers, are predicted in most cases to generate higher harmonics, of the fundamental optical frequency, in the forward direction. The basic equations describing this process are derived by using the multiple-scaling perturbation theory, which leads to the slowly-varying Maxwell and Boltzmann equations. Harmonic generation in the FEL offers a possible means to extend the wavelength range of the device towards high frequency. Numerical calculations are shown for CW operation using a linearly polarized wiggler. Higher harmonic emission becomes enhanced as the magnetic field is increased and as the energy spread in the electron beam is reduced. Coherent pulse propagation in the picosecond pulse regime of the FEL is treated. Coherent transient effects such as laser lethargy are discussed. The effect of laser lethargy is seen to play an important role in the pulsed FEL, as it does in conventional swept-gain amplifiers based on an atomic medium. Numerical calculations of the harmonics in the pulsed FEL are presented. The optical pulses show a ringing behavior which is sensitive to the reflectivity of the cavity mirrors and to the electron current.

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