Because of their importance in the compressions1 of linearly chirped optical pulses, frequency-dependent Optical delay lines have been the subject of considerable recent interest. In this paper, we discuss use of the photon echo process as a dispersive delay mechanism.
It is predicted that linearly chirped optical excitation pulses give rise to photon echoes whose shortness is limited only by the total material bandwidth that contributes to the echo signal. The photon echo process acts as a frequency-dependent optical delay line whose dispersion is determined by the chirp rate of the excitation pulses rather than by their bandwidth. Consequently, long and short pulses can be compressed with equal facility without complicated alignment procedure. Accumulated echoes have similar properties and can be used with trains of weak excitation pulses.
In this thesis, aspects of the use of cryogenically cooled rare-earth-ion-doped crystals in the fields of quantum optics and quantum information processing are addressed. The experiments and theoretical considerations referred to in this thesis are based on the coherent transient interaction between light and the ions in the crystals. A photon echo experiment has been performed where faint optical pulses were accumulated in the crystal. In this experiment, the possibility of single photons acting as two of the optical fields in the photon echo process was investigated. Different aspects on the experiment, which can be viewed as delayed self-interference of a single photon, are discussed in this thesis. A scheme for the possible implementation of quantum information processing in rare-earth-ion-doped crystals is presented. A key feature in this scheme is that small groups of ions, which can be optically manipulated and which interact in a controlled way, can be extracted from a collection of randomly positioned ions in the crystal host. Initial experimental investigations of the scheme, indicating the possibility of implementing quantum gates, are also presented in this thesis. In another experiment, the application of magnetic fields of up to 5 T was seen to increase the lifetime of information stored as frequency-dependent modulation of the population of thulium ions doped into a YAG crystal by several orders of magnitude. This mechanism might be useful in data storage and information processing applications. An experiment in which the same type of crystal was used as the active medium in a photon-echo-based pulse compression experiment, where microsecond long pulses were compressed to nanosecond duration using frequency-chirped light pulses, is also reported in this thesis.
Slow and fast light (SFL) in nonlinear media has attracted considerable interest for several years and has been observed in plenty of configurations. It generally requires a sharp spectral resonance which in turn results in a strong change of the group velocity at the resonance, thus leading to optical delaying or advancement. SFL has also been observed in optical fibres by taking advantage of the parametric gain, stimulated Brillouin or Raman scattering, leading to the development of all-optical tunable fiber-based delay lines at telecommunication wavelengths. But the implications of SFL go well beyond pulse delaying or advancement. As the group and phase velocities have to be distinguished one from another in a slow-light medium, this can have other important implications, in particular on the pulse walk-off or on the frequency chirp. We recently demonstrated in a Raman medium with normal dispersion that pulse walk-off between the pump and the signal can be cancelled out despite the large frequency detuning, leading to an increasing interaction length and enhancement Raman conversion efficiency.