Single pulse compression and multi-bit pulse compression using the photon echo process was investigated.A single pulse could be compressed by a factor of 454 from 10 microseconds to 22 nanoseconds.A 1 O-bits pulse train was compressed by a factor of 92 from 20 microseconds in total length to 212 nanoseconds.The compression factors obtained during this work were an order of magnitude better than those published previously both for single pulse and multi-bit pulse train compression.Observation of the side-band under the envelope of the photon echo signal in multi-bit pulse compression indicates that the bit information is retained in the compression.Some improvements were achieved by optimising the experimental setup during the work.The experimental results were discussed theoretically and were good in agreement with theoretical calculations.The space-time duality of photon echo compression was also analysed in this thesis.The storage material used in the experiment is a Y AG crystal doped with the trivalent rare earth thulium ion with a concentration at 0.1-at.%.The crystal was kept at 4K during the experiment.The absorption, an important characteristic of the crystal was initially measured.The maximum absorption was about 40%, in the range between 7931.50A and 7931.60A with a full width ofhalfmaximum of3.5 A, which corresponds to 19 GHz.A homemade external cavity diode laser equipped with an intra-high coherency and ultrahigh-speed frequency chirping properties was used in the experiments.This system with an intra-cavity electro-optic crystal (EOC) was employed for the optical data compression because of its advantages of simplicity, high quantum efficiency, low cost, and compact size, which is necessary for practical applications in the future.Some critical properties for this laser were investigated.The laser line-width was measured to be 350 KHz over a 200 microseconds duration using the spectral hole burning method and a voltage-chirping rate of about 7 MHz/V was determined by calculations and experimental measurements.
Single pulse compression and multi-bit pulse compression using the photon echo process was investigated.A single pulse could be compressed by a factor of 454 from 10 microseconds to 22 nanoseconds.A 1 O-bits pulse train was compressed by a factor of 92 from 20 microseconds in total length to 212 nanoseconds.The compression factors obtained during this work were an order of magnitude better than those published previously both for single pulse and multi-bit pulse train compression.Observation of the side-band under the envelope of the photon echo signal in multi-bit pulse compression indicates that the bit information is retained in the compression.Some improvements were achieved by optimising the experimental setup during the work.The experimental results were discussed theoretically and were good in agreement with theoretical calculations.The space-time duality of photon echo compression was also analysed in this thesis.The storage material used in the experiment is a Y AG crystal doped with the trivalent rare earth thulium ion with a concentration at 0.1-at.%.The crystal was kept at 4K during the experiment.The absorption, an important characteristic of the crystal was initially measured.The maximum absorption was about 40%, in the range between 7931.50A and 7931.60A with a full width ofhalfmaximum of3.5 A, which corresponds to 19 GHz.A homemade external cavity diode laser equipped with an intra-high coherency and ultrahigh-speed frequency chirping properties was used in the experiments.This system with an intra-cavity electro-optic crystal (EOC) was employed for the optical data compression because of its advantages of simplicity, high quantum efficiency, low cost, and compact size, which is necessary for practical applications in the future.Some critical properties for this laser were investigated.The laser line-width was measured to be 350 KHz over a 200 microseconds duration using the spectral hole burning method and a voltage-chirping rate of about 7 MHz/V was determined by calculations and experimental measurements.
Temporal compressions of optical pulses and pulse trains have been performed by the photon-echo process in Tm-doped YAG at 793 nm. Single-pulse temporal compression by almost a factor of 500 from 10 micros to 22 ns and pulse train compression by a factor of 14 from 5micros to 350 ns with a high-speed frequency-tunable external-cavity diode laser are demonstrated. It is suspected that significantly higher compression could be obtained by improved control of the laser frequency and laser frequency chirps. Theoretically, Tm-doped YAG should be capable of compressing single pulses by almost a factor of 10(7).
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.
The diffraction-limited spot size of a focused laser beam puts an upper boundary on the storage densities in conventional optical data storage. This can be overcome by storing multiple bits of data in each spatial location. In materials with an inhomogeneously broadened absorption line, such as crystals doped with rare-earth ions, frequency can be used as an additional addressing dimension. In some materials the number of spectral channels can be as high as 107. Spectral data storage can be done using coherent transient interactions between light and atoms and can be described in terms of photon echo processes. In this Master's Project the swept-carrier time-domain (SCTD) approach, a hybrid between frequency- and time-domain approaches, is used. An overview of the theory is given, followed by a description ofthe set-up and equipment. A maximum of 330 bits of data have been stored in one spatial location. The necessary conditions for successful storage and retrieval of data have been examined and suggestions are given on how to extend the results further.
This thesis describes experiments aimed at developing a key component in applications such as quantum networks and long-distance quantum communication systems: quantum memories. Quantum memories for light using photon-echo and coherent rephrasing techniques have been developed. The work is carried out on rare-earth-ion-doped inorganic crystals. Several properties are associated with these crystals such as long coherence times and long-lived ground state sublevels that are particularly interesting in connection applications in the area of quantum information science. It is demonstrated the preparation of optical inhomogeneous absorption profiles such that the light only interacts with a specific transition at a selected frequency. Narrow absorbing structures with widths of <100 kHz have been prepared with no absorption in the surrounding spectral interval. Most of the experiments were carried out using Pr3+:Y2SiO5. However, in our search for suitable a Λ-system in the material under consideration, we also performed spectral hole-burning spectroscopy in Nd:Y2SiVO4. As part of the search for host materials for Pr, Pr:La2(WO4)3 crystal was characterized using a variety of methods, such as, hole burning and photon-echoes. Electromagnetically induced transparency was also observed in this crystal. The most important criteria for evaluating quantum memory performance and the most important physical requirements are discussed. After investigating the standard photon echo techniques and controlled reversible inhomogeneous broadening (CRIB) for quantum state storage, we considered an efficient multimode quantum memory protocol; the atomic frequency comb (AFC) protocol. Combs with peaks of widths 100-300 kHz and an optical depth of~ 10 were created by optical pumping inside an emptied region of the inhomogeneous profile of Pr3+:Y2SiO5, allowing us to improve the efficiency of light storage. Light storage combining a photon-echo technique based on an AFC and spin-wave storage have been demonstrated, and an experimental AFC scheme for the storage of weak coherent light pulses in Pr3+:Y2SiO5 is presented. Finally, we have investigated superradiance and slow light effects. Both these effects occur in the high optical depth regime and can influence the memory performance. Under certain conditions superradiance results in the immediate re-emission of the stored light in a single burst of coherent radiation, and inside spectrally structured materials, slow light effects may result when storage is performed.
Spectral hole burning and photon echoes are the techniques for frequency-selective optical memories, which have the potential to increase areal data storage density by a factor 10**7. They also have the capability to perform in-memory data processing. In this thesis, several materials and techniques for optical memories in the frequency- and time domain have been investigated. In the frequency domain, ways to increase the storage density and the working temperature were studied using photon-gated spectral hole burning materials of the metal-tetrabenzoporphyrin derivatives. A selection rule for the electron acceptors in the donor-acceptor electron transfer systems was deduced. By doping the material with two different donors a maximum inhomogeneous line width of more than 30 THz was achieved. A polarization holographic technique was established for the formation and detection of spectral holes. Our results indicate that this technique can provide a better signal-to-noise ratio than that achieved by a conventional holographic technique, in particular for samples of poor optical quality. In the time domain, magnetic field-induced and the intensity-induced dephasing processes were studied in Pr3+ doped in a YAlO3 crystal and a Y2SiO5 crystal, respectively. As a step along the route to make photon echo based optical processing possible, the amplification of photon echo signals by the use of a fiber amplifier (Pr3+-doped ZBLAN) was demonstrated. A gain of 45 was achieved. The erasure of stored data using photon echoes has also been investigated. A technique to diagnose the phase and frequency stability of a light source by the photon echo erasure process was proposed and illustrated. An approach to bit-selective data erasure, that is free from laser phase and frequency fluctuations, is also suggested. A concept for an arbitrary shape pulse generator based on photon echoes and hole-burning was experimentally and theoretically studied. Finally, a comparison between the properties and capabilities of spectral hole burning and photon echoes was made.
In recent years possible applications of the photon echo process in optical processing, data storage systems, bit-rate conversion of optical pulses, time compression of optical pulses etc. have been investigated.Much of this research aim at replacing electrical components in the framework of today's information networks with components that are entirely based on optics.It is likely that we in the future will see more and more of the electrical components linked to a fibre network being replaced by all optical components, e.g.routers and bit-rate converters.The concept of temporal compression of optical pulses, which is the subject of this thesis, could be used to increase the transmission rate through optical fibres and thereby use the full capacity of today's fibres.It should also be mentioned that more basic components, e.g.XOR gates, are studied in this research field and these components could possibly be used in future concepts of a "light-computer".In this thesis a theoretical model of time compression of both single optical pulses and optical pulse sequences using photon echoes is presented.A full analytical treatment was done for gaussian shaped pulses as a first step of building a numerical model.An analytic approximate approach was also used for both square pulses and pulse sequences.A theoretical understanding of the duration, the intensity spectrum and peak intensity of the compressed signals was reached.It is shown that the intensity spectrum of a compressed pulse sequence containing N bits is completely analogous to the pattern observed in the well-known Fraunhofer diffraction experiment with N slits.A numerical model was built and used to evaluate how non-linearities and noise affect the degree of compression.In addition theoretical models were developed to explain the effects of non-linearities and noise and the hope is that these might be used as guidelines on how to design future experiments in order to achieve highest possible degree of compression.Some of the results presented in this thesis is compared with experimental data obtained in the research group during the time this work was going on.