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A presente dissertação estuda a dinâmica uni e tridimensional de uma part cula solitária eletricamente carregada sob a ação de uma onda eletrostática de alta frequência lentamente modulada. A onda dota a partícula de energia potencial elétrica e o seu movimento e conhecido através do emprego do formalismo hamiltoniano, onde se faz a consideração de efeitos relativísticos devido as altas velocidades envolvidas no processo. Enquanto a velocidade máxima experimentada pela partícula permanece suficientemente abaixo da velocidade de fase característica da onda que a acelera, sua dinâmica pode ser bem descrita por uma re nada aproximação ponderomotriz. Com esta abordagem, prevê-se corretamente a velocidade média, máxima e m nima desenvolvida pela partícula ao longo de seu movimento através das curvas que permeiam e envelopam o per l de velocidade. Os limites de validade da aproximação são bem estabelecidos e, uma vez ultrapassados, a partícula com velocidade ressonante e capturada pela onda. Sob as adequadas condições calculadas neste trabalho, o mecanismo de captura instala, espontaneamente, a partícula em fase otima relativa a onda e a acelera a velocidades muito próximas da velocidade da luz no vácuo. Em consonância, o processo de aceleração e otimizado com a focagem da partícula em direção ao eixo de propagação da onda durante um certo intervalo de tempo e de comprimento aproveitáveis. / The present dissertation studies the one and three-dimensional dynamics of an electrically charged solitary particle under the action of a slowly modulated high frequency electrostatic carrier wave. The wave gives the particle electrical potential energy and its movement is known through the use of Hamiltonian formalism, where relativistic e ects are considered due to the high velocities involved in the process. Meanwhile the maximum speed experienced by the particle remains su ciently below the characteristic phase velocity of the accelerating carrier wave, its dynamics can be well described by a re ned ponderomotive approach. With this approach, the average, maximum and minimum speed developed by the particle along its movement through the curves that permeate and envelop the velocity pro le. The limits of validity of the approximation are well established and, once exceeded, the particle with resonant velocity is captured by the wave. Under the appropriate conditions calculated in this work, the capture mechanism spontaneously installs the optimum phase particle relative to the wave and accelerates towards the speed of light in the vacuum. At same time, the acceleration process is optimized by focusing the particle towards the wave propagation axis for a certain usable time interval and length.

In this thesis the nonlinear effects and heating are studied in inductively coupled plasma (ICP) in a regime of anomalous skin effect (nonlocal regime). In this regime the thermal motion of plasma electrons plays an important role, significantly influencing the processes associated with the penetration of electromagnetic field into plasma, such as the ponderomotive effect and heating of plasma by the field. We have developed a linear kinetic theory that describes the electron dynamics in ICP taking into account the electron thermal motion and collisions of electrons. This theory yields relatively simple expressions for the electron current in plasma, the ponderomotive force, and plasma heating. It describes correctly the thermal reduction of ponderomotive force in the nonlocal regime, which has been previously observed experimentally. It also describes the collisionless heating of plasma due to resonant interaction between the electromagnetic wave and plasma electrons. There is a good overall agreement of the results of our theory with the experimental data on ponderomotive force and plasma heating. Using our theory, we predicted a new effect of reduction of plasma heating compared to the purely collisional value, occurring at low frequencies. This effect has not been previously reported. The nonlinear effects of the electromagnetic field on the electron distribution function and on plasma heating, that are not accounted for in the linear kinetic theory, have been studied using a quasilinear kinetic theory, also developed in this thesis. Within the quasilinear approximation we have formulated the system of equations describing the slow response of plasma electrons to the fast oscillating electromagnetic field. As an example, these equations have been solved in the simplest case of cold plasma with collisions, and the nonlinear perturbation of the electron distribution function and its effect on the plasma heating have been found. It has been shown that the nonlinear modification of plasma heating occurs mainly due to the nonlinear effect of the magnetic component of the electromagnetic field. It has also been shown that at high frequencies the nonlinear effects vanish, and the heating is well described by the linear theory. To verify the predicted new effect of plasma heating reduction at low frequencies, as well as to investigate the nonlinear effect of the magnetic field on plasma heating for arbitrary amplitudes of electromagnetic field in plasma, we have developed a 1d3v Particle-In-Cell (PIC) numerical simulation code with collisions. The collisions were implemented into the PIC code using two different techniques: the direct Monte-Carlo technique for the electron-atom collisions, and the stochastic technique based on the Langevin equation for the electron-electron collisions. The series of numerical simulations by this code confirmed the results of our linear theory, particularly the effect of heating reduction at low frequencies that we predicted theoretically. Also, the nonlinear effects of electromagnetic field on plasma heating were studied using the PIC code in the cases of weak and strong electromagnetic fields. It has been shown that in the case of weak electromagnetic fields (corresponding to weak nonlinearity) the nonlinear effects lead to some enhancement of heating (compared to the linear theory) at low frequencies, followed by a small reduction of heating at higher frequencies. This observed nonlinear perturbation of heating in warm plasma with collisions is similar to that predicted by the quasilinear theory for the case of cold plasma with collisions. In the case of strong electromagnetic fields (corresponding to strong nonlinearity) the nonlinear effects lead to a further reduction of heating (compared to the linear theory) at low frequencies, as shown by the simulation, thus adding to the effect of reduction of heating predicted by the linear theory. The nonlinear effects are shown to vanish at high frequencies, as expected.

In this thesis the nonlinear effects and heating are studied in inductively coupled plasma (ICP) in a regime of anomalous skin effect (nonlocal regime). In this regime the thermal motion of plasma electrons plays an important role, significantly influencing the processes associated with the penetration of electromagnetic field into plasma, such as the ponderomotive effect and heating of plasma by the field. We have developed a linear kinetic theory that describes the electron dynamics in ICP taking into account the electron thermal motion and collisions of electrons. This theory yields relatively simple expressions for the electron current in plasma, the ponderomotive force, and plasma heating. It describes correctly the thermal reduction of ponderomotive force in the nonlocal regime, which has been previously observed experimentally. It also describes the collisionless heating of plasma due to resonant interaction between the electromagnetic wave and plasma electrons. There is a good overall agreement of the results of our theory with the experimental data on ponderomotive force and plasma heating. Using our theory, we predicted a new effect of reduction of plasma heating compared to the purely collisional value, occurring at low frequencies. This effect has not been previously reported. The nonlinear effects of the electromagnetic field on the electron distribution function and on plasma heating, that are not accounted for in the linear kinetic theory, have been studied using a quasilinear kinetic theory, also developed in this thesis. Within the quasilinear approximation we have formulated the system of equations describing the slow response of plasma electrons to the fast oscillating electromagnetic field. As an example, these equations have been solved in the simplest case of cold plasma with collisions, and the nonlinear perturbation of the electron distribution function and its effect on the plasma heating have been found. It has been shown that the nonlinear modification of plasma heating occurs mainly due to the nonlinear effect of the magnetic component of the electromagnetic field. It has also been shown that at high frequencies the nonlinear effects vanish, and the heating is well described by the linear theory. To verify the predicted new effect of plasma heating reduction at low frequencies, as well as to investigate the nonlinear effect of the magnetic field on plasma heating for arbitrary amplitudes of electromagnetic field in plasma, we have developed a 1d3v Particle-In-Cell (PIC) numerical simulation code with collisions. The collisions were implemented into the PIC code using two different techniques: the direct Monte-Carlo technique for the electron-atom collisions, and the stochastic technique based on the Langevin equation for the electron-electron collisions. The series of numerical simulations by this code confirmed the results of our linear theory, particularly the effect of heating reduction at low frequencies that we predicted theoretically. Also, the nonlinear effects of electromagnetic field on plasma heating were studied using the PIC code in the cases of weak and strong electromagnetic fields. It has been shown that in the case of weak electromagnetic fields (corresponding to weak nonlinearity) the nonlinear effects lead to some enhancement of heating (compared to the linear theory) at low frequencies, followed by a small reduction of heating at higher frequencies. This observed nonlinear perturbation of heating in warm plasma with collisions is similar to that predicted by the quasilinear theory for the case of cold plasma with collisions. In the case of strong electromagnetic fields (corresponding to strong nonlinearity) the nonlinear effects lead to a further reduction of heating (compared to the linear theory) at low frequencies, as shown by the simulation, thus adding to the effect of reduction of heating predicted by the linear theory. The nonlinear effects are shown to vanish at high frequencies, as expected.

In this thesis we investigate experimentally certain aspects of the interaction of terahertz (THz) radiation with intersubband transitions and excitonic transitions in semiconductor quantum wells. The first part deals with a more fundamental view on an intersubband transition in a symmetric, undoped GaAs/AlGaAs multiple quantum well. After optical excitation of carriers, the considered electronic conduction intersubband transition is probed in the low-intensity linear regime using broadband THz pulses. These pulses are detected via field-resolved electro-optic sampling. While the sample’s terahertz absorption shows the expected single peak of the resonant intersubband transition, the differential transmission spectra, i.e. the photoexcitation-induced changes in transmission, display strong Fano signatures. On the basis of a microscopic theory, we show that they originate from a phase sensitive superposition of THz current and ponderomotive current. The latter one results from the wiggling motion of carriers induced by the accelerating THz field. Our findings demonstrate for the first time that the ponderomotive contribution has to be taken into account also at the lowest THz intensities. The following issues consider the interaction with THz pulses of higher intensity from the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf. In one experiment we investigate efficient second order sideband generation in the GaAs/AlGaAs multiple quantum well mentioned above. To this end a near-infrared laser tuned to excitonic interband transitions is mixed inside the sample with the inplane polarized FEL beam to create the sum- and difference-frequencies between them. We compare the sideband efficiencies for the THz beam tuned to the interexcitonic heavy-hole light-hole transition and to the intraexcitonic heavy-hole 1s-2p transition. In the latter case we achieve a ten times higher n=+2 low-temperature efficiency around 0.1%. This value is comparable to previous studies in the literature, but our approach involves different transitions in a much simpler geometry. At room temperature the efficiency drops only by a factor of 7 for low THz powers. The last part of this thesis addresses another fundamental quantum-mechanical phenomenon: the splitting of an absorption line in a strong THz field. In the same abovementioned quantum well sample the FEL wavelength is tuned near the intraexcitonic 1s-2p heavy-hole transition. The THz radiation induces a power-dependent splitting of the heavy-hole 1s exciton absorption line which manifests itself in the transmitted spectrum of a broadband near-infrared probe beam. The FEL-wavelength-dependent strength of this so-called Autler-Townes splitting is discussed on the basis of a simple two-level model.

A presente dissertação estuda a dinâmica uni e tridimensional de uma part cula solitária eletricamente carregada sob a ação de uma onda eletrostática de alta frequência lentamente modulada. A onda dota a partícula de energia potencial elétrica e o seu movimento e conhecido através do emprego do formalismo hamiltoniano, onde se faz a consideração de efeitos relativísticos devido as altas velocidades envolvidas no processo. Enquanto a velocidade máxima experimentada pela partícula permanece suficientemente abaixo da velocidade de fase característica da onda que a acelera, sua dinâmica pode ser bem descrita por uma re nada aproximação ponderomotriz. Com esta abordagem, prevê-se corretamente a velocidade média, máxima e m nima desenvolvida pela partícula ao longo de seu movimento através das curvas que permeiam e envelopam o per l de velocidade. Os limites de validade da aproximação são bem estabelecidos e, uma vez ultrapassados, a partícula com velocidade ressonante e capturada pela onda. Sob as adequadas condições calculadas neste trabalho, o mecanismo de captura instala, espontaneamente, a partícula em fase otima relativa a onda e a acelera a velocidades muito próximas da velocidade da luz no vácuo. Em consonância, o processo de aceleração e otimizado com a focagem da partícula em direção ao eixo de propagação da onda durante um certo intervalo de tempo e de comprimento aproveitáveis. / The present dissertation studies the one and three-dimensional dynamics of an electrically charged solitary particle under the action of a slowly modulated high frequency electrostatic carrier wave. The wave gives the particle electrical potential energy and its movement is known through the use of Hamiltonian formalism, where relativistic e ects are considered due to the high velocities involved in the process. Meanwhile the maximum speed experienced by the particle remains su ciently below the characteristic phase velocity of the accelerating carrier wave, its dynamics can be well described by a re ned ponderomotive approach. With this approach, the average, maximum and minimum speed developed by the particle along its movement through the curves that permeate and envelop the velocity pro le. The limits of validity of the approximation are well established and, once exceeded, the particle with resonant velocity is captured by the wave. Under the appropriate conditions calculated in this work, the capture mechanism spontaneously installs the optimum phase particle relative to the wave and accelerates towards the speed of light in the vacuum. At same time, the acceleration process is optimized by focusing the particle towards the wave propagation axis for a certain usable time interval and length.

A presente dissertação estuda a dinâmica uni e tridimensional de uma part cula solitária eletricamente carregada sob a ação de uma onda eletrostática de alta frequência lentamente modulada. A onda dota a partícula de energia potencial elétrica e o seu movimento e conhecido através do emprego do formalismo hamiltoniano, onde se faz a consideração de efeitos relativísticos devido as altas velocidades envolvidas no processo. Enquanto a velocidade máxima experimentada pela partícula permanece suficientemente abaixo da velocidade de fase característica da onda que a acelera, sua dinâmica pode ser bem descrita por uma re nada aproximação ponderomotriz. Com esta abordagem, prevê-se corretamente a velocidade média, máxima e m nima desenvolvida pela partícula ao longo de seu movimento através das curvas que permeiam e envelopam o per l de velocidade. Os limites de validade da aproximação são bem estabelecidos e, uma vez ultrapassados, a partícula com velocidade ressonante e capturada pela onda. Sob as adequadas condições calculadas neste trabalho, o mecanismo de captura instala, espontaneamente, a partícula em fase otima relativa a onda e a acelera a velocidades muito próximas da velocidade da luz no vácuo. Em consonância, o processo de aceleração e otimizado com a focagem da partícula em direção ao eixo de propagação da onda durante um certo intervalo de tempo e de comprimento aproveitáveis. / The present dissertation studies the one and three-dimensional dynamics of an electrically charged solitary particle under the action of a slowly modulated high frequency electrostatic carrier wave. The wave gives the particle electrical potential energy and its movement is known through the use of Hamiltonian formalism, where relativistic e ects are considered due to the high velocities involved in the process. Meanwhile the maximum speed experienced by the particle remains su ciently below the characteristic phase velocity of the accelerating carrier wave, its dynamics can be well described by a re ned ponderomotive approach. With this approach, the average, maximum and minimum speed developed by the particle along its movement through the curves that permeate and envelop the velocity pro le. The limits of validity of the approximation are well established and, once exceeded, the particle with resonant velocity is captured by the wave. Under the appropriate conditions calculated in this work, the capture mechanism spontaneously installs the optimum phase particle relative to the wave and accelerates towards the speed of light in the vacuum. At same time, the acceleration process is optimized by focusing the particle towards the wave propagation axis for a certain usable time interval and length.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第18384号 / エネ博第296号 / 新制||エネ||61(附属図書館) / 31242 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 岸本 泰明, 教授 中村 祐司, 教授 松田 一成 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

In this thesis we investigate experimentally certain aspects of the interaction of terahertz (THz) radiation with intersubband transitions and excitonic transitions in semiconductor quantum wells. The first part deals with a more fundamental view on an intersubband transition in a symmetric, undoped GaAs/AlGaAs multiple quantum well. After optical excitation of carriers, the considered electronic conduction intersubband transition is probed in the low-intensity linear regime using broadband THz pulses. These pulses are detected via field-resolved electro-optic sampling. While the sample’s terahertz absorption shows the expected single peak of the resonant intersubband transition, the differential transmission spectra, i.e. the photoexcitation-induced changes in transmission, display strong Fano signatures. On the basis of a microscopic theory, we show that they originate from a phase sensitive superposition of THz current and ponderomotive current. The latter one results from the wiggling motion of carriers induced by the accelerating THz field. Our findings demonstrate for the first time that the ponderomotive contribution has to be taken into account also at the lowest THz intensities. The following issues consider the interaction with THz pulses of higher intensity from the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf. In one experiment we investigate efficient second order sideband generation in the GaAs/AlGaAs multiple quantum well mentioned above. To this end a near-infrared laser tuned to excitonic interband transitions is mixed inside the sample with the inplane polarized FEL beam to create the sum- and difference-frequencies between them. We compare the sideband efficiencies for the THz beam tuned to the interexcitonic heavy-hole light-hole transition and to the intraexcitonic heavy-hole 1s-2p transition. In the latter case we achieve a ten times higher n=+2 low-temperature efficiency around 0.1%. This value is comparable to previous studies in the literature, but our approach involves different transitions in a much simpler geometry. At room temperature the efficiency drops only by a factor of 7 for low THz powers. The last part of this thesis addresses another fundamental quantum-mechanical phenomenon: the splitting of an absorption line in a strong THz field. In the same abovementioned quantum well sample the FEL wavelength is tuned near the intraexcitonic 1s-2p heavy-hole transition. The THz radiation induces a power-dependent splitting of the heavy-hole 1s exciton absorption line which manifests itself in the transmitted spectrum of a broadband near-infrared probe beam. The FEL-wavelength-dependent strength of this so-called Autler-Townes splitting is discussed on the basis of a simple two-level model.

No description available.