Self-phase modulation of a single-cycle terahertz pulse by nonlinear free-carrier response in a semiconductor

We demonstrate the self-phase modulation (SPM) of a single-cycle THz pulse in a semiconductor, using bulk n-GaAs as a model system. The SPM arises from the heating of free electrons in the electric field of the THz pulse, leading to an ultrafast reduction of the plasma frequency, and hence to a strong modification of the THz-range dielectric function of the material. THz SPM is observed directly in the time domain. In the frequency domain it corresponds to a strong frequency-dependent refractive index nonlinearity of n-GaAs, found to be both positive and negative within the broad THz pulse spectrum, with the zero-crossing point defined by the electron momentum relaxation rate. We also observed the nonlinear spectral broadening and compression of the THz pulse.Comment: 5 pages, 6 figure

The Role of the State in Development: A Case Study of Food Security and Vulnerability among Beneficiaries of India's Targeted Public Distribution System (TPDS)

This thesis discusses the role for states and centralised government policies in development intervention. The topic is explored through a case study of India’s Targeted Public Distribution System (TPDS), a large-scale government intervention to enhance food security among India’s poorest households. The central questions of the study were, firstly, which function TPDS serves in the lives of beneficiary households in terms of food security and vulnerability, and secondly, what the study of TPDS can tell about the potential of government programmes in contributing to community development. Qualitative fieldwork was conducted in two districts in the Indian state Odisha through observations, interviews and conversations with beneficiaries, project implementers and government officials. The findings suggest that TPDS – despite being flawed with corruption and targeting errors – is bringing a certain level of food security and resilience to beneficiary households. It is found that the boundaries between the state and society become blurred in the delivery of TPDS and that embedded relations between implementers and beneficiaries contribute to basic needs being met at the household level. Following from this, the thesis argues in favour of a central role for the state in development, while also emphasising the need for society cooperation and involvement