The ultra-wideband pulse

• Main Author: Radnor, Samuel Benjamin Philip
• Other Authors: New, Geoff
• Published: Imperial College London 2008
• Subjects: 535.5
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.446031

Since the birth of mode-locking the temporal duration of optical pulses has radically diminished. In parallel to this, bandwidths have grown so large that almost entire frequency octaves are present in today’s few-cycle pulses. This thesis investigates the character of ultra-wideband pulses in nonlinear environments. Because of the growth in optical bandwidths, traditional definitions and propagation models break down, requiring newer more accurate numerical techniques. A novel approach capturing the uni-directionality of pulses is presented in the form of Gvariables by combining the electric and magnetic field descriptions. These G-variables have the advantage of both an accurate spectral representation and a reduced computational overhead, making them significantly more efficient than existing direct Maxwell solvers. Such approaches are particularly important where large propagation distances and/or transverse dimensions are concerned. Pseudo-spectral techniques play a key role in the success of these wideband models enabling sub-cycle dynamics to be studied. One such phenomenon is Carrier Wave Shocking (CWS), where the optical carrier undergoes self-steepening in the presence of third-order nonlinearity. This process is carefully studied, focussing on the effect of dispersion and the feasibility of its physical realisation. The process is then generalised to arbitrary nonlinear order, where the quadratic form finds potential applications in High Harmonic Generation (HHG). Shock detection schemes are also developed, and agree with analytical solutions in the dispersionless regime. To fully characterise few-cycle pulses, the absolute Carrier Envelope Phase (CEP) must be known. A novel 0 − f self-referencing scheme relying on wideband interference is investigated. By applying robust frequency domain definitions a proposal is made to convert this scheme into one that determines absolute CEP. The scheme maps the level of spectral interference to absolute CEP using numerical simulations.