M. P. Anscombe

Ultrashort-pulse modulation in adiabatically prepared Raman media

We demonstrate the efficient modulation of an approximately 100-femtosecond pulse in a Raman medium coherently prepared by nanosecond pulses. Raman sidebands of the ultrashort pulse spanning 360 THz are generated with an efficiency of >5%. We show that the mechanism permitting the sidebands to be generated is the preparation of a significant vibrational coherence in the medium that is robust to disturbance by an intense short pulse. If the observed sidebands were phase compensated, they would form a short train of approximately ten 3-fs pulses. Focusing would permit the realization of a peak intensity of >10(13) W cm(-2).

Intense 5.1-fs Carrier-Envelope-Phase Controlled Pulse Generation through Filamentation

Intense 5.1-fs pulses were generated through filamentation in argon. The CEO (carrier envelope offset) phase control is investigated of using the intense, octave-spanning spectrum generated during this process, directly for single shot f-2f spectral interferometry.

Generation of frequency-sheared XUV pulses by high harmonic generation

Frequency-sheared and time-separated high harmonics were produced without spatial separation in the target gas by controlling the time-frequency properties of the driving field. Simulations show good agreement within the strong-field approximation.

Coherent VUV and XUV production enhanced by EIT

We report experimental investigations of four-wave mixing schemes in krypton enhanced by electromagnetically induced transparency (EIT). High conversion efficiency was demonstrated and interpreted for vacuum ultraviolet (VUV) generation. Work in progress is described which aims to produce bright extreme-ultraviolet (XUV) light at 87nm using enhancement from an autoionising state.

Frequency Up-Conversion to the Vacuum Ultra-Violet in Coherently Prepared Media

In this contribution we discuss recent work that has demonstrated that electromagnetically induced transparency (EIT) can greatly increase the intensity of coherent vacuum ultra-violet (VUV) radiation (at wavelengths shorter than 130nm) generated in resonant four-wave mixing schemes. We will start by introducing the basic concept of EIT enhanced resonant four-wave mixing, comparing it briefly with other coherently enhanced non-linear frequency up-conversion schemes. Experiments proving this concept in atomic hydrogen in the mid-1990’s will be summarised. Our own recent work on EIT enhanced four-wave mixing in Kr will be presented and recent results demonstrating high conversion efficiencies into the VUV, and the limits placed on this process at high density-length products, will be discussed.

High Efficiency Frequency Up-Conversion Enhanced by Electromagnetically Induced Transparency

Electromagnetically induced transparency (EIT) can enhance the conversion efficiency of a resonant four-wave mixing scheme. This is demonstrated for a scheme in Kr resulting in the generation of a field at 123.6 mn. The absolute VUV radiation yield was measured using a calibrated photodiode in the limit of a large density-length product. Energies of 30 ~ nJ per pulse were produced, with an energy conversion efficiency from the coupling field of ~ 1%. Higher yields are thought to be achievable by the use of a transform limited UV pulse of the same duration as the coupling field and by increasing the coupling laser intensity and the path length in the medium.