Increasing the brightness of harmonic XUV radiation with spatially-tailored driver beams

Bright high harmonic sources can be produced by loosely focussing high peak power laser pulses to exploit the quadratic scaling of flux with driver spot size at the expense of a larger experimental footprint. Here, we present a method for increasing the brightness of a harmonic source (while maintaining a compact experimental geometry) by spatially shaping the transverse focal intensity distribution of a driving laser from a Gaussian to supergaussian. Using a phase-only spatial light modulator we increase the size and order of the supergaussian focal profiles, thereby increasing the number of harmonic emitters more efficiently than possible with Gaussian beams. This provides the benefits of a loose focussing geometry, yielding a five-fold increase in harmonic brightness, whilst maintaining a constant experimental footprint. This technique can readily be applied to existing high harmonic systems, opening new opportunities for applications requiring bright, compact sources of coherent short wavelength radiation

Quasi-phase-matching of high-order-harmonic generation using multimode polarization beating

The generalization of quasi-phase-matching using polarization beating and of multimode quasi-phase-matching (MMQPM) for the generation of high-order harmonics is explored, and a method for achieving polarization beating is proposed. If two (and in principle more) modes of a waveguide are excited, modulation of the intensity, phase, and/or polarization of the guided radiation will be achieved. By appropriately matching the period of this modulation to the coherence length, quasi-phase-matching of high-order-harmonic radiation generated by the guided wave can occur. We show that it is possible to achieve efficiencies with multimode quasi-phase-matching greater than the ideal square wave modulation. We present a Fourier treatment of QPM and use this to show that phase modulation, rather than amplitude modulation, plays the dominant role in the case of MMQPM. The experimental parameters and optimal conditions for this scheme are explored

Intensive alternatives to custody process evaluation of pilots in five areas

A qualitative process evaluation of five Intensive Alternative to Custody (IAC) pioneer areas was undertaken to assess implementation of IAC, identify approaches to implementation and capture the lessons learnt. The findings indicated that many of the persistent offenders (those with at least 29 prior convictions) targeted by pilots were positive about the IAC order. Although intensive, it provided order and stability, allowing them to move away from a criminal lifestyle. Sentencers welcomed the order as a viable alternative to custody. Probation staff and partners were equally positive about its efficacy. Only one in four IAC orders were revoked because requirements were breached, which suggests that the pilots had managed to engage many of the offenders