Novel quasi phase matching of high harmonic generation via advanced dual gas multi jet targets

Ultrafast/attosecond physics is an exciting and dynamic research discipline, revealing atomic and molecular structures/processes with unprecedented spatial and temporal resolution. A significant limitation, however, has been the limited amount of laser energy that can be converted into XUV and soft x-ray regions of the spectrum. This is primarily due to phase mismatch between the driving laser and generated harmonic field, induced by the large free-electron contribution to the refractive index. Quasi-phasematching has been a front runner in the drive towards this objective but to date has been largely confined to low average power 'proof-of-principle' experiments in hollow core capillaries. This proposal seeks to develop a ground breaking new approach to quasi-phasematching developed by our group at QUB - dual gas multi-jet arrays in a capillary free geometry - to an exceptionally high standard.

In this proposal we intend to build upon experimental observations already made which verify this exciting new technique. Together with our collaborators at the HASYLAB (DESY, Hamburg) and TEI Rethymno (Crete) the current design will be extended to generate a high average power harmonic source suitable for seeding the FLASH free electron laser at DESY. In a second strand of this proposal we will use the unique ability of this source to fine-control the phase of HHG emission for intense single attosecond pulse generation. This proposal will form the core of an international collaboration aimed at delivering the first high average power HHG source and intense attosecond pulses, and work will be performed on lasers at QUB, DESY and TEI Crete.

The socio-economic impact of developing complete coherent control of high harmonic generation in gases can be categorized into two main strands.

First to benefit will be the accelerator based ultrafast X-ray source user community - including groups from both science and industry. This community spans materials science (semiconductor industry, advanced materials for solar cell research etc) to diffractive imaging of single molecules for in vivo studies of biomedical samples. Our research will allow better pulse energy stability and focusability of the X-ray radiation produced by these multi billion pound machines, which in turn will allow users to metrologise their samples with unprecedented accuracy.

Secondly, over a longer term, this work will contribute significantly to the downsizing of ultrafast X-ray sources. Controlling the process by which harmonics are generated in gas targets coherently will ultimately lead to compact bright sources. In turn this will provide the basis for moderately priced systems (<£3m) that will be useful in numerous scientific and industrial applications. One excellent example of this is imaging of in vivo cells in aqueous solutions using coherent radiation generated in the 'water-window' region of the spectrum. Allowing onoclogical researchers access to systems capable of delivering bright water window radiation on a regular basis from an in house system (as opposed to competitive slots at large facilities) will expedite our understanding of the basic mechanisms of metastasis and hopefully, in time, lead to better cures/preventative measures for the spread of cancer in the body. Our method for coherent control of the generation process of X-rays in gases is the first step on the road to such a commercially viable device.