Abstract
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.
Highlights
High harmonic generation (HHG) is an established method for producing highly coherent radiation in the XUV region with femtosecond to attosecond pulse durations [1]
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
The flux of a harmonic source can be increased through a variety of methods including phase matching [8], quasi-phase matching [9], as well as increasing the average power of the driver beam by increasing either the pulse energy or repetition rate, or both [10]
Summary
High harmonic generation (HHG) is an established method for producing highly coherent radiation in the XUV region with femtosecond to attosecond pulse durations [1]. The poor conversion efficiency of HHG from the infrared (IR) into the XUV typically restricts harmonic sources to average powers of a few microwatts or lower [2] This limits their use in applications ranging from the production of isolated attosecond pulses [3] to lensless imaging [4, 5]. The harmonic flux is sensitive to other parameters, such as the pulse duration, this quadratic scaling indicates that the focal length should be as long as possible in order to maximize the HHG flux This approach offers a straightforward method for increasing the. This method, which can be applied to a wide range of existing HHG setups, enables the advantage of a loose focussing geometry to be realised while preserving a compact experimental footprint
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