University of Twente Student Theses


Pulse shaping for high harmonic generation

Reinink, Johan (2013) Pulse shaping for high harmonic generation.

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Abstract:Extreme UltraViolet (EUV) radiation covers the spectral range from 124 nm down to 10 nm. This wavelength range is important for many applications, in particular next-generation lithography will use 13.5-nm light. One of the methods to generate coherent light in this wavelength region is highharmonic generation, where a short (~35 fs), infra-red laser pulse is focused to high intensity in a capillary. The extremely nonlinear process that takes place in the capillary generated the EUV radiation. In this thesis we have investigated how the energy in the EUV can be increased, for all harmonics or a single particular harmonic. To this end, the drive laser pulse energy is increased to about 7 mJ. Also, the drive laser system was modified to include a so-called Dazzler for shaping of the pulse it generates. Optimization of EUV generation through shaping of the drive laser pulse is also investigate. An evolutionary algorithm is used for the optimization. To keep the local intensity in the capillary constant, its diameter is also increased from 150 to 500 μm. The increase in total drive laser pulse energy also required modification to the diagnostic section; mainly it needed to be moved to a large distance from the capillary in order to safely separate the IR drive laser pulse from the generated EUV radiation With the modified set-up we first characterized the EUV radiation generated by IR drive laser pulse with an energy in the range of 5 to 7.5 mJ and a duration of 35 fs when it propagates through the capillary filled with Argon. We observed a stable output pulse at low pressures (3 – 7 mbar) and found that the EUV oscillated in position primarily in the x-direction at higher pressures (up to 12 mbar) with increasing amplitude and frequency. The measured spectrum showed that the harmonic orders from 15 to 29 can be generated and that the yield of a particular harmonic can be optimized by tuning the pressure (pressure phase matching). The range of harmonics found is slightly smaller than that found for a capillary with 150 μm diameter. To investigate the effect of pulse shaping on the generation of EUV radiation, we used the Dazzler in combination with evolutionary algorithm to optimize the yield of a particular harmonic. An enhancement of a factor of 9.7 is obtained for the 23rd harmonic compared to the same harmonic produced with the Dazzler in self-compensating mode (i.e., when the laser system is set to produces the shortest pulse. Only phase shaping is used. We also tried to optimize for red- or blue-shifted harmonics and observed a maximum shift of 0.11 nm.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:33 physics
Programme:Applied Physics MSc (60436)
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