Tin droplets; stimulated brillouin scattering; EUV lithography; Laser-produced plasma; Laser pre-pulse
Hudgins Duane, Nieland Alex, Abhari Reza S. (2017), Laser induced shockwave droplet breakup dynamics, in 2017 Source Workshop
, Dublin, IrelandEUV Litho, Inc., Austin, TX USA.
Hudgins Duane, Gambino Nadia, Rollinger Bob, Abhari Reza (2016), Neutral cluster debris dynamics in droplet-based laser-produced plasma sources, in Journal of Physics D: Applied Physics
, 49(18), 185205-185205.
A laser-produced plasma (LPP), which is obtained by irradiating a specific target material with a high power laser, generates spectrally tailored emission. Laser-produced plasmas are a well established method for generating radiation in a broad range of wavelengths. The interaction of a high power laser with a specific target material has been used to generate photon emission in a variety of spectral regions including hard X-Rays, soft X-Rays, ultraviolet radiation including vacuum ultraviolet and extreme ultraviolet and visible radiation. The main field of application of the present work is related to the use of LPP sources for X-ray lithography, and more precisely for extreme ultraviolet (EUV) lithography. At the Laboratory for Energy Conversion (LEC), ETH Zürich, a fully functional high power, tin droplet-based LPP light source has been developed over the last 7 years. The major challenges, which are found in the development of a soft X-ray LPP source, include the source emission stability, the source power and brightness, as well as the mitigation of plasma debris. These challenges are representative for the other fields of application of soft X-ray light sources. For the source plasma, the LEC ALPS group has already performed 3D mapping of EUV emissions and 2D ion mapping. The next step will be ultrafast imaging of the droplet breakup for different time intervals. The PhD student shall perform an experimental study with the actual liquid droplet target in conjunction with the already accomplished plasma diagnostics, providing a complete measured characterization of the plasma dynamics for a droplet-based LPP source. The proposed study would provide insight into the process of droplet spallation.The PhD student shall perform an experimental study of pre-pulse shaping. Sending a laser pre-pulse before the main laser drive pulse to the droplet target can increase the conversion efficiency (CE) of the source and mitigate debris by controlling droplet breakup and target expansion. There is high interest in being able to temporally compress the pre-pulse. A temporally compressed pre-pulse increases the source conversion efficiency at lower pre-pulse powers. Additionally, the potential for target shaping with picosecond pulse trains will be explored utilizing an electro-optic deflector or a specialized pulsed picosecond laser. Beyond providing further insight into droplet spallation, these experiments in picosecond pulse trains will shed light on the effect of periodic shockwaves on the breakup of liquid droplets.In the final phase the PhD student shall perform an experimental study of laser pre-pulse compression utilizing Stimulated Brillouin Scattering (SBS). SBS has been demonstrated as a viable method of temporally compressing 1064nm Nd:YAG high energy laser pulses and is the chosen approach for this work. Fluorocarbons have shown the greatest potential for compression of an Nd:YAG laser. A parametric study will be performed on the effect of pre-pulse compression on the LPP source plasma dynamics.The knowledge acquired of the plasma dynamics during the project will have a significant overall impact on the field of laser-produced plasmas.