Laser Ablation Studies at UCSD and Plans for Time and Space Resolved Ejecta Measurements

Transcription

1 Laser Ablation Studies at UCSD and Plans for Time and Space Resolved Ejecta Measurements M. S. Tillack, Y. Tao, Y. Ueno*, R. Burdt, S. Yuspeh, A. Farkas, 2 nd TITAN workshop on MFE/IFE common research NIFS, Japan 8-9 October 2009 *Komatsu Ltd. EUV Source Research Department, Hiratsuka Japan

2 Overview Part I: Background UCSD activities on laser-matter interactions Ablation physics Dragonfire lab Part II: Ablation studies at UCSD Ablation plume internal structure and expansion dynamics Magnetic field effects on plume dynamics Ion acceleration and charge state evolution Cluster formation by condensation in plumes Spinodal decomposition of surfaces Liquid droplet and microsphere ablation Blow-off and lift-off studies Part III: EUV microscope for ejecta studies Motivation Microscope details Plans

3 Laser-matter interactions research at UCSD spans a wide range of intensities and applications Laser plasmas: EUV lithography, WDM and HED studies (XUV, electron transport) Thermomechanics, phase change, lift-off Relativistic laser plasma Plume studies, LIBS, blow-off optics damage

4 Rapid heating of surfaces creates ablation plumes with complex behavior An ablation plume is a plasma-like substance, consisting of neutral particles, ions, electrons, clusters and fragments from submicron to many microns. Ablation of solid surfaces The basic processes involved in ablation includes energy absorption, strong localized heating, phase transitions, plume acceleration, source-plasma interactions, etc. Even considering its versatility and applicability, much of the detailed physics and chemistry underlying the ablation process are still far from completely understood.

5 Experiments on laser-matter interactions are performed in the Dragonfire Laboratory Energy Sources: Plasma and plume diagnostics: Joule-class Nd:YAG, excimer and CO2 lasers 150-ps plasma interferometry Shadowgraphy Visible and EUV spectroscopy 2-ns gated camera EUV emission imaging in-band energy monitor Faraday cups, ion energy analyzer Other equipment: Precision target positioning Liquid droplet targets Laser diagnostics Surface analysis tools

6 8-ns Nd:YAG (532 nm), 5 GW/cm 2 Studies of the internal structure of plumes revealed plume splitting and sharpening phenomena 150 mtorr air Pure Al slab target data fits a 3-temperature distribution

7 Magnetic fields can have a large effect on plume dynamics Faraday cup signal laser 1.5 cm gap Without B field, 270 ns Reduction of ion kinetic energy. Increase in n e and T e Reduction of the total number of ions reaching the detector. Charge state distribution and neutral particles due to the enhanced collisions induced by magnetic field. Impacts on cluster formation??? With 0.6 T B field, 280 ns TOF of Sn ions with and without magnetic field

8 Recent work is focused on better understanding of ion acceleration and charge state evolution Ion energy and charge state are measured with a time-of-flight electrostatic analyzer Differences in ion acceleration between Nd:YAG and CO 2 LPP were explored using comprehensive plasma diagnostics and EEA Differences in final charge state are attributed to higher initial plasma density in Nd:YAG-produced plasmas Nd:YAG CO 2

9 Strong super-saturation under the influence of ionization leads to nano-size cluster formation ΔG = 4π (r 3 r 3 a )(µ L µ v ) + 4πσ (r 2 r 2 a ) + e2 3V m 2 (1 ε 1 )(r 1 r 1 a ) 0.05 GW/cm 2 Ion jacketing produces seed sites, reducing formation energy 0.5 GW/cm 2 5 GW/cm mtorr He, Si substrate, 532 nm 8-ns Nd:YAG

10 Spinodal decomposition occurs when rapid heating pushes the surface to a metastable state Rapid heating can push surface beyond equilibrium When dp/dv=0, explosive expansion can occur The rate depends strongly on temperature (T/T c >0.9) Delay: 1 µs Gate : 1 µs Delay: 10 µs Gate : 10 µs Delay: 20 µs Gate : 10 µs Delay: 50 µs Gate : 50 µs Laser Target 10 mm Visible emission images from phase explosion Laser: 130 ps, 100 mj, µm, ~10 14 W/cm 2

11 We recently began to study ablation of microspheres and liquid droplets Differences in small targets: 3-d expansion of plasma and plume. Short plasma density scale length affects laser energy deposition. Limited mass affects energy transport and plasma hydrodynamics. Small diameter affects ablation rate, expansion rate, cluster formation, etc. Ablation pressure can break apart liquid droplets above ~10 9 W/cm 2 Interferogram of laser ablated Sn sphere Laser 200 µm

12 Laser blow-off and lift-off have applications in fusion and in industry Blow-off is used for rapid, localized injection of controlled amount of impurities for studies of transport and confinement in plasma devices. Toroidal and radial transport of injected boron was studied in TJ-II using various diagnostics (filterscopes, fast visible camera, bolometer arrays). GaN films and heterostructures are deposited on UV-transparent sapphire substrate. Varactor diodes will be used for tuning microwave power amplifiers for cell phone base-stations.

13 EUV microscopy of ejecta offers several advantages over existing techniques Visible imaging is limited in resolution; Scattering techniques (Rayleigh, Mie) require interpretation of data and are very difficult to implement. Ex-situ analysis lacks ability to diagnose in-flight evolution Direct imaging at 13.5 nm can provide sub-micron spatial resolution, sub-ns time-resolution, and high natural contrast due to submicron absorption depths (compared with x-rays). A wide field of view (several 100 µm) is achievable. Data is obtained in a single shot. Affordable optics and technologies are available due to recent developments in EUV lithography. The light source is compact, powerful, clean, low-cost, and available!

14 This research will provide valuable information for both IFE and MFE, as well as related applications IFE Energetic ions, electrons, neutral particles, and clusters will be a critical issue for IFE optics and chamber. Gas, EM fields, and other debris mitigation techniques have to be employed in the final IFE chamber. MFE Insight into the physics underlying wall ablation, particulate formation and transport induced by transient events. EUV source Fundamental physics for laser ablation, plume expansion into gas and magnetic fields relevant to debris mitigation. PLD Control the size and composition of the cluster formed in ablation and plume expansion in ambient gas and EM fields.

15 Probe plasma EUV microscope design details 90 0 filter Mo/Si mirror plume M2 M2 Detector Wavelength: 13.5 nm Temporal resolution: ~ 100 ns Spatial Resolution: 13/31= 400 nm Pixel size: 13 µm Magnification: 30 Field of view: 13 mm/31= 400 µm Probe plasma size: 500 µm Probe magnification: 1 Probe plasma laser: 1 or 10 µm Probe plasma laser: 0.1 ~ 100 ns Parameters Value (mm) Radius of primary mirror 190 Diameter of primary mirror 50 Radius of secondary mirror 70 Diameter of secondary mirror 12 Distance from plume to primary mirror Magnifica@on 31 Distance from plume to detector

16 Plans for initial measurements An agreement has been reached with ILE-Osaka (Hiroaki Nishimura) to loan an EUV microscope to UCSD Schedule: April 2010: May 2010: July 2010: March 2011: ship EUV microscope installation and testing finish initial data acquisition, return microscope final report With support from TITAN, we will have a unique facility no one has ever tried before open to Japanese students and researchers for detailed studies of ablation plumes and their ejecta physics Schwarzschild optics

17 Acknowledgements Support for this research was provided by: US Department of Energy Lawrence Livermore National Laboratory General Atomics UC Industry-University Collaborative Research Program The von Liebig Center Cymer Inc. KLA-Tencor Komatsu Ltd., EUV Source Research Department (EUVA) and TITAN!