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Experimental Setup of High Harmonic Generation Based Angle Resolved Photoemission Spectroscopy (HHG- ARPES) and Test Measurement on Tungsten (W) [110] Surface

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Experimental Setup of High Harmonic Generation Based Angle Resolved Photoemission Spectroscopy (HHG- ARPES) and Test Measurement on Tungsten (W) [110] Surface Experimental Setup of High Harmonic Generation Based Angle Resolved Photoemission Spectroscopy (HHG- ARPES) and Test Measurement on Tungsten (W) [110] Surface M D SABBIR AHSAN KTH Information and Communication Technology Master of Science Thesis Stockholm, Sweden 2013 TRITA-ICT-EX-2013:277 Experimental Setup of High Harmonic Generation Based Angle Resolved Photoemission Spectroscopy (HHG-ARPES) And Test Measurement on Tungsten (W) [110] Surface M D S A B B I R A H S A N Master of Science Thesis Stockholm, Sweden 2013 TRITA-ICT-EX-2013:277 A Thesis submitted for the degree of Master of Science Experimental Setup of High Harmonic Generation Based Angle Resolved Photoemission Spectroscopy and test measurement on Tungsten W(110) surface Md Sabbir Ahsan December 20, 2013 Performed Ultrafast X-ray Physics group Faculty of Physics Ludwig Maximilians University(LMU) Munich,Germany Supervisor Prof.Dr.Ulf Kleineberg LMU,Germany Examiner Docent. Jonas Weissenrieder KTH,Sweden School of Information and communication Technology Royal Institute of Technology (KTH) Stockholm,Sweden Contents Acknowledgement vii abstract viii 1. Introduction 1 1.1. Significance of studying the surface state: . 2 1.2. Goal of the Thesis . 2 1.2.1. Familiar with Ulrashort pulse Generation and application to gen- erate attosecond pulse: . 3 1.2.2. Experimental setup . 3 1.2.3. Experimental Study . 3 1.3. Thesis structure: . 4 I. Theoretical Background: 5 2. Bandstructure and Fermi surface of solid 6 2.1. Free electrons in solid: . 6 2.2. Energy Bands in a solid: . 8 2.2.1. Electron in a weak periodic potential: . 9 3. Spectroscopic Methods to study surface state 15 3.1. Photoelectron Spectroscopy: . 15 3.1.1. Kinematic of photoemission . 16 3.1.2. Linear response in external field: . 18 3.1.3. Dipole approximation and selection rule: . 19 3.1.4. Model for Photoemission process . 21 3.1.5. Surface and bulk sensitive photoemission . 23 3.2. ARPES tools: . 24 3.2.1. Hemispherical electron analyzer: . 24 3.2.2. Time of flight analyser (TOF) . 24 3.3. Auger Spectroscopy: . 25 3.3.1. Principle: . 25 4. Generation of Ultra-short pulses: From femtosecond laser to attosecond XUV pulse 27 4.1. Mathematical Idea of an ultra-short pulse: . 27 i Contents 4.2. Basic element for generating ultrashort pulse . 29 4.2.1. Gain Medium . 29 4.2.2. Mode locking technique . 29 4.2.3. Dispersion control and pulse compression . 30 4.2.4. Principle of Dispersion compensation . 32 4.2.5. Mirror and output Coupler . 34 4.3. Ionization process in strong laser field . 34 4.4. Generation of attosecond pulse: High Harmonic Generation . 36 4.5. Measuring the pulse duration: . 38 4.5.1. Autocorrelation Technique . 38 4.5.2. Stereo ATI: . 39 4.5.3. Attosecond streaking experiment . 40 II. Experimental setup,results and discussion 42 5. Experimental setup of HHG Based ARPES 43 5.1. Generation of attosecond XUV pulse . 43 5.1.1. Generation of few cycle pulse . 43 5.1.2. HHG setup . 46 5.2. Sample preparation chamber . 47 5.2.1. evaporation chamber . 47 5.2.2. cleaning chamber . 48 5.2.3. Conditioning filament . 49 5.3. ARPES Chamber . 49 5.3.1. sample heater and sputter gun . 50 5.3.2. Double Mirrors . 50 5.3.3. Magnetic field compensation . 51 5.3.4. Ultra high vacuum in ARPES . 53 5.3.5. Connection: Beamline, ARPES and Sample preparation . 56 5.4. Characterization of experimental setup . 56 5.4.1. Determining laser spot size after HCF . 56 5.4.2. Finding the focus point . 57 5.4.3. Energy and time resolution . 58 5.4.4. Determining the time offset . 59 6. Experimental study on Tungsten W(110) surface 60 6.1. Auger spectroscopy on Tungsten(110) . 60 6.1.1. Detection of surface contamination . 60 6.1.2. Sample cleaning: Method and verification . 62 6.2. Crystal property of Tungsten(W) . 64 6.3. Photoemission Spectroscopy on Tungsten (W) . 65 6.3.1. Observation of Conduction band Spectrum . 66 6.3.2. Fermi surface . 68 ii Contents 6.3.3. Bandstructure observation . 70 III. Future work: Improvement, conclusion 72 7. future work 73 7.1. Area of improvements: . 73 7.2. Prospect for time resolved (TR) study:(TR-ARPES) . 75 8. Conclusion 77 A. Calibration of evaporation chamber: 78 B. Helmholtz compensation 79 iii List of Figures 2.1. Electron in an uniform potential . 6 2.2. Fermi surface in free electron model . 7 2.3. Formation of energy bands in a solid . 9 2.4. Bandstructure representation of a solid . 11 2.5. Magnitude of energy gap at zone boundary . 13 2.6. Variation in potential energy . 13 2.7. Band gap of a solid . 14 2.8. Effect of weak periodic potential on Fermi surface . 14 3.1. Photoelectron spectrum . 16 3.2. Photoemission Geometry . 17 3.3. Photoemission process . 18 3.4. Photoemission model . 22 3.5. Energy dependent mean free path . 23 3.6. ARPES electron analyzers . 25 3.7. Auger process . 26 4.1. Diagram of an ultrashort pulse . 27 4.2. Mode locking mechanism . 29 4.3. Kerr-lens mode-locking . 31 4.4. self-phase modulation . 33 4.5. Ionization field in strong Laser field . 34 4.6. Regimes of Nonlinear optics . 35 4.7. higher order harmonic generation process. 37 4.8. HHG Spectrum . 37 4.9. Autocorrelation technique to measure pulse duration . 38 4.10. Measuring few fs pulse duration . 40 4.11. Attosecond streaking experiment . 41 5.1. Chirped pulse amplification to generate femtosecond pulse . 44 5.2. Generation of ultrashort pulse . 45 5.3. Generation of few cycle laser pulse . 45 5.4. Higher order harmonic spectrum . 46 5.5. Sample preparation setup . 48 5.6. tr-ARPES experimental setup . 49 5.7. Sample stage in ARPES chamber . 50 iv List of Figures 5.8. Reflectivity of double mirror . 51 5.9. Effect of magnetic field in PES . 52 5.10. Helmholtz like compensated ARPES chamber . 52 5.11. Ultra High Vacuum system . 55 5.12. 3D view of HHG based ARPES experimental setup . 56 5.13. Determing spot size after HCF . 57 5.14. Harmonic recorded in CCD camera . 58 5.15. Determing Energy and time resolution . 58 5.16. Determing time offset . 59 6.1. Diagram for Auger and Photoemission process . 60 6.2. focusing electron beam on the sample surface . 61 6.3. Auger Process in Tungsten surface . 61 6.4. Auger Spectroscopy to verify surface cleanliness . 63 6.5. Auger peaks from clean W surface . 64 6.6. direction and detector position . 65 6.7. Exciting sample surface with XUV photons . 65 6.8. photoelectron Energy spectrum . 66 6.9. W Photoelectron cross section . 67 6.10. photoelectron energy spectrum . 68 6.11. Fermi Surface of Tungsten(110) . 69 6.12. Fraction of Brillouin zone using current experimental setup . 69 6.13. Tungsten Bandstructure . 70 6.14. Theoretical Bandstructure of Tungsten . ..
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