1. The 7 th Day After First Light Yu He SC Meeting Jul 25, 2013 Milestones Early Guinea Pigs PROBLEMS! Metal Cuprate Topological Insulator Pnictide FeSe Film

2. The Laser Seed laser, 100MHz, IR Amplifier, SHG and FHG Gas Conversion Module (GCM) Dispersion Chamber (DC) Ionization Chamber (IC-P) ARPES Manifold Gas Control Panel (GCP)

3. Milestones Jul 10 Jul 11 Jul 07 Jul 12 Jul 15 Jul 20 Jul 16

4. The ‘Gold’ Standard By proper beam alignment, two step puzzle solved Best Au resolution ~10meV

5. UD92 Bi2212 – half wave plate rotation Polarization changes intensity by 2 folds Signal-background ratio modulated To be motorized To add quarter-wave plate

6. UD92 Bi2212 – reaching zone boundary Reaching zone boundary! Need better stats and even longer time per scan

7. Bi2Se3 – characterize polarization?

8. Bi2Se3 – linear dichroism Z.-H. Zhu et al, PRL 110, 216401 (2013) P-polarization dominates What exactly is the half-wave plate doing to the linear polarization of 11eV? 0.2eV 0.1eV 0 eV -0.1eV

9. Bi2Se3 –Bi2Se3 – circular dichroism Z.-H. Zhu et al, PRL 110, 216401 (2013) 0.2eV 0.1eV

10. Bi2Se3 –Bi2Se3 – circular dichroism Z.-H. Zhu et al, PRL 110, 216401 (2013) 0.2eV Small circular dichroism exists Linear dichroism dominates Rotating half wave plate by θ doesn’t simply rotate linear polarization by 2 θ 0.1eV

11. FeTeSe – blur band and space charging UV power 411uW334uW223uW140uW

12. Strong evidence for space charging Down to 150k counts/second at E F the effect is still visible What’s wrong? FeTeSe – blur band and space charging Pulse duration Average power Repetion rate 11eV~1ns~5uW1MHz 6eV~10ps~?uW80MHz SPEAR 3 1-100ps 10uW @500mA 500MHz- 1MHz

13. FeSe film – reaching zone boundary MΓΓ 18K hv = 21.218eV Helium plasma discharge hv = 10.897eV 1024nm+256nm+256nm

14. FeSe film – reaching zone boundary Back bending clearly observed below Tc Less background at low binding energy Fully reaching zone boundary – powerful tool to study fine structures and subtle changes at M point

15. Problems! Space Charging Polarization Resolution Increase rep rate to 10MHz or more The limiting factor: power or spot size? Pass energy to get around? How keen are we now perusing 100uW power? Motorize What does the wave plate exactly do upstream the GCM? Quarter wave plate for circular dichroism Go beyond 10meV how about 1meV?

16. The END