Space Charging in 11 eV Yu He SC Meeting Jul 25, 2013 Numbers and Conventions UV Power vs 11eV Power EF Position and Width vs ‘Counts’ Questions to be answered

The Laser Seed laser, 1 MHz, IR Amplifier, SHG and FHG Gas Conversion Module (GCM) Dispersion Chamber (DC) Ionization Chamber (IC-P) ARPES Manifold Gas Control Panel (GCP)

IC-P current I 0 (nA) Amplifier current (A) UV Power (×10mW) Laser diode current I diode (A) SHG X’tal temperature FHG X’tal temperature IC-P vapor pressure (mV) Numbers and Conventions

UV power almost scales linearly with seed laser diode current between 4.5A and 7A – confirms the working range Andrew suggested in the manual 11eV power (~ 11eV photon count) scales roughly with cubic(UVPower)

On Gold – all data taken at T=8K PE=2 PE=5 400K340K300K230K 210K150K 110K 80K Counts = 55K 210K 1.9M1.7M1.4M1.2M 970K670K 580K 390K 260K 970K

Numbers and Conventions EF position drifts linearly in ‘electron count (near EF)’, but clearly picks up drifting rate ~ 400uW UV power To get more count, PE=5 performs better in that charging issue develops slower than PE=2 (expected)

Numbers and Conventions EF broadening drifts linearly in ‘electron count (near EF)’, and also clearly picks up drifting rate ~ 400uW UV power Resolution curves almost overlap as a function of UV power between PE=2 and PE=5 – charging issue taking place upstream from detector; Also resolution converges to ~10meV taking to zero flux limit both in PE2 and PE5 case - something else is bottlenecking resolution other than space charging issue

FeTeSe – blur band and space charging UV power 411mW334mW223mW140mW

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 ps 500MHz- 1MHz

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

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

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

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

Bi2Se3 – characterize polarization?

Bi2Se3 – linear dichroism Z.-H. Zhu et al, PRL 110, (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

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

Bi2Se3 –Bi2Se3 – circular dichroism Z.-H. Zhu et al, PRL 110, (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

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

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

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?