PowerPoint Presentation

Space Charging in 11 eVYu HeSC MeetingJul 25, 2013Numbers and ConventionsUV Power vs 11eV PowerEF Position and Width vs CountsQuestions to be answeredThe Laser

Seed laser, 1 MHz, IRAmplifier, SHG and FHGGas Conversion Module (GCM)Dispersion Chamber (DC)Ionization Chamber (IC-P)ARPES ManifoldGas Control Panel (GCP)

IC-P current I0 (nA)Amplifier current (A)UV Power (10mW)Laser diode current Idiode (A)SHG Xtal temperatureFHG Xtal temperatureIC-P vapor pressure (mV)Numbers and Conventions

Numbers and ConventionsUV 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=2PE=5400K340K300K230K210K150K110K80KCounts = 55K210K1.9M1.7M1.4M1.2M970K670K580K390K260K970K

Numbers and ConventionsEF 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 issueFeTeSe blur band and space charging

UV power411mW334mW223mW140mW

Strong evidence for space charging

Down to 150k counts/second at EF the effect is still visible

Whats wrong?FeTeSe blur band and space chargingPulse durationAverage powerRepetion rate11eV~1ns~5uW1MHz6eV~10ps~?uW80MHzSPEAR31-100ps10uW @500mA500MHz-1MHz

9The ENDMilestones

Jul 10Jul 11

Jul 07Jul 12Jul 15Jul 20

Jul 16

The Gold Standard

By proper beam alignment, two step puzzle solvedBest Au resolution ~10meVUD92 Bi2212 half wave plate rotation

Polarization changes intensity by 2 foldsSignal-background ratio modulatedTo be motorizedTo add quarter-wave plateUD92 Bi2212 reaching zone boundary

Reaching zone boundary!Need better stats and even longer time per scanBi2Se3 characterize polarization?

Bi2Se3 linear dichroism

Z.-H. Zhu et al, PRL 110, 216401 (2013)P-polarization dominatesWhat exactly is the half-wave plate doing to the linear polarization of 11eV?0.2eV0.1eV0 eV-0.1eVBi2Se3 Bi2Se3 circular dichroism

Z.-H. Zhu et al, PRL 110, 216401 (2013)

0.2eV

0.1eVBi2Se3 Bi2Se3 circular dichroism

Z.-H. Zhu et al, PRL 110, 216401 (2013)

0.2eVSmall circular dichroism existsLinear dichroism dominatesRotating half wave plate by doesnt simply rotate linear polarization by 2

0.1eVFeSe film reaching zone boundary

M18Khv = 21.218eVHelium plasma dischargehv = 10.897eV1024nm+256nm+256nmFeSe 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 pointProblems!

Space Charging

Polarization

ResolutionIncrease rep rate to 10MHz or moreThe limiting factor: power or spot size?Pass energy to get around?How keen are we now perusing 100uW power?MotorizeWhat does the wave plate exactly do upstream the GCM?Quarter wave plate for circular dichroismGo beyond 10meV how about 1meV?