Signal to Noise Comparison PEEM-3 and SPHINX Gilbert Group

SPHINX on HERMON Ca Movie Lc1-2_ image at eV FOV 180 µm (diameter of the circle, = 526 pixels) Bin 2x2, thus each pixel is 324 nm. A 1µm x 1µm box is well described by a 3 pixel by 3 pixel square. Exp T = 400 ms x 10 img = 4 sec/energy point PEEM-3 SPHINX on HERMON 1-µm box XANES spectra at the Ca L-edge from 1-µm boxes

PEEM-3 File 4-Lc FOV 20 µm, pol=1, single image at eV (79 of 121 image across the Ca L-edge). Each pixel is ~20nm, thus a 1 µmx1µm box is well represented by a 52 pixel by 52 pixel Exp T = 1 sec x 1 img = 1 sec/energy point 1-µm box PEEM-3 XANES spectra at the Ca L-edge from 1-µm boxes SPHINX on HERMON

Single-Pixel Spectra Positions SPHINX on HERMON image (1 pixel = 324 nm) Red scale bar is 5μm PEEM-3 image (1 pixel = 20 nm) Blue scale bar is 5μm

SPHINX on HERMON 184 single-pixel spectra All averaged to obtain noise-free spectrum PEEM single-pixel spectra All averaged to obtain noise-free spectrum We will then use this noise-free spectrum to extract noise from single-pixel spectra Definition of noise (N) used for both PEEM-3 or SPHINX on HERMON

SPHINX on HERMON Noisy, single-pixel spectrum compared to noise-free average spectrum PEEM-3 Noisy, single-pixel spectrum compared to noise-free average spectrum In both plots, the single-pixel spectrum is slightly displaced up, for clarity Definition of noise (N) used for both PEEM-3 or SPHINX on HERMON

SPHINX on HERMON ratio of noisy, single-pixel spectrum divided by noise-free average spectrum (right hand side axis, centered around zero) PEEM-3 ratio of noisy, single-pixel spectrum divided by noise-free average spectrum (right hand side axis, centered around zero) Definition of noise (N) used for both PEEM-3 or SPHINX on HERMON

Definition of signal minus background (S-B) used for both PEEM-3 or SPHINX on HERMON Intensity of single-pixel spectrum at eV is defined as signal S PEEM-3 SPHINX on HERMON Intensity of single-pixel spectrum at 340 eV is defined as “background” S S B B

SPHINX on HERMON S/N for 10 single-pixel spectra PEEM-3 S/N for 10 single-pixel spectra Definition of S/N used for both PEEM-3 or SPHINX on HERMON

peak 1 intensity Pre-edge Pre-edge RMS Signal/Noise = peak 1 intensity / RMS noise

Definition of S/N used PEEM-3 Pre-edge Pre-edge RMS Peak 1 intensity Signal/Noise = Peak 1 intensity / Pre-edge RMS

Calculation Example Peak 1 intensity: RMS: Signal / Noise = 388* *note: This spectrum was averaged of 9 x 9 single-pixel spectra. This averaging reduced the noise in the background, resulting in an increased signal to noise ratio

Data Summary MicroscopeTotal Acquisition Time / Image SettingsSignal to Noise Ratio* Data File Name PEEM-32 sec2 sec x 1 img2781-Lc SPHINX4 sec400 ms x 10 img178Ca327 PEEM-31 sec1 sec x 1 img1454-Lc SPHINX2 sec400 ms x 5 img131Ca325 *Averaged over calculations from 10 single pixel spectra

The flux (for Ca movie 325) was determined with 202 mA beam current in the Aladdin storage ring, at eV photon energy (Ca L 2 peak uncorrected energy), with entrance and exit slits 23 µm and 150 µm, respectively. N A normal-incidence XUV100 silicon photodiode (International Radiation Detectors, Torrance, CA) was used to measure the beamline flux, by measuring the photocurrent on the XUV100, using the conversion factors provided by the same company. Calculations by Rebecca Metzler edited by Pupa Gilbert With slits at 23 and 150 µm, 202 mA in Aladdin, and at eV, the measured photocurrent was x A, therefore the flux was: Photon flux on HERMON beamline at SRC, where SPHINX was installed for this experiment

At the focal position, on the sample, the flux is further attenuated by two reflections: mirrors M2 and M3. The reflectivities of these gold-coated mirrors at 300 eV at the respective incidence angles are 69% and 64.5% (based on 300 eV, not sure what it is for eV – assuming not much different). The flux on the sample, with 202 mA on the HERMON beamline at eV is therefore: At the focal position, and at normal incidence on the sample, using 150 µm exit slit, the illuminated area is 1000 µm x 300 µm = 3 x 10 5 µm 2. Considering the grazing incidence angle on the sample surface of 16°, the illuminated area increases to 3630 µm x 300 µm =1.1 x 10 6 µm 2. The flux density, therefore is: Photon flux and flux density Calculations by Rebecca Metzler edited by Pupa Gilbert