Signal to Noise ComparisonPEEM-3 and SPHINX

Gilbert Group7.11.2011

SPHINX on HERMON

Ca Movie 327 -- Lc1-2_008681 image at 352.6 eVFOV 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-edgefrom 1-µm boxes

PEEM-3

File 4-LcFOV 20 µm, pol=1, single image at 351.9 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-edgefrom 1-µm boxes

SPHINX on HERMON

Single-Pixel Spectra PositionsSPHINX 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 HERMON184 single-pixel spectraAll averaged to obtain noise-free spectrum

PEEM-3258 single-pixel spectraAll 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 HERMONNoisy, single-pixel spectrum compared to noise-free average spectrum

PEEM-3Noisy, 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 HERMONratio of noisy, single-pixel spectrum divided by noise-free average spectrum(right hand side axis, centered around zero)

PEEM-3ratio 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 352.6 eVis defined as signal S

PEEM-3SPHINX on HERMON

Intensity of single-pixel spectrum at 340 eV

is defined as “background”

SS

BB

SPHINX on HERMONS/N for 10 single-pixel spectra

PEEM-3S/N for 10 single-pixel spectra

Definition of S/Nused for both PEEM-3 or SPHINX on HERMON

0 2 4 6 8 10 120

2000400060008000

100001200014000

(Signal - Background) / Noise

Single Pixel Spectra number (arbirary)

Sign

al to

Noi

se R

atio

0 2 4 6 8 10 120

100200300400500600700800

(Signal - Background) / Noise

Single Pixel Spectra Number (arbitrary)

Sign

al to

Noi

se R

atio

Definition of S/N usedfor both PEEM-3 or SPHINX on HERMON

peak 1 intensity

Pre-edgePre-edge

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

Definition of S/N usedPEEM-3

Pre-edge

Pre-edge

Pre-edge RMS

Peak 1 intensity

Signal/Noise = Peak 1 intensity / Pre-edge RMS

Calculation Example

Peak 1 intensity: 175.43 RMS: 0.45242

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

Microscope Total Acquisition Time / Image

Settings Signal to Noise Ratio*

Data File Name

PEEM-3 2 sec 2 sec x 1 img 278 1-Lc

SPHINX 4 sec 400 ms x 10 img 178 Ca327

PEEM-3 1 sec 1 sec x 1 img 145 4-Lc

SPHINX 2 sec 400 ms x 5 img 131 Ca325

*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 353.3 eV photon energy (Ca L2 peak uncorrected energy), with entrance and exit slits 23 µm and 150 µm, respectively. NA 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

XUV100 conversion factor =photon energy (eV)

4.2383.5e ph

Flux(XUV100) 6.876x10 6A

1.602x10 19C

4.29x10 13e s

83.5e ph5.14x10 11ph s

With slits at 23 and 150 µm, 202 mA in Aladdin, and at 353.3 eV, the measured photocurrent was 6.876 x 10-7 A, therefore the flux was:

Photon flux on HERMON beamline at SRC, where SPHINX was installed for this experiment

Flux(HERMON ) 5.14x10 11ph s x0.69x0.645 2.29x1011ph s

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 353.3 eV – assuming not much different). The flux on the sample, with 202 mA on the HERMON beamline at 353.3 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 105 µm2. Considering the grazing incidence angle on the sample surface of 16°, the illuminated area increases to 3630 µm x 300 µm =1.1 x 106 µm2. The flux density, therefore is:

Photon flux and flux density

Calculations by Rebecca Metzler edited by Pupa Gilbert