TEMPO

The beamline is equipped with two APPLE II helical insertion devices. They have periods of 44 mm and 80 mm and allow us to cover the whole energy range of the beamline using the first harmonic.

The picture shows the two insertion devices installed in the straight section of Soleil. The HU80 is quasi-periodic to reduce as much as possible the higher harmonic contamination of the photon beam.

We can see here the magnetic arrangement.

Insertion Device calibration and alignment

The energy calibration of the insertion devices emission is a critical point of the beamline operation in terms of flux, polarization end reliability of the installation. 
Since the very beginning of the beamline commissioning this activity was done in collaboration with the insertion device group of Soleil (GI). Calibration tables for the gap and the phase values of the APPLE II insertion devices where calculated by GI as a function of the photon energy to fit our experimental data obtained by measuring the emission spectra of the ID. The calibration was done for four polarization configurations: linear vertical and horizontal, circular left and circular right. An essential step of the calibration procedure was to define properly the diaphragm size (ID emission cone) and his position at the center of the emission cone of the undulator. The diaphragm was closed to 400 μm and scanned in the horizontal and vertical plane. For each position we obtained the energy spectra presented in Fig. 1 as a function of the photon energy. While moving to the ID axis, the intensity increases and the photon flux maximum is centered to higher photon energies. In the inset, are presented the maximum intensity and the photon energy of the maximum extracted from the spectra as a function of the diaphragm position. 

 Fig. 1: Photon flux spectra measured as a function of the photon energy by scanning vertically the diaphragm closed at 400 microns. The measurements are performed on a calibrated photodiode placed at the sample position. The maximum intensity and the energy of the maximum are reported in the inset as a function of the diaphragm position to define the axis of the insertion device. 

The procedure was applied for the HU44 and the HU80 for the four main polarizations and at some characteristic photon energies. Using the fast scan procedure the data in Fig. 1 can be measured in less than one hour. 

 The first mirror chamber is placed in the radioprotection hutch at about 20 meters from the source. The photon beam is first deflected by a plane mirror. Depending on the incidence angle it can follow two optical paths characterized by a deflection angle of 2 and 4 degrees. The beam is then reflected by a thoroidal mirror placed at 2 or 4 degrees for high and low energy photon respectively. 

The Silicon mirrors are Pt coated and cooled to 100K by a closed circuit of high pressure liquid nitrogen.

The picture shows the three mirrors support inthe clean room during the mirror alignment. The copper tubes are in closed circuit for liquid nitrogen cooling.

Alignement diagnostics

Two slits are placed at the horizontal and vertical focal points of the toroidals mirrors. The transmitted intensity is used as a diagnostics of the extraction region (M1 mirrors) alignment. On the left you can see the intensity beam profile obtained scanning horizontally the position of a vertical slit 50 microns wide, placed before the gratings. It allow us to determine the correct alignment in the horizontal plane. The transmitted intensity presented on the right  is measured while scanning the opening of the entrance slit. The beam size depends on the photon energy, but when the alignment is good, more than 50% of the intensity is transmitted through the minimum slit width of 5 microns.

The monochromator is composed by three plane gratings and two spherical mirrors. The gratings presents a Variable Line Spacing (VLS) to focus on the exit slits and a Variable Groove Depth (VGD) to optimize total photon flux and harmonic rejection at each photon energy.

The monochromator is then characterized by two optical paths : one for low energy  ranges and the other for high energy ranges. The photon energy intervals are summarized in the table.

Alignment procedure

Picture taken during the first monochromator alignemnt. The alignment was carefully verified by Alignment group and Optic group.

Energy Resolution

The resolution tests were performed measuring the ion yield spectra in the energy region close to the resonant 2p excitation of atomic argon as well as the rydberg series of helium and the 1s excitation of molecular nitrogen. The spectra were obtained by monitoring the total number of ions produced in the interaction region between the monochromatic synchrotron radiation beam and an effusive gas jet emanating from a small nozzle. The results obtained for Helium, Argon and Nitrogen are shown in the following panels. In order to extract the Gaussian broadening introduced by the beamline, we have to take into account the intrinsic Lorentzian width of lines. 
The resolving power E/ΔE is higher than 10.000 for the three energies.

Nitrogen 1s absorption edge 

Ar absorption 

He

Spot size on the branch line

The spot size has been measured positioning a fluorescent YAG screen at the sample position and taking an image with CCD camera and a calibrated magnification optic placed at about 300 mm (S. Kubsky, Surface Laboratory).

3D representation of the photon beam intensity

Comparison of the image obtained by ray tracing calculation(left) and of the measured focal spot (right) for the same field of view: 300μm x 300μm.

UHV Photoemission

The main branch of the TEMPO beamline is equipped with a UHV system for surface science experiments. It is composed by a main chamber equipped with a Scienta SES 2002 electron energy analyzer (equipped with a delay line detector) and a preparation chamber with a sample transfer system and a fast entry lock. Ar- sputtering, water cooled evaporators and LEED characterization are available. We have developed two sample environments: one for magnetic dichroism experiments where about 100 Oersted can be applied in the measuring position and one for direct heating of semiconductor samples by current flow.

The UHV Photoemission experimental station in 2008

Detector For Time Resolved experiments

An important part of the TEMPO beamline scientific project is based on time resolved photoemission experiments performed using a pump probe technique. Possible applications are to studies of the electronic structure of laser excited states or the dynamics of surface magnetization. 
The relaxation time of these phenomena can be longer then the interbunch period. It is then indispensable to associate each detected photoelectron to the synchrotron bunch which created it. If this identification is possible , then each repetition rate of the pump can be used for the experiments and the state excited by the laser pump can be probed by the Syncrotron Radiation pulse as a function of the delay Δt between the two pulses. 
The time resolution of the experiment is then limited only by the S.R. pulse width: 30 ps at SOLEIL 
We modified the Scienta SES 2002 electron energy analyser by replacing the CCD Camera by a delay line detector (G.Cautero and coworkers, Elettra, Trieste, It) which can associate each detected photoelectron to the Soleil Clock. This new configuration allows us to perform photoelectron spectroscopy experiments using the isolated bunch when Soleil is injected in hybrid mode.

In the picture the photoemission intensity measured as a function of time on a revolution period (about 1.2 μs) is compared to the Soleil bunch structure during a run in hybrid mode.

This focal spot has been used for the photon beam commissioning. Here we have performed gas phase experiments (M. Meyer, LIXAM) to measure the monochromator resolving power and the total photon flux with a calibrated diode.

First photon beam image at the focal spot registered at the TEMPO beamline

The picture was taken on February 12th 2007 with the monochromator in total reflection mode. The well centered spot is the result of the good work done by the alignment group.

External user equipments can be installed at this focal point:

XPEEM from Lab. L. Néel (Grenoble)

The PEEM from Louis Néel Laboratory (Jan Vogel) has been installed on the branch line since 2008 to perform magnetization dynamics experiments.

(a) Initial magnetic domain structure of a 200 nm wide nanowires after applying some magnetic field pulses.
(b) Domain structure after application of one 10 ns long current pulse with a current density of 4.2 x 1011 A/m2. The direction of  electron flow is indicated in the image. The small white arrows indicate domain walls that have moved, in the direction of the electron flow. The blue arrow points to a new domain that has nucleated.
(c) Domain structure after application of an identical pulse, but in the opposite direction. Some of the domain walls, indicated by small white arrows, have moved back in the opposite direction. These data confirm that the domain wall motion is due to the spin torque effect induced by the spin polarized current. However, the domain wall motion is not exactly reversible, indicating the strong role played by domain wall pinning in our system.

NanoEsca CEA @ TEMPO Beamline

The NanoESCA (Omicron Nanotechnology) experimental station of CEA-LETI, has been installed for two periods of several weeks in 2009 and 2010. The spectro-microscopy set-up is composed by two hemispherical analyzers in cascade which compensate the aberrations introduced by only one hemisphere. The transmission is high enough to work with a high energy resolution (Up to 100meV) in valence band and core level spectromicroscopy experiments. The photon flux was high enough to keep a good lateral resolution of 100nm in valence band experiments and below 100nm in core level. 
A picture of the NanoEsca station installed on the branch of the TEMPO beamline is shown here. The system was operational on the X-ray beam after few days of installation, alignment and baking. The equipment was open to external user projects.

The NanoEsca experimental Station @ TEMPO