> For the complete documentation index, see [llms.txt](https://arpes-1-2.gitbook.io/arpes-1-2/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://arpes-1-2.gitbook.io/arpes-1-2/manuals-arpes-1-2/starting-the-experiment/changing-light-parameters.md).

# Beamline control

Starting beamline control panel; changing photon energy and polarization; adjusting Rx of SMU

## Beamline control software (BLC)

### Taking the beam

Usually the window of beamline control panel is always open on the left monitor. If it was closed you can find it by pressing Start button and typing "BLC".  Alternatively you can use the icon in the taskbar:

![Icon of BLC Starter](https://1019940988-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-M4xyQ1EYH71vPc02yXQ%2Fuploads%2Fg3ZaWkXjpWrMdINnTRzU%2FBLC%20taskbar%20icon.png?alt=media\&token=f3f794b4-e6be-4ce5-a50d-0cbc1f0c5740)

Main menu displays the outline of all beamlines coming from UE112 undulator:

![Only the top branch (marked by a blue frame) is related to 1-squared/1-cubed stations](https://1019940988-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4xyQ1EYH71vPc02yXQ%2F-M_LgBErouYKpC_OmgJb%2F-M_LhEWHykPxTdzUPwpB%2FBLC13_main_1squared.png?alt=media\&token=2fc5814d-c7e0-42f7-9533-3a230c627a55)

Switching Mirror Unit (SMU) is used to switch beam between two main branches, our branch is PGM2. Click on "SMU" button to open the control panel and make sure that circle in front of "PGM2" is green:

![Green indicator "ready" means that SMU is not moving.](https://1019940988-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4xyQ1EYH71vPc02yXQ%2F-M_LgBErouYKpC_OmgJb%2F-M_Li2vf57f6njgHlZcJ%2Fsmuswitch.png?alt=media\&token=7cbe9a0e-d7e9-49cf-804e-09c1832265e2)

If it is not, then make sure that:

1. your neighbors at PGM1 finished their work
2. the beamshutter is closed

After that press the square button in front of "PGM2" to get the light and wait until "PGM2" indicator turns green.

{% hint style="warning" %}
If beam is directed to a wrong branch, beamshutter will not open.
{% endhint %}

SMU\_2 switches beam between 1-Squared (dsl) and 1-Cubed (dsr) endstations. 

{% hint style="info" %}
dsl/dsr means "downstream left/right", which is left/right if you look from the ring towards the endstation.
{% endhint %}

Click on SMU\_2 in the main menu and make sure that the green circle is in front of dsl (1^2):

![In this screenshot beam is at 1-Squared](https://1019940988-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4xyQ1EYH71vPc02yXQ%2F-M_LgBErouYKpC_OmgJb%2F-M_LjbHj1ysxnbwHatmN%2Fsmuswitch1.png?alt=media\&token=3d0a88c8-0a5f-47cb-a8ef-4a9f4de131d1)

If it is not, then make sure that:

1. your neighbors at 1-Cubed finished their work
2. the beamshutter is closed

After that press the square button in front of "dsl" to get the light and wait until "dsl" indicator turns green.

{% hint style="success" %}
After finishing your shift it is a good tone to switch the beam to your neighbors, this way you tell them that you finished and they will not need to worry about step #1.
{% endhint %}

### Changing photon energy

![](https://1019940988-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4xyQ1EYH71vPc02yXQ%2F-M_MqCEu4dE84Poaj7bP%2F-M_MqXlW482JKcLaTjTO%2FMonochromator.png?alt=media\&token=f07acddb-7281-4a8b-bc56-529e15a59564)

Open the blue panel by pressing **UE112-PGM2** button in the main menu, insert the required value of photon energy in the field **Energy (eV).** While inserting values cursor should remain inside the field. Press enter. After that monochromator will be set to the specified photon energy and undulator gap will be adjusted according to the loaded ID table (ID=Insertion Device). 

{% hint style="warning" %}
ID tables are different for each light polarization! Make sure that you are using the right one (see [section about light polarization](/arpes-1-2/manuals-arpes-1-2/starting-the-experiment/changing-light-parameters.md#changing-light-polarization) for more details).

In the top left button you should see **ID On**, if ID is Off, then only monochromator will move resulting in a very low intensity.

If you see error "ID is local" please check [this section](/arpes-1-2/manuals-arpes-1-2/starting-the-experiment/changing-light-parameters.md#controlling-undulator-status).
{% endhint %}

### Manually adjusting SMU for different photon energies (now it's done [automatically](/arpes-1-2/manuals-arpes-1-2/starting-the-experiment/auto-beam-position-control.md)!)

After changing the photon energy beam will deflect from optimal trajectory and start hitting one of the beamline slits (one can see it on the top-right monitor). Therefore beam position has to be adjusted for each photon energy. This procedure has been automated (see details [here](/arpes-1-2/manuals-arpes-1-2/starting-the-experiment/auto-beam-position-control.md)).

If you still need to fix this manually, go to SMU112\_1 panel and press **SMU/experts** -> **PGM2**. 

{% hint style="danger" %}
**! Important !** 

Use only **SMU112\_1** that is closer to the ring! **Not** SMU112\_2! If you moved wrong SMU, it is not critical for operation, but don't forget to tell the beamline scientist, then correct parameters can be recovered.
{% endhint %}

The following panel will appear:

![](https://1019940988-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4xyQ1EYH71vPc02yXQ%2F-M_MqCEu4dE84Poaj7bP%2F-M_MsYkchHUFxnorALfL%2FSMU_experts.png?alt=media\&token=aa536da1-0c49-4d29-bcb2-60be31dfdfe3)

Use **only** the middle parameter (M3 Left Rx) and change the value using + or - until you reach maximum photoemission intensity. Please refer to the dedicated camera image of the horizontal apertures for guidance. Both apertures are covered with phosphorus thus UV radiation is visible. In the adjusted position the 90% of the beam should come through the gap between the apertures and only some shoulders are visible on the phosphorus.

{% hint style="success" %}
Use step 0.1 for large changes in photon energy and 0.02 for fine tuning.

Rules of thumb about the directions: \
If you increase $$h\nu$$, the Rx value should be reduced and vice-versa.\
If you see the beam to the right from the slit, you need to increase Rx and vice-versa.
{% endhint %}

{% hint style="warning" %}
Actual value of Rx is shown on the left (in the picture it is **203300**, not 191200), you can write it down for you favourite energies. Value in the box is just what you entered last time.
{% endhint %}

### Changing light polarization

In the blue monochromator panel press button "**Monochromator experts**" (top-left corner). In the pop-up menu select "**Undulator**". After some time a panel with a graph will appear, press "**Related panels**" in the top-left, in the pop-up menu press "**Select Table**".

Press the button in the right-bottom and select one of the four tables (Linear Horizontal, Linear Vertical, Elliptic +/-). Now the table is selected, ***but undulator and monochromator did not move yet***! 

Go again to the blue monochromator panel, click inside the energy field and press enter (**even if you did not change the photon energy value**). This will start the movement of monochromator and undulator with respect to the new table. Movement can take some time, wait until blue panel shows "**Ready**".

{% hint style="info" %}
Tip: circular polarization can be used to suppress the second harmonic signal (e.g. if you see core levels in the valence band or above the Fermi level, they are most probably coming from the synchrotron radiation with energies $$2h\nu$$, $$3h\nu$$ etc. that can pass through the monochromator).
{% endhint %}

### Controlling undulator status

To check the actual status of undulator press the big button **UE112** on the very left of the main menu.\
This panel is mainly useful for troubleshooting. First of all, "ID control:" should be **remote**. Sometimes after machine group restores the beam they need to open undulator gaps and they control IDs "locally", i.e. from the control room. After the beamshutters are open again, the "ID control:" may remain in "**local**" status, then you must change it to "**remote**" using this panel. 

You can also directly check the gap value and the values of undulator shifts that are used to control light polarization (linear horizontal polarization should correspond to shifts of 0, in linear vertical parallel shift is 56 mm).

![](https://1019940988-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4xyQ1EYH71vPc02yXQ%2F-MhsODLlmyyzSmUDzZfk%2F-MhsOz0HhFRu0ofD_xon%2FUndulator_status.png?alt=media\&token=8d395dd9-951a-415b-87b5-ea681e013198)