Lasers

We currently have four diode lasers shooting at the cell at about 30W each at a wavelength of ~795nm (NIR). The light is carried down to the Hall from the laser lab behind Hall A counting House by 75m long fibers. These fibers are connected to the five legs of the 5-to-1 combiner the output of which goes through an assembly of polarizing optics and finally hits the target cell pumping (upper) chamber. This page describes in detail the procedure to turn lasers ON and OFF, and what to keep an eye on for safety of the fibers and the lasers.

    ⇒ Turning Lasers ON
    ⇒ Turning Lasers OFF
    ⇒ Checking Fiber Temperatures
    ⇒ Frequently Asked Questions

1. Make sure that the oven temperature is at least 170 °C. Ideally it should be around 235-245 °C. Also, have the lasers VNC window and Spectrum Analyzer VNC window running on the main target Windows machine. See here how to run them.
2. On the Linux machine on the left, open the laser controls panel. (hlamain → Polarized 3He Target Controls → Main Laser Controls → Laser 1, Laser2, Duo 1.)
3. Follow this rule closely: Always wait about one minute before turning the next laser on.
4. Set the current for Laser 2 to 35A and hit Enter. Do this while the cursor is in the text window else the changes will not be accepted. The readback value should change to 35A. (This might already be set; in that case, go to the next step in this list.)
5. Hit Enable, wait 5 seconds and hit Start. A green rectangle should appear next to the Start button, and the status shoulld change to ON. Two other checks to verify the lasers are on: the Spectrum Analyzer should show something non-flat (similar to the sample taped to the monitor, but maybe a bit shallow) and the light on laser 1 in the laser VNC window should turn on.
6. Wait a minute!
7. Set the current for Laser 3 to 35A (if it is not already set). Then do the usual Enable → Start.
8. Wait a minute!
9. In the Duo Laser window, set the current on Duo Laser 1 to 35A AND current on Duo Laser 2 to 0A. This is important. Then wait a minute. Then set Duo Laser 2 current to 35A and hit Enter.
10. Now, all four lasers should be running. The spectrum should match the sample taped to the monitor and all four lights on the laser front panels on the laser VNC window should be on.
11. The oven temperature will rise by about 5 C°. This is normal. It'll go down to the set T in a while.

Hit stop on all the four laser windoes. Status should say Disabled and the rectangle next to the Stop button should be lit. Spectrum will be flat and laser panel lights will be off. Oven temperature will go down a little for a while.

On the he3laser computer window, there should be a few temperature readouts visible, as seen in the figure below:

These indicate the optical fiber temperatures. These are not yet interlocked to the lasers but I'll do it as soon as I get the chance. In the meanwhile, please keep an eye on the readouts - especially the first one on the left in the window - and if any of them rises significantly, page me at 584-5751. You might want to turn lasers off if the change is drastic.

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