Check and flatten the wavefront in laser room
This procedure assumes that the wavefront sensor (WFS) and focus imaging are already setup, and no significant modification was added to the configuration.
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The focus of the 1m lens is picked off by a flipping mirror and imaged by a 10X objective (currently shared with Inj Far camera) coupled to a CCD camera.
Check WFS alignment and measure wavefront
The WFS beampath is stable if DM Near and DM Far are well aligned. The HASO #7677 is dedicated to measure the wavefront in the laser room.
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- Close the WaveView software. All setting will be saved automatically in the session that you used.
Flatten the wavefront using closed loop.
- Open the WaveTune. The default settings are shown below. Click OK and continue. You will see the following error because the Pharao camera is not connected. It is fine to click CONTINUE. If other errors pop up, it means that the HASO or DM connection is not correct. It will most likely be the DM (wavefront corrector) as shown below. In that case, power cycle the DM controller and reconnect the ethernet cable between DM controller and the server until the error clears. This might happen when there's a power outage or after tunnel measurement.
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- Flatten the wavefront using closed loop.
- Go back to the AO tab.
- Save the current position of the pistons if you think it may be useful. It should remain unchanged from before calibration.
- In AO tab, make sure that correction mode is set to "Auto." Use "costum" only if you want to correct to a reference wavefront, i.e. in tunnel. The saved settings are generally good without change.
- However, if desired, you can change the loop settings in the loop configurator. There you can set the desired maximum number of Zernike orders. For 20-shot average on the fully amplified beam, recommended setting is between 10 – 15. If you want to try higher orders, select Auto in the security check to avoid pistons are driven too far. Use finite number of closed loop correction (normally between 5 – 15).
- Optionally you could open the WFS window and chose "PSF" to observe the strehl ratio during the loop.
- Click the run arrow in the main menu, then select Close loop on. It will run for the number of loops that you have set and stop. Usually the wavefront can be flatten to 50nm RMS and difficult to go down further.
- Check the Inj Far or other far field imaging after the DM during the loop to ensure that the loop works.
- Save the piston positions after the loop.
- Depending on the results, recalibrate the pistons after the loop and repeat the loop to further optimize the wavefront if needed. Typically the strehl ration will exceed 0.9 after 1 loop run.
Close the program. Wait until the following message box shows up. All settings will be save to the current session.
Check and save the new wavefront after loop.
- Open WaveView and save the new wavefront and Zernike polynomials. Make sure that the leading Zernike coefficients (Astigmatism, coma, trefoil, etc.) are optimized compared to before the loop. Now you have flattened the wavefront in the laser room.
- Close the program and exit remote desktop.
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