Laser LEAP

From Northwestern University Center for Atom-Probe Tomography

[edit] Laser shut down and start (as of May 12, 2006)

[edit] Laser On-Off Policy

Since the laser diodes have a limited lifetime (1000h guaranteed), the laser is to be shut down by the last laser user of the day, in particular over night and over the weekends. This is done by pressing the 'stop' Laser Head button in the 'Instrument admin' tab of the LCC, select device 'Laser'.

[edit] How to turn the laser back on

• Laser start procedure: Press the 'start' Laser Head button in the 'Instrument admin' tab of the LCC, select device 'Laser'.The laser currently has four states: Off, Start-up, Warm-up, and On. Start-up takes about 2-3 min and this is the time until the laser diodes produce a pulse (The LED's on the laser rack turn from orange to green and HV1 lights up green). The button in the admin tab and also the status indicator change color to yellow. The laser can be used after this initial start-up time. It takes, however, longer for the laser and all components between the laser and the tip to fully thermally equilibrate during the warm-up period, and during this period small fluctuations (10-20%) of the laser power may be observed. The laser power is monitored continously and the measured value displayed during a laser run in the 'statistics' pane. After one hour, it is assumed that all components have stabilized and the button and status indicator change to green. This period of one hour is empirically determined by Imago and is the time after which they did not observe any drift of the laser power anymore, the system can, however, reach 'reasonable' stability much earlier. When the laser pulse frequency is changed, the system needs to reequilibrate and monitoring the measured laser power is recommanded.
  • Since following a start-up of the laser, typically routines are performed for which a perfectly stable laser power is not absolutely essential (such as running a test aluminum tip, aligning the tip to be investigated), there is no reason to wait for the laser system to fully equilibrate. If your experiment is sensitive to small fluctuations, however, you may want to turn on the laser one hour before you start your critical experiment. A feature that lets us program the laser to start up at a given time on a given day has been requested from IMAGO.
• To perform a laser pulse energy calibration (recommanded after the laser has warmed-up), click the 'calibration' button in LCC->Instrument admin->laser.