Laser calibration procedure


This describes how to calibrate the laser power. This will allow the user to know how much average power he or she is delivering for a given setting on the Pockels cell. The Pockels cell is the device that attenuates the laser power in real time, but it does not have units of Watts.

It is recommended that the laser calibration be done at least once a week; it is great if it is done every morning before an experiment.

Normal laser calibration procedure

Set up

    1. Power up the laser and start PrairieView.

    2. Put on the objective that you would like to calibrate (different objectives will pass different amounts of light so use the objective that you want).

    3. Set the laser to the wavelength of light that you want. The relationship between power in Watts and Pockels cell setting will only be valid for a specific wavelength. If you need to use multiple wavelengths in your experiment, be sure to perform multiple calibrations and make different entries in the table.

    4. Grab the power meter. Currently we use a ThorLabs PM100D. It includes a power cable and a sensor. Hook up the sensor and, if necessary, plug in the unit (battery power may or may not be sufficient depending upon how charged it is).

    5. Set the power meter sensor under the objective by using some sort of stage. (In the past, we have used a flashlight for this purpose, or the Narishige patch manipulator.) Consider taping the sensor down so it doesn't move during the calibration procedures. The center of the sensor should be close to the objective tip but not touching it.

    6. Make sure the power meter "wavelength setting" is set to about 800nm and that the range will allow you to see quantities up to 110mW.

    7. Open the laser calibration table page. Be sure you can are able to edit it. Add an entry for today's date, and note the bias voltage on the ConOptics Model 302RM.

    8. Now we will put the microscope in the mode to shine light straight through the objective. First, open both the "hard" and "soft" shutters by clicking "Hard Shutter". You should hear the shutter click open.

    9. Under the tools menu, choose "Center Galvos". This will arrange the galvonometric mirrors such that the laser points straight through the objective.

Calibration steps:

    1. Look at the laser power on the meter. Slide the pockels cell slider until you see 5mW of power on the meter. Record this value on the laser calibration table page.

    2. Increase the power again until you get 10mW of power, and record the pockels necessary to produce 10mW.

    3. Continue increasing the pockels cell value until you hit increments of 10mW, up to the maximum that you observe (which may be around 100mW). Record these pockels values in the laser calibration table page.


    1. Under the "Tools" menu, turn off "Center Galvos"

    2. Close the hard shutter.

    3. Put away the stage, power meter, etc.

    4. Leave the laser as you want (probably closing the shutter, perhaps putting into standby mode)

    5. Turn off the 2-photon if needed (using


  • What if I get no power for lots of pockels?

      • Check to make sure 1) the laser shutter is open, 2) the hard and soft shutters are open, 3) the turret is in the right position (position 1), 4) the slider on the turret is pulled out (for LSM).

  • What if I get a lot less peak power than I expect?

      • Check alignment, or ask someone to check the alignment. It could be that the laser is not pointing in the correct direction.