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1. FAQ

1.1. Video Tutorials

If you are new to the Digilock or are wondering if the Digilock could be the right tool for you, you might find our 3-part tutorial series helpful.

To view the video files downloaded from our web site you will need to have a Quicktime®-compatible media player. Alternatively you can visit the TOPTICA YouTube channel

Part 1 - Introduction

In this tutorial we will give you an introduction to the user interface of the Digilock Software,
and provide an overview of its main features.

Part 2 - Basic locking

In this Digilock tutorial we will introduce you to simple locking techniques using the PID module,
and lock a laser to an atomic reference. To take full advantage of this video, you should be familiar
with operating your laser, and have a basic understanding of active frequency stabilization and the
operating principles of a PID regulator.

Part 3 - Advanced locking

In the third part of our tutorial series we will gradually increase the complexity of our locking setup.

First, we will apply top of fringe locking to a doppler-free signal, using the lock-in module.
In the second step, we will use both PID modules for a two branch feedback loop, where one branch
is assigned to low frequency noise, whereas the other branch is dedicated to the higher frequency components.

To follow this tutorial you should already be familiar with the graphical user interface, and the autolock feature
of the Digilock. You should also have an understanding of the working principle of a lock-in regulator.




1.2. When opening a saved profile I get the message that it already exists


In the dialog window labelled "Select folder with DigiLock profiles" you only need to navigate to the folder containing the desired profile and then click "Current Folder".  In the subsequent window labelled "Open DigiLock profile" you should select the individual profile to load.  This error is generated by double-clicking an individual profile in the first window.  See screenshots below.

After clicking the proper button you will be presented with the following dialog.


1.3. Is it possible to lock onto the Precise Input?

No. Setting of the Jumper (as described in section 11.1 of the user manual) will create a physical connection between Precise In and Main In, so that one will effectively use Main In for the measurement.

1.4. Why can the Precise Input not be used as an input for the LI/PDH module?

Because the Precise In is limited to 200 kHz sample rate whereas the LI/PDH function is capable of modulation frequencies up to 25 MHz.

1.5. Once the signal is locked, the "dot" in the display appears to jump up and down. Why?

This might be related to the configuration of the autolock. To test that, please try the following

  1. In the Function list select "Settings"
  2. Select the "Visibility" tab
  3. Activate "Autolock" within "Advanced Functions"
  4. In the Function List select "Lock"
  5. Click on the "Autolock" tab
  6. In the lower half click the "Advanced" tab
  7. Make sure that the settings for "Cursor snap to set point" is NOT activated and that the "Smart Assistance" feature "Setpoint" is activated

More information about these features can be found in section of the user manual.

1.6. Why is there a lateral offset between the signal curve and the point that indicates the lock point?

In auto-lock mode the oscilloscope works in x-y mode. When locking the scan shown was the last acquired before the lock was enabled.  The offset represents the real drift of the laser relative to the last scan. The effect should become more pronounced if the locking peak is near the edge of the scan window.

1.7. Why is the amplitude for scanning via DTC/DCC limited to 13V, whereas the scan for the SC can be up to 150V?

The DigiLock can only send up to 13 V to the backplane channels that connect it to the other modules. The SC amplifies this signal by a factor of 15 and the Digilock automatically displays the scaled value. This scaling, however, does not happen in the DTC/DCC.

1.8. I get the warning that "Main out" is near or has reached its limit.

This is because the offset value for Main Out is saturated. This can be fixed in the following way:

The accumulation of offset at Main Out is actually a feature (that can be switched off, see below).
Normally when selecting "Unlock and restart scan" it is preferable to have the scan centered around the spectroscopy feature onto which the laser was initially locked. For this reason, the integrator value of the PID is transferred to the offset of the PID output channel. If you lock and unlock frequently, these offsets might add up until the total offset is saturated.

You can disable this feature in the PID tab under the "Settings" menu as shown in the attached screenshot.