MesaPhotonics VideoFROG FROGscan, User Manual

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Chapter 4. Aligning a LASER Beam into FROGscan
Page 36 FROGSCAN USER’S MANUAL 09/07/2018 Vs 003
4.2 Aligning a LASER Beam into FROGscan using Alignment Cameras
The camera alignment option was added to FROGscan systems to simplify LASER beam alignment into
FROGscan.
The camera on the right ( Focusing Mirror Camera , see Figure 1) is positioned such that the distance
between the Focusing Mirror – Camera Diverter Mirror – Camera Lens corresponds to the distance
between the Focusing Mirror – Overlap Mirror – Crystal. Therefore, this camera displays the overlap of
the two beams as they would appear in the crystal. This overlap in the crystal is required to generate the
Signal Beam.
The camera on the left ( Fixed Delay Camera , see Figure 1) is installed in place of the Exit iris and
displays the Fixed beam as it would exit through the Exit Iris.
To begin the alignment, proceeds as follows:
7. Direct the LASER beam through the Entrance Iris and Center Iris using the external mirrors as
described in 4.1.
8. Start the Alignment mode by clicking on the Alignment Mode switch in the Setup and Alignment mode
Panel (Figure 22).
Starting this mode causes the diverter mirror to rotate into the beam path between the Focusing
Mirror and the crystal, causing both the Servo Beam and the Fixed Beam to be diverted to the
camera.
A popup screen appears that shows the images from the cameras (Figure 23).
The Focusing Mirror Cameras (top) displays the overlap of both beams as they would appear in the
crystal.
The image recorded by the Fixed Delay Beam Camera (bottom) corresponds to the position of the
beam as it travels through the Exit Iris.
The bottom half of the beam goes to the Servo Mirror (variable delay) and the top half to the Fixed
Delay Mirror (the camera image is upside-down). The Fixed Delay Beam appears as a semi-circle in
this Figure due to the spatial, zero dispersion beam splitter used in FROGscan. The focused spot
appears oval because it is approximately the Fourier transform of the semi-circular beam.
The cursors aid in positioning the beams for optimal alignment and are stored whenever the
alignment mode is ended. During initial setup, the cursors positions are from the factory. A screen
capture showing the factory alignment is provided in the documents with your instrument.
9. Upon initial input of the laser into FROGscan, at least one beam should be visible in the cameras. If
the beams are off-center after the LASER beam was aligned sub-optimally into FROGscan, adjust
FROGscan by sliding it on the optical table until the beams are close to their ideal position.
10. Secure FROGscan on the optical table using the three clamps provided.
11. Align beams precisely using two external mirrors.
12. Check for overlap of the beams on the camera. Block one of the beams by setting the Diverter Mirror
Position control to Block Only One Beam . A change in the intensity of the overlapping beams should
be observable in the top panel as the diverter mirror is moved from blocking only one beam to
blocking both beams.
13. Set the cursors so they intersect the beams displayed in the top panel.
14. Once the beams are positioned correctly, the alignment mode can be turned off by clicking on END
ALIGNMENT MODE in the popup window. This closes the popup window, restores the diverter mirror
to the “off” position (unblocking the beams), unloads the camera drivers, and reconnects the
spectrometer to the computer. Do not exit by clicking on “X” at the top right of the screen.
A few seconds is normally required to place the system back into the data acquisition mode.