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4.4 Aligning the Light Lever Force Sensor
Aligning the light lever force sensor is greatly facilitated by understanding the optical path of
the light in the sensor. The following figure shows the light path and the effect of turning the
adjustment knobs on the light lever.
left/right
Photodetector
Gain Switch
Motion of the red dot in the Pre-
Scan window when the detector
adjust knobs are turned clockwise.
4.4.1 Tips for Aligning the Light Lever Force Sensor
1.
Bringing the cantilever within a milimeter of the sample's surface can help the user see
the laser on the sample.
2.
If the cantilever does not align within a few minutes, try another cantilever.
3.
After replacing a cantilever, the laser and photo-detector adjustments are usually less
than a single turn.
4.
The adjustment screws have backlash; sometimes the motion is not perfectly linear.
5.
The detector has two modes: high and low gain. High gain allows more laser light
through the detector than low gain. Low gain is commonly used for tip scanning
systems.
6.
When in vibrating mode, if the resonance peak appears inverted at the top, reduce the
amplitude slider. If further adjustments are necessary, switch the detector gain from
high to low.
7.
If the Beam Position is not aligned within a few turns of the adjustment knobs, the
photo-detector can be manually adjusted by loosening the set screws holding the
detector down and repositioning the detector so that the Top + Bottom signal is maxi-
mized while the Beam Position is mostly centered.
V 1.1 / LS-AFM Users Guide
up/down
Motion of the laser spot when the laser
adjust knobs are turned clockwise.
left/right
up/down
Laser
Section 4-4
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