THORLABS DMH40-F01, Руководство по эксплуатации

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© 2021 Thorlabs
2 Operating Principle
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2.3 Closed Loop Control
The Thorlabs Deformable Mirror software allows for closed loop control using a sensor and the
DMH40 to be set up in order to achieve flat, spherical, or other wavefront shapes. Basically,
there are two methods to build closed loop feedback: either by using a photo detector with the
analog feedback input of the DMH40 (1) or by using a wavefront sensor feedback loop with the
respective software solution (2).
1) Analog Feedback Loop
A part of the manipulated beam, derived from a polarization independent beam splitter, is direc-
ted via a focusing lens and a pin hole onto a photo detector (PD). The output signal of the
photo detector is connected to an
Analog Feedback Connector (not included). This Analog
Feedback Connector can then be plugged into the DMH40 analog feedback input jack. The
feedback values can be used to optimize the adaptively adjusted wavefront. A simple max
search algorithm can be programmed (not included in the GUI or driver) to optimize the wave-
front without a wavefront sensor.
This feedback method works for 2 cases:
a. Flat Wavefront
If the beam focus is located exactly in the plane of the pinhole, the optical power incident on the
photo detector will be at a maximum in the case of an ideally flat wavefront.
b. Spherical Wavefront
If the focal point is located in front of or behind the pinhole, the optical power into the photo de-
tector will be maximized when the wavefront is spherical.
The analog feedback input (2.5 mm stereo jack) of the DMH40 provides two separate inputs
dedicated to voltage and current feedback signals. The current input can be connected directly
to a photodiode.
Note
There is no internal calibration for the current and voltage values. These are just feedback val-
ues that are suited for maximum search algorithms but not for exact measurements!
2) Wavefront Sensor Feedback Loop
Using the measurement results of a Thorlabs Wavefront Sensor, the Thorlabs Deformable Mir-
ror software can control the wavefront reflected from the DMH40 according to the settings. This
way it is possible to generate a flat wavefront.
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