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Lena/Aug 2016: Difference between revisions
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== 08/30/2016 ==
=== The problem ===
The magnetometer can take the vector measurements in two channels: X and Y. The Y is orthogonal to both pump and probe, and provides the sensitivity to the main direction at DC, while the X direction signal is demodulated at 1kHz. An LabVIEW filter in FPGA is setup to separate the two signals. The Y signal is obtained by low-pass filtering the signal with two 2-order Butterworth filters, while the X signal is obtained by multiplying the time signal by a reference and low-pass filtering it by the same filters.
[[File:2016.08.18_Ch_1_Probe_Noise_Time_Series.PNG|thumb|Digitization noise]]
The problem is that the Y channel often has large digitization noise (see the picture). The digitization noise disappears when one of the Butterworth filters is deleted (but then the filtering is insufficient).
=== Investigating the filter response ===
We want to find how much the filtering affects the noise of the X and Y channels. To do that we take two measurements:
==== Investigating the filter response ====
- Technical noise (lasers disabled, basically constant voltage comes in from the PD into the preamplifier and then into FPGA)
- 10 Hz AC signal coming straight into FPGA. Expecte
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