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Message ID: 2383     Entry time: Fri Aug 2 16:15:01 2019
Author: Nathan Holland 
Type: DailyProgress 
Category: 2micronLasers 
Subject: Frequency Noise Measured by 2um Mach Zehnder. 

Here I follow, essentially, the same setup as in attachment 2 of elog 2377. The difference is that I measured the LO path and IFO paths sequentially, not concurrently. This allowed me to measure at 125 kilosamples per second. Note that there is an error in the pymoku conversion tool when recording on channel 2 only. To circumvent this record both paths with channel 1.

Shown in attachment 1 is the frequency noise of the 2um Mach Zehnder interferometer. Attachment 2 shows the measured phase noises of the individual paths. Attachment 3 contains the plotted frequency spectra, and phase to frequency conversion factor. The conversion factor from phase, in radians, to frequency is:

\frac{c}{2 \, \pi \, n \, { \Delta L }_{\text{IFO}} }

The table below gives the values necessary to calculate this. It is 2.73 x 106 Hz rad-1.

Parameter Value Notes
LO arm length 2.103 m  
Delay line arm length 14.6 m Approximation. Awaiting exact value from Aidan.
Refractive Index 1.4

Assuming SiO2. From refractiveindex.info

Awaiting manufacturer response for precise value.

The smoothed spectra below were generated by this code. The full time series data is too large to upload here, at 272 MB when doubly compressed. Low frequency data is difficult to obtain due to the length of time that there is sufficient SNR for the phasemeter to lock onto the 80 MHz signal. Locking the Mach Zehnder could resolve this problem.

Attachment 1: Measured_Mach_Zehnder_frequency_noise_SmoothMedian__20190805.pdf  22 kB  Uploaded Mon Aug 5 14:55:59 2019  | Hide | Hide all | Show all
Attachment 2: Measured_phase_spectra_2um_Mach_Zehnder_BB_SmoothMedian__20190805.pdf  32 kB  Uploaded Mon Aug 5 14:56:07 2019  | Show | Hide all | Show all
Attachment 3: 2um_MachZehnder_frequency_noise__20190805.hdf5  17 kB  Uploaded Mon Aug 5 14:56:22 2019
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