NAOJ GW Elog Logbook 3.2
Previously the EOM was rotated by 45 degree, and then input polarization was along x axis of lab frame. The modulation depth observed was not that good. This was because the input polarization was parallel to the crystal. The crystal is already rotated by 45degree inside the housing of EOM. So, we we should either rotate the input polarization by 45deg or the EOM. I took the path of least action and rotated the polarization by 45deg using a polarizer.
The input polarization was tuned to become circular using QWP, HWP. Then polarizer was installed in rotator mount. I inject for now a 45degree rotated polarization. The power of input pol is now 0.86mW.
The transmission of EOM is 0.85mW. So, transmision is around 98%.
I then apply modulation at 189.969KHz, using a noninverting amplifier circuit from Fig 1. Previously I was using Inv amplifier design, but the matched impedance with moku halves the input voltage. So, I went for a high impedance circuit design using Noninv amplifier. I took into account the losses in the circuit during simulation, which predicts the maximum voltage I have is 286V. I want to install transformer after opamp, to amplify more. If you are impedance matched your circuit will always act as voltage divider circuit, and the input voltage will be halved. A high-z circuit helps achieve no drop in input voltage of the circuit. For our circuit, to ensure minimal reflection, the cable should not be long (1km).
The modulation is observed after a polarizer in cross polarizer configuration, with the input polarizer. The response is shown in Fig 2. The data was noted from the spectrum analzyer as PSD units, Vp-p/sqrt(Hz). I then multplied this value to convert to power using coversion factor of photodiode.
My circuit seems to have saturated after 2.5Vp-p input or so. I need to investigate this. But, the response of the modulation doesn't change after 2.5V.
I use the power ratio to compute the maximum voltage I am reaching now, and it's around 255V.
Data is saved in 'C:\Users\atama\Dropbox\EOM 2D\EOM 1\Characteristics_20250304.txt'
Also, I observed the change in the oscilloscope of values duirng modulation and without modulation. The mean value of voltage remains same as 2.15V. The peak to peak value is the only one which changes.
The spectrum of laser modulation at 2.5Vp-p from moku, with harmonics.
Yesterday, I had noted the PSD units of voltage. As the ratio power is Outputpower/Input power, I redid measurements to take into account only Vp-p. In the following plot you can see the saturation after 2.5V or so. ]
