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 PSL Not logged in Message ID: 1017     Entry time: Wed Jul 11 11:13:38 2012     In reply to: 1014
 Author: Sarah Type: DailyProgress Category: Laser Subject: Transfer Functions

Tara and I measured the correlation between Voltage and Power behind ACAV, and applied the found calibration to get the TF magnitude in the units of Hz/Watt.

Intro:

We wanted to convert the previously measured TF magnitude (elog 1005) into units of Hz/Watt, as opposed to the previously used Hz/RIN. See attached elog (1014) for an explanation of why these units have a more applicable meaning and application.

Setup/Data Obtained:

We measured the power immediately behind ACAV, the power immediately before the pd (there is a beam splitter between the first and second power measurements), and the corresponding voltage after the pd. The pd gain was set to 20dB. I plotted the results and fit each data set: The fit equations are:

pd fit: y = 5680.4x + 0.036843

cavity fit: y = 2923.3x + 0.027703

Where y is the voltage (Volts) after the pd and x is the power (Watts) in front of the pd for the pd fit, and right behind the cavity for the cavity fit.

TF Magnitude in Hz/Watt:

Using the slope of the line relating the power behind the cavity to the voltage as the calibration, I was able to convert the previously measured TF magnitude into the units of Hz/Watt, and plot it against the calculated TF (elog 1014) magnitude in units of Hz/Watt (calculated using Cerdonio et al's results): Application to Noise Budget:

I also plotted the RIN induced noise using the TF in units of Hz/Watt using :

Frequency Noise = TF[Hz/Watt] * RIN * Power_in

I used an input power of 2mW, and the RIN from 6/13 behind ACAV. The frequency noise generated is a factor of 1.4 larger than that generated using the TF in units of Hz/RIN. Since the TF in Hz/RIN was measured, it is more reliable. This discrepancy indicates that the TF magnitude is also probably too high, and there is a possible error in the calibration constant used to convert voltage to power, or possibly an error in the power readings.

 Attachment 2: TF_calc_meas.fig  31 kB  Uploaded Wed Jul 11 14:28:07 2012
 Attachment 4: Voltage_Power_Calibration.fig  11 kB  Uploaded Wed Jul 11 17:47:16 2012
 Attachment 5: plot_tf_unit.m.zip  2 kB  Uploaded Wed Jul 11 17:47:28 2012
 Attachment 7: nb_TF_unit.fig  308 kB  Uploaded Wed Jul 11 17:50:05 2012
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