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Nick Brewer: Difference between revisions
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* The reflection dip percentage <math>\eta=1-\frac{I_R}{I_{in}}</math>
A couple days ago I shined 84.1 mW of 1055 nm light through the input coupler and measured 4.4 mW transmitted, that corresponds to an input reflectivity of <math>R_{in}</math> = 0.9476. I tried to measure the reflection off of the flat surface of the input coupler to account for that but I was unable to see anything; the reflected beam was too big and bright. In the future I should try again with less power.
After aligning the cavity today I measured the finesse by just looking at the ratio of the FSR to the FWHM of the cavity peaks and found <math>F</math> = 65.5.
I also measured the cavity dips from the reflected beam and found that the dip minimum to be 1.01 V and the max value to be 1.21 V. I am confused whether 1.01/1.21 is <math>\eta</math> in the formula above or if it is just <math>I_R/I_{in}</math>.
Once the cavity was tuned and the temperature was adjusted to be at the optimal value, we measured 5.5 mW of green (I'm almost positive we used the right wavelength settings on the power meter). The input power was ~45 mW. That is an efficiency of ~12%. If I take <math>\eta=1.01/1.21 \rightarrow I_R/I_{in}=0.165</math> and figure out the mode matching coefficient with the other measured values above, I get m=0.84 (very well mode matched...almost too well). If there is 45 mW of power before the cavity, and the mode matching coefficient is 0.84, that means that 36 mW of power is being coupled into the cavity. When I ran the Matlab code I wrote to simulate the cavity enhancement, I find that for and input coupler with T=0.05, we should expect ~12% efficiency. This result is so close to what we measured that I almost certainly calculated something wrong. If I use <math>I_R/I_{in}=1.01/1.21=0.83</math>, I get a mode matching coefficient of m=0.12, which corresponds to 5.4 mW getting coupled into the fiber, which is less than the green power we got out.
'''5/20/14'''
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