Will edited Our_beam_had_a_power__.tex  over 8 years ago

Commit id: de2b9d9ba83082d0faf3d144b5e6a24d2cac0b42

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Our beam had a power of 1 mW. It passed through the rubidium cell, which contained both rubidium 85 and rubidium 87, and hit a photodiode. The photodiode was connected to anSRS fast  amplifier to convert the current output to a voltage  with a gain of 1250, which 1250. The output of the amplifier  was connected to monitored by  an oscilloscope from which we could collect data. The ti:sapphire laser frequency was scanned by applying a linear ramp to the internal cavity of the laser. By changing the length of the cavity, the frequency of the laser is also changed. The cavity length, and thus the frequency of the laser, was changed using a sawtooth function with period T=1 s. The cavity length is controlled by a piezo electric (PZT). After analysis, the PZT appeared to have noticeable nonlinear effects, which results in a not perfectly linear frequency scan, see section .  To monitor the frequency of our light, we used a Bristol Wavemeter. The wavemeter is a scanning Michelson interferometer. For information on how this wavemeter works, see reference .  Out attempt to use the wavemeter as a frequency calibration ultimately failed. The intent was to calibrate the time axis of our transmission graph with a frequency. As mentioned above, the frequency should follow the same sawtooth function as the cavity length.  Unfortunately the wavemeter was not stable enough across a single scan to do this, as can be seen in Figure~\ref{fig:FrequencyScan}. The ti:sapphire laser cavity also drifts in time making exactly repeatable scans not possible.  This instability contributes an additional systematic error that was too time intensive to study for this experiment. We scanned the laser over a frequency range for each of the electronic transitions, tuning the central frequency of our scan to make sure that the absorption was happening in the middle of each scan. The absorption curve for Doppler spectroscopy is a convolution between a Gaussian and a Lorentzian, but we fit to a Gaussian for the reasons described in \textbf{section} . An example of our data fitted to a Gaussian is shown in Figure~\ref{fig:NegativeGaussian}.