Procedure and Apparatus
Procedure
The laser is a tunable diode laser meaning the wavelength of the laser can be changed by changing the current or temperature or both. The beam splitter reflects 10 % of the laser beam to the gold mirror and through the rubidium cell to the absorption detector. The 90% of the beam that passes through the beam splitter is reflected off of two mirrors so that it goes through the rubidium cell in the opposite direction as the 10% beam(Saturation Spectroscopy). The emission photodiode is to the side of the rubidium cell and the laser beam does not go into it because its function is to pick up the emission radiation from the rubidium atoms. The optical isolator in front of the laser keeps the laser beam from being reflected back into the laser and disrupting it in any way. The function generator is there so that the input current to the laser can be ramped. The oscilloscope was also hooked to a computer which recorded the data.
We knew that the excitation of rubidium occurred at 794.98 nm from a previous lab. So by replacing the absorption photodiode with the Wavemeter Jr. we found the current and temperature at which the laser's wavelength was 794.98 nm. We then changed the current over a range to make sure that no mode hops occurred during that range. Then we set up the apparatus so that we could use the Lamb dip method(See apparatus diagram). The function generator was hooked up to the current source so that we could scan over a region of wavelengths, even smaller than the range determined earlier. The photodiodes were connected to the oscilloscope so that we could see the absorption and emission. The lights had to be off in order for the emission to be detected. A triangle wave was used from the function generator, and data was taken over one rise of the triangle wave.
Once the data was recorded it was analyzed to find the difference
in frequency between the peaks to find the hyperfine structure
of rubidium.
