Experiments with Supersonic Beams as a Source of Cold Atoms

Figure 5.24: A schematic of the tellurium saturated absorption spectroscopy setup.
The frequency of the pump beam is offset by double passing through a 57 MHz AOM
that compensates for the frequency difference between the line in tellurium and the
1/4 harmonic of the hydrogen line. Figure Courtesy Travis Bannerman.
is mode-matched to a second doubling cavity, which is identical to the first except
that it uses a beta barium borate (BBO) crystal as the nonlinear medium instead
of LBO. The BBO crystal is used because of its optical properties in the UV. The
second doubling cavity produces approxiately 2 mW of light at 243 nm.
Between the first and second doublers, approximately 10 mW of 486 nm light
is picked out of the beam and used in a saturated absorption spectroscopy setup to
lock the diode laser frequency. More detail on saturated absorption spectroscopy can
be found in [111]. Molecular tellurium is used as a frequency reference for the diode
since the lines around 486nm have been mapped to better than 1MHz [112–114], and
the i2 line has been found to be approximately 57MHz above the 1/4 harmonic of the
1S − 2S transition [115]. This frequency difference can be compensated for by double
passing the pump beam of the saturated absorption setup through an acousto-optic
modulator (AOM), as shown in figure 5.24. The spectroscopy signal is fed back to
the piezo on the diffraction grating, locking the laser frequency. More detail on the
laser setup can be found in [116].
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