Experiments with Supersonic Beams as a Source of Cold Atoms

the electron g-factor which causes the resonance energy of the the 1S − 2S transition
to vary with magnetic field. The g-factor varies with the principle quantum number
n as [108]
ge(n) =ge
This leads to a frequency shift of [109]
1 − α2
3n2
. (5.5)
δν = 186kHz/T. (5.6)
In the quadrupole trap, this corresponds to shift of up to 65 kHz, which will limit the
resolution of any spectroscopy performed in the trap.
5.4.1.2 The Hydrogen Laser
The laser which will be used to excite the 1S −2S transition is currently under
construction. The original design was based on the laser described in [110]. To create
light at 243 nm, a diode laser at 972 nm was amplified and frequency doubled twice.
This laser was found not to produce enough power at 243 nm to efficiently drive the
transition, and the front end of the laser is currently being replaced with an optically
pumped semiconductor laser (OPSL) at 972 nm which should enable more UV power
to be generated.
A schematic of the original laser system constructed by Travis Bannerman is
shown in figure 5.23. A tunable extended cavity diode laser (ECDL) is used to produce
single-mode light at 972 nm. Because the laser frequency must be quadrupled, and
the eventual excitation is a two-photon process, phase noise in the laser must be
reduced as much as possible. A diffraction grating mounted 27 cm from the diode
creates a long cavity with acts as a flywheel, reducing high-frequency phase noise.
The frequency of the laser can be tuned by changing the angle of the diffraction
grating with a piezo stack, and the frequency and single mode operation of the laser
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