dc.description.abstracteng | This thesis describes the implementation of a high precision laser system which, as a first
demonstration of its capabilities, has been used to measure electronic transitions from
the X²Π₃⸝₂, v''=0, J''=3/2 rovibronic ground state to the 12 lowest levels of the A²Σ⁺,
v'=0 vibronic state in the hydroxyl radical (OH) and the 16 lowest levels of the same
vibronic state in the deuterated hydroxyl radical (OD). The relative uncertainty of the
absolute frequency measurements is within a few parts in 10¹¹. These electronic transition
frequencies are determined by comparing the spectroscopy laser with reference frequency
standards using an optical frequency comb (OFC). The OFC transfers the high short
term stability of a narrow-linewidth I₂ stabilized referenced laser onto the spectroscopy
laser around 308 nm. The second reference used with the OFC is an atomic clock, which
provides an absolute accuracy of the measured transitions frequencies. The OH and the
OD molecules are inside a highly collimated molecular beam, with the ultraviolet (UV)
laser beam propagating perpendicular to it. This setup reduces possible pressure shifts
and Doppler-broadening. Additionally, the laser beam is retroreflected to reduce Doppler-shifts.
Shifts due to Zeeman-, AC-Stark- and saturation-effects are also considered in the
analysis, in an effort to determine the zero-field transition frequencies.
Previous studies determined the absolute A ← X transition frequencies with an accuracy
of approximately 100 MHz, based on rich Fourier-transform spectra. In contrast, this
thesis supplies absolute electronic transition frequencies with an uncertainty of less than
100 kHz. These new measurements of the optical transition frequencies were combined
with existing data for fine and hyperfine splittings in the A state and used to fit the parameters
of an effective Hamiltonian model of the A²Σ⁺, v'=0 state of each isotopologue.
Some of these newly-determined spectroscopic constants, are orders of magnitude more
precise than the previous values.
Future experiments will benefit from the improved accuracy of the electronic excitation
frequencies determined in this experiment. As a next step, a new mid-infrared laser will
be used to probe the vibrational excitation frequencies of OH. This OFC-stabilized mid-infrared
optical parametric oscillator (OPO), which provides a narrow linewidth and wide
tuning range, is also described in this thesis. | de |