The research presented in this thesis addresses the development of directly diode
pumped Yb3+:KY(WO4)2 and Yb: bre lasers, operating at several-hundred-MHz
repetition frequencies and investigates their suitability as the basis of high-e ciency,
convenient, low-cost and moderate precision optical frequency combs.
The design, construction, and characterisation of a 1042-nm 1-GHz Yb3+:KY(WO4)2
femtosecond laser is presented, achieving pulses with an average power output of 770
mW, bandwidths of 3.8 nm, and durations of 278 fs. The laser achieved an opticalto-
optical conversion e ciency and slope e ciency of 61% and 69%, respectively, and
the relative intensity noise was <0.1%. Spectral broadening of the output pulses
in a photonic crystal bre with a negative dispersion wavelength of 975 nm and a
core diameter of 3.7 m resulted in a supercontinuum with a bandwidth of 400 nm,
which was insu cient to enable f-2f referencing.
A re-designed Yb:KYW laser was demonstrated, operating at a pulse repetition
frequency of 666 MHz and producing pulses with reduced durations of 220 fs and
increased bandwidths of 5 nm, while maintaining an average output power of >700
mW. Repetition-frequency locking was implemented on this laser and had the e ect
of reducing its relative intensity noise from 1.1% to 0.5%, with limitations on the
locking stability being traced to cantilever-like vibrational modes of the mirrormount
assemblies.
A fully stabilised 1030-nm Yb: bre frequency comb operating at a pulse repetition
frequency of 375 MHz was developed. The comb spacing was referenced to
a Rb-stabilised microwave synthesiser and the comb o set was stabilised by generating
a supercontinuum containing a coherent component at 780.2 nm, which was
heterodyned with a 87Rb-stabilised external cavity diode laser to produce a radiofrequency
beat used to actuate the carrier-envelope o set frequency of the Yb: bre
laser. The two-sample frequency deviation of the locked comb was 235 kHz for an
averaging time of 50 seconds, and the comb remained locked for over 60 minutes
with a root mean squared deviation of 236 kHz
