Industrial applications increasingly demand femtosecond and picosecond pulse duration laser systems with a range of wavelengths from the near infrared to the ultraviolet. This paper reports a dual function thin slab femtosecond amplifier system operating at a range of wavelengths via frequency conversion. A Yb:YAG thin slab amplifier was demonstrated that incorporates both the pre-amplifier and power amplifier functions in a single crystal. To ensure efficient, homogenous pumping of the thin slab a novel diode bar imaging technique is used. The combination of the homogenous pumping and the unique amplifier architecture enables average output powers < 200 W to be maintained across a range of pulse repetition frequencies from 1 MHz to 40 MHz with a pulse duration of 50 ps at a wavelength of 1030 nm and M<sup>2</sup> ~ 1.2. The pulse was compressed to a duration of 900 ± 100 fs with a compressor efficiency of < 90 %. A modified LXR100 system which is based on this technology was used as the fundamental 1030 nm source, with output powers up to 130 W, from 1 MHz – 10 MHz and pulse durations in the 900 fs regime. Second harmonic generation of 515 nm was achieved by coupling the beam into a type-1 critically phase matched LBO crystal to enable efficient conversion whilst avoiding damage. Second harmonic generation of 515 nm to < 95 W at a conversion efficiency of ~74 % and pulse energy of < 96 μJ and M<sup>2</sup> < 1.3 was achieved. Further wavelength conversion was undertaken by coupling the 515 nm and unconverted 1030 nm output into a second LBO crystal for third harmonic generation. Type-1 and type-2 phasematching configurations for third harmonic generation were investigated, with an output power of < 20 W and pulse energy of < 20 μJ achieved at 343 nm with a conversion efficiency with respect to incident 1030 nm of < 21 % for both configurations.