  We demonstrate a versatile technique for generating continuously
wavelength-tunable laser waveforms, with mJ pulse energies and ultrashort pulse
durations down to few-cycle in the ultraviolet C and visible spectral ranges.
Using the processes of self-phase modulation or Raman-induced spectral
broadening, we substantially expand the spectrum of a femtosecond 1030 nm
Yb:CaF$_{2}$ laser, allowing for an extensive wavelength-tunability of the
second and fourth harmonics of the laser within the visible and ultraviolet C
spectral regions at 460-580 nm and 230-290 nm. In addition, our approach
exploits nonlinearly assisted self-compression in the second harmonic
upconversion of the spectrally broadened infrared pulses with high-order
dispersion. This results in 8-30 femtosecond pulses in the visible with an
intensity enhancement of up to 30 times. Such an ultrashort visible and
ultraviolet C source is ideal for investigating ultrafast dynamics in
molecules, solids, and bio and nano systems. Furthermore, this tunable light
source enables the generation of bright, narrow-bandwidth, continuously
wavelength-tunable, coherent light in the extreme ultraviolet to soft X-ray
spectral region. Theoretically, the X-ray pulse structure can consist of
sub-200 as pulse trains, making such a source highly suitable for dynamic
multidimensional imaging. This includes coherent diffractive imaging of
ferromagnetic nanostructures where resonant X-ray scattering is essential, as
well as X-ray absorption spectroscopies of advanced quantum materials at
pico-nanometer spatial and atto-femtosecond temporal scales.
