Novel laser materials with small quantum defects and laser architectures supporting high pulse energies and at high average power have been identified as critical needs for accelerator science. High repetition rates maximize the number of parameters that can be varied in a given experiment, increase the average flux of secondary particle and radiation sources, and increase the amount of data that can be collected or the number of experiments that can be performed. This need has motivated research and development of ytterbium-doped laser amplifiers at 1 µm wavelength, which are now capable of supporting sub-picosecond pulse durations with pulse energy in excess of 1 J and average power exceeding 1 kW.
At the same time, longer-wavelength lasers with high peak and average powers are desired, due both to the λ2 ponderomotive scaling of electron dynamics, and to their attractiveness for pumping longer-wavelength parametric amplifiers (OPCPAs) in the mid-infrared. Tm- and Ho-doped yttrium lithium fluoride (YLF) gain media, which can support amplified pulses with central wavelength of 2 µm and pulse durations as short as 100 fs, are particularly attractive for high-energy, high-average power amplification, due to the small quantum defects that can be obtained with “two-for-one” pumping in Tm:YLF and in-band pumping in Ho:YLF, and their long storage lifetimes which allow efficient multi-pulse extraction schemes.
One of the primary challenges with both Tm:YLF and Ho:YLF amplifiers is the development of suitable ultrafast seed sources for high-energy amplifiers. To meet the needs of the ultrafast science community, such a source must have short pulse duration and moderately high pulse energy to limit gain narrowing and amplified spontaneous emission, as well as stable carrier-envelope phase for attosecond pulse generation and waveform-sensitive experiments. To date, this has been realized by using optical parametric amplifiers based on 0.8 µm or 1 µm pump pulses, which are highly inefficient and complex. In this project, we will develop a hybrid architecture, based on the combination of a frequency-shifted fiber frequency comb and a solid-state regenerative amplifier with gain narrowing and high-order dispersion compensation, which can serve as a compact, “turn-key” front-end for next-generation ultrafast 2 µm lasers. The platform will be demonstrated using highly-stable Er:fiber frequency comb technology, which will be shifted from 1.55 µm to 2.05 µm in a highly nonlinear fiber, and amplified in a Tm,Ho:fiber pre-amplifier followed by a Ho:YLF chirped pulse amplifier with both inter- and extra-cavity gain narrowing and dispersion compensation. To achieve these goals, we leverage team members' expertise in low-noise, low-SWaP Er:fiber frequency combs and nonlinear device packaging, in multilayer optics and compressor design, and in the technology needs for studying waveform-controlled laser acceleration and high-order harmonic generation at relativistic intensities.
The technical knowledge gained during the development of the proposed laser front-end would benefit future development of both Tm- and Ho-doped lasers, which are likely to find increasing applications in for pumping TW-class mid-IR OPCPA lasers and in double-CPA architectures for producing petawatt-class pulses with high energy and high repetition rate over the coming decade.
