Technology for ultrafast lasers at 2-µm wavelength

This project addresses the needs outlined in Section C56-35 of the Topics for FY 2023 Phase I, Release 2 DoE SBIR/STTR and more specifically the lasers of Type III and IV listed in the table shown in this section. Over the past decade, a growing number of applications have emerged that require stable, high energy and high repetition rate 2 µm wavelength lasers either for direct use or to drive secondary sources either into the mid-IR or the soft X-ray. Long-wavelength ultrafast lasers have been identified as promising drivers for the acceleration of proton or light ions with applications for highly targeted cancer therapy. Laser systems with energies in the multi-mJ, multi-kHz parameter range at 2 µm wavelength have also been identified as ideal sources to produce coherent soft X-ray radiation into the waterwindow via high harmonic generation (HHG). This soft-X-ray radiation find applications in the study of novel quantum materials or for the inspection of Si wafers in semi-conductor fabs. Over the past decade, there have been efforts to develop 2 µm wavelength lasers as well as all necessary components in this spectral region. These efforts have mainly followed three orientations: (i) ultrafast, mJ, hundreds of kHz Tm-doped fiber lasers, (ii) ultrafast, kHz, mJ-level Cr2+:chalcogenide solid-state lasers and (iii) few-ps, kHz, tens of mJ Ho-doped solid-state lasers. Despite these efforts, the maturity of 2 µm ultrafast lasers still lags behind that of 1 µm systems. In particular, there is currently no clear pathway to scale ultrashort (sub-ps), 2 µm wavelength pulses to the hundreds of mJ at tens to hundreds of Hz and higher repetition rates. In this work, we propose to investigate the spectroscopic and thermo-optic properties of Ho:CALGO, Ho:CaF2, and engineered Ho:YLF and assess their suitability for the direct amplification of optical pulses to the tens to hundreds of mJ at sub-ps duration and investigate repetition rate limitations at these energy levels. CALGO and CaF2, when doped with Yb-ions have successfully enabled the simultaneous amplification of high energy and broadband pulses. While the literature is scarce on the topic – the few papers that have investigated the spectroscopic properties of Ho:CALGO and Ho:CaF2 do show promise in their potential to amplify ultrashort pulses to high energies. The Phase I of this project will be focused on studying the feasibility of a laser amplifier that would directly deliver tens to hundreds of mJ pulses with duration ideally in the sub-300 fs duration regime. The Phase II of the project would be focused on designing and constructing such laser system, building upon DoE funded work at KMLabs that has already been productive .