The temporal contrast requirements for high-power laser pulses have become increasingly stringent with rising irradiance levels. Over the past decade, in addition to discrete pre-pulses, spatiotemporal pulse pedestals have attracted significant attention as a major limiting factor for contrast quality in chirped-pulse amplification systems, primarily caused by imperfections in their stretching and compression optics. In this work, we present the first direct high-resolution single-shot measurement of these contributions in the spatiotemporal domain using an imaging spectrometer in combination with a two-dimensional self-referenced spectral interferometer.

We demonstrate a high-efficiency, high-power Er:CaF2 single-crystal fiber (SCF) continuous-wave (CW) laser pumped by a 976 nm laser diode. By carefully analyzing the thermal lensing effect and optimizing mode matching, we achieved a maximum CW output power of 10.02 W, corresponding to a slope efficiency as high as 32.2% for pump power below 25 W. To the best of our knowledge, this represents the highest output power ever reported for 2.8 μm SCF lasers, approximately an order of magnitude higher than previous results. In addition, a wavelength redshift beyond 2.8 μm was observed at high power, extending beyond the strong absorption region of water vapor. These results indicate that Er-doped CaF2 SCFs are promising candidates for high-power mid-infrared lasers.