This Letter reports on the results of experiments aimed at obtaining high-quality super-smooth surfaces by investigating the laser polishing of fused silica. A maximum reduction in root-mean-square roughness to 0.156 nm was achieved, and laser-polished surfaces exhibited virtually no micro-defects or damage. A subsequent analysis using a multi-physics numerical model revealed the underlying physical mechanism of laser polishing of fused silica. The model simulated the surface smoothing process of laser polishing and demonstrated the effects of surface tension, the Marangoni effect, light pressure, and gravity in the process. It was found that the surface tension dominates the surface smoothing process, and it is a critical factor for achieving sub-nanometer micro-roughness of laser polishing of fused silica. Additionally, the model was successfully applied to predict the residual surface roughness of laser polishing.

Compressing high-energy laser pulses to a single-cycle and realizing the “λ³ laser concept”, where λ is the wavelength of the laser, will break the current limitation of super-scale projects and contribute to the future 100-petawatt and even Exawatt lasers. Here, we have realized ultra-broadband gold gratings, core optics in the chirped pulse amplification, in the 750–1150 nm spectral range with a > 90% −1 order diffraction efficiency for near single-cycle pulse stretching and compression. The grating is also compatible with azimuthal angles from −15° to 15°, making it possible to design a three-dimensional compressor. In developing and manufacturing processes, a crucial grating profile with large base width and sharp ridge is carefully optimized and controlled to dramatically broaden the high diffraction efficiency bandwidth from the current 100–200 nm to over 400 nm. This work has removed a key obstacle to achieving the near single-cycle 100-PW lasers in the future.

Laser damage in fused silica, particularly ultraviolet laser damage, is still a key problem limiting the development of high-power laser systems. In this Letter, a combined process of chemical etching and C O 2 laser polishing was applied to ground fused silica. A super-smooth surface with a root-mean-square roughness of 0.25 nm was achieved through this combined process. Furthermore, the combined process can reduce the introduction of photoactive metal impurity elements, destructive defects, and chemical-structure defects, resulting in a 0% probability damage threshold nearly 33% higher than a conventional chemical mechanical polished sample for a 7.6 ns pulse at a wavelength of 355 nm.

We report a grating solution for achieving broadband and polarization-independent properties that brings a laser combining system to much higher power levels. The grating, with a high-refractive-index-contrast bilayer ridge, was designed and successfully fabricated based on high-power laser coatings, lithography, and ion-beam etching technology. The measured $-1$st order non-polarized reflective diffraction efficiency of the grating exceeds 98% over the wavelength range of 1.023–1.08 μm, and the highest value is 99.15%.

Subsurface damage (SSD), having a great impact on the laser-induced damage threshold (LIDT) of ultra-smooth optics applied in high-power laser systems, should be tightly controlled. An improved total internal reflection microscopy (TIRM), combined with digital image processing techniques, is proposed to quantitatively inspect SSD. With the characteristic that there is a relatively small depth of field (DOF) for a microscope at high magnification (50×), a series of SSD images are captured along with the microscope focusing at different depths under the surface by means of micro-focusing control. The definition of each image is calculated through wavelet transformation. By simulation, the relationship between the definition of TIRM images and the depth of the SSD has been established. According to the definition curve, the SSD depth is acquired. Fused silica glasses polished after fine grinding are measured non-destructively by our TIRM setup. The results show that the improved TIRM is a useful method to evaluate SSD. It is helpful to improve the efficiency of optical fabrication.