We present the design and fabrication approach of a rugate narrow band minus filter. A method for the fabrication of graded-index coatings by rapidly alternating deposition of low (SiO<sub>2</sub>) and high (Al<sub>2</sub>O<sub>3</sub>) refractive index materials is introduced, and this technology was used to fabricate a rugate structure. This paper mainly discusses about rugate narrow band minus filter design and fabrication approach. The experimental results show the measured transmittance spectra are in good agreement with the designed value. The laser-induced damage threshold (LIDT) of the narrow band rugate minus filter is measured.
Optics manufactured by mechanical grinding and polishing inevitably will bring surface/subsurface damages and defects during the machining process. Laser polishing has been demonstrated as a technique capable of achieving ultra-smooth surface with no damage and low-defects, but by far optics polished by this technology are only sufficient for illumination applications. To achieve high quality optics, high precision laser ablation has been proved to be a promising technology for shape correction. With pulsed CO<sub>2</sub> laser, high precision laser ablation can be performed by direct evaporation of unwanted surface asperities. To acquire nanometer scale high precision ablation, an accurate control and meticulous adjustment of temperature should be needed. Herein, a mathematical model has been established to assist the understanding of the thermal mechanism of CO<sub>2</sub> laser ablation and subsequently a series of simulations have been extended to investigate the phase change of evaporation. The temperature of fused silica irradiated by CO<sub>2</sub> laser can be controlled via laser power and pulse duration. To achieve nanometer ablation depth, a gentle evaporation regime at low laser intensity is necessary. The results indicated that the ablation depth linearly depend on laser fluence and depth control levels of nanometer are obtainable with the control of laser fluence.
The structure properties of random mask of antireflective structure prepared by the thermal dewetting process are investigated. As a low-cost and large-scale technique, the mask obtained in our work has a great prospect in the field of solar cell and high power laser system. Ultrathin films of amorphous Ag are deposited on the fused silica by magnetron sputtering. By fast thermal annealing the structures in Ag film are agglomerated on the substrate and form mask. The influence of different thickness and annealing temperature on the structure properties of random mask are studied. The surface morphologies are characterized by scanning electronic microscopy. The suitable conditions to obtain excellent quality Ag nanomasks with the pebble particles are achieved.