Deep UV Laser Micromachining System
The F2 laser produces 7.9-eV photons that are known to damage UV-grade fused-silica glasses in long exposures, possibly through absorption involving three- and four-group silicon-ring structures. In low-GeO2 (i.e., 5%) glasses, the 157-nm photons directly bridge the ~7.1-eV bandgap, which allows access to strong singlephoton photosensitivity mechanisms without the need of traditional enhancement techniques.
Using a custom-designed 157-nm excimer laser micromachining system, a series of novel MFFPI sensors are created. Because these micro fiber-optic sensors are directly engraved on silica or sapphire fibers through formation of high-quality, in-line FP etalons, they can offer a number of outstanding advantages, such as very small size, selftemperature compensation, high-temperature (>300°C) survivability, and capability for mass production. These sensors can easily measure strain, pressure, refractive index, temperature, and acceleration in harsh environments.
Figure 3.14 Schematic of micromachining system based on 157-nm excimer laser. (From Ran, Z. L. et al. 2007. Optics Letters, 32(21), 3071-3073.)
The custom-designed 157-nm laser micromachining system is shown in Figure 3.14. The optical absorption coefficient at 157 nm has a high value of up to ~20,000 cm-1, making it possible to achieve high-quality cool machining of silica or sapphire fibers. The 157-nm laser micromachining system consists of a 157-nm pulsed laser, an optical focusing system with 25x demagnification, and a precise translation stage used to mount the fiber to be engraved. The maximum single pulse energy, pulse width, and pulse repetition rate of the 157-nm laser are 35 mJ, 15 ns, and 50 Hz, respectively.