The milligram-scale torsion pendulum, suspended by an ultrathin silica fiber, is a highly sensitive instrument for measuring extremely weak force or torque. This requires the fiber diameter to be at the micrometer level or smaller. We present the formation of micrometer-diameter silica fiber using a ${\mathrm{CO}}_2$ laser–based pulling machine. A theoretical model for the laser heating and pulling process is established, revealing that the fiber diameter $d$ depends on the laser power $P$ and the feed-to-pulling speed ratio $v_f/v_p$ as $d\propto P^{-0.5}$ and $d\propto (v_f/v_p{)}^{0.5}$, respectively. In the presented pulling machine, the ${\mathrm{CO}}_2$ laser beam is split into four beams for symmetrical heating, and two guide rails are controlled separately to pull the silica rod. Using this machine, silica fiber with a mean diameter of $3.7\pm 0.6\text{μ}\mathrm{m}$ and a length of 10 cm has been fabricated. The dependence of fiber diameter on laser power and speed ratio were verified by pulling the fibers under different parameters. Furthermore, a pulled silica fiber was welded with a mirror, using the ${\mathrm{CO}}_2$ laser, to form a torsion pendulum. The quality factor of the torsion pendulum was measured to be $(4.02\pm 0.04)\times {10}^5$ at room temperature, demonstrating the low mechanical dissipation of the fabricated silica fiber. We demonstrate a feasible method for producing and evaluating micrometer-scale silica fiber, which supports the development of a milligram-scale torsion pendulum for precision measurement.

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• Gravitational wave detection
• Fibers
• Laser applications
• Bend & torsion tests
• Gravitational wave detectors
• Materials modeling
• Precision measurements
• Sample preparation