Fig. 1. Design of the curved capillary: (a) schematic view of the curved plasma channel on a sapphire substrate; (b) typical cross-section of the laser etched channel on the substrate.

Fig. 2. Schematic diagram of a plasma channel generated by high-voltage discharging of a gas-filled capillary.

Fig. 3. Scheme for plasma density measurement inside the capillary: (a) diagram of the optical fiber detector for spectrum collection; (b) normalized discharge current waveform and collection gate (labeled by the dashed box); (c) typical spectrum detected by a CCD; (d) typical calculated density distribution along the capillary.

Fig. 4. Effects of different gas-filling modes on the plasma density distribution: (a) single-side gas-filling; (b) two-side gas-filling.

Fig. 5. Plasma density distribution along the laser propagation direction in the curved capillary with different back pressures: (a) single-side gas-filling mode; (b) two-side gas-filling mode. The discharge voltage is 22 kV.

Fig. 6. Effects of the discharge voltage on the longitudinal plasma density distribution: (a) single-side gas-filling mode; (b) two-side gas-filling mode. Here the back pressure is fixed to be 15 psig for all cases.

Fig. 7. Measurement of the radial plasma density distribution: (a), (b) raw spectral images when the gas back pressure is 15 and 30 psig, respectively; (c) effects of back pressure on the radial plasma density distribution, where the marked results are measured and the curves are fitted; (d) dependence of the channel radius (r₀) on the discharge voltage. The discharge voltage for (a), (b) and (c) is 22 kV.

Fig. 8. Temporal evolution of a plasma channel: (a) normalized discharge current in the capillary; (b) evolution of r₀ and n₀ when the back pressure is 25 psig and the discharge voltage is 26 kV.

Fig. 9. (a) Focused laser spot at the entrance of the curved capillary in a vacuum. (b) Laser spot at the exit of the curved capillary without discharging. (c) Guided laser spot at the exit of the curved capillary with discharging.