Fig. 1. Anti-resonant waveguide schematic. (a) Transmission of the light field when the resonant wavelength is satisfied; (b) transmission of the light field when the resonant wavelength is not satisfied

Fig. 2. AR-HCF drawing flow chart. (a) Drawing glass capillary; (b) stacking capillary; (c) drawing optical fiber preform; (d) drawing optical fiber

Fig. 3. AR-HCF parameters. (a) Scanning electron microscopy image of fiber cross section (outer diameter of the fiber is 220 μm and core diameter is 43 μm); (b) fiber loss spectrum (0.06 dB/m@2.5 μm)

Fig. 4. Simulation results of mode field characteristics and transmission characteristics of ice cream type AR-HCF. (a) HE₁₁ mode and second order mode with a transmission wavelength of 2.5 μm in the fiber; (b) loss of the fundamental mode and second order mode

Fig. 5. Principle of absorption spectrum

Fig. 6. Near-infrared and mid-infrared linestrengths of H₂O and CO₂ at 2000 K (from HITRAN2016). (a) H₂O; (b) CO₂

Fig. 7. TDLAS system diagram

Fig. 8. Spots at different distances after collimation

Fig. 9. High temperature water vapor absorption signal of different transmission fibers. (a) High-temperature water vapor absorption signal when ZBLAN optical fiber is used as the transmission medium, and 4029.52 cm^-1 is the high-temperature water vapor absorption line; (b) high temperature water vapor absorption signal when AR-HCF is used as the transmission medium,and 4029.78 cm^-1 and 4029.52 cm^-1 are the water vapor absorption lines at room temperature and high temperature, respectively

Fig. 10. Comparison of baseline fitting before and after vacuum pumping of AR-HCF