*Article* **Fabrication of Microchannels in a Nodeless Antiresonant Hollow-Core Fiber Using Femtosecond Laser Pulses**

**Paweł Kozioł 1,\*, Piotr Jaworski 1, Karol Krzempek 1, Viktoria Hoppe 2, Grzegorz Dudzik 1, Fei Yu 3,4, Dakun Wu 3,4, Meisong Liao 3, Jonathan Knight <sup>5</sup> and Krzysztof Abramski <sup>1</sup>**


**Abstract:** In this work, we present femtosecond laser cutting of microchannels in a nodeless antiresonant hollow-core fiber (ARHCF). Due to its ability to guide light in an air core combined with exceptional light-guiding properties, an ARHCF with a relatively non-complex structure has a high application potential for laser-based gas detection. To improve the gas flow into the fiber core, a series of 250 × 30 μm microchannels were reproducibly fabricated in the outer cladding of the ARHCF directly above the gap between the cladding capillaries using a femtosecond laser. The execution time of a single lateral cut for optimal process parameters was 7 min. It has been experimentally shown that the implementation of 25 microchannels introduces low transmission losses of 0.17 dB (<0.01 dB per single microchannel). The flexibility of the process in terms of the length of the performed microchannel was experimentally demonstrated, which confirms the usefulness of the proposed method. Furthermore, the performed experiments have indicated that the maximum bending radius for the ARHCF, with the processed 100 μm long microchannel that did not introduce its breaking, is 15 cm.

**Keywords:** antiresonant hollow core fibers; femtosecond laser micromachining; microchannel fabrication; microstructured fibers
