In this work, we present for the first time a laser-based dual gas sensor utilizing a silica-based Antiresonant Hollow-Core Fiber (ARHCF) operating in the Near- and Mid-Infrared spectral region. A 1-m-long fiber with an 84-µm diameter air-core was implemented as a low-volume absorption cell in a sensor configuration utilizing the simple and well-known Wavelength Modulation Spectroscopy (WMS) method. The fiber was filled with a mixture of methane (CH₄) and carbon dioxide (CO₂), and a simultaneous detection of both gases was demonstrated targeting their transitions at 3.334 µm and 1.574 µm, respectively. Due to excellent guidance properties of the fiber and low background noise, the proposed sensor reached a detection limit down to 24 parts-per-billion by volume for CH₄ and 144 parts-per-million by volume for CO₂. The obtained results confirm the suitability of ARHCF for efficient use in gas sensing applications for over a broad spectral range. Thanks to the demonstrated low loss, such fibers with lengths of over one meter can be used for increasing the laser-gas molecules interaction path, substituting bulk optics-based multipass cells, while delivering required flexibility, compactness, reliability and enhancement in the sensor’s sensitivity.

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.

In this paper, we analyze the performance of diffusion-based gas distribution in antiresonant hollow-core fiber-based gas absorption cells. Performed theoretical analysis was based on Fick’s second law using the OpenFOAM® software and finite volume method (FVM), followed by an experimental verification of the obtained simulations. The diffusion time was tested for a 1.25 m long fiber, with laser-micromachined microchannels. Full analysis of the correlation between the microchannel count, position, and separation on the rate at which the fiber-based gas cell was filled with the target gas was presented. Experimental results showed that with the proper microchannel configuration, the purely-diffusion-based gas exchange time in the 1.25 m fiber could be reduced from 6 h, down to 330 s. Obtained results correlated with the simulations, giving perspective for the development and implementation of novel miniaturized passively filled gas absorption cells for compact laser spectrometers.

This paper presents a method of manufacturing 3D metamaterial structures using laser radiation. Our proposed material, aluminum nitride (AlN), by interaction of a high-energy laser beam undergoes a direct metallization process, a result of which a conductive aluminum layer is formed on the ceramic surface at the spot of the laser radiation. Using this unique feature on all six sides of an AlN ceramic cube, the designed cross-pairs were mapped. Unit cells were exposed to an electromagnetic wave, by which the occurrence of the resonant areas of reflectance and transmittance for 7.27 GHz and 9.14 GHz was observed. To demonstrate the property of the negative refractive index a prism made out of manufactured cubes was created. For a wave propagating through a wedge-shaped prism for certain frequency bands, a negative refraction angle was observed.

In this work, a novel configuration of a photothermal gas sensor is demonstrated. The measured gas sample is delivered to a gas cell placed inside the linear cavity of a 1.55 m mode-locked fiber laser. The gas refractive index modulation resulting from the excitation by an auxiliary continuous wave laser is efficiently probed by analyzing the phase shift of the self-heterodyne beatnote signal of the mode-locked laser. IQ demodulation combined with Wavelength Modulation Spectroscopy-based signal analysis was employed to optimize and simplify the data acquisition and analysis. A proof-of-concept experiment with detection of carbon dioxide at 2 m wavelength yielded a noise equivalent absorption of 2.2510-7 for 1000 s integration time. The proposed sensor configuration is versatile and can be used to probe any gas molecule, provided an appropriate excitation source is used to induce the photothermal effect.