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 paper, the combination of using an anti-resonant hollow-core fiber (ARHCF), working as a gas absorption cell, and an inexpensive, commercially available watch quartz tuning fork (QTF), acting as a detector in the quartz-enhanced photothermal spectroscopy (QEPTS) sensor configuration is demonstrated. The proof-of-concept experiment involved the detection of methane (CH₄) at 1651 nm (6057 cm⁻¹). The advantage of the high QTF Q-factor combined with a specially designed low-noise amplifier and additional wavelength modulation spectroscopy with the second harmonic (2f-WMS) method of signal analysis, resulted in achieving a normalized noise-equivalent absorption (NNEA) at the level of 1.34 × 10⁻¹⁰ and 2.04 × 10⁻¹¹ W cm⁻¹ Hz^−1/2 for 1 and 100 s of integration time, respectively. Results obtained in that relatively non-complex sensor setup show great potential for further development of cost-optimized and miniaturized gas detectors, taking advantage of the combination of ARHCF-based absorption cells and QTF-aided spectroscopic signal retrieval methods.

In this paper, dual-band gas detection using a combination of the light-induced thermoelastic spectroscopy (LITES) and an antiresonant hollow-core fiber-based (ARHCF) gas absorption cell is demonstrated. The broad wavelength operation capability of a standard 32 kHz quartz tuning fork and the self-developed fiber-based gas absorption cell was exploited to demonstrate quasi-simultaneous detection of N₂O and CO₂, at 4570 nm (2188.2 cm⁻¹) and 2006 nm (4985.9 cm⁻¹), respectively. The signal analysis was based on the wavelength modulation spectroscopy technique, allowing to achieve a noise equivalent absorption coefficient (NEA) of 8.6 × 10^–7 cm⁻¹ and 1.7 × 10^–6 cm⁻¹ for N₂O and CO₂, respectively. The results indicate that the combination of ARHCFs with the LITES method is well suited for the design of broadband gas detectors and show remarkable potential in the fabrication of miniaturized, versatile and relatively inexpensive gas sensors operating over a wide spectral range, thus allowing multigas detection.

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.

We present the first demonstration of using the second harmonic generation effect to upconvert dissipative soliton resonance laser pulses. We have designed and built two independent dissipative soliton resonance lasers, emitting rectangular shaped, nanosecond pulses in the 1.06 μm and 1.56 μm wavelength regime, respectively. Periodically poled lithium niobate crystals with appropriate periods were used as the nonlinear medium. Dissipative soliton resonance pulses with central wavelengths of 532 nm and 780 nm and pulse energies of 0.15 μJ and 0.02 μJ were generated as the result of the second harmonic generation effects. Conversion efficiencies of 30% and 4% were obtained for conversion of 1.06 μm and 1.56 μm pulses, respectively.