Gas-filled Hollow-core Fiber Research Articles

Quasi-all-fiber structure CW mid-infrared laser emission from gas-filled hollow-core silica fibers

A quasi-all-fiber structure CW mid-infrared fiber lasers based on gas-filled hollow-core fibers (HCFs) is firstly reported here. Through a thermally tapered single-mode fiber, the CW tunable 1.5 μm fiber pump light is coupled into an acetylene-filled anti-resonance HCFs, and the coupling point is sealed with epoxy glue to ensure the stability and gas tightness, then the HCFs is filled with acetylene gas by a specially designed small gas cell, just like an end cap. When the pump is precisely tuned to the resonance with the absorption lines of acetylene, CW mid-infrared emission around 3.1–3.2 μm is generated at room temperature with maximum power of ~180 mW and slope efficiency of ~14%. The laser threshold is also discussed as function of acetylene pressure. This work opens new opportunities for all-fiber mid-infrared lasers of new wavelengths those unavailable for traditional rare-earth-doped fibers.

Midinfrared Pulse Generation by Pumping in the Normal-Dispersion Regime of a Gas-Filled Hollow-Core Fiber

Based on numerical simulations, the authors offer a midinfrared pulse source that uses hollow-core optical fiber filled with gas. Such a source could find applications across a large variety of sectors in science and technology (particularly biomedical), due to its conceptual simplicity. The approach taken in this work resolves all major issues related to pulse generation in the midinfrared spectral region. The system promises to be highly robust against noise, and has a major advantage over existing devices, in using a pump in the 1-$\ensuremath{\mu}$m wavelength range, which is readily available.

Optimal pulse propagation in an inhomogeneously gas-filled hollow-core fiber

We study optical pulse propagation through a hollow-core fiber filled with a radially inhomogeneous cloud of cold atoms. A co-propagating control field establishes electromagnetically induced transparency. In analogy to a graded index fiber, the pulse experiences micro-lensing and the transmission spectrum becomes distorted. Based on a two-layer model of the complex index of refraction, we can analytically understand the cause of the aberration, which is corroborated by numerical simulations for a radial Gaussian-shaped function. With these insights, we show that the spectral distortions can be rectified by choosing an optimal detuning from one-photon resonance.

Energetic few-cycle pulse compression in gas-filled hollow core fiber with concentric phase mask**Project supported by the National Natural Science Foundation of China (Grant No. 61521093), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB1603), the International Science and Technology Cooperation Program of China (Grant No. 2016YFE0119300), and the Program of Shanghai Academic/Technology Research Leader, China

The compression of high-energy, linearly polarized pulses in a gas-filled hollow core fiber (HCF) by using a concentric phase mask is studied theoretically. Simulation results indicate that using a properly designed concentric phase mask, a 40-fs input pulse centered at 800 nm with energy up to 10.0 mJ can be compressed to a full width at half maximum (FWHM) of less than 5 fs after propagating through a neon-filled HCF with a length of 1 m and diameter of with a transmission efficiency of 67%, which is significantly higher than that without a concentric phase mask. Pulses with energy up to 20.0 mJ can also be efficiently compressed to less than 10 fs with the concentric phase mask. The higher efficiency due to the concentric phase mask can be attributed to the redistribution of the transverse intensity profile, which reduces the effect of ionization. The proposed method exhibits great potential for generating few-cycle laser pulse sources with high energy by the HCF compressor.

Multioctave supercontinua from shock-coupled soliton self-compression

Fiber-optic multioctave supercontinuum generation is a unique resource for ultrafast optical science, enabling ultrabroadband frequency-comb technologies and paving the way for the photonics of subcycle field wave forms. Extension of these methods to the midinfrared spectral range encounters numerous challenges, calling for radically new approaches in fiber optics and short-pulse generation technologies, as well as for closing the gaps in our understanding of optical nonlinearities in the midinfrared range. Here, we confront these challenges by showing that multioctave supercontinua spanning from the ultraviolet to the midinfrared range can be generated by shock-wave-coupled soliton self-compression of ultrashort midinfrared pulses in a gas-filled antiresonance-guiding hollow-core photonic-crystal fiber. Analysis of the fiber output spectra, measured within a broad range of gas pressures and input driver energies, shows that multioctave supercontinuum generation in this setting becomes possible due to soliton self-compression coupled to shock-wave pulse self-steepening, yielding extraordinarily short, sub-half-cycle field transients.

Deep-UV to Mid-IR Supercontinuum Generation driven by Mid-IR Ultrashort Pulses in a Gas-filled Hollow-core Fiber

Supercontinuum (SC) generation based on ultrashort pulse compression constitutes one of the most promising technologies towards ultra-wide bandwidth, high-brightness, and spatially coherent light sources for applications such as spectroscopy and microscopy. Here, multi-octave SC generation in a gas-filled hollow-core antiresonant fiber (HC-ARF) is reported spanning from 200 nm in the deep ultraviolet (DUV) to 4000 nm in the mid-infrared (mid-IR) having an output energy of 5 μJ. This was obtained by pumping at the center wavelength of the first anti-resonant transmission window (2460 nm) with ~100 fs pulses and an injected pulse energy of ~8 μJ. The mechanism behind the extreme spectral broadening relies upon intense soliton-plasma nonlinear dynamics which leads to efficient soliton self-compression and phase-matched dispersive wave (DW) emission in the DUV region. The strongest DW is observed at 275 nm which corresponds to the calculated phase-matching wavelength of the pump. Furthermore, the effect of changing the pump pulse energy and gas pressure on the nonlinear dynamics and their direct impact on SC generation was investigated. This work represents another step towards gas-filled fiber-based coherent sources, which is set to have a major impact on applications spanning from DUV to mid-IR.

Multioctave supercontinuum from visible to mid-infrared and bend effects on ultrafast nonlinear dynamics in gas-filled hollow-core fiber.

Broadband supercontinuum generation is numerically investigated in a Xe-filled nested hollow-core antiresonant (HC-AR) fiber pumped at 3μm with pulses of 100fs duration and 15μJ energy. For a 25cm long fiber, under 7bar pressure, the supercontinuum spectrum spans multiple octaves from 400nm to 5000nm. Furthermore, the influence of bending on ultrafast nonlinear pulse propagation dynamics is investigated for two types of HC-AR fibers (nested and non-nested capillaries). Our results predict similar nonlinear dynamics for both fiber types and a significant reduction of the spectral broadening under tight bending conditions.

Laser-Induced Dispersion With Stimulated Raman Scattering in Gas-Filled Optical Fiber

Laser-induced dispersion provides an all-optical means for dynamically controlling light propagation. Previous works on dispersion control with a laser beam make use of Kerr non-linearity, electromagnetic-induced transparency, and stimulated Brillouin scattering in optical fibers. Here we report, for the first time to our knowledge, optically controllable dispersion with stimulated Raman scattering in a gas-filled hollow-core optical fiber and show that flexible dispersion tuning can be achieved by varying optical pump power and wavelength as well as gas concentration and pressure in the hollow core. As an example of application, we demonstrated the use of such laser-induced dispersion for high-sensitivity hydrogen detection and achieved a normalized detection limit of 17.4 ppm/(m·W) with dynamic range over four orders of magnitude.

Generation of a single-cycle pulse using a two-stage compressor and its temporal characterization using a tunnelling ionization method

A single-cycle laser pulse was generated using a two-stage compressor and characterized using a pulse characterization technique based on tunnelling ionization. A 25-fs, 800-nm laser pulse was compressed to 5.5 fs using a gas-filled hollow-core fibre and a set of chirped mirrors. The laser pulse was further compressed, down to the single-cycle limit by propagation through multiple fused-silica plates and another set of chirped mirrors. The two-stage compressor mitigates the development of higher-order dispersion during spectral broadening. Thus, a single-cycle pulse was generated by compensating the second-order dispersion using chirped mirrors. The duration of the single-cycle pulse was 2.5 fs, while its transform-limited duration was 2.2 fs. A continuum extreme ultraviolet spectrum was obtained through high-harmonic generation without applying any temporal gating technique. The continuum spectrum was shown to have a strong dependence on the carrier-envelope phase of the laser pulse, confirming the generation of a single-cycle pulse.

Towards all-fiber structure pulsed mid-infrared laser by gas-filled hollow-core fibers

We report here on a diode-pumped pulsed mid-infrared laser source based on gas-filled hollow-core fibers (HCFs) towards an all-fiber structure by the tapering method. The pump laser is coupled into an acetylene-filled HCF through a tapered single-mode fiber. By precisely tuning the wavelength of the diode to match different absorption lines of acetylene near 1.5 μm, mid-infrared emission around 3.1–3.2 μm is generated. With 2 m HCFs and 3 mbar acetylene gas, a maximum average power of 130 mW is obtained with a laser slope efficiency of ∼24%. This work provides a potential scheme for all-fiber mid-infrared fiber gas lasers.

1.56 μm and 2.86 μm Raman lasers based on gas-filled anti-resonance hollow-core fiber

We report here a single-pass 1.56 μm fiber gas Raman laser in a deuterium-filled hollow-core fiber and a 2.86 μm cascade fiber gas Raman laser with methane in the second stage. The maximum output powers at 1.56 and 2.86 μm are 27 and 8.5 mW with Raman conversion efficiency of 30% and 42%, respectively. The results offer a new method to produce a 1.5 μm fiber source and prove the potential of the cascade fiber gas Raman laser in extending the available wavelength.

Poor-man’s model of hollow-core anti-resonant fibers

We investigate various methods for extending the simple analytical capillary model to describe the dispersion and loss of anti-resonant hollow-core fibers without the need of detailed finite-element simulations across the desired wavelength range. This poor-man's model can with a single fitting parameter quite accurately mimic dispersion and loss resonances and anti-resonances from full finite-element simulations. Due to the analytical basis of the model it is easy to explore variations in core size and cladding wall thickness, and should therefore provide a valuable tool for numerical simulations of the ultrafast nonlinear dynamics of gas-filled hollow-core fibers.

Long-Lived Refractive-Index Changes Induced by Femtosecond Ionization in Gas-Filled Single-Ring Photonic-Crystal Fibers

Plasma recombination always follows photoionization of gas by intense femtosecond laser pulses, causing refractive-index changes via thermal and hydrodynamic effects. In gas-filled hollow-core photonic-crystal fibers, these phenomena are induced by self-compressing pulses with $\ensuremath{\mu}$J energies. Probing from the side of the fiber, the authors see refractive-index changes lasting tens of $\ensuremath{\mu}$s, and plasma-driven acoustic waves that excite MHz vibrations in the microstructure of the fiber. These results are important for the development of high-intensity, high-repetition-rate lasers where, in addition to nonlinear optics, plasma physics and optoacoustics also become relevant.

Spectral broadening of radially polarized pulses through a gas-filled hollow-core fiber

Spectral broadening of a radially polarized (RP) pulse in a gas-filled hollow-core fiber (HCF) is experimentally studied. Broad spectrum covering from 540 nm to 1070 nm is obtained. It is found that the output spectrum preserves the RP state after nonlinear propagation in HCF, both for the components in the input pulse and for the newly generated spectral portion. This method shows great potential in generating RP sources with unprecedented spectral width, and may also be extended to other kinds of cylindrical vector beams.

Generation of ultrashort pulses by four wave mixing in a gas-filled hollow core fiber

The four wave mixing (FWM) process is widely exploited for the generation of tunable ultrashort light pulses. Usually this process is driven in bulk materials, which are however prone to optical damage at high pump laser intensities. A tunable source of ultrashort 10 μJ level pulses in the visible spectral region is described here. In particular, we report on the implementation of FWM driven by a two-color ultrafast laser pulse inside a gas-filled hollow core fiber (HCF). Due to the high-damage threshold and the long interaction distance, the HCF-based FWM configuration proves to be suitable for high-energy applications. Moreover, this technique can be potentially used for ultrashort pulses generation within a wide range of spectral regions; a discussion on the possibility to extend our scheme to the generation of few-cycle mid-IR pulse is provided.

ЭФФЕКТИВНЫЙ РАМАНОВСКИЙ ЛАЗЕР НА ДЛИНЕ ВОЛНЫ 4,42 МКМ НА ОСНОВЕ ПОЛОГО СВЕТОВОДА ИЗ КВАРЦЕВОГО СТЕКЛА

In this paper we consider mid-infrared Raman lasers based on gas-filled hollow-core silica fibers and provide theoretical and experimental analysis of factors that limit the efficiency and output power of these lasers. As a result, we realized an efficient ns-pulsed 4.42 {\mu}m Raman laser based on an 1H2-filled revolver silica fiber. Quantum efficiency as high as 36 % is achieved, and output average power as high as 250 mW is demonstrated. The possibilities of further improving the laser efficiency are discussed.

Generation of few-cycle radially-polarized infrared pulses in a gas-filled hollow-core fiber**Project supported by the National Natural Science Foundation of China (Grant No. 61521093), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB16), the International S & T Cooperation Program of China (Grant No. 2016YFE0119300), and the Program of Shanghai Academic/Technology Research Leader, China (Grant No.

We perform a numerical study for temporally compressing radially-polarized (RP) infrared pulses in a gas-filled hollow-core fiber (HCF). The dynamic transmission and nonlinear compression of RP pulses centered at wavelengths of 0.8 μm, 1.8 μm, 3.1 μm, and 5.0 μm in HCFs are simulated. By comparing the propagation of pulses with the same optical cycles and intensity, we find that under proper conditions these pulses can be compressed down to 2–3 cycles. In the transverse direction, the spatiotemporal beam profile ameliorates from 0.8-μm to 1.8-μm and 3.1-μm pulses before the appearance of high-order dispersion. These results show an alternative method of scaling generation for delivering RP infrared pulses in gas-filled HCFs, which can obtain energetic few-cycle pulses, and will be beneficial for relevant researches in the infrared scope.

Multi-stage generation of extreme ultraviolet dispersive waves by tapering gas-filled hollow-core anti-resonant fibers.

In this work, we numerically investigate an experimentally feasible design of a tapered Ne-filled hollow-core anti-resonant fiber and we report multi-stage generation of dispersive waves (DWs) in the range 90-120 nm, well into the extreme ultraviolet (UV) region. The simulations assume a 800 nm pump pulse with 30 fs 10 µJ pulse energy, launched into a 9 bar Ne-filled fiber with a 34 µm initial core diameter that is then tapered to a 10 µm core diameter. The simulations were performed using a new model that provides a realistic description of both loss and dispersion of the resonant and anti-resonant spectral bands of the fiber, and also importantly includes the material loss of silica in the UV. We show that by first generating solitons that emit DWs in the far-UV region in the pre-taper section, optimization of the following taper structure can allow re-collision with the solitons and further up-conversion of the far-UV DWs to the extreme-UV with energies up to 190 nJ in the 90-120 nm range. This process provides a new way to generate light in the extreme-UV spectral range using relatively low gas pressure.

2.6 mJ/100 Hz CEP-stable near-single-cycle 4 μm laser based on OPCPA and hollow-core fiber compression.

A carrier-envelope-phase-stable near-single-cycle mid-infrared laser based on optical parametric chirped pulse amplification and hollow-core fiber compression is demonstrated. A 4μm laser pulse with 11.8mJ energy is delivered from a KTA-based optical parametric chirped pulse amplification (OPCPA) with 100Hz repetition rate, and compressed to 105fs by a two-grating compressor with efficiency over 50%. Subsequently, the pulse spectrum is broadened by employing a krypton gas-filled hollow-core fiber. Then, the pulse duration is further compressed to 21.5fs through a CaF2 bulk material with energy of 2.6mJ and energy stability of 0.9% RMS, which is about 1.6 cycles for a 4μm laser pulse. The carrier envelope phase of the near-single-cycle 4μm laser pulse is passively stabilized with 370mrad.

Nonlinear dynamic of picosecond pulse propagation in atmospheric air-filled hollow core fibers

Atmospheric air-filled hollow core (HC) fibers, representing the simplest yet reliable form of gas-filled hollow core fiber, show remarkable nonlinear properties and have several interesting applications such as pulse compression, frequency conversion and supercontinuum generation. Although the propagation of sub-picosecond and few hundred picosecond pulses are well-studied in air-filled fibers, the nonlinear response of air to pulses with a duration of a few picoseconds has interesting features that have not yet been explored fully. Here, we experimentally and theoretically study the nonlinear propagation of ~6 ps pulses in three different types of atmospheric air-filled HC fiber. With this pulse length, we were able to explore different nonlinear characteristics of air at different power levels. Using in-house-fabricated, state-of-the-art HC photonic bandgap, HC tubular and HC Kagomé fibers, we were able to associate the origin of the initial pulse broadening process in these fibers to rotational Raman scattering (RRS) at low power levels. Due to the broadband and low loss transmission window of the HC Kagomé fiber we used, we observed the transition from initial pulse broadening (by RRS) at lower powers, through long-range frequency conversion (2330 cm-1) with the help of vibrational Raman scattering, to broadband (~700 nm) supercontinuum generation at high power levels. To model such a wide range of nonlinear processes in a unified approach, we have implemented a semi-quantum model for air into the generalized nonlinear Schrodinger equation, which surpasses the limits of the common single damping oscillator model in this pulse length regime. The model has been validated by comparison with experimental results and provides a powerful tool for the design, modeling and optimization of nonlinear processes in air-filled HC fibers.