Mid-infrared dispersive wave generation in gas-filled photonic crystal fibre by transient ionization-driven changes in dispersion.
ABSTRACT: Gas-filled hollow-core photonic crystal fibre is being used to generate ever wider supercontinuum spectra, in particular via dispersive wave emission in the deep and vacuum ultraviolet, with a multitude of applications. Dispersive waves are the result of nonlinear transfer of energy from a self-compressed soliton, a process that relies crucially on phase-matching. It was recently predicted that, in the strong-field regime, the additional transient anomalous dispersion introduced by gas ionization would allow phase-matched dispersive wave generation in the mid-infrared-something that is forbidden in the absence of free electrons. Here we report the experimental observation of such mid-infrared dispersive waves, embedded in a 4.7-octave-wide supercontinuum that uniquely reaches simultaneously to the vacuum ultraviolet, with up to 1.7?W of total average power.Dispersive wave emission in gas-filled hollow-core photonic crystal fibres has been possible in the visible and ultraviolet via the optical Kerr effect. Here, Köttig et al. demonstrate dispersive waves generated by an additional transient anomalous dispersion from gas ionization in the mid-infrared.
Project description:Deep-UV (DUV) supercontinuum (SC) sources based on gas-filled hollow-core fibers constitute perhaps the most viable solution towards ultrafast, compact, and tunable lasers in the UV spectral region, which can even also extend into the mid-infrared (IR). Noise and spectral stability of such broadband sources are key parameters that define their true potential and suitability towards real-world applications. In order to investigate the spectral stability and noise levels in these fiber-based DUV sources, we generate an SC spectrum that extends from 180?nm (through phase-matched dispersive waves - DWs) to 4 ?m by pumping an argon-filled hollow-core anti-resonant fiber at a mid-IR wavelength of 2.45 ?m. We characterize the long-term stability of the source over several days and the pulse-to-pulse relative intensity noise (RIN) of the DW at 275?nm. The results indicate no sign of spectral degradation over 110?hours, but the RIN of the DW pulses at 275?nm is found to be as high as 33.3%. Numerical simulations were carried out to investigate the spectral distribution of the RIN and the results confirm the experimental measurements and that the poor noise performance is due to the high RIN of the mid-IR pump laser, which was hitherto not considered in numerical modelling of these sources. The results presented herein provide an important step towards an understanding of the noise mechanism underlying such complex light-gas nonlinear interactions and demonstrate the need for pump laser stabilization.
Project description:In supercontinuum generation, various propagation effects combine to produce a dramatic spectral broadening of intense ultrashort optical pulses. With a host of applications, supercontinuum sources are often required to possess a range of properties such as spectral coverage from the ultraviolet across the visible and into the infrared, shot-to-shot repeatability, high spectral energy density and an absence of complicated pulse splitting. Here we present an all-in-one solution, the first supercontinuum in a bulk homogeneous material extending from 450 nm into the mid-infrared. The spectrum spans 3.3 octaves and carries high spectral energy density (2 pJ nm(-1)-10 nJ nm(-1)), and the generation process has high shot-to-shot reproducibility and preserves the carrier-to-envelope phase. Our method, based on filamentation of femtosecond mid-infrared pulses in the anomalous dispersion regime, allows for compact new supercontinuum sources.
Project description:Directly accessing the middle infrared, the molecular functional group spectral region, via supercontinuum generation processes based on turn-key fiber lasers offers the undeniable advantage of simplicity and robustness. Recently, the assessment of the coherence of the mid-IR dispersive wave in silicon nitride (Si3N4) waveguides, pumped at telecom wavelength, established an important first step towards mid-IR frequency comb generation based on such compact systems. Yet, the spectral reach and efficiency still fall short for practical implementation. Here, we experimentally demonstrate that large cross-section Si3N4 waveguides pumped with 2 μm fs-fiber laser can reach the important spectroscopic spectral region in the 3-4 μm range, with up to 35% power conversion and milliwatt-level output powers. As a proof of principle, we use this source for detection of C2H2 by absorption spectroscopy. Such result makes these sources suitable candidate for compact, chip-integrated spectroscopic and sensing applications.
Project description:Nonlinear optical processes are governed by the relative-phase relationships among the relevant electromagnetic fields in these processes. In this Report, we describe the physics of arbitrary manipulation of Raman-resonant four-wave-mixing process by artificial control of relative phases. As a typical example, we show freely designable optical-frequency conversions to extreme spectral regions, mid-infrared and vacuum-ultraviolet, with near-unity quantum efficiencies. Furthermore, we show that such optical-frequency conversions can be realized by using a surprisingly simple technology where transparent plates are placed in a nonlinear optical medium and their positions and thicknesses are adjusted precisely. In a numerical simulation assuming practically applicable parameters in detail, we demonstrate a single-frequency tunable laser that covers the whole vacuum-ultraviolet spectral range of 120 to 200?nm.
Project description:Ultrafast supercontinuum generation in gas-filled waveguides is an enabling technology for many intriguing applications ranging from attosecond metrology towards biophotonics, with the amount of spectral broadening crucially depending on the pulse dispersion of the propagating mode. In this study, we show that structural resonances in a gas-filled antiresonant hollow core optical fiber provide an additional degree of freedom in dispersion engineering, which enables the generation of more than three octaves of broadband light that ranges from deep UV wavelengths to near infrared. Our observation relies on the introduction of a geometric-induced resonance in the spectral vicinity of the ultrafast pump laser, outperforming gas dispersion and yielding a unique dispersion profile independent of core size, which is highly relevant for scaling input powers. Using a krypton-filled fiber, we observe spectral broadening from 200?nm to 1.7??m at an output energy of ? 23??J within a single optical mode across the entire spectral bandwidth. Simulations show that the frequency generation results from an accelerated fission process of soliton-like waveforms in a non-adiabatic dispersion regime associated with the emission of multiple phase-matched Cherenkov radiations on both sides of the resonance. This effect, along with the dispersion tuning and scaling capabilities of the fiber geometry, enables coherent ultra-broadband and high-energy sources, which range from the UV to the mid-infrared spectral range.
Project description:Mid-infrared region of electromagnetic spectrum has increased a lot of scientific and technical interest because of its utility to figure out the molecular fingerprints. Current mid-infrared light sources including quantum cascade lasers, thermal-emitters, and synchrotron radiation are not suitable for various potential applications where we require coherent, portable and broadband light sources. During the current decade, several efforts have been put forwarded to extend the spectral range of the supercontinuum. However, the coherent mid-infrared supercontinuum spectrum in the mid-infrared region has been demonstrated rarely. Here, we demonstrate a coherent mid-infrared supercontinuum using a tapered chalcogenide fiber pumped at various wavelength ranging from 2?µm to 2.6?µm. Experimental observations show that the supercontinuum spectrum extending from ~1.6?µm to 3.7?µm can be achieved using a 3?cm long tapered chalcogenide step-index optical fiber pumped with femtosecond laser pulses at 2.6?µm. To the best of our knowledge, using short pump wavelengths at 2?µm to 2.6?µm in an all-normal dispersion engineered chalcogenide glass fiber, the coherent supercontinuum spectrum has been reported first time. Such coherent broadband light source has its key prominence for the various prospective applications in the fields of bio-medical, sensing, and multiplex coherent anti-Stokes Raman scattering microspectroscopy.
Project description:Solitons are localized waves formed by a balance of focusing and defocusing effects. These nonlinear waves exist in diverse forms of matter yet exhibit similar properties including stability, periodic recurrence and particle-like trajectories. One important property is soliton fission, a process by which an energetic higher-order soliton breaks apart due to dispersive or nonlinear perturbations. Here we demonstrate through both experiment and theory that nonlinear photocarrier generation can induce soliton fission. Using near-field measurements, we directly observe the nonlinear spatial and temporal evolution of optical pulses in situ in a nanophotonic semiconductor waveguide. We develop an analytic formalism describing the free-carrier dispersion (FCD) perturbation and show the experiment exceeds the minimum threshold by an order of magnitude. We confirm these observations with a numerical nonlinear Schrödinger equation model. These results provide a fundamental explanation and physical scaling of optical pulse evolution in free-carrier media and could enable improved supercontinuum sources in gas based and integrated semiconductor waveguides.
Project description:The discovery of optical solitons being understood as temporally and spectrally stationary optical states has enabled numerous innovations among which, most notably, supercontinuum light sources have become widely used in both fundamental and applied sciences. Here, we report on experimental evidence for dynamics of hybrid solitons-a new type of solitary wave, which emerges as a result of a strong non-instantaneous nonlinear response in CS2-filled liquid-core optical fibres. Octave-spanning supercontinua in the mid-infrared region are observed when pumping the hybrid waveguide with a 460?fs laser (1.95??m) in the anomalous dispersion regime at nanojoule-level pulse energies. A detailed numerical analysis well correlated with the experiment uncovers clear indicators of emerging hybrid solitons, revealing their impact on the bandwidth, onset energy and noise characteristics of the supercontinua. Our study highlights liquid-core fibres as a promising platform for fundamental optics and applications towards novel coherent and reconfigurable light sources.Here, Chemnitz et al. report experimental evidence for hybrid solitons - a type of solitary wave, which emerges as a result of a strong non-instantaneous nonlinear response in CS2-filled liquid-core optical fibres, demonstrating efficient soliton-driven supercontinuum generation.
Project description:Short duration, intense pulses of light can experience dramatic spectral broadening when propagating through lengths of optical fibre. This continuum generation process is caused by a combination of nonlinear optical effects including the formation of dispersive waves. Optical analogues of Cherenkov radiation, these waves allow a pulse to radiate power into a distant spectral region. In this work, efficient and coherent dispersive wave generation of visible to ultraviolet light is demonstrated in silica waveguides on a silicon chip. Unlike fibre broadeners, the arrays provide a wide range of emission wavelength choices on a single, compact chip. This new capability is used to simplify offset frequency measurements of a mode-locked frequency comb. The arrays can also enable mode-locked lasers to attain unprecedented tunable spectral reach for spectroscopy, bioimaging, tomography and metrology.
Project description:A new gas absorption module, the substrate-embedded hollow waveguide (eHWG) model, is proposed. It consists of a substrate with a curved channel and a hollow waveguide. The hollow waveguide is curved into the channel and works as a gas absorption cell as well as a transmission medium for mid-infrared light. Owing to the low loss property of the hollow waveguide, the signal-to-noise ratio (SNR) was improved for the sensing system. A polycarbonate (PC) base tube was used to obtain flexibility in the fabrication of the hollow waveguide. A silver (Ag) layer and a silver iodide (AgI) layer were inner-coated to ensure a low loss property at the fingerprint wavelength of methane gas. A sensing system was established using a Fourier transform infrared spectrometer (FTIR), an external detector, and an eHWG. Experimental investigations were carried on the sensing performance of eHWGs with various channel shapes. Comparison studies were made on eHWGs embedded with Ag-coated or Ag- and AgI-coated hollow waveguides. The Ag- and AgI-coated hollow waveguides with inner diameters of 0.7, 1.4, and 2.0 mm were used in the eHWGs. The large bore waveguide had low loss but high bending additional loss. The large bore waveguide had a low detection limit due to high coupling efficiency with the light source. A limit of detection (LOD) as low as 2.7 ppm was attained for the system using the eHWG with the long and large bore waveguide.