Mid-infrared Broadband Research Articles

Modeling the Broadband Mid-Infrared Dispersion Compensator Based on ZBLAN Microfiber

The waveguide dispersion profiles of (ZrF4–BaF2– LaF3 – AlF3 – NaF) (ZBLAN) microfiber in the mid-infrared (mid-IR) regime have been investigated numerically. The results show that ZBLAN microfiber has large normal dispersion for wavelength ranging from 2 to 5 $\mu \text{m}$ by tailoring the fiber geometry. Moreover, the Tm-doped mode-locked fiber laser has been modeled with the ZBLAN microfiber as the dispersion compensator, and the ultrafast pulse around 2 $\mu \text{m}$ can be generated. The results confirmed the availability of the dispersion compensator for mid-IR ultrafast photonics.

Simulation study of mid-infrared supercontinuum generation in Ge23Sb12S65-based chalcogenide photonic crystal fiber

Abstract We conducted a numerical study of mid-infrared (MIR) supercontinuum (SC) generation with femtosecond pulses in Ge 23 Sb 12 S 65 chalcogenide photonic crystal fiber (PCF). This PCF has multilayer air holes in the cladding region, which renders its flexibility for controlling the dispersion and confinement loss of the fiber. The broad and flat dispersion profiles and the low confinement loss of the designed PCF combined with the wide MIR transparent window of Ge 23 Sb 12 S 65 chalcogenide glass largely contributed to the broadband MIR SC generation. Owing to the ultra-high nonlinearity of the designed Ge 23 Sb 12 S 65 PCF, an ultra-broadband SC ranging from 1.9 μm to 9.3 μm was obtained in a 15 cm fiber by applying a very low pump power of 165 W at 3.3 μm wavelength.

Broadband high-power mid-IR femtosecond pulse generation from an ytterbium-doped fiber laser pumped optical parametric amplifier.

We report on a high-power periodically poled MgO-doped lithium niobate (MgO:PPLN)-based femtosecond optical parametric amplifier (OPA), featuring a spectral seamless broadband mid-infrared (MIR) output. By modifying the initial chirp and spectrum of the mode-locked seed laser, the Yb fiber pump laser exhibits a final output power of 14 W with sub-200-fs pulse duration after power amplification and compression. When the OPA was seeded with a broadband amplified spontaneous emission (ASE) source, a damage-limited 0.6 W broadband MIR radiation was experimentally obtained under the pump power of 10.15 W at 82 MHz repetition rate, corresponding to an overall OPA conversion efficiency of 32.7%. The 3 dB bandwidth of the mid-IR idler was 291.9 nm, centering at 3.34 μm.

Low loss Ge-As-Se chalcogenide glass fiber, fabricated using extruded preform, for mid-infrared photonics

Chalcogenide glass fibers have attractive properties (e.g. wide transparent window, high optical non-linearity) and numerous potential applications in the mid-infrared (MIR) region. Low optical loss is desired and important in the development of these fibers. Ge-As-Se glass has a large glass-forming range to provide versatility of choice from continuously varying physical properties. Recently, broadband MIR supercontinuum generation has been achieved in chalcogenide fibers by using Ge-As-Se glass in the core/clad. structure. In the shaping of chalcogenide glass optical fiber preforms, extrusion is a useful technique. This work reports glass properties (viscosity-temperature curve and glass transition) and optical losses of Ge-As-Se fiber fabricated from an extruded preform. A robust cut-back method of fiber loss measurement is developed and the corresponding error calculation discussed. MIR light is propagated through 52 meters of a fiber, which has the lowest loss yet reported for Ge-As-Se fiber of 83 ± 2 dB/km at 6.60 μm wavelength. The fiber baseline loss is 83-90 dB/km across 5.6-6.8 μm, a Se-H impurity absorption band of 1.4 dB/m at 4.5 μm wavelength is superposed and other impurity bands (e.g. O-H, As-O, Ge-O) are ≤ 20 dB/km. Optical losses of fiber fabricated from different positions of the extruded preform are investigated.

Mid-infrared supercontinuum generation in a novel AsSe2-As2S5 hybrid microstructured optical fiber.

novel AsSe(2)-As(2)S(5) hybrid MOF (HMOF) is designed and fabricated by the rod-in-tube drawing technique. The core is made from AsSe2 glass and the cladding is made from As(2)S(5) glass. The loss is ~1.2 dB/m at ~3000 nm. Zero dispersion wavelength (ZDW) of the HMOF is ~3380 nm. Supercontinuum (SC) generation in a 2 cm-long HMOF is investigated with the pump wavelengths of ~3062, 3241 and 3389 nm from a tunable optical parametric oscillator (OPO) system. Broadband midinfrared (MIR) SC generation with the spectrum from ~1256 to 5400 nm is obtained with the peak power of ~1337 kW at the wavelength of ~3389 nm.

Hollow Core Bragg Fibers With a Heterostructured Cladding Based on Ternary One-Dimensional Photonic Crystal for Mid-infrared Broadband and Low-Loss Transmission

We propose a hollow core Bragg fiber (HC-BF) with a heterostructured cladding based on the ternary 1-D photonic crystal (T-1DPC) in this paper. The distinguishing ternary unit cell of T-1DPC is formed from a polyetherimide (PEI) layer sandwiched by two As2Se3 layers of the same thickness. We demonstrate its capability for mid-infrared broadband and low-loss transmission by numerically simulating and analyzing the omnidirectional photonic bandgap (OPBG) and the modal loss characteristics. The results show that the T-1DPC-based heterostructured cladding can effectively broaden the OPBG, which is only due to the blue-shift of the lower bandgap edge wavelength. Compared with that for the binary-1DPC-based HC-BF, the transmission loss for the T-1DPC-based HC-BF can be reduced by three orders of magnitude over most of the OPBG range. The large loss contrast is essentially attributed to the enhancement of the multilayer reflection from the T-1DPC-based cladding. Most notably, for a T-1DPC-based cladding with three groups, the transmission band with loss lower than 0.01 dB/m for the HE11 mode can cover almost the whole 3 to 5 μm range, with the exception of several loss peaks near the short-wavelength edge. Even with the cladding material absorption included, the transmission loss for the HE11 mode in the T-1DPC-based HC-BF can be still lower than 0.1 dB/m over the whole OPBG range.

4H‐SiC: a new nonlinear material for midinfrared lasers

AbstractNonlinear optical (NLO) frequency conversion is commonly used for generating midinfrared (MIR) lasers that offer light sources for a variety of applications. However, the low laser damage thresholds of NLO crystals used so far seriously limit the output power of MIR lasers. Here, a new nonlinear material 4H‐SiC is demonstrated for producing MIR laser. Broadband MIR radiation ranging from 3.90 to 5.60 μm is generated in 4H‐SiC by phase‐matched difference‐frequency generation for the first time. The results may open a door to practically utilize wide‐bandgap semiconductors with high laser damage thresholds as NLO materials for high power output of MIR lasers.

Generation of Phase-Stable Sub-Cycle Mid-Infrared Pulses from Filamentation in Nitrogen

Sub-single-cycle pulses in the mid-infrared (MIR) region were generated through a laser-induced filament. The fundamental (ω1) and second harmonic (ω2) output of a 30-fs Ti:sapphire amplifier were focused into nitrogen gas and produce phase-stable broadband MIR pulses (ω0) by using a four-wave mixing process (ω1 + ω1 - ω2 → ω0) through filamentation. The spectrum spread from 400 cm-1 to 5500 cm-1, which completely covered the MIR region. The low frequency components were detected by using an electro-optic sampling technique with a gaseous medium. The efficiency of the MIR pulse generation was very sensitive to the delay between the fundamental and second harmonic pulses. It was revealed that the delay dependence of the efficiency came from the interference between two opposite parametric processes, ω1 + ω1 - ω2 → ω0 and ω2 - ω1 - ω1 → ω0. The pulse duration was measured as 6.9 fs with cross-correlation frequency-resolved optical gating by using four-wave mixing in nitrogen. The carrier-envelope phase of the MIR pulse was passively stabilized. The instability was estimated as 154 mrad rms in 2.5 h.

Asynchronous mid-infrared broadband optical parametric oscillator for dual-comb spectroscopy

Two asynchronous, broadband 3.3+µm pulse trains with a stabilized repetition+rate difference of up to 5+kHz were generated from a single optical parametric oscillator. With additional carrier+envelope+offset stabilization, it could be applied to coherent dual+frequency+comb spectroscopy.

Phase-stable sub-cycle mid-infrared conical emission from filamentation in gases

Sub-single-cycle pulses in the mid-infrared (MIR) region were generated through a conical emission from a laser-induced filament. Fundamental and second-harmonic pulses of 25-fs Ti:sapphire amplifier output were focused into argon to produce phase-stable broadband MIR pulses in a well-focusable ring-shaped beam. The beam profile and spectrum of the MIR field are accurately reproduced with a simple calculation based on a four-wave mixing process. The ring-shaped pattern of the MIR beam originates from a dramatic confocal-parameter mismatch between the MIR field and the laser beams.

Generation of a mid-infrared broadband polarized supercontinuum in As2Se3 photonic crystal fibers

A simplified structure of birefringent chalcogenide As2Se3 photonic crystal fiber (PCF) is designed. Properties of birefringence, polarization extinction ratio, chromatic dispersion, nonlinear coefficient, and transmission are studied by using the multipole method, the finite-difference beam propagation method, and the adaptive split-step Fourier method. Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm, we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail, with femtosecond pulses at a wavelength of 4 μm as the pump pulses. Especially, mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm. Their spectral width at −20 dB reaches up to 12 μm. In the birefringent PCF, we find that the supercontinuum generation changes with the pump alignment angle. Research results show that no coupling between eigenpolarization modes are observed at the maximum average power (i.e., 37 mW), which indicates that the polarization state is well maintained.

Widely Wavelength-Tunable Two-Colored Solitons and Small Spectral Component for Broadband Mid-Infrared Wavelength Generation in a Highly Birefringent Photonic Crystal Fiber

With a highly birefringent photonic crystal fiber (HB-PCF) specially designed and fabricated in our laboratory, the two-colored solitons and small spectral component formed by the balance between the dispersion and birefringence effect are generated above 2000 nm when the polarization direction of pump pulse is aligned along the fast and slow axis of HB-PCF. When the average power of the pump at 870 nm increases from 100 to 300 mW, the broadband solitons at the fast and slow axis and small spectral component can be efficiently generated from 2120 to 2230 nm, 2070 to 2180 nm, and 2260 to 2370 nm, and the tunable wavelength range can be up to 300 nm. To the best of our knowledge, the largest span of soliton wavelength shift over 1300 nm is achieved. The widely tunable soliton pulse and small spectral component can provide the particularly useful short-pulse source for the mid-infrared photonics and spectroscopy.

The Vela and Geminga pulsars in the mid-infrared

The Vela and Geminga pulsars are rotation powered neutron stars, which have been identified in various spectral domains, from the near-infrared to hard $\gamma$-rays. In the near-infrared they exhibit tentative emission excesses, as compared to the optical range. To check whether these features are real, we analysed archival mid-infrared broadband images obtained with the Spitzer Space Telescope in the 3.6--160 $\mu$m range and compared them with the data in other spectral domains. In the 3.6 and 5.8 $\mu$m bands we detected at $\sim$ (4--5)$\sigma$ significance level a point-like object, that is likely to be the counterpart of the Vela pulsar. Its position coincides with the pulsar at < 0.4 arcsec 1$\sigma$-accuracy level. Combining the measured fluxes with the available multiwavelength spectrum of the pulsar shows a steep flux increase towards the infrared, confirming the reality of the near-infrared excess reported early, and, hence, the reality of the suggested mid-infrared pulsar identification. Geminga is also identified, but only at a marginal 2$\sigma$ detection level in one 3.6 $\mu$m band. This needs a farther confirmation by deeper observations, while the estimated flux is also compatible with the near-infrared Geminga excess. The detection of the infrared excess is in contrast to the Crab pulsar, where it is absent, but is similar to the two magnetars, 4U 0142+61 and 1E 2259+586, showing similar features. We discuss X-ray irradiated fall-back discs around the pulsars, unresolved pulsar nebula structures, and pulsar magnetospheres as possible origins of the excesses. We note also possible infrared signatures of an extended tail behind Geminga and of the Vela plerion radio lobes.

Coherent mid-infrared broadband continuum generation in non-uniform ZBLAN fiber taper

A simple method is described for efficient, asymmetric and coherent continuum generation in the mid-infrared region based on the dynamics of a stabilized soliton in the vicinity of a second dispersion zero of a nonlinear fiber. The mechanism involves nonlinear soliton compression, Raman self-frequency shift and resonant emission of a dispersive (Cherenkov) wave in a non-uniformly tapered ZBLAN fluoride fiber pumped by a low-power compact femtosecond laser at 1.55 microm. The fiber taper features a continuous shift of the second zero dispersion wavelength, which facilitates the progressive shift in the wavelength of the dispersive wave generated by the stabilized soliton. Numerical solution of the generalized nonlinear Schrödinger equation, which accounts for the exact wave-length dependence of dispersion and nonlinear coefficients, shows robust generation of near-octave continuum spanning 1.5-3 microm wavelength range.

High-speed laser-induced fluorescence and spark plug absorption sensor diagnostics for mixing and combustion studies in engines

Simultaneous high-speed in-cylinder measurements of laser-induced fluorescence of biacetyl as a fuel tracer and mid-infrared broadband absorption of fuel and combustion products (water and carbon dioxide) using a spark plug probe are compared in an optical engine. The study addresses uncertainties and the applicability of absorption measurements at a location slightly offset to the spark plug when information about mixing at the spark plug is desired. Absorbance profiles reflect important engine operation events, such as valve opening and closing, mixing, combustion, and outgassing from crevices.

Perspectives in Radiative Transfer and Interferometry: Protoplanetary Disks

Near-infrared and mid-infrared broad band interferometric observations of young stellar objects trace the inner part of the warm dusty circumstellar environment (smaller than a few AUs) and can be used to constrain its physical properties, in particular to characterize the size, location and composition of the emitting region. Because the spatial frequency coverage of current instruments remain sparse, modeling, including detailed radiative transfer (RT), is necessary to get a precise estimate of these properties.

Unravelling the ultrafast photodecomposition mechanism of dibenzoyl peroxide in solution by time-resolved IR spectroscopy

The ultrafast photo-fragmentation of dibenzoyl peroxide (DBPO) is studied using femtosecond UV excitation at 266 nm and mid-infrared broadband probe pulses to elucidate the dissociation mechanism. With the help of (13)C-labeled DBPO it was possible to unambiguously assign transient IR bands in the fingerprint region to the benzoyloxy radical. Our experiments show that the fragmentation is controlled by the S(1)-lifetime of DBPO and within 0.4 +/- 0.2 ps leads to a benzoyloxy/phenyl radical pair plus CO(2)via concerted bond breakage of the O-O and the phenyl-C(carbonyl) bond. 20% of the radical pairs geminately recombine to phenyl benzoate on a timescale of 70 ps.

Femtosecond IR Spectroscopy of Peroxycarbonate Photodecomposition: S1-Lifetime Determines Decarboxylation Rate

The ultrafast photofragmentation of arylperoxycarbonates R-O-C(O)O-O-tert-butyl (R = naphthyl, phenyl) is studied using femtosecond UV excitation at 266 nm and mid-infrared broadband probe pulses to elucidate the dissociation mechanism. Our experiments show that the rate of fragmentation is determined by the S1-lifetime of the peroxide, i.e., the time constants of S1 decay and of CO2 and R-O* formation are identical. The fragmentation times are solvent dependent and for tert-butyl-2-naphthylperoxycarbonate (TBNC) vary from 25 ps in CH2Cl2 to 52 ps in n-heptane. In the case of the tert-butylphenylperoxycarbonate (TBPC) the decomposition takes 5.5 ps in CD2Cl2 and 12 ps in n-heptane. The CO2 fragment is formed vibrationally hot with an excess energy of about 5000 cm(-1). The hot CO2 spectra at high energy can be modeled assuming Boltzmann distributions with initial vibrational temperatures of ca. 2500 K which relax to ambient temperature with time constants of 280 ps in CCl4 and 130 ps in n-heptane. In CCl4 the relaxed spectra at 1.5 ns show 3.5% residual excitation in the n = 1 level of the asymmetric stretch vibration.

Diffraction limited near-infrared imaging of the Red Rectangle by bispectral analysis

We present a new method for infrared speckle imaging mainly based on the bispectral analysis algorithm applied to extended objects. The eciency of the reconstruction procedure is increased by a relaxation process making use of redundancies in the pupil plane. The method is applied to near- and mid-infrared data sets of the Red Rectangle (CRL 915) inK,L 'a nd M-bands leading to diraction limited maps of the post-AGB (Asymptotic Giant Branch) bipolar nebula. Studying the morphology of the Red Rectangle at sub-second of arc scale allows to decompose the near and mid-infrared broadband spectrum in two parts: the radiated light from the central part of the nebula and the radiated light from the lobes to the north and south. This decomposition indicates that, in addition to scattering of the light from a central source, thermal extended emission from warm dust may also be important at arsecond and subarcsecond scales in this bipolar nebula.

Optical conductivity of the Hubbard and t-J models.

We calculate the optical conductivity \ensuremath{\sigma}(\ensuremath{\omega}) of the Hubbard and t-J models on 10- and 16-site lattices, respectively, using a Lanczos method. Results are presented for various values of the couplings U/t, J/t, and band fillings, using free- and periodic-boundary conditions. We discuss the behavior of the kinetic energy in the ground state, the distribution of spectral weight of \ensuremath{\sigma}(\ensuremath{\omega}) between low and high energies and the sum rule. Indications of a Drude-like peak at low energy in the one-hole subspace are observed in both models. Assuming that holes behave like independent (mass-renormalized) particles in the normal state of the superconductors, our results also suggest that the optical midinfrared broadband observed experimentally can be explained by hole excitations of strongly correlated systems.