mid-IR Range Research Articles

Electrically tunable optical devices based on graphene-split-ring-resonator periodic multilayers at mid-infrared frequencies

In this work, we demonstrate that photonic crystals made with alternating layers of graphene and nanometer-scale split-ring-resonator metamaterials can be treated as single negative-index materials with broad zero-ϕeff gaps in the mid-IR frequency range. These provide a versatile platform for the fabrication of anti-interference multichannel filters whose tunability can be realized flexibly by adjusting the conductivity of the graphene layer. Specifically, by inserting dielectric defects into the periodic system, one can obtain tunable tunneling modes inside the zero-ϕeff gap, which are highly robust against scaling and structural disorder. Moreover, without altering the structure of the system, the number of defect modes multiplies as the graphene chemical potential is decreased appropriately. In addition, the tunneling modes are nearly invariant with the incident angle in the range of 0°–5°. Also, the bandwidths of the tunneling modes are compressed by decreasing the chemical potential, which could be utilized to improve the Q values of the filters. Furthermore, THz amplification could also be accomplished when taking into account the damping constant of the permittivity of graphene. As a result, these characteristics may facilitate the design of optical devices in the mid-IR range, especially leading to more practical applications of these filters.

Mid-infrared characterization and modelling of transparent conductive oxides

Mid-infrared spectroscopic characterization of doped layers is a rapid, contactless and non-destructive method of determining doped semiconductor layer properties, being used as an inline monitoring tool in industrial environments. Extending this technique to transparent conductive oxides (TCOs) would be tremendously beneficial, which otherwise requires intensive characterization to determine the layer properties. This work analyzes the usefulness of IR reflectometry in characterizing three different types of TCOs deposited on glass. An optical model is developed which fits to the experimental reflectance data and estimates critical parameters like effective mass ratio, plasma frequency and the complex refractive index of the layers in the mid-IR range.

LiGaS2 crystal growth under low temperature gradient conditions by the modified Bridgman method

LiGaS2 (LGS) is a promising nonlinear optical material for the generation of coherent radiation in the mid IR range. However, the production of large crystals of optical quality is complicated by the strong incongruent evaporation of volatile components at the temperatures above melting point. Such evaporation leads to deviations from the crystal stoichiometry during the growth process. In this paper the value of the LGS melt superheating in classical Bridgman–Stockbarger method was determined using the mathematical modeling. On the other hand, we designed a modified furnace and tested it: This allowed us to decrease the melt superheating down to 5 K.

Microstructured Fibers Based on Tellurite Glass for Nonlinear Conversion of Mid-IR Ultrashort Optical Pulses

Compact fiber-based sources generating optical pulses with a broadband spectrum in the mid-IR range are in demand for basic science and many applications. Laser systems producing tunable Raman solitons in special soft-glass fibers are of great interest. Here, we report experimental microstructured tellurite fibers and demonstrate by numerical simulation their applicability for nonlinear soliton conversion in the mid-infrared (-IR) range via soliton self-frequency shift. The fiber dispersion and nonlinearity are calculated for experimental geometry. It is shown numerically that there are two zero dispersion wavelengths for the core size of 2 μm and less. In such fibers, efficient Raman soliton tuning is attained up to a central wavelength of 4.8 μm using pump pulses at 2.8 μm.

Nonlinear Optical Method of Determination the Chirp of Broadband Femtosecond Laser Pulse in IR-Range

A new method for determining the chirp of a femtosecond broadband IR laser pulse at a central wavelength of 2.5 μm, based on the generation of a spectral supercontinuum in the field of a spectrally limited femtosecond laser pulse, propagating in a single mode fiber based on chalcogenide glass, and subsequent noncollinear generation of radiation at summary frequency by spectrally limited and spectral broadened supercontinuum femtosecond pulses is proposed. The time dependences of the instantaneous frequency of a femtosecond broadband pulse, obtained both from the results of numerical integrations of the equation describing the process of spectral supercontinuum generation and from the results of two-dimensional distributions of dynamic spectrograms are presented. It is shown that the proposed method allows one to determine the chirp of a broadband femtosecond IR laser pulse, formed during the soliton propagation mode in a fiber, with a relative error of no more than 5%, but the chirp of a broadband femtosecond IR laser pulse, formed in the process of non-soliton propagation in a fiber, with a relative error of no more than 10%.The presented results can be used in the development of a nonlinear optical phase correlator for determination the phase and time profile of a femtosecond laser pulse in the mid-IR range.

Visible pump-mid infrared pump-broadband probe: Development and characterization of a three-pulse setup for single-shot ultrafast spectroscopy at 50 kHz.

We report here an experimental setup to perform three-pulse pump-probe measurements over a wide wavelength and temperature range. By combining two pump pulses in the visible (650 nm-900 nm) and mid-IR (5 μm-20 μm) range, with a broadband supercontinuum white-light probe, our apparatus enables both the combined selective excitation of different material degrees of freedom and a full time-dependent reconstruction of the non-equilibrium dielectric function of the sample. We describe here the optical setup, the cryogenic sample environment, and the custom-made acquisition electronics capable of referenced single-pulse detection of broadband spectra at the maximum repetition rate of 50 kHz, achieving a sensitivity of the order of 10-4 over an integration time of 1 s. We demonstrate the performance of the setup by reporting data on a mid-IR pump, optical push, and broadband probe in a single crystal of Bi2Sr2Y0.08Ca0.92Cu2O8+δ across the superconducting and pseudogap phases.

Imprint and transfer fabrication of freestanding plasmonic membranes

This paper reports an imprint and transfer approach for the rapid and inexpensive fabrication of the ultra-thin freestanding plasmonic membrane (FPM) that supports surface plasmon resonances. The imprint and transfer fabrication method involves the soft imprint lithography on an ultrathin polymer film, transfer of the perforated polymer film to a supporting frame, subsequent deposition of gold, and final removal of the polymer film. Without using any sophisticated lithography and etching processes, the imprint and transfer method can produce freestanding gold membranes with 2D arrays of submicrometer-sized holes that support plasmonic modes in the mid-wavelength infrared (mid-IR) range. Two FPM devices with an array constant of 4.0 and 2.5 μm have been simulated, fabricated, and measured for their transmittance characteristics. The fabricated FPMs exhibit surface plasmon polariton Bloch mode and extraordinary optical transmission (EOT) with the enhanced local field around the membrane. The effects of membrane thickness and angle dispersion on the FPM were investigated to show the tuning of EOT modes in IR. Furthermore, we demonstrated the refractometric sensing and enhanced IR absorption of the FPM device for its potential in chemical and biomolecule sensing applications.

Temperature Dependences of the Spectra of Aqueous Solutions of Alkali Metal Chlorides in the Mid-IR Range

Temperature dependences of the spectra of aqueous solutions of LiCl, KCl, RbCl, CsCl with concentrations of 3 M in the mid-IR range in the temperature range of 39 to 2°C are studied. Average rate $$\frac{{\Delta \nu }}{{\Delta T}}$$ of the temperature shift of the wavenumber of the maximum of absorption bands of valence (ν1, 2ν2, ν3), composite ν2 + νL, and deformation ν2 vibrations of the water molecule for the studied solutions of alkali metal chlorides are obtained. Based on the observed patterns of the displacement of these absorption bands as the temperature changes, a conclusion is drawn regarding structural changes in these solutions. Values $$\frac{{\Delta \nu }}{{\Delta T}}$$ for solutions with similar values of distilled water are compared, showing that there are differences between the structural variations in water and in the studied solutions as the temperature changes. The numerical values of the energy and the length of hydrogen bonds between water molecules are calculated with decreasing temperature for all studied solutions; the energy of hydrogen bonds rises as the temperature falls, while their length is reduced in all of the studied solutions.

Dispersion tailoring of photonic crystal fibers for flat-top, coherent, and broadband supercontinuum generation

A double-clad AsSe2-based photonic crystal fiber possessing ultra-flat near-zero dispersion has been introduced, here to achieve flat-top and coherent supercontinuum generation at Mid-IR range. Also, the required conditions to obtain flat-top, broadband, and coherent supercontinuum generation have been discussed based on the systematic study carried out here, by GNLSE regarding the input pump pulse characteristics and the dispersion regime. The proposed photonic crystal fiber in this study, presents nearly-zero all-normal dispersion of about D ∼ −3.4 ps(nm.km)−1 corresponding to minimum group velocity dispersion at 6.9 μm. For the pump pulse with λ = 6.9 μm, time duration of T = 50 fs, and low peak power of P = 1 kW, a coherent flat-top supercontinuum generation has been realized with the span of 4.14 μm and 4.97 μm at 8 dB and 20 dB levels, respectively. Moreover, a figure of merit covering the essential characteristics of supercontinuum generation spectra (bandwidth, coherency, and flatness) has been introduced to compare the performance of different structures. It has been shown that β 2 tailoring with near-zero and flat characteristic is essential to achieve higher figure of merit.

Influence of Ho2O3 on Optimizing Nanostructured Ln2Te6O15Anti‐Glass Phases to Attain Transparent TeO2‐Based Glass‐Ceramics for Mid‐IR Photonic Applications

The transparent TeO2‐based glass‐ceramics (GCs) have yet to achieve the breakthrough in photonic technologies, because of poor understanding in optimizing the growth of nanostructured crystalline phases. In the present investigation, the size effect of phase‐separation‐induced, nanostructured Ln2Te6O15‐based (Ln: Gd, Ho) “anti‐glass” phase in Ho2O3‐modified TeO2‐based TTLG (in mol%, 80TeO210TiO25La2O35Gd2O3) glass has considered to achieve transparent GCs. Raman study of TTLG glass reveals the presence of TeO3, TeO3 + 1, and TeO4 units with average TeO coordination number as 3.49. The formation of nanostructured Ln2Te6O15 phases in GCs is confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. Furthermore, TEM analysis confirms that an increase of Ho2O3 concentration has reduced the size of phase‐separated domains in nanoscale with superstructure formation to attain transparent GCs. The superiority of this obtained transparent GCs as photonic material for near‐IR (NIR) to mid‐IR (MIR) range has been established by the realization of enhanced luminescence intensities and bandwidth at ≈2900 nm (Ho3+: 5I6 → 5I7) and ≈2050 nm (Ho3+: 5I7 → 5I8). This study offers an opportunity to fabricate the various accessible lanthanide ions‐doped and/or co‐doped TTLG glass with control over nanostructure, to design a series of GCs which are transparent from visible to MIR range.

Investigation of WSi and NbN superconducting single-photon detectors in mid-IR range

Spectral characteristics of WSi and NbN superconducting single-photon detectors with different surface resistance and width of nanowire strips have been investigated in the wavelength range of 1.3-2.5 μm. WSi structures with narrower strips demonstrated better performance for detection of single photons in longer wavelength range. The difference in normalized photon count rate for such structures reaches one order of magnitude higher in comparison with structures based on NbN thin films at 2.5 μm.

Dynamic control of spontaneous emission rate using tunable hyperbolic metamaterials.

We numerically investigate the dynamic control over the spontaneous emission rate of quantum emitters using tunable hyperbolic metamaterials (HMMs). The dispersion of a metal-dielectric thin-film stack at a given frequency can undergo a topological transition from an elliptical to a hyperbolic dispersion by incorporating a tunable metal or dielectric film in the HMM. This transition modifies the local density of optical states of the emitter and, hence, its emission rate. In the visible range, we use an HMM consisting of TiN and ${{\rm Sb}_2}{{\rm S}_3}$Sb2S3 and show considerable tunability in the Purcell enhancement and quantum efficiency as ${{\rm Sb}_2}{{\rm S}_3}$Sb2S3 phase changes from amorphous to crystalline. Similarly, we show tunable Purcell enhancement in the telecommunication wavelength range using a ${\rm TiN}/{{\rm VO}_2}$TiN/VO2- HMM. Finally, tunable spontaneous emission rate in the mid-IR range is obtained using a ${\rm graphene}/{\rm MgF}_2$graphene/MgF2 HMM by modifying the graphene conductivity through changing its chemical potential. We show that using a metal nitride (for the visible and NIR HMMs) and a fluoride (for the mid-IR HMM) is important to get an appreciable change in the effective permittivity of the thin-film multilayer stack.

Terahertz shifted Fano resonance-induced plasmon-soliton in graphene-plasmonic waveguide with magnetic impurities

Abstract Fano resonance is a quantum effect particularly useful for determining the optical spectra of semiconductor heterostructures and radiation enhancement of semiconductor-based devices. We deal with the nonlinear amplitude equation to find the nonlinear plasmon modes and breather solutions in a magnetic impurities-added graphene-plasmonic waveguide at near and mid-IR frequency range. The results show that the coupling degree between the plamon modes and breather solutions in order to form plasmon-solitons is intensely influenced by the effective nonlinear refraction assigned to the waveguide and also by the Fermi energy; tunable plasmon-solitons can be formed with a lowly required bias voltage. We also deduce that the stable plasmon-solitons and subsequently the most condensed radiative feature with the largest effective propagation length can be obtained at interband transition edge if the resonance of the effective nonlinear refraction is of Fano type. The reason is inferred as the presence of a reversible mechanism caused by the optical doping which in turn bears a successive competition between the diffraction and nonlinearity. Accordingly, we indicate that the Fano resonance- induced plasmon-soliton modes supported by the Co-added graphene-plasmonic waveguide experience a frequency shift up to Δω = 60 THz in contrast to the plasmon-soliton modes in the pristine graphene-based waveguide. This in turn, proposes a novel technique for the spectroscopy of magnetic impurities-added graphene-dielectric heterostructures. On the other hand, very sensitive modulation of the nonlinear response tunable with a low Fermi energy as presented in this study can delineate modern schemes for the next generation graphene plasmonic devices including the nanoscale radiation sources, modulators, biosensors and couplers.

The Influence of Interfacial Effects on the Electron Spectrum of GaAs/AlGaAs Structures Used for the Creation of Mid-IR Photodetectors

It is shown that transient processes arising in the growth chamber of a molecular beam epitaxy (MBE) system influence the structure of interfaces and electron spectrum of quantum wells in GaAs/AlxGa1 –xAs heterostructures used for the creation of photodetectors (PDs) operating in the mid-IR range. These processes lead to a low-frequency shift of the PD operating transition, appearance of interband transition lines (forbidden by selection rules) in the absorption spectrum, and decrease in the energy shift between quantum-confinement levels formed by light and heavy holes. These effects provide a simple approach to contactless evaluation of the quality of interfaces in GaAs/AlxGa1 –xAs heterostructures for PDs.

Graphene-based hyperbolic metamaterial as a switchable reflection modulator.

A tunable graphene-based hyperbolic metamaterial is designed and numerically investigated in the mid-infrared frequencies. Theoretical analysis proves that by adjusting the chemical potential of graphene from 0.2 eV to 0.8 eV, the reflectance can be blue-shifted up to 2.3 µm. Furthermore, by modifying the number of graphene monolayers in the hyperbolic metamaterial stack, we are able to shift the plasmonic resonance up to 3.6 µm. Elliptic and type II hyperbolic dispersions are shown for three considered structures. Importantly, a blue/red-shift and switching of the reflectance are reported at different incident angles in TE/TM modes. The obtained results clearly show that graphene-based hyperbolic metamaterials with reversibly controlled tunability may be used in the next generation of nonlinear tunable and reversibly switchable devices operating in the mid-IR range.

External Cavity Quantum Cascade Laser-Based Mid-Infrared Dispersion Spectroscopy for Qualitative and Quantitative Analysis of Liquid-Phase Samples.

Acquisition of classical absorption spectra of liquids in the mid-IR range with quantum cascade lasers (QCLs) is often limited in sensitivity by noise from the laser source. Alternatively, measurement of molecular dispersion (i.e., refractive index) spectra poses an experimental approach that is immune to intensity fluctuations and further offers a direct relationship between the recorded signal and the sample concentration. In this work, we present an external cavity quantum cascade laser (EC-QCL) based Mach-Zehnder interferometer setup to determine dispersion spectra of liquid samples. We present two approaches for acquisition of refractive index spectra and compare the qualitative experimental results. Furthermore, the performance for quantitative analysis is evaluated. Finally, multivariate analysis of a spectrally complex mixture comprising three different sugars is performed. The obtained figures of merit by partial least squares (PLS) regression modelling compare well with standard absorption spectroscopy, demonstrating the potential of the introduced dispersion spectroscopic method for quantitative chemical analysis.

Development of MWCNT thin film electrode transparent in the mid-IR range

In this research carbon nanotube-based thin film electrodes, with high transparency in mid-infrared range, were developed as a replacement for indium tin oxide electrodes. The thin film electrodes were prepared from polyelectrolyte and multi-walled carbon nanotubes by layer-by-layer assembly. Polyethyleneimine (PEI) and carboxylic multi-walled carbon nanotubes (MWCNT-COOH) were deposited alternately on glass substrates. Samples with different number of bilayers (PEI + MWCNT-COOH) were prepared. Thickness of the films varied between 80 and 240 nm, depending of the number of bilayers. After deposition of each bilayer, the samples were dried at 120 °C for 10 min. The fabricated films were characterized using Raman spectroscopy, high-resolution scanning microscopy (HRSEM) and transmission electron microscopy (TEM). Transparency of the films was measured in UV/Vis and IR ranges, utilizing UV/Vis spectrophotometer and FTIR spectrometer respectively. Sheet resistance of the films was measured with four-point probe method and the resistance values obtained were ranging from 6 kΩ/sq up to 23 kΩ/sq, depending on the number of layers.

Conductor-backed dielectric metasurface thermal emitters for mid-infrared spectroscopy

A conductor-backed dielectric metasurface thermal emitter at mid-IR frequencies with narrowband emissivity is experimentally demonstrated. The metasurface emitter consists of a high permittivity silicon resonator on top of a ground plane, whose resonant mechanism is explained using image theory. The resonator, placed close to a copper ground plane, is designed to produce a magnetic resonance, resulting in a low-profile device with a single emission peak in its subwavelength frequency range. The thermal emitter is next fabricated using common CMOS processes. Frequency dependent optical constants of plasma-enhanced chemical vapor deposited films of Si, SiO2, and evaporated Cu are also reported in the mid-IR range. Narrowband thermal emission is successfully obtained at around 7.22μm (41.5 THz), which corresponds to the absorption band of SO2. The Q-factor of about 37 is achieved with a peak emissivity of 0.65, which is significantly higher compared to the reported Q-factors of state-of-the-art plasmonic resonators.

Лазерная генерация коллоидных кремниевых наночастиц, легированных серой и углеродом

Unique silicon nanoparticles doped with sulfur and carbon, as well as partially oxidized, were obtained by nanosecond laser ablation of silicon in liquid carbon disulfide. Their detailed structural, chemical and optical characterization was carried out by scanning and transmission electron microscopy, IR spectroscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. Studies have shown that the sulfur content in the particles is about 1 at. %, due to which they show significant absorption in the mid-IR range.

The influence of iron concentration on the cathodoluminescence kinetics in the mid-IR range in ZnSe:Fe crystals

Integral intensity and kinetics dependences of cathodoluminescence of ZnSe:Fe crystals in mid-IR spectral range was studied. Concentration of iron varied from 0.01 to 14 wt.%. The experiments were carried out in 77 - 300 K temperature range. It is established that the luminescence pulse rise time is longer than excitation pulse at low iron concentration at 77 K temperature. The increasing ones lead to shortening of the luminescence pulse rise time, decreasing of the luminescence lifetime and increasing of the luminescence intensity in mid-IR. The annealed ZnSe:Fe concentration series in vapour Zn are reproduced the same trends. The nature of observed experimental effects is discussed.