Mid-infrared Emission Properties Research Articles

Polarization switching in a mid-infrared Er:YAlO3 laser

We report on a polarization-resolved study of mid-infrared emission properties of Er3+-doped orthorhombic yttrium aluminum perovskite YAlO3 single crystal. For the 4I11/2 → 4I13/2 Er3+ transition, the stimulated emission cross section is 0.20 × 10−20 cm2 at 2919 nm for light polarization E ‖ c. Pumped by an Yb-fiber laser at 976 nm, the 10 at.% Er:YAlO3 laser delivered 1.36 W at 2919 nm with a slope efficiency of 31.4%, very close to the Stokes limit, a laser threshold as low as 33 mW and a linear polarization. Pump-induced polarization switching between E || b and E || c eigen states was observed and explained by excited-state absorption from the terminal laser level.

Mid-infrared emission properties of erbium-doped fluorite-type crystals

We report on a comparative study of the spectroscopic properties and mid-infrared laser performance of five 5 at.% Er3+-doped fluorite-type crystals MF2, including parent compounds CaF2, SrF2, BaF2, and solid-solution (“mixed”) ones (Ca,Sr)F2 and (Sr,Ba)F2. In the M = Ca → Sr → Ba series, the host matrix phonon energy decreases, the absorption and mid-infrared emission spectra of Er3+ become narrower and more structured, and the luminescence lifetimes of the 4I11/2 and 4I13/2 Er3+ manifolds increase. The Er3+ transition probabilities were calculated using the Judd-Ofelt theory. In the “mixed” compounds, the Er3+ ions tend to reside in the larger / heavier cation environment. The low-temperature (12 K) spectroscopy evidences the presence of a single type of clusters at this doping level; the crystal-field splitting for Er3+ ions in clusters was determined. Continuous-wave low-threshold laser operation at ∼2.8 µm (the 4I11/2 → 4I13/2 transition) was achieved with all five Er3+:MF2 crystals. The maximum achieved laser slope efficiency was 37.9% (Er3+:CaF2), 23.5% (Er3+:SrF2) and 17.2% (Er3+:BaF2).

Spectroscopy and 2.8 µm laser operation of disordered Er:CLNGG crystals.

We report on the first, to the best of our knowledge, laser operation on the 4I11/2 → 4I13/2 transition of erbium-doped disordered calcium lithium niobium gallium garnet (CLNGG) crystals with broadband mid-infrared emission properties. A 41.4 at.% Er:CLNGG continuous-wave laser generated 292 mW at 2.80 µm with 23.3% slope efficiency and a laser threshold of 209 mW. Er3+ ions in CLNGG feature inhomogeneously broadened spectral bands (σSE = 1.79 × 10-21 cm2 at 2.79 µm; emission bandwidth, 27.5 nm), a large luminescence branching ratio for the 4I11/2 → 4I13/2 transition of 17.9%, and a favorable ratio of the 4I11/2 and 4I13/2 lifetimes, exhibiting values of 0.34 ms and 1.17 ms (for 41.4 at.% Er3+), respectively.

Polarization-anisotropy of mid-infrared emission properties of Er3+ ions in YAlO3 crystal – INVITED

We report on a polarization-resolved study of mid-infrared emission properties of Er3+ ions in the orthorhombic YAlO3 crystal. For the 4I11/2 → 4I13/2 transition, σSE reaches 0.20×10-20 cm2 at 2919 nm (for light polarization E || c). Pump-induced polarization switching between the E || b and E || c eigen-states is observed in an 10 at.% Er:YAlO3 laser. Pumped by an Yb-fiber laser at 976 nm, this laser delivers 0.77 W at 2919 nm with a slope efficiency of 31.4% being close to the Stokes limit and a laser threshold of 33 mW.

Effect of biphasic-phase on the mid-infrared emission properties of Pr3+ doped GeSe2-Ga2Se3 chalcogenide glass ceramics

Mid-infrared (MIR) laser operating at 2–5 μm has gained increasing interest because of the extensive applications in fields from biomedicine, sensing to nanomaterial science. Chalcogenide glass (ChG) is a kind of matrix that is promising for MIR laser due to its low phonon energy and wide infrared transmittance region. However, significant challenges in the enhancement of MIR optical properties of rare-earth ion-doped ChGs still exist. Here, enhanced MIR emission was realized in Pr3+-doped chalcogenide glass ceramics (ChGCs). By controlling the heat treatment temperature and duration, biphasic-phase nanocrystals of Ga2Se3 and GeSe2 were successively precipitated in the glass host. Compared to the as-prepared glass, the GCs exhibit an obvious increase in emission intensity by more than 5 times. The improvement of the MIR emission may be induced by the enhanced cross-relaxation between Pr3+ ions and the increased multiple scattering effects. Furthermore, the obtained ChGC enables large stimulated emission cross section 0.42 × 10−20 cm2 at 2.44 μm and 0.62 × 10−20 cm2 at 4.75 μm. The superior optical properties of the ChGC indicate that it is an attractive candidate for MIR laser.

Growth and mid-infrared emission properties of "mixed" fluorite-type Er:(Ca,Sr)F2 and Er:(Ba,Sr)F2 crystals

Fluorite-type 5 at.% Er3+:(M1,M2)F2 (M1 = Ca, Ba; M2 = Sr) crystals were grown by the conventional Bridgman technique and a comparative study of their spectroscopic properties was performed. The vibronic properties of the fluorite-type crystals were studied by Raman spectroscopy. The Er:(M1,M2)F2 crystals exhibited a slightly inhomogeneous broadening of mid-infrared luminescence spectra as compared to the ‘parent’ compound, Er:SrF2. The luminescence lifetimes of the 4I11/2 and 4I13/2 manifolds were measured, e.g., for the Er:(Ca,Sr)F2 crystal, the luminescence lifetimes were estimated to be 8.64 ms and 5.64 ms, respectively, representing a favorable ratio for mid-IR laser operation.

Mid-infrared emission properties of the Tm3+-doped sesquioxide crystals Y2O3, Lu2O3, Sc2O3 and mixed compounds (Y,Lu,Sc)2O3 around 1.5-, 2- and 2.3-μm

Tm3+-doped sesquioxides Y2O3, Lu2O3 and Sc2O3 are well known for their emissions around 2 μm (3F4 →3H6 transition). We study here their absorption and emission properties, both at 2 μm and at 1.5 μm (3H4 → 3F4) and 2.3 μm (3H4 → 3H5), by considering that the totality of the Tm3+ ions or only part of them are contributing to the line intensities. The study is also extended to the Tm3+-doped mixed compounds LuYO3, LuScO3 and YScO3. The results obtained in terms of radiative lifetimes and branching ratios, as derived from a Judd-Ofelt analysis of the absorption data, thus appear to be more consistent with the measured fluorescence decays, by assuming that only 75% of the Tm3+ ions, those sitting into C2 symmetry sites, are involved in the absorption and the emission spectra. The registered emission spectra are then calibrated in cross section unit and some of them compared between each other depending on the method (reciprocity, modified reciprocity or Füchtbauer method) which is used. Calculations are finally carried out to predict the cross section of important excited-state transitions which are involved in the two-step excitation pumping of the 3H4 emitting level around 1.05 μm (3F4 → 3F2,3) and 1.45 μm (3F4 → 3H4).

ZnS enhancing the infrared emission of Er3+ doped oxyfluorosulfide glasses with low hydroxyl content

Different content of ZnS was introduced into Er3+ doped oxyfluorosulfide glasses to explore the effect on the near- and mid-infrared emission properties. The results indicate the addition of a small amount of ZnS can substantially enhance the near- and mid-infrared emission intensity. However, more ZnS (7%) will lead to glass devitrification and decrease the infrared emission intensity greatly. XRD, Raman spectra and DSC tests prove the small amount of ZnS has no obvious effect on the transparency, phonon energy and thermal properties of these glasses. FTIR spectra reveal the addition of ZnS can reduce the content of hydroxyl groups obviously, which is the main reason for the enhancement of infrared emission. Our results show that the proper amount of ZnS is beneficial to reduce hydroxyl content and enhance the near- and mid-infrared emission of these Er3+-doped oxyfluorosulfide glass.

Structural evolution, crystallization behaviour and mid-infrared emission properties in Yb/Ho codoped oxyfluoride germanosilicate glass ceramics with varied Si/Ge ratio

Changes in glass structure and crystallization behaviour from oxyfluoride silicate glass to oxyfluoride germanate glass were studied by modifying the ratio of Si/Ge in oxyfluoride germanosilicate glass ceramics, and transparent glass ceramic with low light scattering and efficient mid-infrared emissions were obtained. The NaYF4 nanocrystals crystallization ability of oxyfluoride glass was decreased with the increase in Ge content, which can be attributed to the weakened oxide and fluoride phase separation in GeO2-rich glass. Upconversion and down-conversion emission spectra together with Ho3+: 5I6 energy level fluorescent decay curves have been discussed for SiO2-rich glass ceramics and GeO2-rich glass ceramics, in which the fluoride crystallization induced the decrease of multi-phonon non-radiative decay rates plays the main role in the energy transfer processes. The influence of Si/Ge ratio on 2 μm and 3 μm fluorescent emissions in glasses and glass ceramics, and its link with glass network structural changes were discussed. The optimized Yb/Ho codoped oxyfluoride germanosilicate glass ceramic with low light scattering, high peak emission cross section(11.18 × 10−21cm2) and maximum gain coefficient (1.387 cm−1) at 2888 nm provides a potential application in the development of new 3 μm laser devices based on transparent oxyfluoride glass ceramic materials.

Design of Multimodal Absorption in the Mid-IR: A Metal Dielectric Metal Approach.

Specific control on the mid-infrared (mid-IR) emission properties is attracting increasing attention for thermal camouflage and passive cooling applications. Metal–dielectric–metal (MDM) structures are well known to support strong magnetic polariton resonances in the optical and near-infrared range. We extend the current understanding of such an MDM structure by specifically designing Au disc arrays on top of ZnS–Au–Si substrates and pushing their resonances to the mid-IR regime. Therefore, we combine fabrication via lift-off photolithography with the finite element method and an inductance–capacitance model. With this combination of techniques, we demonstrate that the magnetic polariton resonance of the first order strongly depends on the individual disc diameter. Furthermore, the fabrication of multiple discs within one unit cell allows a linear combination of the fundamental resonances to conceive broadband absorptance. Quite importantly, even in mixed resonator cases, the absorptance spectra can be fully described by a superposition of the individual disc properties. Our contribution provides rational guidance to deterministically design mid-IR emitting materials with specific narrow- or broadband properties.

The mid-infrared emission properties and energy transfer of Tm3+ /Er3+ co-doped tellurite glass pumped by 808/980nm laser diodes

The spectral performance of the Tm3+/Er3+ co-doped tellurite glass under the pump at 808/980 nm and the energy transfer process between Tm3+ and Er3+ were mainly studied. The mid infrared fluorescence spectra showed that when the concentration of doped Er3+ ion was 0.5mol%, the fluorescence intensity of 1.8 μm and 2.7 μm reached the peak. While at the pump of 980 nm, the maximum occurred in 1mol% of Er3+ ions. Under 808/980 nm pumping system, different energy transfer mechanisms between Tm3+ and Er3+ ions were accordingly proposed. The maximum emission cross section of 0.5 Tm3+/0.5Er3+ codoped sample can reach 4.68 × 10−21 cm2 at 1886 nm. When P was 0.4, the gain of Tm3+:3F4→3H6 at 1852–2100 nm started to be positive while its maximum gain coefficient was 0.91 cm−1, and its central wavelength was 1887 nm. Therefore, the large emission cross section and the high gain are conducive to the Tm3+/Er3+ co-doped tellurite glass to obtain low threshold value and high gain of the 2 μm laser output.

Study of Mid-Infrared Emission and Structural Properties of Heavy Metal Oxide Glass and Optical Fibre Co-Doped with Ho3+/Yb3+ Ions.

Bismuth-germanate glasses with low hydroxide content co-doped with Ho3+/Yb3+ ions have been investigated in terms of structural and spectroscopic properties. To reduce OH- ions content and improve transmittance value at the wavelength of 3.1 µm, the glass synthesis has been carried out in low vacuum conditions (45–65 mBar). The composition of the host glass based on heavy metal oxides affects the maximum phonon energy (hωmax = 724 cm−1), which low value has a positive impact on the mid-infrared emission parameters. Emission band at the wavelength of 2.87 µm was observed in glass co-doped with mol% 0.25 Ho2O3/0.75 Yb2O3 under 980 nm high power laser diode wavelength excitation. Lifetime measurements of the Yb3+:2F5/2 quantum level indicate efficient Yb3+ → Ho3+ energy transfer (η = 61%). The developed active bismuth-germanate glass was used as the core of optical fibre operating in the mid-infrared region.

Bright Mid-Infrared Photoluminescence from Thin-Film Black Phosphorus.

Recently rediscovered layered black phosphorus (BP) provides rich opportunities for investigations of device physics and applications. The band gap of BP is widely tunable by its layer number and a vertical electric field, covering a wide electromagnetic spectral range from visible to mid-infrared. Despite much progress in BP optoelectronics, the fundamental photoluminescence (PL) properties of thin-film BP in mid-infrared have rarely been investigated. Here, we report bright PL emission from thin-film BP (with thickness of 4.5 to 46 nm) from 80 to 300 K. The PL measurements indicate a band gap of 0.308 ± 0.003 eV in 46 nm thick BP at 80 K, and it increases monotonically to 0.334 ± 0.003 eV at 300 K. Such an anomalous blueshift agrees with the previous theoretical and photoconductivity spectroscopy results. However, the observed blueshift of 26 meV from 80 to 300 K is about 60% of the previously reported value. Most importantly, we show that the PL emission intensity from thin-film BP is only a few times weaker than that of an indium arsenide (InAs) multiple quantum well (MQW) structure grown by molecular beam epitaxy. Finally, we report the thickness-dependent PL spectra in thin-film BP in mid-infrared regime. Our work reveals the mid-infrared light emission properties of thin-film BP, suggesting its promising future in tunablemid-infraredlight emitting and lasing applications.

Comprehensive studies of the Ag+ effect on borosilicate glass ceramics containing Ag nanoparticles and Er-doped hexagonal NaYF4 nanocrystals: morphology, structure, and 2.7 μm emission

AbstractIn this work, we have performed a comprehensive investigation of the Ag+ concentration effect on the morphological, thermal, structural, and mid-infrared emission properties of novel oxyfluoride borosilicate glasses and glass ceramics containing both Ag nanoparticles and erbium-doped hexagonal NaYF4 nanocrystals. The effect of Ag+ ions on the glass forming and crystallization processes was discussed in detail by glass structural analysis. It was found that the Ag+ concentration can affect the distribution of Na+ ion and bridge oxygen in boron-rich and silicon-rich phases, which induced the transformation between BO3 triangles and BO4 tetrahedra during crystallization process. In addition, there was a turning point when the doped Ag+ ion concentration reached its solubility in the borosilicate glass. Furthermore, the enhancement of the 2.7 μm emission and the reduction of the lifetime of the 4I13/2 level were observed both in glasses and in glass ceramics, and its origin was revealed by qualitative and quantitative analyses of the Er3+-Ag nanoparticles (localized electric field enhancement) and Er3+-Er3+ (nonradiative resonance energy transfer) interactions within glasses and glass ceramics. Moreover, the high lifetime of the 4I11/2 level (2.12 ms) and the peak emission cross section in 2.7 μm (6.8×10−21 cm2) suggested that the prepared glass ceramics have promising mid-infrared laser applications.

Nd3+ doped fluorochlorozirconate glass: 3.9 μm MIR emission properties and energy transfer

The Nd3+ doped fluorochlorozirconate (FCZ) glass was prepared by melt-quenching method. The 3.9 μm emission from Nd3+ ions is attributed to the two-photon absorption process. The strong emission transition at 3.9 μm fluorescence peak intensity, corresponding to the 4G11/2→2K13/2 transition, is directly proportional to the NaCl concentration. With the increase of the Cl- ions amount, the mid-infrared (MIR) luminescent intensity is significantly enhanced. Additionally, the Judd-Ofelt (J-O) parameter Ω 2 is larger than that of the fluorozirconate (FZ) glass, which indicates the covalency of the bond between RE ions and ligand is stronger as Cl- ions substitution of F- ions in chloride FZ glass. The X-ray diffraction (XRD) patterns show that the amorphous glassy state keeps the FZ glass network structure. In brief, the advantageous spectroscopic characteristics make the Nd3+-doped FCZ glass be a promising candidate for application of 3.9 μm emission.

2 μm emission performance in Tm3+/Er3+ codoped silicate glasses under 800 nm and 980 nm excitation

In this paper, mid-infrared 2μm emission properties and energy transfer mechanism were investigated in Er3+/Tm3+ co-doped silicate glasses with optimized extra-low hydroxyl content ∂OH- (0.73cm−1). The intensity parameters Ωt (t=2,4,6) were calculated from the measured absorption spectra based on the Judd-Ofelt theory. The energy transfer efficiency from the Er3+:4I13/2 level to the Tm3+:3F4 level was calculated and reached up to 91.2% under 980nm LD pumps and quantum efficiency is 63%. Meanwhile, the 1.85μm band stimulated absorption and emission cross-sections of Tm3+:3F4→3H6 transitions were also obtained and analyzed. In addition, the measured ΔT (evaluate the glass forming ability) is as high as 297°C, which shows that the silicate glass (SBET) possess good thermal stability. Hence, all of the present investigations indicate that the Er3+/Tm3+ co-doped silicate glasses have potential applications in 2μm laser materials and may provide beneficial guide for investigation of population behaviors of Tm3+ ions at 2μm emissions.

Synthesis and spectroscopy of high concentration dysprosium doped GeS2[sbnd]Ga2S3[sbnd]CdI2 chalcohalide glasses and fiber fabrication

0.2%–3% weight of Dy3+ ions doped 64GeS2·16Ga2S3·20CdI2 glasses were synthesized, and their spectroscopic properties were investigated. It was shown that the host glass could dissolve as much as 3% Dy3+ ions without deteriorating the glass transparency. The mid-infrared (MIR) emissions of the glasses did not present remarkable concentration quenching when the Dy3+ ions concentration was less than 0.6%. It was also shown that the MIR emission properties could be significantly improved by reducing SH/OH impurities in the glasses. The spectral analyses indicated that the 2.9 and 4.3 μm emissions of Dy3+ ions in the glass showed relatively large stimulated emission cross sections. The glass doped with as high as 0.4% Dy3+ ions was successfully drawn into fibers, indicating good potential of the doped glass for MIR lasers.

Broadband mid-infrared 2.8 μm emission in Ho3+/Yb3+-codoped germanate glasses

This work reports the mid-infrared emission properties around 2.85μm in Ho3+/Yb3+ codoped germanate glasses. The glass not only possesses considerably low OH− absorption coefficient (0.24cm−1), but also exhibits low phonon energy (790cm−1). A large spontaneous transition probability (36.66s−1) corresponding to the Ho3+:5I6→5I7 transition has been calculated based on the Judd–Ofelt theory. Besides, a broad 2.85μm fluorescence has been successfully observed and a reasonably model has been proposed to unravel the origin of the broadening emission band. Moreover, the peak emission cross sections of the glass is as high as 9.2×10−21cm2, and the maximum gain per unit length at 2.85μm could be as high as 4.3dB/cm. Results indicate that the prepared germanate glass is a promising candidate for 2.85μm mid-infrared laser materials applications.

Highly efficient mid-infrared 2 μm emission in Ho^3+/Yb^3+-codoped germanate glass

This work reports the mid-infrared emission properties around 2 μm in Ho3+/Yb3+ codoped germanate glasses. The glass not only possesses good chemical durability and good thermal stability but also has high mid-infrared transmittance around 2 μm (90%). In addition, the glass possesses considerably low OH− content (20.45 ppm) and large spontaneous transition probability (103.38 s−1) corresponding to the Ho3+:5I7→5I8 transition. Moreover, the measured lifetime of Ho3+:5I7 level is as high as 7.68 ms, and the quantum efficiency at 2 μm can reach 79.4%. The energy transfer processes of Yb3+:2F5/2 level and Ho3+:5I6 level were quantitatively analyzed according to the rate equation. Results indicate that the prepared germanate glass is a promising candidate for 2 μm mid-infrared laser materials applications.

Dy3+-doped Ga–Sb–S chalcogenide glasses for mid-infrared lasers

Novel Ga–Sb–S chalcogenide glasses doped with different amount of Dy3+ ions were prepared. Their thermal stability, optical properties, and mid-infrared (MIR) emission properties were investigated. The glasses show good thermal stability, excellent infrared transparency, very low phonon energy (∼306cm−1), and intense emissions centered at 2.95, 3.59, 4.17 and 4.40μm. Three Judd–Ofelt intensity parameters (Ω2=8.51×10−20cm2, Ω4=2.09×10−20cm2, and Ω6=1.60×10−20cm2) are obtained, and the related radiative transition properties are evaluated. The high quantum efficiencies and large stimulated emission cross sections of the MIR emissions (88.10% and 1.11×10−20cm2 for 2.95μm emission, 75.90% and 0.38×10−20cm2 for 4.40μm emission, respectively) in the Dy3+-doped Ga–Sb–S glasses make them promising gain materials for the MIR lasers.