Mid-infrared Laser Applications Research Articles

Design of tensile-strained GeSn/SiGeSn structure for low threshold mid-infrared laser application

The plasticity of GeSn alloy energy band has promoted the development of silicon-based photoelectric integration and optical interconnection. A tensile-strained GeSn/SiGeSn double heterostructure laser wrapped with Si3N4 stress liner is designed and characterized theoretically. The triaxial tensile strain is introduced into the GeSn/SiGeSn heterostructure laser by the Si3N4 linear stressor. The lower threshold current density and higher optical gain of the GeSn/SiGeSn laser can be achieved by tuning the band structure and carrier distribution in the active region with tensile strain and Sn compositions. Compared with the relaxed device, the value of ne ,Γ/ne ,total for the Ge0.90Sn0.10/Si0.315Ge0.499Sn0.186 heterostructure laser wrapped with 300 nm Si3N4 linear stressor is increased to 30.6% at n e,total of 1018 cm−3, the laser λ can be extended to 3.44 μm, and the J th is reduced from 206 to 59 A/cm2.

Design and fabrication of a tellurite hollow-core anti-resonant fiber for mid-infrared applications

The hollow core anti-resonant fibers (HC-ARFs) based on soft glass are in high demand for 3-6 µm laser delivery. A HC-ARF based on tellurite glass with 6 touching capillaries as cladding was designed and fabricated for the first time, to the best of our knowledge. A relatively low loss of 3.75 dB/m at 4.45 µm was realized in it. The effects of capillary number, core diameter, wall thickness of capillary, and material absorption loss on the loss of the HC-ARF were analyzed by the numerically simulation. The output beam quality was measured and the influence of bending on the fiber loss was discussed. The results of numerical simulation suggested that the theoretical loss of the prepared fiber can be reduced to 0.1 dB/m, indicating that tellurite HC-ARFs have great potential for mid-infrared laser applications.

Efficient and tunable broadband mid-infrared luminescence through energy transfer in CsPb1-x(Er/Yb/Ho)xBr3 perovskite fluoride glasses for CO2 monitoring in H2 energy

Inorganic CsPbBr3 perovskites have garnered significant attention for their excellent optoelectronic properties, particularly in the visible region. However, their great potential for mid-infrared applications has rarely been reported. In this study, we successfully synthesized CsPb1-x(Er/Yb/Ho)xBr3-ZBLAN perovskite fluoride glasses, which exhibit efficient and tunable broadband mid-infrared luminescence. We utilized this perovskite material to fabricate a detection device for measuring carbon dioxide impurity concentrations in hydrogen energy systems. By substituting the Pb2+ ions with rare earth ions Er3+/Yb3+/Ho3+, we achieved continuous tunability within the wavelength range of 2.6–3 μm. Absorption and emission cross sections (σabs and σem) of 0. 25CsPb1-x(Er/Yb/Ho)xBr3-ZBLAN are 3.14×10−20 cm2 and 3.45×10−20 cm2. These findings highlight the potential of CsPb1-x(Er/Yb/Ho)xBr3 perovskite fluoride glasses for future applications in broadly tunable mid-infrared light emitting and laser technologies. Overall, our results demonstrate the broad utility of CsPb1-x(Er/Yb/Ho)xBr3 perovskite fluoride glass for tunable mid-infrared luminescence and laser applications.

Growth, structure and spectroscopic properties of Er:YSr3(PO4)3 disordered crystal for mid-infrared laser applications

Mid-infrared lasers in the ⁓ 3 µm region activated by Er3+ ion has attracted considerable attention due to their important applications. Herein, a heavy concentration (30 mol%) Er3+ ion doped YSr3(PO4)3 (Er:YSP) single crystal with a high crystalline quality was grown through the Czochralski pulling method. The structure of single crystal was ascertained to be cubic system with the point group 4¯3m using the powder X−ray diffraction and Rietveld structural refinement methods. Furthermore, the band structure and density of states of the crystal were analyzed by the first principal calculations. The absorption and fluorescence spectra were also investigated. An intense absorption band located at 974 nm with a full width half-maximum of 18 nm, where the absorption cross section was obtained to be 3.72 × 10−21 cm2. The full width half-maximum value of emission band centered at about 3090 nm is up to be 140 nm, which is very suitable for realizing ultrashort pulses and tunable lasers. In addition, the fluorescence lifetime of the upper 4I11/2 and lower 4I13/2 levels were obtained to be 0.65 ms and 5.37 ms, respectively. All the results show that the disordered structure crystal Er:YSP could potentially serve as a laser medium for the ⁓ 3µm region.

Realizing particle population inversion of 2.7 μm emission in heavy Er3+/Pr3+ co-doped low hydroxyl fluorotellurite glass for mid-infrared laser

In this work, the population bottleneck of Er3+: 4I11/2 → 4I13/2 was overcome for the first time in heavy Er3+/Pr3+ co-doped TeO2–BaF2–La2O3–LaF3 (TBLL) low hydroxyl fluorotellurite glasses. Infrared emission spectra and fluorescence lifetime decay curves reveal that Pr3+ ions could deplete the electrons from the Er3+: 4I13/2 level faster than those from the Er3+: 4I11/2 under 980 nm excitation. Specifically, the energy transfer (ET) efficiency of the Er3+: 4I13/2 → Pr3+: 3F3,4 process (ET1) reached 96.27%, while that of the Er3+: 4I11/2 → Pr3+: 1G4 process (ET2) is only 2.17% in the Er3+/Pr3+ co-doped glass. Additionally, the energy transfer mechanism of Er3+ and Pr3+ ions was investigated using the Dexter theory, where the energy transfer microscopic parameters CD-A are 13.21 × 10−40 cm6/s and 0.89 × 10−40 cm6/s for the ET1 and ET2 processes, respectively. Finally, a numerical simulations laser model was developed to discuss the laser properties of the Er3+/Pr3+ co-doped TBLL fibers. The simulation results indicate that a 2.7 μm laser with a maximum output power of 2.26 W and slope efficiency of 13.89% could be achieved when the fiber background loss is reduced to 0.5 dB/m. The above results suggest that the Er3+/Pr3+ co-doped TBLL glass has great potential applications in mid-infrared fiber lasers.

Influence of Nd3+ concentration on mid-infrared emission in PbF2 crystal co-doped with Ho3+ and Nd3+ ions

A promising series of HoyNdxPb(1–x–y)F2 (x = 0, 0.01, 0.02, 0.03, 0.04; y = 0.02) crystals was grown by the Bridgman method. The influence of the Nd3+ ions concentration on mid-infrared (∼2.0, ∼2.9 and ∼3.9 μm) fluorescence emissions of Ho3+ ions in the PbF2 crystal excited by 808 nm laser diode was investigated in this work. The energy transfer mechanism between Nd3+ ions and Ho3+ ions under different concentrations of the Nd3+ ions was systematically analyzed. The results show that the Nd3+ ions have good sensitization and deactivation effect on the Ho3+ ions to stimulate the mid-infrared fluorescence emissions. The experimental analysis proves that the sensitization efficiency of the Nd3+ ions is relatively stable at around 93.45% with varying Nd3+-doping concentrations. Concentration dependence studies indicate that the concentration of the Nd3+ ions has significant influence on mid-infrared emissions. When the doping concentration of the Nd3+ ions is up to 2.0 at%, the intensity of ∼2.0, ∼2.9 and ∼3.9 μm emissions all reach the maximum. The output characteristics of a 3.9 μm laser are simulated, and it is found that with the increase of the Nd3+-doping concentration, the peak power, pulse width, and peak energy all meet the trend of first increasing and then decreasing, and Ho0.02Nd0.02Pb0.96F2 crystal displays the best performance. All the results show that the Nd3+/Ho3+ co-doped PbF2 crystals might act as a useful optical medium for mid-infrared laser applications.

Effects of Ho3+ concentration on the fabrication and properties of Ho: Y2O3-MgO nanocomposite for Mid-infrared laser applications

Infrared transparent Ho: Y2O3-MgO nanocomposite ceramics with a volume ratio of 50:50 (RE2O3: MgO) were prepared by combining sol-gel powder synthesis and hot-pressing sintering techniques. In order to obtain Ho: Y2O3-MgO nanocomposite ceramics with fine grain size, dense microstructure and homogeneous phase domains, the effect of sintering temperature and Ho3+ doping concentration were studied. Transmittance and SEM measurement revealed that the grain size of 3 at.% Ho: Y2O3-MgO ceramic sintered at 1250 °C is 141 nm, and the transmission is up to 85.2% at 5 μm. The detailed spectroscopic investigation of x at.% Ho: Y2O3-MgO (x = 1, 3, 5, 7, 9, 15) ceramics was performed. The nanocomposites exhibited photoluminescence properties similar to that of Ho: Y2O3 crystals and ceramics. In addition, the thermal conductivity of 3 at.% Ho: Y2O3-MgO ceramic is 13.04 W/m·K, which is superior to that of Ho:Y2O3 ceramics. The high transmission, excellent thermal conductivity, and outstanding optical characteristics indicated that Ho: Y2O3-MgO ceramics is a promising material for efficient infrared solid-state laser.

PECVD-derived graphene saturable absorber mirror for 2.8 μm pulsed Er:ZBLAN fiber laser

Graphene has been emerging as an ideal mid-infrared saturable absorber (SA) due to its broadband absorption, ultrafast nonlinear optical response, high stability and thermal tolerance. However, the current routes (e.g. chemical vapor deposition and spin coating) for constructing graphene SAs are suffering from the limited flexibility in substrate choice and the introduction of impurities during the transfer process, resulting in poor film quality and unstable laser modulation. Here, we demonstrate a high-quality graphene SA mirror (GSAM) grown directly on calcium fluoride (CaF2) substrate by a low-temperature plasma enhanced chemical vapor deposition (PECVD) method for mid-infrared pulse modulation. The controllable growth of high-quality graphene film on the nickel-modified CaF2 substrate is realized by adjusting the growth time and hydrocarbon ratio during PECVD process. Consequently, the GSAM shows excellent nonlinear optical absorption with the modulation depth of 11.2%. By inserting the GSAM into the Er:ZBLAN fiber laser, a stable passive Q-switched (QS) operation can be achieved with an average output power of 142 mW and a pulse width of 300.2 ns. The slope efficiency of QS laser is up to 17.4% and the peak power is 7.76 W. Our strategy paves the way for developing high quality and modulation stability GSAM towards industrial applications of pulsed mid-infrared lasers.

Intense broadband 3.1 μm emission in Er3+-doped fluoroaluminate-tellurite glass for mid-infrared laser application

Er3+ single doped fluoroaluminate-tellurite glasses were made by employing a conventional melt-quenching technique. A strong fluorescence around 3.1 μm was achieved from Er3+-doped fluoride glasses, under a 980 nm laser diode pump, which was assigned to the Er3+: 4S3/2 → 4F9/2 radiation transition process. The up-conversion and mid-infrared spectra of emission for fluoroaluminate-tellurite glasses with various concentrations of Er3+ ions dopant was researched. In addition, the calculated fluorescence lifetime value about 3.1 μm reaches 0.48 ms. The findings indicate that fluoroaluminate-tellurite glasses doped with Er3+ have prospects of being developed into 3.1 μm mid-infrared fiber and laser materials.

Novel 3.1 µm and enhanced 2.7 µm emissions in Er3+ doped fluorotellurite glasses ceramic

A detailed spectroscopic analysis was reported in a series of Er3+ doped 60TeO2-30ZnF2-10NaF (mol%, TZNF60) glass ceramics. When compared with the precursor fluorotellurite glass, the corresponding glass ceramic owns broader 2.7 µm emission with a FWHM of 193 nm and relatively invariable decay lifetime of 1.40 ms. In additions, a novel 3.1 µm emission also arised from Er3+ ions 4I11/2→4I13 /2 transition was observed after heating treated the precursor glass. The combination of absolute elimination of OH group (~0.01 cm−1), and lower phonon energy of NaF crystals (~400 cm−1) is beneficial to the realization of the intense 2.7 µm and newfangled 3.1 µm emissions. By analyzing the results of XRD and SEM, it is found that more Er3+ ions embedded into the NaF nano-crystallized circumstance with the prolong of holding time, resulting in bigger stimulated emission cross sections with a maximum of 5.5 × 10−20 cm2 and longer lifetime (≥2.44 ms) and therefore greater FOM value of 12.85 × 10−20 ms cm2 for 3.1 µm emission. As result, it is considered that Er-doped fluorotellurite glass ceramic is a potential host material for the applications of broad band mid-infrared lasers.

Dy3+-doped Ga2S3-Sb2S3-La2S3 chalcogenide glass for mid-infrared fiber laser medium

We report a new Dy3+-doped Ga2S3-Sb2S3-La2S3 (GSLS) chalcogenide glass for mid-infrared (mid-IR) laser applications. With the addition of La2S3 into the previously studied Ga2S3-Sb2S3 glass, the thermal stability of the base glass is significantly enhanced. The glass with the composition 20Ga2S3-75Sb2S3-5La2S3 (mol.%) shows the best thermal stability for fiber drawing, and the glass can be doped with up to 5 mol.% Dy2S3. The Dy3+-doped GSLS bulk glasses and a multimode fiber exhibit intense emissions at 2.95 μm and 4.40 μm. Spectroscopic analyses show that the mid-IR emissions are with high quantum efficiencies and large stimulated emission cross sections, indicating that Dy3+-doped GSLS glass is a promising candidate for mid-IR fiber laser medium.

Spectroscopic properties of ErF3 doped tellurite–gallium oxyfluoride glass for ∼3 μm laser materials

ErF3-doped TeO2–Ga2O3–BaF2–AlF3–Y2O3 (TGBAY) glasses with high fluorescence efficiency and a high thermal damage threshold were developed for potential mid-infrared fiber laser applications. A model 2.7-μm fiber laser based on this material was analyzed using rate and propagation equations. Under 808 and 980 nm laser pumping, fluorescence emissions with central wavelength at 1.55 and 2.73 μm were detected. Based on the Judd–Ofelt (J–O) theory, the intensity parameters (Ωλ, λ = 2, 4, and 6) and radiative transition property were calculated and characterized through absorption and emission spectra. The results indicated that tellurite–gallium oxyfluoride glass had a high glass transition temperature (Tg, ∼391 °C), large emission cross sections at 1.55 μm (6.32 × 10−21 cm2) and 2.73 μm (9.68 × 10−21 cm2) as well as a longer fluorescence lifetime (6.84 ms at 1.55 μm and 262 μs at 2.73 μm) relative to the conventional Er3+-doped tellurite glass. The temperature dependence of the emission spectra indicated that TGBAY-2Er glass was more favorable to achieve infrared emission at low temperatures. Numerical simulation revealed the feasibility of achieving a ∼2.7 μm fiber laser operation based on the developed Er3+-doped tellurite–gallium oxyfluoride glass fiber.

Nonlinear optical property and mid-infrared Q-switched laser application at 2.8 μm of PtSe2 material

Recent progress on platinum diselenide (PtSe2) nanosheet makes it a promising candidate material for broadband nanophotonic devices, especially when operating in the mid-infrared spectral region. Herein, the layered PtSe2 is successfully prepared by a chemical vapor deposition (CVD) method and employed as a saturable absorber (SA) to generate 2.8 μm mid-infrared Q-switched laser. The nonlinear optical measurements reveal efficient saturable absorption effect at 2.8 μm, presenting a saturation fluence of 1.12 ± 0.14 mJ/cm2 and a modulation depth of 11 ± 2%. A laser pulse as shortest as 141.8 ± 1.4 ns is generated by Er3+:YAP/PtSe2 laser with the maximum output power of 780.0 ± 4.3 mW and the highest pulse repetition rate of 296.2 ± 3.8 kHz. These results indicate that layered PtSe2 is a promising SA for mid-infrared pulsed laser, which provides a further application potential for ultrafast photonic devices in mid-infrared region.

Optical properties of mid-infrared Cr2+:ZnSe single crystals grown by chemical vapor transporting with NH4Cl

In the recent two decades, Cr2+:ZnSe crystals have been widely used as a gain media for 2∼3 μm mid-infrared lasers. However, it still remains a huge challenge for researchers to meet more and more requirements on the crystals with high qualities and large sizes. In this work, one Cr2+:ZnSe single crystal with a diameter of about 15 mm was successfully grown by chemical vapor transporting (CVT) with NH4Cl in a closed quartz ampoule without any seed. The transmission of as-grown crystal is up to 70% in the UV-VIS-NIR region and is with an intense characteristic absorption of Cr2+ near 1770 nm. The X-ray photoelectron spectroscopy (XPS) shows that the incorporation of chlorine anions does not significantly affect the valence distribution of components in the crystal. The mid-infrared photoluminescence spectra show a strong and broad emission band centered at 2400 nm with a width of 600 nm under the 1770 nm laser excitation at room temperature. The calculated cross sections of absorption and emission were 1.31×10−18 and 1.4×10−18 cm2, respectively. The measured photoluminescence decay time was about 6.9 μs at room temperature. It is confirmed that the method of CVT with NH4Cl is suitable for the growth of Cr2+:ZnSe single crystals, which are expected to have a promising prospect in mid-infrared laser applications in further.

Broadband fluorescence emission and laser demonstration in large mode waveguide structure in Yb3+ doped germanate glass

A stable composition (against crystallization) of germanate glass doped with Yb3+ for mid-infrared laser applications is presented. Broad emission spectrum of Yb3+ was obtained for the fabricated glass. Laser operation was demonstrated in 13 mm long waveguide written in the glass using a femtosecond laser operating at 524 nm center wavelength sending 250 fs ultrashort pulses. The resulting CW laser operated at 1.04 µm in the fundamental mode of the waveguide. The propagation loss through the waveguide was 0.6 dB/cm at 1550 nm for 45 µm diameter of the modified structure. The mode analysis of the developed waveguide structure is also presented in COMSOL Multiphysics to study the electric field distribution through different modes of propagation in the waveguide and the confinement loss associated to them.

Nonparabolicity effects on carrier lifetimes in bulk Hg1-xCdxTe alloys and Mid-Infrared 2D Hg1-xCdxTe/CdTe Single Quantum Well Lasers

We report on a theoretical study of nonparabolicity (NP) effects on carrier lifetimes in narrow energy bandgap bulk (3D) Hg 1-x Cd x Te ternary alloys and their related 2D Hg 1-x Cd x Te/CdTe Single Quantum Well (SQW) nanostructures for Mid-infrared (MIR) Laser applications. Carrier lifetime (τ) calculations are performed within both the parabolic and the 4-band CB + HH + LH + SO nonparabolic models. We show that NP affects strongly all three main scattering processes: Auger, Schockley-Read-Hall (SRH), and radiative recombination (RR). At 300 K and in mid-Cd contents (0.4 < x < 0.6) 3D Hg 1-x Cd x Te alloys, Auger 1 is shown to be the dominant τ limiting factor. In 2D Hg 1-x Cd x Te/CdTe SQW nanostructures, we show that RR turns out to be the dominant τ limiting process. This strongly reduced influence of Auger1 process in 2D Hg 1-x Cd x Te/CdTe SQW nanostructures is the result of the strong 2D quantum confinement induced amplification of NP effects via much stronger electron (CB) and all three hole (HH, LH, SO) energy subbands interactions and mixing. As a consequence, NP effects are finally shown to significantly improve all main 2D Hg 1-x Cd x Te/CdTe SQW Laser parameters in the MIR λ range with an optimum at x = 0.45 and for wide enough QW with L z ≥ 100 Å. • Nonparabolicity effects on carrier lifetimes in Hg 1-x Cd x Te 3D and 2D MIR Lasers. • Auger scattering processes are dominant at 300 K in 3D Hg 1-x Cd x Te alloys (0.3 < x < 0.6). • Radiative recombination is dominant 300 K in 2D Hg 1-x Cd x Te/CdTe QW (x ≥ 0.40). • NP affects strongly carrier lifetimes, and consequently, all main laser parameters. • NP improves Laser emission wavelength, optical gain and threshold current densities.

Tm3+ codoping for mid-infrared laser applications of Dy3+ doped CaF2 crystals

We report here on a spectroscopic study of Dy3+-doped and Tm3+-Dy3+ doped CaF2 as promising candidates to develop crystalline waveguide laser sources around 3 μm. The advantages of Tm3+ ions as sensitizers to improve the excitation of Dy3+ ions in CaF2 is demonstrated: an energy transfer efficiency from Tm3+ to Dy3+ ions of 99.6% has been reached for Dy3+ concentration as high as 2 at.%, by considering a Tm3+ ratio set at 5 at.%. Moreover, the behavior of such doped crystals in a laser waveguide configuration has been modeled and the modeling results show that it seems possible to achieve promising laser perspectives around 3 μm, with laser thresholds in the watt level for singly doped Dy3+:CaF2 and around 0.2–0.3 W for codoped Tm3+-Dy3+:CaF2, presenting both laser efficiencies in the order of 30%. Finally, the saturation of the absorption which is observed in the modeling for such codoped Tm3+-Dy3+:CaF2 waveguide at Dy3+ concentration below 1% is discussed and its origin is explained.

Mid-Infrared, Green and Red Emission in Ho3+ - Er3+ Co-Doped Phosphate Glasses

Over the past decades, phosphate glasses show ample advantages in laser technology because of their excellent optical properties like a low glass transition temperature, low phonon energy, large infrared transmission window, and high gain density. The inclusion of lead and alkali earth metals to these phosphate glasses also improves the chemical durability of glasses, which have more advantages in smart cards, medical applications, and micro-batteries. The optimum environment for chemical durability and incorporating rare earth ions can be achieved by the interaction between sulphate and phosphate ions. Moreover, phosphate glasses mixed with alkali sulphate provides scope for micro battery applications. The presence of network modifiers like Pb2+, Zn2+ in phosphate glasses introduces structural modifications and increases the number of non-bridging oxygens (NBOs) in glass network. The metal oxides like PbO, Bi2O3 makes phosphate glass suitable for rare earth ion incorporation by softening the glass and provides better distribution by controlling the formation of clusters. The wide variety of rare earth ions in the phosphate glasses leads to wide range of applications in optoelectronic devices.To overcome the difficulty associated with lack of a useful absorption band at 980 nm of Ho3+ ion (easy excitation by commercial laser diode (LD)), rare earth ions such as Tm3+, Yb3+, and Er3+ can be introduced. Especially, among them, Er3+ exhibit strong absorption at 980 nm. Due to the narrower energy gap between Er3+: 4I13/2 and Ho3+: 5I7 states, the emission of Ho3+ ions can be enhanced by addition of Er3+. So, the Er3+/Ho3+ co-doped glasses have promising applications in mid-infrared (MIR) laser applications with 980 nm LD. In view of this, the set of the Er3+/Ho3+ co-doped sodium-sulfo lead phosphate glasses was prepared with the molar composition of (20-x-y) Na2SO4-20PbO-60P2O5-xEr2O3-yHo2O3 (x=0.5, y= 0.2, 0.4, 0.6, 0.8, 1.0 mol %) named as GEH-y glass and coded as GExHy. To explore various possible applications, all prepared glasses are characterised by EDS, XRD, FTIR, absorption, photoluminescence and lifetime profiles. All results are computed and few of them are compared with other glasses.We present results focused on both mid infrared and visible emission properties of Er3+/Ho3+ions in sodium-sulfo lead phosphate (GExHy) glasses. These materials exhibit simultaneously DC (down-conversion) and UC (up-conversion) photoluminescence (PL) by excitation at 379 nm and 980 nm. The favourable concentration of Ho2O3 was estimated from the analysis of NIR PL spectra for Ho3+: 2.0 mm and Er3+: 1.5 mm. In GExHy glasses, the increase in intensity near 2.0 mm with decrease in intensity at 1.5 mm infers to energy transfer process between Er3+ and Ho3+ ions.Under lexc= 379 nm the Er3+ ions are pumped to the 4G11/2 excited state and depopulate {via multi phonon relaxation MPR1} at lower 4S3/2, 2H11/2, and 4F9/2 levels and then relaxed to the 4I15/2 ground state by emitting weak and strong green emission bands along with weak red emission related to 4S3/2→4I15/2 (522 nm), 2H11/2→4I15/2 (544 nm), and 4F9/2→4I15/2 (657 nm) transitions, respectively. The up-conversion energy transfer (ET) analysis with 980 nm LD excitation, undergoes the following mechanism: Ground state absorption (GSA) : Er: 4I15/2 + hν → Er: 4I11/2 Excited State Absorption (ESA1) : Er: 4I11/2+ hν → Er: 4F7/2 Excited State Absorption (ESA2) : Er: 4I13/2 +hν → Er: 4F9/2 CR1 (Cross Relaxation) : Er: 4I11/2+Ho: 5I6→ Er: 4I15/2+Ho: 5F4 CR2 (Cross Relaxation) : Er: 4I13/2+Ho: 5I6→ Er: 4I15/2+Ho: 5F5 ET1: Er: 2S3/2+Ho: 5I8→ Er: 4I15/2+Ho: 5S2+5F4 ⇒ Ho: 5S2+5F4 → 5I8 (545 nm) ET2 : Er: 4F9/2+Ho: 5I8→ Er: 4I15/2+Ho: 5F5 ⇒ Ho: 5F5→5I8 (659 nm) MPR2: Ho: 5S2+5F4 → 5F5 ET3: Er: 4I11/2+Ho: 5I8→ Er: 4I15/2+Ho: 5I6 ⇒ Er: 4I13/2 → 4I15/2 (1554 nm) ET4: Er: 4I13/2+Ho: 5I8→ Er:4I15/2+Ho Fig. 1 Schematic energy level diagram of GE0.5H0.8 glass.The maximum energy transfer efficiency of GExHy samples is 75.5% and with the increase of Ho3+ ions, the lifetime decay has been reduced from 5.06 ms to 1.24 ms. The absorption and stimulated emission cross-sections of Er3+:1.5 mm and Ho3+: 2.0 mm were calculated. Moreover, the FWHM × σemi was estimated for Ho3+:5I7→5I8 transition to estimate the probable MIR laser emission. The CIE color coordinates were estimated from both DC and UC PL spectra. All the results indicated that the prepared GExHy glasses have promising material applications in mid-infrared solid-state lasers and telecommunications. In addition, efficient green and red emission makes these glasses attractive for the phosphor applications. Figure 1

Study on 2.86 µm emission properties of Ho3+-doped low-hydroxyl ZnF2 based fluoride glasses for mid-infrared laser applications

Ho3+-doped low-hydroxyl (OH-) ZnF2 based fluoride glasses were prepared by using the conventional melt-quenching method in a glove box. The glasses have a composition of ZnF2-BaF2-SrF2-YF3-HoF3 (ZBSY-H), and the absorption coefficient of OH- in the ZBSY-H glasses was calculated to be only ∼0.003 cm−1 at 2.86 µm. Under the excitation of an 1120 nm laser, efficient 2.86 µm emissions were observed in the ZBSY-H glasses. The emission cross section of the ZBSY-H glasses was also calculated, and the corresponding value was ∼7.19 × 10−21 cm2. These results indicated that the ZBSY-H glasses were potential candidate for 2.86 µm laser applications.

A 1.[formula omitted] Tm: YLF external cavity mode conversion vortex laser based on LD off-axis pump

In this work, a 1.9μm Tm:YLF high-order vortex laser output is realized for the first time based on LD off-axis pumping technology. By adjusting the off-axis displacement of the output coupling mirror accurately, the maximum topological charge up to m=20 for stable Hermite–Gaussian (HGm,0) mode is achieved. The conversion of high-order HGm,0 to Laguerre–Gauss (LGm,0) modes are further realized by a π/2 mode converter, and the topological charge and chirality of LGm,0 modes are measured by the Mach–Zehnder (MZ) interferometer system. The maximum output power of the LG1,0 mode vortex laser was measured to be 8.5W with the central wavelength of 1908.8 nm. The wavelength and the power instability are less than 0.72 nm and better than ± 5.9%, respectively. This work proves that the 1.9μm Tm:YLF laser has the potential to achieve continuous tuning and easy chirality control for the high-order vortex optical mode output, and lays a foundation for high-power mid-infrared vortex laser applications.