AlGaAs Laser Diode Research Articles

Study of structural and magnetic properties of laser-irradiated zinc ferrite material

Crystalline ZnFe2O4 (zinc ferrite) material was prepared using the sol–gel technique and converted in the forms of 3 pellets, out of which 2 pellets were irradiated at room temperature by pulsed Nd:YAG laser with 1.5 W, λ = 532 nm named ZF1 and continuous AlGaAs diode laser of 4 W, λ = 808 nm called ZF2, respectively, while the 3rd pellet was kept as control and named ZF. Synchrotron X-ray Diffraction (S-XRD) reveals the marginal variation in the structure having the lattice parameters of 8.4364 Å for ZF, 8.4176 Å for ZF1 and 8.4187 Å for ZF2. The porosity after laser irradiation has been increased to 10.87% for ZF1 and 10.84%, for ZF2 from 10.28% for ZF. The blocking temperature (TB) has been ∼15 K for all samples. There had been a slight variation in the magnetization of irradiated pellets at 5 and 300 K compared to ZF. The separation between ZFC and FC curves, the measure of interaction between Fe ions has increased for irradiated pellets when compared with the separation for ZF. Moreover, magnetization (M) versus applied magnetic field (H) at 5 K in the range of ±1 T shows the ferrimagnetic behaviour and this ordering has been seen up to TB as visible from M-T curves, whereas the material becomes superparamagnetic above TB as observed from M-T & M-H measurements.

Laser irradiation effects on the dielectric properties of zinc ferrite at room temperature

Zinc ferrite (ZF) nanomaterials were synthesised by the sol–gel auto-combustion method. Synchrotron-XRD confirms the formation of the pure F-d3m spinel structure whereas EDX reveals the composition of synthesised nano ZF. We investigated and compared the dielectric properties of un-irradiated pellet ZF-UI and irradiated pellets ZF-I1 (pulsed Nd:YAG laser dose of 1.2 W, λ = 1064 nm), ZF-I2 (pulsed Nd:YAG laser dose of 1.5 W, λ = 532 nm) and ZF-I3 (continuous AlGaAs diode laser of 4 W, λ = 808 nm) at room temperature. Dielectric constant (ε′) decreased prominently for ZF-UI while it decreased gradually for ZF-I1 and its decrement for ZF-I2 and ZF-I3 is very slow whereas dielectric constant (ε ″) decreased prominently for ZF-UI and ZF-I1while reduced slowly for ZF-I2 and ZF-I3 in the low-frequency region. ε′ becomes ∼69% for ZF-I1 and ∼9% for ZF-I2 and ZF-I3 at a higher frequency of 2 MHz whereas ε ″ for radiated samples becomes steady and nearly equitable at higher frequencies in comparison to that of ZF-UI in the measured frequency range of 10 kHz to 2 MHz. Dielectric loss (tan δ) of all irradiated samples has decreased and become ∼33% for ZF-I3, 43% for ZF-I2, nearly equal for ZF-I1 at 104 Hz and then decreased continuously up to 2 MHz when compared to tan δ for ZF-UI. The Jonscher power law has been fitted in measured ac conductivity (σ ac) with angular frequency (ω) graphs. DC conductivity (σ dc), temperature-dependent parameter B(T) and frequency exponent (n) have been extracted. σ dc for all irradiated samples has decreased and become nearly 51% for ZF-I1, 3% for ZF-I2 and 2% for ZF-I3 in comparison to that of ZF-UI whereas B(T) increased to 1.6 times for ZF-I3 and decreased to 0.7 times for ZF-I1 and 0.2 times for ZF-I2 while n shows slight decrement for ZF-I2 and ZF-I3. Interpretation from Cole–Cole plots for un-irradiated and irradiated pellets is in agreement with our investigations. These results suggest that the dielectric properties of ZF can be controlled and tuned by laser irradiation.

Cascade lasing at ∼2 μm and ∼2.3 μm in a diode-pumped Tm:YVO4 laser.

We report on the cascade continuous-wave operation of a diode-pumped Tm:YVO4 laser on the 3F4 → 3H6 (at ∼2 μm) and 3H4 → 3H5 (at ∼2.3 μm) Tm3+ transitions. Pumped with a fiber-coupled spatially multimode 794 nm AlGaAs laser diode, the 1.5 at.% Tm:YVO4 laser yielded a maximum total output power of 6.09 W with a slope efficiency of 35.7% out of which the 3H4 → 3H5 laser emission corresponded to 1.15 W at 2291-2295 and 2362-2371 nm with a slope efficiency of 7.9% and a laser threshold of 6.25 W.

Spectroscopic characterization of Tm:CaYAlO4 shaped crystal fibers grown by the micro-pulling-down method

Tm3+-doped CaYAlO4 (Tm:CALYO) shaped crystals fibers with various doping concentration of 2 at.%, 3 at.%, 5 at.% and 7 at.% have been successfully grown by the micro-pulling-down (μ-PD) method. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curves were analyzed at room temperature. The absorption bands of 3H6→3H4 transition centered at around 800 nm match well with commercial AlGaAs laser diode pumping sources. For 7 at.% Tm:CALYO crystal fiber, the full width at half maximum (FWHM) of the emission band for π polarization at 1806 nm was 225.4 nm. The fluorescence of 3F4 level decreased strongly as the thulium concentration increased. All the results indicate that Tm:CALYO crystal fibers are promising for ultrashort and tunable laser operation.

Growth and spectral characteristic of Nd:CaMgSi2O6 crystal

A 0.56 at.% Nd:CaMgSi2O6 single crystal was successfully grown by the Czochralski method, the crystal’s polarized absorption spectra, fluorescence spectra and lifetime were investigated in details. Based on J-O theory, the line strengths, spontaneous transition rates, fluorescence branching ratios, and radiative lifetime were obtained. The strong and broad absorption band at around 803 nm matches well with the emission wavelength of AlGaAs laser diodes. There are three strong emission peaks located at 1055, 1081, and 1115 nm in fluorescence spectra. A laser output power of 0.262 W at 1055.25 nm with the slope efficiency of 16 % was obtained. The intense multi-wavelength emissions from the Nd: CaMgSi2O6 crystal indicate that such a crystal could be used advantageously for a multi-wavelength laser operation.

Enhanced 1.5 μm emission of Tm3+ via Pr3+ deactivation in PbF2 crystal

Tm3+ doped and Tm3+,Pr3+ co-doped PbF2 single crystals with high quality were grown by Temperature Gradient Technique (TGT). The absorption spectra, fluorescence spectra, and lifetimes were investigated at room temperature. The absorption transition of Tm3+:3H6→3H4 matches well with the pumping source of the AlGaAs laser diode. The 1.5 μm emission intensity originating from Tm3+: 3H4→3F4 transition was enhanced significantly by co-doping Pr3+ ions. The energy transfer efficiency from the Tm3+: 3F4 level to the Pr3+: 3F2 level is as high as 90.2%, indicating that the Pr3+ ion is an effective deactivate ion for enhancing the ∼1.5 μm emission in Tm,Pr:PbF2 crystal. The results indicated that Tm,Pr:PbF2 crystal would be the promising candidate for 1.5 μm laser output.

Nd3+ doped CaLaGa3O7: Growth, structure, and optical properties of a disordered laser crystal

A new disordered crystal of Nd3+-doped CaLaGa3O7 (Nd: CLGO) was successfully grown using the Czochralski method for the first time. The effective segregation coefficient of Nd3+ ions in CLGO was calculated to be 0.68. A systematic investigation of the crystal structure characteristics, fluorescence lifetime, polarized absorption spectra, and emission spectra of Nd: CLGO crystal at room temperature was reported. The maximal absorption cross-sections at 808 nm were 3.18 and 1.34 × 10−20 cm2 for π-polarization and σ-polarization with an FWHM of 16 and 10 nm, respectively, indicating the good pumping efficiency of laser diodes (LDs). The emission cross-sections at 1061 nm of π- and σ-polarization were 7.23 and 6.90 × 10−20 cm2 with an FWHM of 18.8 and 27.8 nm, respectively. Moreover, the measured fluorescence lifetime was 250 μs? Based on the spectral parameters, several important laser parameters were calculated to assess the laser capability. The above results indicate that Nd: CLGO crystal is a promising disordered laser host with AlGaAs LD pumping, and is suitable for generating ultrashort pulse lasers.

Growth, Optical, and Spectroscopic Properties of Pure and Nd3+-Doped GdSr3(PO4)3 Crystals with Disordered Structure.

Disordered crystals have attracted immense attention for the generation of ultrashort laser pulses due to their good thermomechanical characteristics and wide emission bandwidths. In this work, a Gd-based orthophosphate crystal, GdSr3(PO4)3, (GSP), and a Nd3+-doped GdSr3(PO4)3 crystal, (Nd:GSP), were obtained by the Czochralski method. The crystal structure, optical properties, electronic band structure, laser damage threshold, and hardness of the GSP crystal were comprehensively investigated. It exhibited a disordered structure due to the random distribution of Sr and Gd atoms in the same Wyckoff site, which caused inhomogeneous spectral broadening. Additionally, it exhibited a short UV absorption cutoff edge (<200 nm), a large band gap (5.81 eV), and a high laser damage threshold (∼1850 MW/cm2). The spectral properties and Judd-Ofelt calculations of the Nd:GSP crystals were analyzed. A wide absorption band at 803 nm, with a full width at half-maximum value of 20 nm, makes the Nd:GSP crystal suitable for the efficient pumping of AlGaAs laser diodes. Sub-100-fs pulses could be supported by its 25 nm emission bandwidth. Hence, the GSP crystal could be a promising disordered crystal laser matrix.

Characterization and Ex Vivo Application of Indocyanine Green Chitosan Patches in Dura Mater Laser Bonding.

Dura mater repair represents a final and crucial step in neurosurgery: an inadequate dural reconstruction determines dreadful consequences that significantly increase morbidity and mortality rates. Different dural substitutes have been used with suboptimal results. To overcome this issue, in previous studies, we proposed a laser-based approach to the bonding of porcine dura mater, evidencing the feasibility of the laser-assisted procedure. In this work, we present the optimization of this approach in ex vivo experiments performed on porcine dura mater. An 810-nm continuous-wave AlGaAs (Aluminium Gallium Arsenide) diode laser was used for welding Indocyanine Green-loaded patches (ICG patches) to the dura. The ICG-loaded patches were fabricated using chitosan, a resistant, pliable and stable in the physiological environment biopolymer; moreover, their absorption peak was very close to the laser emission wavelength. Histology, thermal imaging and leak pressure tests were used to evaluate the bonding effect. We demonstrated that the application of 3 watts (W), pulsed mode (Ton 30 ms, Toff 3.5 ms) laser light induces optimal welding of the ICG patch to the dura mater, ensuring an average fluid leakage pressure of 216 ± 105 mmHg, falling within the range of physiological parameters. This study demonstrated that the thermal effect is limited and spatially confined and that the laser bonding procedure can be used to close the dura mater. Our results showed the effectiveness of this approach and encourage further experiments in in vivo models.

Bifunctional Nd:CaSrNb2O7 crystal: A potential self-frequency-doubling laser material candidate

One of the convenient methods to obtain green laser is by self-frequency-doubling (SFD) technique, the key is the SFD laser crystal. In this article, a bulk single crystal of 3.34 at.% Nd:CaSrNb2O7 was successfully grown by Czochralski method at about 1481 °C. Its spectral and thermal properties were investigated. There is a broad and strong absorption band at around 804 nm, which is very suitable for AlGaAs laser diode pumping. The polarized emission spectra show large emission cross-sections and full width at half maximum at around 1068 nm, and the fluorescence lifetime is 202 μs? Moreover, the fluorescence quantum efficiency reaches to 98.6%. The long lifetime, large emission cross-section, and high fluorescence quantum efficiency of Nd:CaSrNb2O7 crystal indicate that it is easy to achieve laser oscillation. The second harmonic generation intensity of 3.34 at.% Nd:CaSrNb2O7 crystal is about 3 times that of KH2PO4, and phase matching can be realized in this crystal. All these results show that Nd:CaSrNb2O7 is a good bifunctional crystal, which possesses laser and nonlinear optical functions simultaneously, and also demonstrate that it is a promising SFD material.

Self-Q-switched and multicolor operation of a Tm:LuAG laser.

In this paper, we report self-Q-switched (SQS) and three-color operation of an all-solid-state Tm:LuAG laser for the first time to our knowledge. In the experiments, a low-cost 3 W AlGaAs laser diode was used to end-pump the Tm:LuAG crystal inside a four-mirror x cavity. In typical continuous-wave (cw) operation, as high as 754 mW output power was obtained with 49% power efficiency at 2023 nm. Three-color and SQS operations were initiated by fine tuning of the curved mirror separation within the stability range of the resonator. In the three-color regime, the Tm:LuAG laser produced two extra, i.e., 2019 and 2033 nm, wavelength oscillations in addition to on at 2023 nm. As high as 542 mW output power was observed in this regime. To the best of our knowledge, this is the first stable three-color laser operation obtained with an isotropic gain medium without having any birefringent elements in the cavity. Furthermore, the SQS operations were also observed at other curved mirror separations. In the SQS regime, the Tm:LuAG laser produced as fast as 13.3 kHz repetition rate pulses and as high as 42.5 µJ pulse energy. Analysis of power-dependent repetition rate data gave an estimated value of 2% for the round-trip saturable loss of the crystal. As far as we know, this is the first cw-pumped stable SQS 2 µm laser that contains an ordered isotropic gain medium as well as the highest pulse energy obtained in any cw-pumped SQS laser.

Photobiomodulatory properties of the AlGaAs laser diode on local toxic actions induced by Bothrops leucurus venom

Photobiomodulatory properties of the AlGaAs laser diode on local toxic actions induced by Bothrops leucurus venom

Low-cost multimode diode-pumped Tm:YAG and Tm:LuAG lasers

We report a continuous-wave operation of Tm:YAG and Tm:LuAG lasers pumped with a low-cost, multimode AlGaAs laser diode. First, the lifetime and the absorbance behavior of 5 mm, 6 % Tm$^{3+}$-doped YAG and LuAG crystals were thoroughly investigated. A low-cost multimode 3W laser diode at 781 nm was then used as a pump source for the Tm$^{3+}$-doped laser systems. Using three different output couplers, up to 636 mW of output power was obtained from Tm:YAG laser, with a slope efficiency of 29 % at 2017 nm. The maximum output power was 637 mW in the Tm:LuAG laser, with a slope efficiency of 28 % at 2023 nm. The lasing performances showed a decreasing slope efficiency with an increasing level of output coupling, which leads to a high upconversion. Furthermore, using a birefringent filter in the resonators, the laser outputs were tuned from 1942 to 2086 nm in the Tm:YAG resonator and from 1931 to 2107 nm in the Tm:LuAG case.

Low-cost multi-mode diode pumped Tm:YLF laser: Multi-color & Q-switching operations

In this paper, we report a low-cost multi-mode AlGaAs laser diode pumped broadly-tunable solid-state Tm:YLF laser at room-temperature operating in two different regimes: multi-color and Q-switching. A low-cost multi-mode AlGaAs laser diode, driving 3 W power at 780 nm, was used to excite the 3% Tm3+-ion doped YLF laser. In the continuous-wave regime, 650 mW of output power was obtained at 1942 nm with 41% power efficiency (indicates high cross-relaxation). The output wavelength can be tuned between 1831 and 2031 nm with a birefringent filter (BRF). To the best of our knowledge, this range is the broadest tuning range obtained from a Tm:YLF laser in 2 μm band. Furthermore, multi-color laser operations were observed by translating the crystal inside the cavity (without BRF) i.e. three two-color, two three-color and one four-color were obtained. As far as we know, these results are the first demonstration of three- and four-color 2 μm laser. Additionally, Q-switching regime were obtained by adding a saturable absorber into the cavity. In this regime, the repetition frequencies can be arranged between 16 and 100 kHz with a maximum of 2.7 W peak power and 2.39 μJ pulse energy by translating the saturable absorber along the stability region.

Photobiomodulation Therapy in Bone Repair Associated with Bone Morphogenetic Proteins and Guided Bone Regeneration: A Histomorphometric Study

To evaluate the efficacy of photobiomodulation for bone repair of critical surgical wounds with implants of bone morphogenetic proteins (BMPs) and bovine biological membranes, using histological and histomorphometric analysis. Tissue engineering has been developing rapidly through the use of various biomaterials for the treatment of bone defects, such as mechanical barriers consisting of biological membranes and implants of biomaterials for bone supply. Thirty-two male rats were divided into four groups (n = 8): group I-C: control; group II-PT: photobiomodulation therapy; group III-PM: Gen-Pro® BMPs+Gen-Derm® membrane; and group IV-PMPT: Gen-Pro® BMPs+Gen-Derm® membrane+photobiomodulation therapy. A 3 mm bone cavity was performed in the upper third of the lateral surface of the right rat femur to obtain a bone defect considered to be critical. The irradiated groups received seven applications of AlGaAs diode laser 830 nm, P = 40 mW, continuous wave (CW) emission mode, f ∼ 0.6 mm, 4 J/cm2 per point (north, south, east, and west) at 48 h intervals, for a total of 16 J/cm2 per session (final dose: 112 J/cm2). Bone repair was evaluated at sacrifice 15 and 30 days after the procedure. The specimens were embedded in paraffin and stained with hematoxylin and eosin and Picrosirius for analysis by light microscopy and by the Leica interactive measurement module software. Statistical analysis was performed (p < 0.05%). Histological analysis confirmed the histomorphometric results, with the experimental groups showing bone neoformation of significantly higher quality and quantity at the end of 30 days compared with the control group. Photobiomodulation therapy was effective for bone repair mainly when associated with BMPs and a biological membrane. The results of this study are promising and stimulate further scientific and clinical research.

Thermal and spectral characterization of Cr3+:MgWO4—a promising tunable laser material

This paper reports the growth, thermal and polarized spectral properties of Cr3+:MgWO4 crystal. Cr3+:MgWO4 crystal with dimensions of 20×18×13mm3 was grown successfully by a top-seeded solution growth method. The average thermal expansion coefficients are 10.47×10−6K−1, 15.68×10−6K−1 and 10.75×10−6K−1 along a-, b- and c-axis, respectively. The thermal conductivity is 8.69W/(mK) at room temperature. Both of the absorption and emission spectra show strong polarization characteristics. There is a broad and strong absorption band at around 790nm, which means that Cr3+:MgWO4 crystal is suitable for AlGaAs laser diode pumping. The crystal has a broad emission band at 961nm with a full width at half-maximum of 202nm; the emission cross-section is about 1.8×10−19cm2. The results show that Cr3+:MgMoO4 crystal can be regarded as a potential tunable laser gain medium.

Growth, nonlinear optical and self-frequency-doubled properties of LaGdCOB and Nd:LaGdCOB single crystals

High optical quality La0.09Gd0.91Ca4O(BO3)3 and Nd0.03La0.08Gd0.89Ca4O(BO3)3 crystals, grown by Czochralski (Cz) pulling method, were investigated for their nonlinear optical (NLO) and laser properties. These crystals were found to possess moderate birefringence (0.0320 at 1064 nm), wide transparency (320–2300 nm) and large effective nonlinear effects (deff ∼1.2 pm/V), which were suitable for green laser generation. The second-harmonic-generation (SHG) phase matching (PM) properties, including PM curve, deff, angular acceptance and walk-off angle were investigated. Both of the calculations and experiments have indicated that the 1064 nm optimum PM direction which has maximum deff (∼1.2 pm/V) and SHG conversion efficiency (57.1%) locate in the second octant, i.e. (113.5°, 48.6°). Pumped by the 0.8 μm AlGaAs laser diodes (LD), the self-frequency-doubling (SFD) performance of Nd0.03La0.08Gd0.89Ca4O(BO3)3 crystal was evaluated, where as much as 115 mW green light at 546 nm was obtained with a (113°, 48.9°)-cut, 6 mm long and uncoated Nd0.03La0.08Gd0.89Ca4O(BO3)3 sample.

Growth, structure, thermal properties and spectroscopic characteristics of Nd3+-doped KGdP4O12 crystal.

A single crystal of Nd3+-doped KGdP4O12 was successfully grown with the top-seeded solution growth and slow cooling (TSSG−SC) technique. It crystallizes in space group C2/c with cell parameters a = 7.812(2) Å, b = 12.307(3) Å, c = 10.474(2) Å, β = 110.84(3)° and Z = 4. The IR and Raman spectra also indicated that the phosphoric polyhedra of Nd:KGdP4O12 has a cyclic symmetry. The chemical composition of the crystal was analyzed and the distribution coefficient of Nd3+ was calculated. The crystal morphology of KGdP4O12 was identified using X-ray diffraction. The compound has good thermal stability to 920°C. Its specific heat and thermal conductivity were determined for potential applications. The spectral properties of Nd:KGdP4O12 indicates that it exhibits broad absorption and emission bands, which are attributed to low symmetry of the crystal. The broad absorption band around 798 nm has a full-width at half-maximum (FWHM) of 14.8 nm and is suitable for AlGaAs laser diode pumping. Moreover, 5 at% Nd3+-doped KGdP4O12 crystal has a long luminescence lifetime of 300 μs and a high quantum efficiency of 96%.

Electrically injected photon-pair source at room temperature.

One of the main challenges for future quantum information technologies is the miniaturization and integration of high performance components in a single chip. In this context, electrically driven sources of nonclassical states of light have a clear advantage over optically driven ones. Here we demonstrate the first electrically driven semiconductor source of photon pairs working at room temperature and telecom wavelengths. The device is based on type-II intracavity spontaneous parametric down-conversion in an AlGaAs laser diode and generates pairs at 1.57 μm. Time-correlation measurements of the emitted pairs give an internal generation efficiency of 7×10(-11) pairs/injected electron. The capability of our platform to support the generation, manipulation, and detection of photons opens the way to the demonstration of massively parallel systems for complex quantum operations.

Effect of uniaxial stress on electroluminescence, valence band modification, optical gain, and polarization modes in tensile strained p-AlGaAs/GaAsP/n-AlGaAs laser diode structures: Numerical calculations and experimental results

The effects of uniaxial compression in [110] direction on energy-band structures, heavy and light hole mixing, optical matrix elements, and gain in laser diodes with “light hole up” configuration of valence band levels in GaAsP quantum wells with different widths and phosphorus contents are numerically calculated. The development of light and heavy hole mixing caused by symmetry lowering and converging behavior of light and heavy hole levels in such quantum wells under uniaxial compression is displayed. The light or heavy hole nature of each level is established for all considered values of uniaxial stress. The results of optical gain calculations for TM and TE polarization modes show that uniaxial compression leads to a significant increase of the TE mode and a minor decrease of the TM mode. Electroluminescence experiments were performed under uniaxial compression up to 5 kbar at 77 K on a model laser diode structure (p-AlxGa1−xAs/GaAs1−yPy/n-AlxGa1−xAs) with y = 0.16 and a quantum well width of 14 nm. They reveal a maximum blue shift of 27 meV of the electroluminescence spectra that is well described by the calculated change of the optical gap and the increase of the intensity being referred to a TE mode enhancement. Numerical calculations and electroluminescence data indicate that uniaxial compression may be used for a moderate wavelength and TM/TE intensity ratio tuning.