980-nm Diode Laser Research Articles

Investigation on LD-pumped acousto-optically Q-switched pulse burst 1064 nm laser

Pulse-burst lasers with high pulse energy and high repetition rate are widely applied in the fields of laser diagnostics, such as Planar Laser-Induced Fluorescence (PLIF). In this paper, we reported a pulse-burst Nd:YVO4/Nd:YAG Maser Osillator Power Amplifier. The laser oscillator operates at 1064nm with a YVO4/Nd:YVO4 crystal end-pumped by an 808nm laser diode (LD). During the pumping duration of 1ms the pulse-burst laser contains 10, 50 and 100 pulses with the burst energies of 6mJ, 6.7mJ and 6.9mJ, when repetition rates are 10kHz, 50kHz and 100kHz, respectively. After amplification by a LD-side-pumped Nd:YAG module, the burst-pulse energies reach 64‍ ‌mJ, 61mJ and 62mJ, corresponding to single pulse energies of 6.4mJ, 1.2mJ and 0.6mJ, at repetition rates of 10kHz, 50kHz and 100kHz.

946 nm Nd: YAG double Q-switched laser based on monolayer WSe2 saturable absorber.

In this paper, we report a 946nm double Q-switched laser side pumped by an 808-nm pulse laser diode (LD). A layered tungsten diselenide (WSe2) saturable absorber (SA) together with an MgO doped LiNbO3 electro-optic (EO) modulator is applied to double Q-switch the Nd: YAG laser, producing trains of nanosecond-duration pulses with 500 Hz repetition rate. Such WSe2 saturable absorbers are fabricated by chemical vapor deposition (CVD) in a hot wall chamber and then embedded into a resonant mirror. The achieved pulse energy of double Q-switched laser at 946 nm is approximately 2.63 mJ with 10.8 ns pulse width and the peak power is round 244 kW, corresponding to the beam quality factors of M2x = 3.846,M2y = 3.861. Monolayer WSe2 nanosheets applied in the experiment would be a promising SA for passive Q-switching operation.

Spectroscopic investigations of 1.06 µm emission and time resolved Z-scan studies in Nd3+-doped zinc tellurite based glasses

Zinc tellurite based glasses (TZNbTiNd: TeO2 + ZnO + Nb2O5 + TiO2) doped with various Nd3+ concentrations (0.01, 0.05, 0.1, 0.5, 1.0, 1.5 and 2.0mol% Nd2O3) were prepared and characterized through absorption, emission and decay rate measurements. Judd-Ofelt intensity parameters were derived from the absorption spectrum and used to calculate the radiative properties for the 4F3/2 → 4IJ/2 (where J = 9, 11 and 13) transitions of Nd3+ ions. Strong near infrared emission at 1.062µm (4F3/2 → 4I11/2) has been obtained for all the glasses upon 808nm diode laser excitation. The decay times from 4F3/2 level is found to be quite single exponential for different concentrations of Nd3+ ions with a shortening of lifetime with increasing concentration. In these measurements, the electronic refractive index variation is associated with the difference in the polarizabilities (Δαp) of the Nd3+ ion in its ground and excited states. The results indicate that in tellurite glasses, Δαp is relatively very high (4 × 10−25cm3) compared to other Nd3+-doped glasses. We also measured the imaginary part of the non-linear refractive index (n2′′) due to absorption saturation. Hence, the spectroscopic results indicate that the investigated glasses are potentially applicable as a 1062nm laser host as well as optical devices.

Low-cost, fast and easy production of germanium nanostructures and interfacial electron transfer dynamics of BODIPY–germanium nanostructure system

Germanium nanostructures are prepared by electrochemical etching of n-type Sb-doped (100) oriented germanium (Ge) substrates with resistivity of 0.01 Ω cm. Ge substrates are etched in an electrochemical double cell containing hydrofluoric acid and ethanol solution at room temperature. Although the use of illumination source is essential for etching of an n-type semiconductor material, the influence of illumination source type on the germanium surface morphology has not yet been investigated. In this work, the illumination effect is studied by halogen lamp, white LED, 470- and 405-nm pulsed diode laser. It is demonstrated that different Ge surface morphologies such as nanocone, nanorod, nanoplate and nanopyramid are obtained using different illumination source. The current density, anodization time and pulsed laser power density effects on Ge nanopyramid are investigated in order to optimize anodization conditions. The most uniform and continuous Ge nanopyramid array is obtained at the current density of 30 mA/cm2 for 45 min under cathode side illumination with 470-nm pulsed diode laser. It is observed that the nanostructured Ge surfaces exhibit a broad photoluminescence band between 400 and 650 nm. Time-resolved fluorescence spectroscopy studies of electron transfer process between BODIPY dye and Ge nanostructures are reported. The obtained fluorescence lifetime data are analyzed in the light of the Marcus electron transfer theory to determine the conduction band energy level of nanostructured germanium substrates.

Investigation of an LuAG:Ce translucent ceramic synthesized via spark plasma sintering: Towards a facile synthetic route, robust thermal performance, and high-power solid state laser lighting

The aim of this study is to investigate a thermally robust green-yellow color converter for high-power solid state laser lighting applications. LuAG:Ce translucent ceramics (TCs) were synthesized via the spark plasma sintering (SPS) technique and LiF was used as additive. The as-prepared ceramics show remarkably superior thermal and luminescent properties: a high external quantum efficiency (77%), a low thermal quenching (4.1% drop at 200°C), a good thermal conductivity (6.3Wm−1K−1), and a high reliability (only a 1.9% drop after 1000h, at 85°C and 85% humidity). A prototype lamp using the TC (and a 450nm laser diode), with the increasing driving power (up to 8.7W), shows increasing luminous flux (238–472lm) with stable luminous efficiency (54.3-56.6lm/W). This indicates that the translucent ceramic can be used for high-power laser-lighting.

A simple, compact, low-cost, highly efficient thermometer based on green fluorescence of Er3 +/Yb3 +-codoped NaYF4 microcrystals

We developed a highly efficient optical thermometer based on intensity ratio of upconversion green fluorescence of Er3+/Yb3+-codoped NaYF4 microcrystals. The sensor consists simply of a 980nm laser diode, one narrow-band interference filter, two lenses, one Si-photocell and one multimeter, while being without use of spectrometer and additional electronics. The device not only has a simple, compact structure (hence a low cost), but also displays highly efficient sensing performance, characterized by large signal-to-noise ratio due to strong fluorescence intensity, high thermal resolution and sensitivity, which have the values 1.3K and 1.24×10−2K−1, respectively, at the physiological temperature 310K. The excellent sensing performance of the device was further confirmed by the results of the measurements repeated using a spectrometer. The thermometer is highly generalized that can be applied to other luminescent materials, and shows great potential for the physiological temperature sensing in biological tissues and cells.

High power, high efficiency continuous-wave 808 nm laser diode arrays

The continuous-wave 100W-class 808nm laser diode arrays with extremely high power conversion efficiency of 68% were reported at the heatsink temperature of 25°C. To the best of our knowledge, this was the highest power conversion efficiency at continuous-wave 106W 808nm laser diode array with 50% fill factor so far. An asymmetric broad waveguide epitaxial structure with very low internal optical loss of 0.5cm−1 was presented. In order to improve the efficiency, various fill factor devices were studied. The 50W laser diode array with 30% fill factoir and 1.0mm cavity length demonstrated power conversion efficiency of 71% at heatsink temperature of 15°C.

La2O2CN2:Yb3+/Tm3+ nanofibers and nanobelts: novel fabrication technique, structure and upconversion luminescence

For the first time, La2O2CN2:Yb3+/Tm3+ upconversion luminescence nanofibers and nanobelts were successfully fabricated via cyanamidation of the respective relevant La2O3:Yb3+/Tm3+ nanofibers and nanobelts which were obtained by calcining the electrospinning made PVP/[La(NO3)3+Yb(NO3)3+Tm(NO3)3] composite nanofibers and nanobelts. The morphologies, structures, and properties of the nanofibers and nanobelts are investigated. The diameters of La2O2CN2:Yb3+/Tm3+ nanofibers and width of La2O2CN2:Yb3+/Tm3+ nanobelts with the thickness of 112 nm are 109 ± 4.3 nm and 1.8 ± 0.2 μm at 95% confidence level, respectively. Upconversion luminescent analysis manifests that La2O2CN2:Yb3+/Tm3+ nanofibers and nanobelts emit intense blue emissions around 476 nm corresponding to 1G4→3H6 energy level transitions of Tm3+ ions under the excitation of a 980-nm diode laser. For the La2O2CN2:30%Yb3+/x%Tm3+ nanofibers, the blue emission intensity increases when the Tm3+ concentration is increased from 0.1 to 0.5% and then decreases as the Tm3+ concentration is further increased from 0.5 to 1.0%, so the Tm3+ optimum concentration is 0.5%. For the La2O2CN2:y%Yb3+/0.5%Tm3+ nanofibers, when the concentration of Tm3+ is fixed at 0.5%, the blue emission intensity increases when the Yb3+ concentration is increased from 5 to 30% and then decreases as the Yb3+ concentration is further increased from 30 to 40%. Therefore, the optimum concentration of Yb3+ is 30%. Thus, the optimum molar concentration ratio of Yb3+ to Tm3+ ions is 60:1 in the as-prepared La2O2CN2:Yb3+/Tm3+ nanofibers. The formation mechanisms of the La2O2CN2:Yb3+/Tm3+ nanostructures are also proposed. The novel technique can be applied to prepare other rare earth oxycyanamide nanostructures of various morphologies.

Photon and electron beam pumped luminescence of Ho3+ activated CaMoO4 phosphor

This study reports on the photoluminescence and cathodoluminescence behavior of combustion synthesized CaMoO4:Ho3+ phosphor. X-ray diffraction and scanning electron microscopy revealed the formation of single phase tetragonal structure consisting of well-prepared evenly distributed micro-sized grains. Power tunable visible upconversion and infrared emissions were detected upon excitation with a 980nm diode laser. Consequently, near white and dominant green emissions resulted from the synthesized phosphor induced by the ultraviolet and blue photons at 262nm and 455nm wavelengths, respectively. The electron beam irradiation produced the same emissive behavior as for the photoluminescence but degradation of the cathodoluminescence intensity was found with prolonged irradiation time. The chemical stability under prolonged electron bombardment was also tested with X-ray photoelectron spectroscopy. The observed emission characteristics are explained in detail.

Optical and structural properties of Nd:MgO:LiNbO3 crystal irradiated by 2.8-MeV He ions

We report the optical and structural properties of helium-implanted optical waveguides in Nd:MgO:LiNbO3 laser crystals. The prism-coupling method is used to investigate the dark-mode properties at the wavelength of 632.8 nm. The spontaneous generation of ultraviolet, blue, red, and near-infrared fluorescence emissions is demonstrated under excitation with an 808-nm laser diode. The effects of ion irradiation on the structural properties are characterized using the high-resolution X-ray diffraction technique. The results show that the initial luminescence properties of Nd:MgO:LiNbO3 crystals are slightly modified by irradiation with 2.8 MeV He ions at fluences of 1.5 × 1016 ions/cm2 at room temperature.

Temperature characteristics of green upconversion fluorescence of Er3+-doped SrGdGa3O7 crystal

Temperature characteristics of 980-nm-upconverted green 530 and 550nm fluorescence of Er3+-doped SrGdGa3O7 single crystal have been studied for temperature sensing purposes. To achieve that, a simple experimental setup has been developed that consists of a 980nm laser diode, two interference filters, two Si-photocells and two multimeters, while without use of monochromator or focusing lens for fluorescence collection. The study shows that the Er3+-doped SrGdGa3O7 crystal displays strong green emission intensity (hence good signal-to-noise ratio) and high temperature sensitivity of fluorescence intensity ratio of the 530 and 550nm emissions, which is (5.6–104.0) × 10−3K−1 in the considered temperature range 100–430K, depending on the temperature. In addition, the experiments were repeated using a spectrometer and consistent results of temperature characteristics were obtained. Present study shows that the Er3+-doped SrGdGa3O7 crystal is a promising host material for optical temperature sensing.

Self-frequency doubling in a laser-active whispering-gallery resonator.

Lasing and self-frequency doubling are achieved in a millimeter-sized laser-active whispering-gallery resonator made of neodymium-doped lithium niobate. A low-cost 808-nm laser diode without external frequency stabilization is sufficient to pump the neodymium ions. Laser oscillation around 1.08μm drives a frequency-doubling process within the same cavity providing green light. The electrical-optical efficiency of the system reaches up to 2×10-4. To the best of our knowledge, this is the first demonstration of combining lasing and χ(2) frequency conversion in a single high-Q whispering-gallery resonator. This approach is general and can be applied to other materials and other nonlinear optical processes.

Influence of silica surface coating on optical properties of Er3+-Yb3+:YMoO4 upconverting nanoparticles

Er3+-Yb3+:YMoO4@SiO2 core@shell upconversion (UC) nanoparticles (NPs) with its particle size ∼35nm and shell thickness ∼3nm synthesized via Stöber method have explored its thermal stability, particle morphology and optical properties. The optical band gap energy clearly shows the effect of surface coating of silica layer across the surface of core@shell NPs due to increase in the crystallite size. Due to presence of silica layer across the core NPs, the UC emission intensity corresponding to the 2H11/2, 4S3/2→4I15/2 transition has been increased about ∼10 times in the core@shell NPs than the core NPs. Temperature dependent study using thermally coupled 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions in the biological temperature range (300–368K) has been performed. The maximum sensitivity ∼2.36%K−1 at 368K, which is ∼12 times greater than the core NPs of the core@shell UC NPs has been reported. Thermal heat gain by the core@shell NPs within 311–343K temperature range is suitable for hyperthermia based cancer treatment has been reported. The core@shell NPs show good dispersibility in different biological solvents such as water, methanol and DMSO. Moreover, the core@shell NPs dispersed with biological solvents show good luminescence stability without interactions with solvent molecules which could minimize the thermal effect caused by the 980nm diode laser excitation. As a consequence, Er3+-Yb3+:YMoO4@SiO2 core@shell NPs have suitable applications for making optical devices namely upconvertors, LEDs, optical bioprobes, etc.

Sensitization and deactivation effects of Nd3+on the Ho3+ : 3.9 μm emission in a PbF2 crystal.

The use of Nd3+ codoping for sensitizing the Ho3+ ion and enhancing the ∼3.9 μm emission from Ho3+:I55→I65 was investigated in the PbF2 crystal for the first time, to the best of our knowledge. The ∼3.9 μm fluorescence emission properties and energy transfer mechanism of the as-grown crystals were investigated. The results show that the Nd3+ ion can act as a sensitizer to the Ho3+ ion, providing an efficient excitation channel, making the Ho3+/Nd3+:PbF2 crystal propitious to be pumped by commercialized InGaAs laser diodes (LDs). Moreover, an enhanced ∼3.9 μm emission was obtained in the Ho3+/Nd3+:PbF2 crystal due to the codoping of Nd3+ ions, leading to an efficient energy transfer from a lower laser level of Ho3+:I65 to Nd3+:I15/24, while having little influence on the higher laser level of Ho3+:I55. These advantageous spectroscopic characteristics indicate that the Ho3+/Nd3+:PbF2 crystal might have potential application in ∼3.9 μm mid-infrared lasers under a conventional 808nm LD pump.

Mid-infrared photo-luminescence and energy transfer around 2.8 μm from Dy3+/Tm3+ co-doped tellurite glass

Tellurite glasses co-doped with Dy3+ and Dy3+/Tm3+ have been synthesized. Emission around 2.8μm is successfully obtained in present glass upon excitation of a conventional 808nm laser diode. Judd-Ofelt intensity parameters and radiative properties of Dy3+ ions are calculated using the Judd-Ofelt theory. The luminescence characteristics and energy transfer mechanism are investigated and discussed. According to the absorption, fluorescence spectra and lifetime measurements, Tm3+ ions can effectively absorb excitation and transfer their energy to Dy3+ ions with high efficiency (up to 86.80%). Hence, the results demonstrate that Dy3+/Tm3+ co-doped tellurite glasses possessing excellent spectroscopic properties is a potential medium for mid-infrared laser.

Effect of NaF/RE (RE=Yb, Tm) molar ratio on the morphologies and upconversion properties of NaYbF4:Tm3+ microrods

Tm3+ doped β-NaYbF4 with different aspect ratios has been synthesized by a facile hydrothermal method. A different morphology and size of β-NaYbF4 microrods were obtained by changing the NaF/RE (RE=Yb,Tm, 99.5% Yb3+, 0.5% Tm3+) molar ratio. The morphology and size of products were explored by SEM, and the influences of the NaF/RE molar ratio on the microrod size were evidenced by XRD. It is shown that the size and morphology of the products can be precisely controlled by modulation of the NaF/RE molar ratio. β-NaYbF4 microrods with 35μm in length and 7.5μm in diameter were prepared when NaF/RE molar ratio is 6. Intense ultraviolet emissions at 290nm, 345, and 361nm and visible emissions at 451 and 494nm were observed in Tm3+ doped NaYbF4 microrods with an excitation of a 980nm diode laser. The effect of NaF/RE ratio on growth rate has been proposed.

The generation of Q-switched erbium-doped fiber laser using black phosphorus saturable absorber with 8% modulation depth

We report a generation of the Q-switched laser operating in 1.55-micron region by using black phosphorus (BP) as a saturable absorber (SA). A 980-nm laser diode was pumped into Erbium-doped fiber (EDF) gain medium in ring cavity configuration. The BP-based SA was prepared by mechanically exfoliating the BP crystal using scotch tape. The obtained BP-tape SA has a modulation depth of 8 %. To realize a Q-switching operation, a small piece of the tape is then integrated into between two fiber ferrule tips. A stable Q-switching operation started at 40 mW. The maximum repetition rate obtainable at 28.57 kHz, with pulse width of 5.35 μs. This finding shows the BP is one of the promising material to work as an SA for pulsed laser generation.

Monitoring of early catastrophic optical damage in laser diodes based on facet reflectivity measurement

We propose a convenient, inexpensive technique to monitor the fast early stage of catastrophic optical damage (COD) in 808-nm high-power laser diodes (LDs). Using an optical system based on the 1550-nm laser diode illuminant and photodiode, we measured the facet reflectivity, which gives information about the surface morphology of the output facet with a temporal resolution of 2 ns, allowing us to trace the rapid early COD process in a transient, real-time mode. The formation of the detected 4-μm-long COD damaged area, which caused a local uneven surface at the output facet and a rapid drop in facet reflectivity at 1550 nm from 28% to 2%, was completed within 20–30 ns, 10 ns shorter than that in the longer-wavelength devices.

Rapid sealing of porcine renal blood vessels, ex vivo, using a high power, 1470-nm laser, and laparoscopic prototype.

Energy-based, radiofrequency (RF) and ultrasonic (US) devices currently provide rapid sealing of blood vessels during laparoscopic procedures. We are exploring infrared lasers as an alternate energy modality for vessel sealing, capable of generating less collateral thermal damage. Previous studies demonstrated feasibility of sealing vessels in an in vivo porcine model using a 1470-nm laser. However, the initial prototype was designed for testing in open surgery and featured tissue clasping and light delivery mechanisms incompatible with laparoscopic surgery. In this study, a laparoscopic prototype similar to devices currently in surgical use was developed, and performance tests were conducted on porcine renal blood vessels, ex vivo. The 5-mm outer-diameter laparoscopic prototype featured a traditional Maryland jaw configuration that enables tissue manipulation and blunt dissection. Laser energy was delivered through a 550 - ? m -core-diameter optical fiber with side-delivery from the lower jaw and beam dimensions of 18 - mm ? length × 1.2 - mm ? width . The 1470-nm diode laser delivered 68 W with 3-s activation time, consistent with vessel seal times associated with RF and US-based devices. A total of 69 fresh porcine renal vessels with mean diameter of 3.3 ± 1.7 ?? mm were tested, ex vivo. Vessels smaller than 5-mm diameter were consistently sealed (48/51) with burst pressures greater than malignant hypertension blood pressure (180 mmHg), averaging 1038 ± 474 ?? mmHg . Vessels larger than 5 mm were not consistently sealed (6/18), yielding burst pressures of only 174 ± 221 ?? mmHg . Seal width, thermal damage zone, and thermal spread averaged 1.7 ± 0.8 , 3.4 ± 0.7 , and 1.0 ±

High quality colloidal GdVO4:Yb,Er upconversion nanoparticles synthesized via a protected calcination process for versatile applications

GdVO4:Yb,Er upconversion nanoparticles with high crystallinity and water dispersibility have been synthesized by a facile hydrothermal approach followed by a protected calcination treatment. The crude GdVO4:Yb,Er nanoparticles obtained by hydrothermal approach show cubic morphology with a diameter of about 45nm. A layer of SiO2 was coated on the surface of nanoparticles to avoid particles growth and aggregation during thermal treatment. After the dissolution of SiO2 layer by chemical etching in aqueous NaOH solution, the as-prepared highly crystalline GdVO4:Yb,Er nanoparticles not only maintain their nanostructure properties but show high chemical stability and good water dispersibility. Intense green upconversion luminescence is achieved under the 980nm laser diode excitation. The approach reported here can be “borrowed” to guide the synthesis of other oxide-based luminescent nanoparticles and will access their suitability for many technologically important applications.