Laser Emission Characteristics Research Articles

Growth and spectroscopic properties of Ca3(Ta,Ga)5O12:Pr3+ single crystal as a promising new laser material in the visible domain

Structurally disordered Pr3+-doped Ca3(Ta,Ga)5O12 - Pr:CTGG single crystal was grown by the Czochralski technique for the first time and its spectroscopic properties were investigated. Modified Judd-Ofelt analysis was applied to determine spectroscopic and laser emission characteristics. Based on low-temperature absorption and emission spectra, the partial energy levels of Pr3+ ions have been obtained and a multicenter structure of the optical spectra was highlighted. The electron-phonon interactions were also observed in the emission spectra corresponding to the 3P0 → 3H4 transition under different excitation wavelengths. The fluorescence decays of the 3P0 and 1D2 levels were measured. The emission cross-sections corresponding to the 3P0 → 3H4 (486.5 nm) and 3P0 → 3F2 (652.7 nm) transitions were found to be σem = 19 × 10−20 cm2 and σem = 15 × 10−20 cm2, respectively. The values for other parameters that may predict the possibility of achieving efficient laser emission, especially at 486.5 nm, such as quantum efficiency (ⴄ = 50 %), gain bandwidth (σem× Δλeff, = 32.2 × 10−26 cm3), and optical gain (σem× τmeas = 12.86 × 10−25 cm2 s) were determined. The obtained results indicate that the Pr:CTGG crystal has a high potential for obtaining efficient laser emission in the blue domain.

Design and construction of tunable solid-state dye laser pumped by flashlamp

Over the past six decades, dye laser technology has improved substantially. The usage of solid matrices containing laser dyes is becoming more and more popular as a viable substitute for the traditional liquid dye solutions. In this research, we designed and built a tunable solid dye laser device which consists of three main parts. (i) The active material producing the laser beam, which is a polymer rod [glycidyl methacrylate (GMA) polymer] doped with the laser dyes pyrromethene 597 (PM-597) or Nile blue (Nb-690). (ii) The pumping source is xenon linear flashlamp driven by a homemade power supply. (iii) Two broadband mirrors providing the optical feedback stable optical resonator. The properties of the gain medium and hence the laser emission characteristics were determined, and the results showed the efficiency of the homemade tunable solid dye laser device, that is suitable for a variety of applications.

RE3+-Doped Ca3(Nb,Ga)5O12 and Ca3(Li,Nb,Ga)5O12 Crystals (RE = Sm, Dy, and Pr): A Review of Current Achievements.

Spectroscopic characteristics of RE3+ ions (RE = Sm, Dy, and Pr) doped in partially disordered Ca3Nb1.6875Ga3.1875O12-CNGG and Ca3Li0.275Nb1.775Ga2.95O12-CLNGG crystals are reviewed in detail to assess their prospects as laser crystals with emission in the visible spectral domain. All investigated crystals were grown using the Czochralski crystal growth technique. High-resolution absorption and emission measurements at different temperatures, as well as emission dynamics measurements, were performed on the grown crystals. The spectroscopic and laser emission characteristics of the obtained crystals were determined based on the Judd-Ofelt parameters. The obtained results indicate that CNGG:RE3+ and CLNGG:RE3+ (RE = Sm, Dy, and Pr) crystals can be promising materials for lasers in the visible range.

A Thin‐Film Flexible Defect‐Mode Laser

AbstractLaser emission from a flexible defect‐mode structure consisting of two photopolymerized liquid crystal thin films separated by a dye‐doped polymethylmethacrylate defect layer is demonstrated. A simple and cost‐effective film transfer technique is used to fabricate the flexible laser and the corresponding laser emission characteristics, which shows single‐mode laser emission at λ = 582 nm, with an excitation threshold of Eth = 12.3 ± 0.5 µJ cm−2 per pulse and a slope efficiency of ηs = 6.0 ± 0.3%, are presented. The polarization state of the laser emission are also presented and are compared with the findings reported in the literature. Finally, laser‐beam steering is demonstrated up to 42° by subjecting the device to a mechanically induced deformation that creates a radius of curvature of 5 mm, which is of potential interest for conformable and wearable technology platforms.

Development of highly fluorescent distyryl dyes for liquid crystal lasers

We developed new reddish fluorescent distyryl dyes, showing strong fluorescence around 600 nm, for optoelectronic devices. They have high fluorescent quantum efficiencies over 0.8, with large Stokes’ shifts exceed 60 nm in 1,4-dioxane. These features of new dyes are desirable for optoelectronic applications such as electroluminescent and dye-laser devices. We fabricated distributed feedback cholesteric liquid crystal lasers using the dyes and observed laser oscillation at a low excitation power of ∼22 nJ/pulse. Laser emission characteristics of the dyes are partly different from expectation from steady-state dichroic measurements. The origin of the discrepancy is discussed considering the relaxation process of the dyes.

Silver nanoparticles filled hollow polymer fiber laser with enhanced photostability

In the present work we demonstrate multimodal laser emission characteristics from dye doped hollow polymer fiber filled with silver nanoparticle solution. The ring resonator structure was a hollow polymer fiber doped with Rhodamine B (RhB). The technique of filling metal nanoparticles inside the hollow dye doped polymer fiber laser was found to be an extremely simple method of optical feedback for lasing action. For silver nanoparticles filled structure we observe a dual threshold mechanism. An easy tuning of the system was achieved by varying the concentration of silver nanoparticles. The silver nanoparticles filled hollow polymer fiber exhibited enhanced photo-stability even at high pump powers. The Q factor achieved was greater than 6.5 × 103 in this case.

Cavity design peculiarities and influence of SESAM characteristics on output performances of a Nd:YVO4 mode locked laser oscillator

In this work we report on the output performances of a Nd:YVO4 picosecond (ps) laser oscillator that was passively modulated by different semiconductor saturable absorber mirrors (SESAMs). The laser emission characteristics are given for SESAM used in Z-type and W-type cavities under similar pumping conditions. Q-switch mode-locking (QML) regime was obtained in the Z-type resonator whereas the W-type oscillator enabled stable mode-locking (ML) operation. For the W-type cavity ML performances are reported for two SESAMs with distinct parameters. Thus the use of a SESAM with 10 ps long recovery time allowed ML operation with pulses of 11.1 nJ energy and 15 ps duration (0.74 kW peak power) at 158 MHz repetition rate; the average power at 1.06 μm was 1.75 W for 5.17 W pump power at 809 nm. Employing a second SESAM with 0.5 ps short recovery time, the Nd:YVO4 laser yielded pulses with increased 13.4 nJ pulse energy and shorter, 12.5 ps, duration (1.1 kW peak power) at 158 MHz repetition rate, corresponding to 2.11 W average power; the pump power was 5.09 W. The results highlight the significant role of the SESAM parameters as well as of the implemented cavity design for the construction of a ps laser source of high performance.

Controlling Disorder by Electric-Field-Directed Reconfiguration of Nanowires To Tune Random Lasing.

Top-down fabrication is commonly used to provide positioning control of optical structures; yet, it places stringent limitations on component materials, and oftentimes, dynamic reconfigurability is challenging to realize. Here, we present a reconfigurable nanoparticle platform that can integrate heterogeneous particle assembly of different shapes, sizes, and chemical compositions. We demonstrate dynamic control of disorder in this platform and use it to tune random laser emission characteristics for a suspension of titanium dioxide nanowires in a dye solution. Using an alternating current electric field, we control the nanowire orientation to dynamically engineer the collective scattering of the sample. Our theoretical model indicates that a change of up to 22% in scattering coefficient can be achieved for the experimentally determined nanowire length distribution upon alignment. Dependence of light confinement on anisotropic particle alignment provides a means to reversibly tune random laser characteristics; a nearly 20-fold increase in lasing intensity was observed with aligned particle orientation. We illustrate the generality of the approach by demonstrating enhanced lasing for aligned nanowires of other materials including gold, mixed gold/dielectric, and vanadium oxide.

III-Nitride multiple disk-in-wire laser structures: Effects of crystal orientation and spacer size

Atomistic numerical simulations have been carried out to study the performance of recently reported optical structures based on nonpolar multiple disk-in-wire In0.08Ga0.92 N/GaN material system. The simulations are performed with an augmented version of the open-source NEMO 3-D software that uses a fully-atomistic valence force-field (VFF) for strain distributions and empirical sp3s*-spin tight-binding model to compute the electronic structure. Both linear and nonlinear components of internal polarization field have been included using a recently proposed first-principles based polarization model. When compared to conventional c-plane based polar structures, the nonpolar device exhibits a much weaker (yet non-zero) internal potential and improved laser emission characteristics. In particular, it is found that the optical transition probability is a strong function of the internal fields and could be tuned via engineering the spacer size.

Nd3+-doped transparent tellurite ceramics bulk lasers

We report on the laser emission of the polycrystalline ceramic obtained from the full and congruent crystallization of the parent glass 1Nd3+:75TeO2-12.5Bi2O3-12.5Nb2O5 composition. In particular, the current work underlines the importance of carefully controlling the heat treatment in order to solely crystallize the Bi0.8Nb0.8Te2.4O8 cubic phase and consequently avoid the formation of the BiNbTe2O8 orthorhombic phase that would be detrimental for optical purpose. The structure, microstructure and photoluminescence properties of the resulting transparent tellurite ceramics are characterized. The continuous-wave and gain-switching laser performances reveal that the emission remains perfectly single transversal mode in the range of pump powers explored. The maximum output power achieved was ~28.5 mW, for a pump power threshold of ~67 mW, and with associated efficiency and slope efficiency of ~22.5% and ~50%, respectively. These data definitely stand among the best results obtained so far for bulk laser tellurite materials and thus demonstrate the potential of such polycrystalline transparent ceramics as optically active materials. Finally, the laser emission characteristics in pulsed regime, at low and high repetition rates, are also provided: more than 6.5 W of peak power at a repetition rate of 728 kHz can be obtained.

Laser emission characteristics of the capillary of dye-doped liquid crystal

The dye doped liquid crystal filling tunable laser has been widely adopted in many areas, such as optical communication, sensor and medical imaging with a low cost. The temperature-sensitive refractive indice of liquid crystal makes it a filling material suitable for being used in the capillary. The existing studies have introduced the liquid crystal filled with capillary, which has the complicated craft and big cost. As is well known, the capillary has the advantages of the easy preparation and low cost, but the liquid crystal filled capillary based dye doped liquid crystal filling tunable laser is rarely studied. Dye-doped cholesteric liquid crystal (CLC) based tunable laser has many advantages such as small-size, low-threshold, high-efficiency, wide-tunability with wavelength varying from ultraviolet to infrared. So It shows great promise in applications of single-chip experiment, biological identification and sensor. To develop high-efficiency dye-doped CLC tunable lasers for different potential applications, it is crucial to explore their emission performances in three laser emission modes:distributed feedback (DFB), whispering gallery modes (WGMs) and random laser (RL). We theoretically propose and experimentally demonstrate the characteristics of laser emission based on dye-doped CLC in capillary tubes which are treated with the photo-alignment PI films. Firstly, we prepare capillary tubes filled with dye-doped CLC with three inner diameters of 100 m, 200 m and 300 m. By using a double-frequency Nd:YAG 532 nm laser as a pump source, the emission spectra, energy thresholds and temperature dependent tunabilities in the cases with and without PI films are analyzed, respectively. It is clearly shown that dye-doped CLC in the capillary with the PI films generate DFB-mode lasing and WGMs lasing. Experimental results show that the capillaries with thinner-inner diameters and PI films have lower emission threshold energies than without PI films, the former threshold can be reduced to as low as 4.5 J mm-2. Meanwhile, with temperature increasing, the DFB wavelength is blue-shifted, resulting in a central wavelength tuning range of 5.9 nm. Then high performance WGM with an FSR of 1.05 nm is created when the temperature is increased up to as high as 43 ℃. It can be found that the laser emission with photo-alignment PI films shows an optimum RL mode with less laser emission peaks than the laser emission without photo-alignment PI films. In this work we propose and demonstrate that a capillary based dye-doped CLC tunable laser with photo-alignment PI films can easily work with three emissions:DFB-mode, WGMs or RL by changing optical field and the applied temperature. The above research results provide valuable clues and methods to develop high-quality dye-doped CLC based tunable laser, filter, optical switch and sensor.

Effect of photonic stop-band on the modes of a weakly scattering DCM-PVA waveguide random laser

We present an experimental study on the effect of the photonic stop-band (PSB) on the random laser (RL) emission characteristics of a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) doped polyvinyl alcohol (PVA) film (DCM-PVA). The film, having its refractive index greater than the substrate and density variations at the microscopic scale, acts as a disordered active planar waveguide. The propagation losses for the transverse magnetic (TM) and transverse electric (TE) modes of the waveguide are observed to be 0.50 and 0.74 dB/cm, respectively, at λ = 632.8 nm. The waveguiding DCM-PVA film is then sandwiched between two silica 3-D photonic crystals (opals). The overlap of the DCM-PVA photoluminescence with the PSB of the opals is controlled by the choice of the particle size used for opal fabrication. The random lasing threshold studies have been carried out for both TM and TE polarizations for opals with different particle sizes. A reduction in the threshold of RL emission, with respect to the DCM-PVA waveguide, by about 20 times (to 0.67 mJ/cm2) is observed when the photoluminescence of the DCM-PVA film overlaps with the PSB of the opal structure for TM polarization, showing that the embedding of an RL in an engineered PSB material is an effective way to reduce the thresholds of RLs.

Synthesis of Nanocrystals by Using Thermal Treatment with an Electric Furnace and Laser Heating and Emission Characteristics of Doped Rare-Earth Ions

Synthesis of Nanocrystals by Using Thermal Treatment with an Electric Furnace and Laser Heating and Emission Characteristics of Doped Rare-Earth Ions

Structure and temperature effects on Nd3+ spectra in polycrystalline mixed scandium aluminum garnets Y3ScxAl5−xO12

New spectroscopic data obtained from high resolution low temperature absorption and emission spectra of Nd3+ in mixed scandium aluminum garnets Y3ScxAl5−xO12 – (x=0–2) translucent ceramics revealed transition dependent composition effects: modification of the shapes (Lorentz at x=0 and 2, quasi-Gauss at x=1, x-dependent asymmetric for other x values, with obvious multicenter structure for low x), widths and shifts of the lines. Nd3+ electronic structure dependence on structural changes with composition is analyzed in terms of nephelauxetic effect and maximum splitting of manifolds: Sc3+ co-doping reduces the nephelauxetic effect, and the increase of 4F3/2 splitting from 85cm−1 (x=0) to 98cm−1 (x=2) denotes the lowering of local symmetry. The multicenter structure and inhomogeneous broadening of Nd3+ lines is attributed to crystal field distributions determined by the random occupancy of the octahedral sites by Sc3+ and Al3+. For low x (0.2) the resolved two satellites S1, S2 that accompany Nd:YAG lines are correlated to anisotropic crystal field perturbations produced by the n.n. Sc3+ by analogy to those determined by Y3+-antisites (excess of Y3+ ions that enter in octahedral sites of the melt-grown YAG crystals). The temperature evolution of the Nd3+ spectral characteristics (line intensity, shift, broadening) in the 10–300K range is analyzed in terms of thermal population of the Stark levels, of the effect on electron–phonon interaction and on lattice expansion. The relevance of the spectroscopic properties on the laser emission characteristics in these systems is discussed.

Laser emission from diode-pumped Nd:YAG ceramic waveguide lasers realized by direct femtosecond-laser writing technique

We report on realization of buried waveguides in Nd:YAG ceramic media by direct femtosecond-laser writing technique and investigate the waveguides laser emission characteristics under the pump with fiber-coupled diode lasers. Laser pulses at 1.06 μm with energy of 2.8 mJ for the pump with pulses of 13.1-mJ energy and continuous-wave output power of 0.49 W with overall optical efficiency of 0.13 were obtained from a 100-μm diameter circular cladding waveguide realized in a 0.7-at.% Nd:YAG ceramic. A circular waveguide of 50-μm diameter yielded laser pulses at 1.3 μm with 1.2-mJ energy.

Saturation of laser emission in a small mode volume organic microcavity

We demonstrate that the laser output power of an organic microcavity saturates with the pump energy shortly above the lasing threshold. The extent of the saturation correlates with the volume of the optical mode and is strongly enhanced in a small-mode volume λ/2 microcavity. The laser emission characteristics under different pumping conditions unambiguously show that the effect is due to the finite number of absorbing molecules per mode that are efficiently saturated at higher pump powers. A modified set of rate equations is applied to obtain a theoretical description of the lasing dynamics and to account for the flattening of the integrated output power above the lasing threshold. These equations provide a basis to describe the occurrence of saturation at high excitation levels in dependence on the pump pulse duration and the number of absorbing molecules in the mode volume.

Multicenter structure of the optical spectra and the charge-compensation mechanisms in Nd:SrWO4 laser crystals

An analysis of the high resolution optical spectra (10 and 300 K) of the self-stimulated Raman scattering active Nd:SrWO4 crystal was performed. Crystals doped only with low concentrations of Nd or codoped with Na+ or Nb5+ grown in N2 or air atmosphere were investigated. The single Nd-doped crystals show five main centers, whereas codoping with Na+ in the ratio Na/Nd=3/1 (in melt) simplifies considerably the spectra. Codoping with Nb5+ does not lead to a dominant center and introduces a new one. Growth in air revealed the role of the oxygen in the charge compensation and multicenter structure of the spectra. The spectral characteristics of the nonequivalent centers (levels, intensities, and polarization) function on concentration of Nd3+ and of codoping ions and growth conditions were analyzed. The polarization data show that only one center has ideal local symmetry S4. Based on the crystal structure, previous results, and the new spectral data, an attempt to connect various spectral nonequivalent centers to the charge compensators (Sr2+ vacancies, interstitial oxygen, Na+, and Nb5+) is made and structural models for various centers are proposed. The implications of these findings on the laser emission characteristics and on the selection of the pumping transitions are also discussed.

Random lasing from a nanoparticle-based metal–dielectric–dye medium

We report on enhancement of random laser operation due to surface plasmon (SP) effects from the addition of Ag nanoparticles to an Al2O3 scatterer based random laser. SP resonance provides a localized electromagnetic field enhancement near the surface of the Ag particle, which results in the creation of an enhanced gain region at the particle's surface. The hybrid dye–dielectric–metallic nanoparticle random laser's emission characteristics are investigated as a function of Ag particle concentration and pump energy fluence. When operating in the modestly scattering regime, the hybrid Ag and Al2O3 scatterer based random laser experiences an increase in peak emission intensity, and a decrease in the emission linewidth with the addition of Ag particles.

Emission characteristics of optically pumped GaN-based vertical-cavity surface-emitting lasers

The laser emission characteristics of a GaN-based vertical-cavity surface-emitting laser with two dielectric distributed Bragg reflectors were investigated under optically pumped operation at room temperature. The laser emitted wavelength at 415.9nm with an emission linewidth of 0.25nm and threshold pumping energy of 270nJ. The laser has a high characteristic temperature of about 278K and high spontaneous emission coupling factor of 10−2. The laser emission showed single and multiple spot emission patterns with spectral and spatial variations under different pumping conditions.

Spectroscopic investigation of Nd 3+ in ASL

Nd 3 + -activated strontium lanthanum aluminate Sr 1 - x Nd y La x - y Mg x Al 1 2 - x O 1 9 (ASL: Nd) crystals are investigated especially for 4 F 3 / 2 → 4 I 9 / 2 laser emission in 900 nm range. The optimisation of laser emission characteristics requires a detailed knowledge of spectral features and their dependence on composition. The spectral investigation of Nd 3 + in ASL on an extended composition range (especially small x) reveals new spectral features. Connecting spectral and structural data, the role of charge compensator Mg 2 + ion in the structure of the two main Nd 3 + structural centers in ASL, C 1 and C 2 , is proposed. It is inferred that these results enable a rigorous selection of the optimal composition for improving laser properties.