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An in-depth analysis and description of, to the best of our knowledge, the first subnanosecond pulse duration optical parametric generator (OPG) based on a fan-out grating design MgO-doped periodically-poled lithium niobate (MgO:PPLN) crystal is presented. Pumped by high energy subnanosecond pulse duration Q-switched Nd:YAG microlaser pulses, our OPG provides high output energies ranging from tens to hundreds of μ J with up to 45% conversion efficiency and enables fast and precise wavelength tuning across the near-to-mid infrared spectral regions (1414–4303 nm) just by laterally displacing the fan-out crystal without the need for temperature tuning. Limits of operation of the device were found in terms of the laser-induced damage threshold (LIDT) of the fan-out MgO:PPLN crystal. The OPG was fully characterized in terms of spectral, energy, and spatial properties of the signal wave, and analyzed experimentally and theoretically for the feasibility of producing broadband infrared output through non-collinear quasi-phase-matching and conversion of the fan-out grating structure into a chirped one. • Fan-out OPG tuning (1.4 – 4.3 μ m) was achieved by laterally displacing the crystal. • Subnanosecond, μ J energy pulses with up to 45% conversion efficiency were obtained. • Signal spatial beam quality highly depended on pump focusing conditions. • LIDT of a fan-out MgO:PPLN was examined for subnanosecond laser pulses. • The feasibility of broadband infrared output was explored via non-collinear QPM. [ABSTRACT FROM AUTHOR]

• By analyzing the effect of Nd3+ doping concentration on the photothermal conversion efficiency of Nd:NaGdF 4 nanoparticles under continuous wave laser irradiation, the highest value in NaNdF 4 as a nanoscale heat source in the microstructure can reach 82.5%, which is greater than the currently reported nanoheaters. • The nanoheater is doped into the silica core by infrared laser ablation of microfibers, and the 793 nm trigger laser is injected axially through the fiber stem to trigger the photothermal effect, so that the PMMA-coated microcavity maintains a high intrinsic Q factor during all-optical tuning process, and possesses improved integration. • The nanoheater-doped microlaser achieves a wavelength tuning range of over 3.1 nm within the applied power intensity range of 1 to 1.62 W/mm2, which is more than 2.5 times larger than that of the undoped microlaser, confirming that nanoheater doping is an effective way to improve all-optical wavelength tunability. A novel all-optical tunable microlaser based on a polymer-coated microcavity embedded with a high-efficiency nanoheater is proposed. The large refractive index contrast between polymer and air helps to generate whispering gallery mode (WGM) resonances, so lasing from polymer microshells can be obtained via total internal reflection. Under the continuous triggering of a 793 nm laser, a maximum photothermal conversion efficiency of 82.9% was achieved using the Nd3+ heavily doped NaGdF 4 nanocrystal (NC) as a nanoscale heat source. The nanoheater was doped into the silica core by infrared laser ablation of the microfiber without contact with the WGM, enabling the coated microcavity to maintain a high Q factor up to 1.6 × 106. Significant heat transfer is achieved by the nanoheater absorbing the 793 nm trigger light pumped via the fiber stem, and the lasing wavelength is all-optical tuned over 3 nm at the applied power intensity range of 1 to 1.62 W/mm2. Furthermore, a tuning sensitivity of up to 1.86 nm/(W mm−2) is realized. The excellent photothermal properties of the lanthanide-doped nanoheater make the proposed microlaser attractive for future microelectronic device applications in all-optical networks. [ABSTRACT FROM AUTHOR]

We demonstrate ultralow-threshold neodymium-doped silica microsphere lasers on a silicon chip with lasing wavelengths of ~900 nm and ~1060 nm. Neodymium-doped microsphere cavities are fabricated with a series of doping concentrations using silica sol–gel films. Experimentally, we observe single-mode lasing emissions from the high-Q microsphere cavities with a threshold of as low as 1.2 µW. [ABSTRACT FROM AUTHOR]

We report on fabrication of dye-doped polymer photonic-molecule (PM) microlasers by femtosecond laser direct writing (FsLDW) and investigate their lasing behaviors by changing the distance between the two disks in the microcavities. It is found that when the distance of two disks becomes smaller, the coupling between two disks occurs, leading to a decrease of the lasing modes. But, when two disks are crossed, the circular symmetric of whispering-gallery mode cavities are broken, increasing the lasing thresholds. With the three-dimensional (3D) fabrication capacity of FsLDW, our result opens up a possibility of investigating complex 3D coupled microcavities for photonic device integration. [ABSTRACT FROM AUTHOR]

Abstract: CdS nanobelts were fabricated by a vapor transport method in the absence of a catalyst. The scanning electron microscopy and transmission electron microscopy demonstrated that the CdS nanobelts had regular morphology, smooth surface and single-crystalline structure. Under the excitation of 325nm line of a femtosecond pulsed laser, the amplified spontaneous emission with the typical band narrowing process was observed. The Fabry–Perot mode lasing action in a single CdS nanobelt was observed by the confocal micro-photoluminescence technique. The result indicated that the CdS nanobelt can be used as ideal microlaser material in the future optoelectronic devices. [Copyright &y& Elsevier]

Abstract: We introduce a portable, all-liquid microlaser based on optically pumped dye-doped emulsion microdroplets held in a single beam optical trap. We show high stability of the laser emission spectra during prolonged optical manipulation of the droplets within an immiscible host liquid. We investigate the effects of droplet size and dye concentration on the spectral position of lasing wavelength and show how these parameters can be used for the emission wavelength tuning. We also study shifting of the average lasing wavelength to the blue side of the spectrum due to dye photobleaching. The presented optically manipulated fluidic microlasers are disposable and can be easily combined with microfluidic chip technology. This makes them especially attractive for on-chip applications in chemical and biological analysis and sensing. [Copyright &y& Elsevier]

Abstract: Lasing in fluorescent polystyrene microbeads embedded in gelatin of different density is reported up to a gelatin concentration of 30%, corresponding to a refractive index of 1.38. Above that value, the resonator modes become too broad for operation above threshold with a critical Q-factor of about 14,000. As a proof of applicability of these microlasers as remote microsensors inside of dense media, the resonator mode positions were used for quantification of the gelatin refractive indices, yielding the same linear dependency on gelatin concentration for both microlasers operated below and above threshold. [Copyright &y& Elsevier]

Abstract: Room-temperature low-threshold (0.55mJ/cm2) lasing in UV-region was observed in ZnO powders with tetrapod-like shape of crystallites. Zinc oxide powders were prepared by high-temperature pyrolysis of zinc-containing organic salts. The lasing characteristics were stable and reproducible from pulse to pulse and varied from point to point on the sample surface due to random displacement of crystallites on the sample surface and the dispersion of the crystallite sizes. The lasing spectra were characterized by clear mode structures, the full width of lasing lines at half maximum being equal to ∼0.2nm. The main characteristics of the lasing spectra indicated that we observed the lasing from single ZnO tetrapod working as high-Q microcavity (microlaser). [Copyright &y& Elsevier]

Abstract: Er3+-doped glasses have been a subject of great interest in the recent years for their application in the areas of guided wave optical amplifiers and lasers. Oxide–glass matrices, in particular, offer the advantage of relatively simple fabrication processes—both for bulk glasses and optical fibers—and have demonstrated quite good properties in the 1.5μm wavelength band. Here we present some results we have obtained in the development of different silica-based glasses and in their application to the production of integrated optical amplifiers and microspherical lasers. As to the former application, two classes of silica glasses have been produced and investigated, namely a melted soda-lime–alumino-silicate glass and a sol–gel silica–hafnia glass. Both of them exhibit a wide emission bandwidth and seem quite promising for broadband optical amplifiers. We also demonstrated low-threshold microlasers, based on whispering gallery mode spherical resonators, fabricated in different oxide glasses. [Copyright &y& Elsevier]

Abstract: We consider waveguides formed by single or multiple two-dimensional chaotic cavities connected to leads. The cavities are chaotic in the sense that the ray (or equivalently, classical particle) dynamics within them is chaotic. Geometrical parameters are chosen to produce a mixed phase space (chaotic regions surrounding islands of stability where motion is regular). Incoming rays (or particles) cannot penetrate into these islands but incoming plane waves dynamically tunnel into them at a certain discrete set of frequencies (energies). The support of the corresponding quasi-bound states is along the trajectories of periodic orbits trapped within the cavity. We take advantage of this difference in the ray/wave behavior to demonstrate how chaotic waveguides can be used to design beam splitters and microlasers. We also present some preliminary experimental results in a microwave realization of such chaotic waveguide. [Copyright &y& Elsevier]

Composite laser devices of passively Q-switched Nd:YAG were prepared by optical contacting between Nd:YAG and Cr,Ca:YAG crystal wafers followed by prolonged heating at elevated temperatures. Heating of the composite devices under reducing and/or oxidizing environments allowed to control the Cr4+ ion concentration in the Cr,Ca:YAG, thus affecting its absorption saturation behavior. Optical absorption saturation measurements on partially reduced Cr,Ca:YAG crystal were performed. Residual absorption of the saturable absorber at 1064 run results from the Cr4+ ion excited-state absorption. Laser damage threshold at the gain/absorber interface of the composite device, 14.7 J/cm2, is higher than at the entrance face. The device thus obtained was end-pumped by a fiber-optic-coupled diode laser, and exhibited short (∼5 ns), high repetition-rate pulsing. [Copyright &y& Elsevier]

Two-photon absorption (TPA) induced polymerization is a very promising way for three-dimensional (3D) microfabrication. However, the necessity to use onerous femtosecond Ti:sapphire lasers appears as a major drawback for this technology. We present a new symmetrical conjugated ketone with terminal amino groups that can initiate TPA photopolymerization of acrylates when irradiated with an inexpensive Nd-YAG microlaser. This compound shows broad band TPA between 800 nm and 1100 nm with a cross-section of 100×10−50 cm4 s photon−1 at the photoinitiation wavelength (1.06 μm). The efficiency of this new initiator is evaluated by the determination of the threshold of absorbed energy density for polymerization. [Copyright &y& Elsevier]

Layered double hydroxide (LDH) has been promoted and applied as photoluminescent functional materials responding to environmental stimuli in recent years. In this work, a kind of hydroxy double salts, zinc hydroxide nitrate (Zn 5 (OH) 8 (NO 3) 2 ·2H 2 O, Zn-HDS) was fabricated from zinc oxide and zinc nitrate solution under ambient conditions. To further obtain the regular morphology of Zn-HDS as cavity, the aforementioned Zn-HDS was dehydrated by aging at 100 °C for 16 h. The effective conversion from amplified spontaneous emissions (ASE) into lasing emissions of a single cubic Zn-HDS cavity was observed with the help of micro-photoluminescence spectra system (μ-PL spectra system) and 325 nm line of a femtosecond pulsed laser as excitation source. The result indicated that the cubic Zn-HDS cavity can be applied as desirable microlaser material for optoelectronic devices. • The cubic zinc hydroxide nitrate cavity was successfully synthesized by two-step method under low temperature. • The high optical gain was obtained from cubic zinc hydroxide nitrate cavity. • The cubic zinc hydroxide nitrate present tunable emission from amplified spontaneous emissions to lasing action. [ABSTRACT FROM AUTHOR]

• We present a WGM microlaser based on dual erbium-doped microspheres. • The dual microsphere microcavity laser has a narrower linewidth than that of a single microsphere microcavity laser and more sensitive to the change of pump source power. It also has the advantages of cost, small size, low threshold and continuous wavelength tunability. • The microlaser can greatly reduce the volume of optical integrated devices and reduce the cost of optical components, which promotes the development of large-scale integration with other optical communication elements such as waveguides, optical modulators, and optical fibers. We demonstrate a low-cost whispering gallery mode tunable microlaser based on dual erbium-doped microspheres, which is created by directly doping erbium ions when melting the tapered fiber tip by electrode discharge of a fusion splicer. The incident light from the tapered fiber is diverged into the microsphere and stimulates whispering gallery mode. The light field of whispering gallery mode interacts with the internal gain material, erbium ions, and ends up with lasing. The quality factor (Q) value of the device is up to 1.4 × 104. When the pumping laser power changes continuously from 4.6 mW to 7.5 mW, the lasing wavelength shifts from 1560.14 nm to 1560.49 nm, the lasing emission power can be tuned from 0.25 µW to 0.41 µW. [ABSTRACT FROM AUTHOR]

• Thermo-optical effects in tellurite glass microspheres were studied experimentally and theoretically. • Temperature distributions and shifts of WGMs were calculated for different parameters. • Tm-doped tellurite glass microspheres were produced and characterized. • Wavelength shifts of WGMs depending on the heat power were measured. The tremendous progress made in recent years in the production of tellurite glasses has led to the development of different optical elements and devices on their basis such as microresonators and microlasers. The investigation of tellurite glass microresonators is of great importance for many potential applications. We studied theoretically and experimentally the nonlinear thermo-optical effects in tellurite glass microresonators under continuous-wave laser pumping. We calculated the temperature distributions for both, steady-state and transient non-stationary regimes and simulated shifts of the resonant wavelengths of whispering gallery modes. We produced Tm-doped tellurite glass microspheres and measured the resonant wavelength shifts as functions of the heat power. Our experimental results are in a good agreement with the theoretical predictions. [ABSTRACT FROM AUTHOR]

Biocompatible microlasers, generally made of bio-derived materials, are promising for biosensing and cell-tracking. These kinds of lasers offer favourable opportunities like biocompatibility and biodegradability but the materials used often require complicated synthesis and high cost. In this work, we demonstrate that polyvinyl alcohol (PVA), a synthetic water-soluble low-cost polymer, with fascinating properties such as good transparency, biocompatibility, biodegradability is an excellent candidate for making laser cavity. Using a simple and effective technique, dye-doped PVA microspheres can be fabricated with various sizes from 10 to 200 μ m. These microspheres can act as excellent lasers under optical excitation with a lasing threshold of ∼ 2 μ J/mm2 and Q factor of lasing modes of ∼ 3000. The lasing mechanism is studied and it is ascribed to whispering gallery mode (WGM). Size-dependent lasing characteristics including lasing spectrum, quality (Q) factor and lasing threshold are investigated. Owing to the ease of fabrication, the cost-effectiveness, the biocompatibility of the PVA material, our biocompatible microlasers are promising for future biosensing applications. [ABSTRACT FROM AUTHOR]

• The first detailed theoretical study of Tm-doped tellurite microlasers is presented. • The original approach to numerical simulation is used. • The possibility of single-color and multi-color lasing is analyzed. • Diagrams of generation regimes depending on Q-factors and pump power are shown. We present the first detailed theoretical analysis of multi-color continuous wave lasing in Tm-doped tellurite spherical microresonators with whispering gallery modes pumped at a wavelength of 792 nm. The numerical model is based on solving a system of equations for intracavity field amplitudes and rate equations using the parameters of Tm-doped tellurite glass measured in the previous experiments. All fundamental whispering gallery modes in the gain bands are taken into account. We demonstrate diagrams of generation regimes depending on Q-factors and pump power, which show a possibility of single-color lasing at a wavelength of ~1.9 μm, two-color lasing at wavelengths of ~1.9&1.5 μm and at ~1.9&2.3 μm, and three-color lasing at wavelengths of ~1.9&1.5&2.3 μm. Such microlasers can play a significant role in sensing applications. [ABSTRACT FROM AUTHOR]