Generation of vector polarization in a Nd:YAG laser.

We demonstrated the generation of an azimuthally and radially polarized laser beam in a Nd:YAG laser in which a birefringent yttrium vanadate (c-cut YVO4) crystal was used as the intra-cavity polarization discriminator. AP and RP with respective output 2.4W (o-o efficiency of 35.4%, M2 = 2.3) and 2.52W (o-o efficiency of 37.2%, M2 = 2.4) were generated at absorbed pump power 6.78W. We discuss a simple method for converting between azimuthal and radial polarizations by only regulating input pump power and mechanism of mode selection in the laser. This vector laser will facilitate many applications.

Thin-rod Yb:YAG amplifiers for high average and peak power lasers.

The concept of a high-power thin-rod Yb:YAG laser amplifier with high-brightness diode pumping was proposed. The principle of the amplifier parameter variation aimed at achieving an efficient signal gain at different power levels was developed. Three versions of thin-rod gain modules were implemented, where small and strong signal gains were studied experimentally. The ultrafast laser system with high average power (28 W) and high pulse energy (2.5 mJ) was created on the basis of the unique thin-rod gain modules.

Yb3+-doped CaF2-LaF3 ceramics laser.

Highly transparent ceramic is an attractive gain medium for high-power lasers due to its high fracture toughness, homogeneity, and size scalability. Here we report the first Yb3+-doped CaF2-LaF3 ceramics laser. Codoping of La3+ ion can reduce the formation of Yb2+ ions and enhance the laser efficiency. In the laser experiment, the maximum output power of 4.36 W and the maximum slope efficiency of 69.5% were obtained with a 3% La, 2% Yb sample and a 2% La, 1% Yb sample, respectively. Due to the combined properties of Yb:CaF2 and a ceramic laser gain medium, Yb:CaF2-LaF3 ceramic is a promising gain medium for a high-power ultrashort pulse laser and amplifier.

Thin-tapered-rod Yb:YAG laser amplifier.

The concept of the thin-tapered-rod Yb:YAG amplifier with waveguide pumping is proposed and implemented. It is shown that such an amplifier demonstrates considerably higher small signal gain and is less affected by thermal effects than the thin-rod ("single-crystal fiber") amplifier. In the developed amplifier, a small signal gain as high as 23 per pass is achieved.

Multi-wavelength Yb:YAG/Nd3+:YVO4 continuous-wave microchip Raman laser.

Multi-wavelength continuous-wave (CW) Raman lasers in a laser diode pumped Yb:YAG/Nd3+:YVO4 microchip Raman laser have been demonstrated for the first time to our best knowledge. The multi-wavelength laser of the first Stokes radiation around 1.08 µm has been achieved with a Raman shift of 261 cm-1 for a-cut Nd:YVO4 crystal corresponding to the fundamental wavelength at 1.05 µm. Multi-wavelength laser operation simultaneously around 1.05 and 1.08 µm has been achieved under the incident pump power between 1.5 and 1.7 W. Multi-wavelength Raman laser with frequency separation of 1 THz around 1.08 µm has been obtained when the incident pump power is higher than 1.7 W. The maximum Raman laser output power of 260 mW at 1.08 µm is obtained and the corresponding optical-to-optical conversion efficiency is 4.2%. Elliptically polarized fundamental laser and linearly polarized Raman laser were observed in an Yb:YAG/Nd:YVO4 CW microchip Raman laser. The experimental results of linearly polarized, multi-wavelength Yb:YAG/Nd:YVO4 CW microchip Raman laser with adjustable frequency separation provide a novel approach for developing potential compact laser sources for Terahertz generation.

Thermal effects in Yb:YAG single-crystal thin-rod amplifier.

This work presents a new design for the laser gain module based on a ytterbium-doped yttrium aluminum garnet (Yb:YAG) single-crystal thin rod. Thermal effects (temperature, phase, and polarization distortion of laser radiation) and small signal gain are investigated both experimentally and theoretically. We then analyzed the influence of thermal effects and amplified spontaneous emission on the power scaling of the laser based on the gain module. A small signal gain as high as 3.3 per pass was experimentally achieved.

Demonstration of a Yb3+-doped Lu3Al5O12 ceramic thin-disk laser.

Yb:LuAG ceramic is very promising for thin-disk laser and amplifier architectures since it exhibits a higher thermal conductivity at high doping concentrations and a larger emission cross section than Yb:YAG. In this Letter, we present what we believe to be the first demonstration of a thin-disk laser based on Yb:LuAG ceramic. A maximum output power of 101 W with an optical efficiency of 56% and a slope efficiency of 64% was obtained with a multimode laser resonator. Fundamental-mode laser operation with near diffraction limited beam quality (M2≈1.22) was also achieved. The fundamental-mode laser resonator showed the output power of 49 W, an optical efficiency of 31%, and a slope efficiency of 44%. A linearly polarized output beam was demonstrated in multimode operation using an intracavity Brewster window. The depolarization loss was measured to be as low as 0.15% per round trip.

1 W single-frequency Tm-doped ZBLAN fiber MOPA around 810 nm.

We demonstrate a tunable narrow-linewidth fiber MOPA system around 810 nm for the light source of the Sr optical lattice clock. The coherent cw light source with a wavelength of 813.42 nm was generated by a combination of a narrow linewidth external-cavity laser diode and a Tm-doped ZBLAN fiber amplifier, which was upconversion-pumped by an Yb-doped fiber laser at 1064 nm. The maximum output power of 1.1 W was obtained with the launched power of 17 W, which is the highest power obtained from a Tm-doped fiber amplifier ever reported.

Study of the thermo-optical constants of Yb doped Y2O3, Lu2O3 and Sc2O3 ceramic materials.

Thermally induced depolarization and thermal lens of three Konoshima Chemical Co. laser-ceramics samples Yb(3+):Lu(2)O(3)(C(Yb) ≈ 1.8 at.%), Yb(3+):Y(2)O(3)(C(Yb) ≈ 1.8 at.%), and Yb(3+):Sc(2)O(3) (C(Yb) ≈ 2.5 at.%) were measured in experiment at different pump power. The results allowed us to estimate the thermal conductivity of the investigated ceramic samples and compare their thermo-optical properties. The thermo-optical constants P and Q and its sign measured for these materials at the first time.

Difficulty in placement of a left-sided double-lumen tube due to aberrant tracheobronchial anatomy.

A rare case of a tracheal bronchus coexisting with a left-shifted carina and an acute angle of left main bronchus is presented. A 66 year old man with a history of colon cancer was scheduled for right thoracoscopic pericardial window due to recurrent pericardial effusion. After induction of anesthesia, the trachea was intubated using a 39-French, left-sided double lumen tube (DLT); the DLT was positioned with fiberoptic bronchoscopic guidance. Significantly high airway pressure was noticed as we initiated one-lung ventilation after the patient was positioned in the left lateral decubitus position. While repositioning the DLT, we found an aberrant tracheal bronchus. Although multiple attempts were made to adjust the DLT so as to achieve lung isolation, we could not place the DLT in the appropriate position due to abnormal and distorted anatomy. Lung isolation was unsuccessful; both lungs were carefully ventilated with small tidal volumes.

Strong bias in the bacterial CRISPR elements that confer immunity to phage.

Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas systems provide adaptive immunity against phage via spacer-encoded CRISPR RNAs that are complementary to invasive nucleic acids. Here, we challenge Streptococcus thermophilus with a bacteriophage, and used PCR-based metagenomics to monitor phage-derived spacers daily for 15 days in two experiments. Spacers that target the host chromosome are infrequent and strongly selected against, suggesting autoimmunity is lethal. In experiments that recover over half a million spacers, we observe early dominance by a few spacer sub-populations and rapid oscillations in sub-population abundances. In two CRISPR systems and in replicate experiments, a few spacers account for the majority of spacer sequences. Nearly all phage locations targeted by the acquired spacers have a proto-spacer adjacent motif (PAM), indicating PAMs are involved in spacer acquisition. We detect a strong and reproducible bias in the phage genome locations from which spacers derive. This may reflect selection for specific spacers based on location and effectiveness.

Single-frequency ytterbium doped photonic bandgap fiber amplifier at 1178 nm.

1178 nm single-frequency amplification by Yb doped photonic bandgap fiber has been demonstrated. 24.6 W output power and 12 dB gain were obtained without parasitic lasing and also stimulated Brillouin scattering. 1.8 dB suppression of Brillouin gain by an acoustic antiguiding effect has been found in the Yb doped photonic bandgap fiber.

CW and mode-locked operation of Yb(3+)-doped Lu3Al5O12 ceramic laser.

CW laser operation and first mode-locked laser operation of Yb:LuAG ceramic are reported. Efficient CW laser operation was obtained with maximum output power of 2.14 W and a 72% slope efficiency. Femtosecond mode-locked laser operation was achieved with pulse duration of 699 fs and a 200 mW average output power.

High power Yb-doped photonic bandgap fiber oscillator at 1178 nm.

An ytterbium-doped solid-core photonic bandgap fiber oscillator in an all-fiber format is investigated for high power at an extreme long wavelength. The photonic bandgap fiber is spliced with two fiber Bragg gratings to compose the cavity. The sharp-cut bandpass distributed filtering effect of the photonic bandgap fibers efficiently suppresses amplified spontaneous emission in the conventional high-gain region. Fine adjustment of the short cut-off wavelength by coiling with tighter diameter is performed to suppress parasitic lasing. A record output power of 53.6 W with a slope efficiency of 53% at 1178 nm was demonstrated.

Expanding the table: the web as a tool for participatory adaptive management in California forests.

Participatory adaptive management is widely promoted as the new paradigm in public lands management. It is grounded in two underlying principles - that management experiments and diverse sources of information should be used to continually refine management in complex ecological systems, and that the public must be included throughout the adaptive management process. Access to scientific results and exchange of information is at the core of both of these principles. The recent proliferation of Internet communities and web-based participation tools raises the question of how the Internet might help facilitate information exchange in participatory adaptive management. Using a case study approach, the role of web technologies in facilitating the flow of transparent and useful information was examined in a participatory adaptive management project focused on Forest Service vegetation management treatments in California's Sierra Nevada. Three evaluation methods were used: analysis of web usage and content, a survey of active participants, and a review of comments posted to the project website. Results suggest that the web played an important role throughout the adaptive management cycle by supporting communication through disseminating information to the public and increasing the transparency of the scientific process. The web played a small, but important role in public consultation, by providing a forum for targeted questions and feedback from the public. Internet technology did not actively support the two-way flow of information necessary for mutual learning. Web technology complements face-to-face interactions and public meetings, rather than replacing them.

Continuous wave and mode-locked Yb3+:Y2O3 ceramic thin disk laser.

CW and mode-locked laser operation based on an Yb3+:Y2O3 ceramic thin disk is reported. In CW laser operation, an output power of 70 W with an optical-to-optical efficiency of 57.4% was achieved. A higher slope efficiency of 70% was also obtained with a 50-W pump laser diode with more suitable emission characteristics. In mode-locked laser operation, pulses as short as 547 fs with an average power of 7.4 W were obtained. To our knowledge, this is the first demonstration of a high power CW and mode-locked laser operation based on Yb3+:Y2O3 ceramic thin disks.

Generation of radially and azimuthally polarized beams in Yb:YAG laser with intra-cavity lens and birefringent crystal.

We demonstrated the operation of cw diode-pumped Yb:YAG laser in radial or azimuthal polarized (RP or AP) beams using a combination of birefringent uniaxial crystal (c-cut YVO4 or α-BBO) and lens as intra-cavity elements. RP and AP doughnut modes (M2 = 2-2.5, polarization extinction ratio 50-100:1) with output power up to 60 mW were generated. Apart from doughnut modes, RP or AP ring-like off-axis oscillations and multi-ring beams with mixed RP and AP were also observed at the output of this laser scheme. Using intra-cavity short focus lenses with spherical aberrations AP or RP modes of higher orders was obtained. Mechanism of mode selection in the laser is discussed. The large variety of beams with axially symmetric polarizations from the output of the proposed laser scheme may find applications in different fields.

Radially polarized and passively Q-switched fiber laser.

We report, for the first time to our knowledge, a radially polarized and passively Q-switched Yb-doped fiber laser. By using a Cr(4+):YAG crystal as a saturable absorber and a photonic crystal grating as a polarization mirror, a radially polarized pulse is produced, which has 202 W of peak power, 75 ns duration, and ~92% polarization purity at a 56.6 kHz repetition rate. The Q-switched pulse with radial polarization from the fiber laser would facilitate numerous applications.

Efficient, high-power, and radially polarized fiber laser.

We demonstrate an ytterbium-doped fiber laser that emits high-power radially polarized light efficiently. In this study, a photonic crystal grating (PCG) was used as a polarization-selective output coupler, and the power of the radially polarized laser reached 2.42 W with a slope efficiency of 45.9% and a polarization purity of 96%. The results reveal that the inclusion of the PCG mirror into the fiber laser are particularly promising for generating high-power radially polarized light efficiently in view of its many important applications.

Multi-pulse oscillation and instabilities in microchip self-Q-switched transverse-mode laser.

Multi-transverse-mode competition, coupling induced instabilities and multi-pulse or satellite pulse oscillations were investigated experimentally and theoretically in laser-diode-pumped Cr,Nd:YAG self-Q-switched microchip lasers under large pump beam diameter. The different transverse modes have great effects on the laser pulse temporal characteristics such as pulse profile, pulse width, instability of peak power and repetition rate jitter. Multi-transverse-mode, multi-pulse oscillation and periodical pulsation were observed by varying the pump beam diameter.The effect of transverse modes on the instability and multi-pulse oscillation were studied by modified coupled rate equations by taking into account the transverse-mode competition of inversion population under different pump conditions. The numerically simulated results are in good agreement with the experimental results. These results show that the multi-pulse oscillation and instability in the pulse train were attributed to different transverse mode coupling and competition. The peak power instabilities and pulse repetition rate jitter of the laser pulses due to transverse mode coupling were also investigated.