High Power CW Operation Research Articles

4.6 GHz lower hybrid wave power control system for EAST.

In order to achieve steady state operation in experimental advanced superconducting tokamak (EAST), a 6 MW/4.6 GHz lower hybrid current drive system with twenty-four 250 kW/4.6 GHz high power klystron amplifiers (model VKC7849A) has been developed. A 4.6 GHz lower hybrid wave (LHW) power control system (4.6 GHz LPCS) with continuous wave mode has been set up, which was used to control the LHW power as needed. This paper introduces the architecture and software design of LPCS system, including microwave preamplifier subsystem, power measurement subsystem, power control computers, and so on. Proportional integral differential (PID) closed-loop control time is less than 100 μs due to the use of high-speed acquisition cards and user-programmable Field Programmable Gate Arrays. So far, high power CW operation and power control experiments with PID feedback mode by plasma parameters (beta, loop voltage, and so on) were performed in detail. Results show that 4.6 GHz LPCS is stable and reliable, suggesting that it meets the needs of EAST.

High temperature laser diode based on a single sheet of quantum dots

A single sheet of high-density InGaAs quantum dots (QDs) is used as a gain medium of InGaAs–GaAs–AlGaAs lasers. The devices operate at high power in the continuous mode beyond 160 °C with an emission wavelength up to ∼1.27 μm. At short cavity lengths a strong broadening (>300 nm) of the electroluminescence spectrum is observed at high current densities, permitting light sources for broadly wavelength tuneable and multi-wavelength infrared lasers based on a single gain chip, and related frequency conversion devices for the whole visible spectrum range. High power cw operation (>2 W) limited by catastrophic optical mirror damage is realized.

Progress in the ITER electron cyclotron heating and current drive system design

An electron cyclotron system is one of the four auxiliary plasma heating systems to be installed on the ITER tokamak. The ITER EC system consists of 24 gyrotrons with associated 12 high voltage power supplies, a set of evacuated transmission lines and two types of launchers. The whole system is designed to inject 20MW of microwave power at 170GHz into the plasma. The primary functions of the system include plasma start-up, central heating and current drive, and magneto-hydrodynamic instabilities control. The design takes present day technology and extends towards high power CW operation, which represents a large step forward as compared to the present state of the art. The ITER EC system will be a stepping stone to future EC systems for DEMO and beyond.The EC system is faced with significant challenges, which not only includes an advanced microwave system for plasma heating and current drive applications but also has to comply with stringent requirements associated with nuclear safety as ITER became the first fusion device licensed as basic nuclear installations as of 9 November 2012.Since conceptual design of the EC system established in 2007, the EC system has progressed to a preliminary design stage in 2012, and is now moving forward towards a final design. The majority of the subsystems have completed the detailed design and now advancing towards the final design completion.

Tapered Fiber Bundle 7$\,\times\,$1 End-Pumping Coupler Capable of High Power CW Operation

A high efficiency tapered fiber bundle (TFB) 7 × 1 end-pumping coupler with a handle pumping power of 3.01 kW and a coupling efficiency of 99.4% was reported. The coupling efficiency of the TFB 7 × 1 end-pumping coupler is calculated by the 3-D beam propagation method. According to the theoretical results, the excellent TFB 7 × 1 end-pumping coupler is manufactured successfully in experiment.

Continuous wave and mode-locked Yb^3+:Y_2O_3 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.

High-power singlemode CW operation of 1.5 µm-range quantum dot GaAs-based laser

Narrow ridge stripe lasers with metamorphic InAs/InGaAs quantum dots grown using molecular beam epitaxy on GaAs substrates emit in the 1.5 µm wavelength range demonstrating a differential quantum efficiency of about 50%, singlemode operation, and maximum continuous-wave power of 220 mW limited by thermal roll-over. Absence of beam filamentation is demonstrated up to the highest power levels studied.

High power CW operation of InGaAsN lasers at 1.3µm

Room temperature, continuous-wave operation at 1.3 µm is reported for InGaAsN triple quantum well lasers. The layers were grown by MBE using an RF-coupled plasma source for nitrogen. Large broad area lasers exhibit very low threshold current density down to 680 A/cm2 and a slope efficiency of 0.59 W/A (output per two facets). Maximum output powers of 2.4 and 4 W are reached at 10°C under CW and pulsed operation, respectively. These values are a significant improvement over those previously published for lasers in the InGaAsN material system.

High-power "Watt-level" CW operation of diode-pumped 27 �m fiber lasers using efficient cross-relaxation and energy transfer mechanisms

We report the demonstration of high power (660 mW) CW operation of a diode-pumped mid-IR Er fiber laser. This was achieved by using efficient depopulation of the lower laser level via enhanced cross-relaxation between Er ions and energy transfer to Pr ions (at doping densities much higher than those used previously in Er:ZBLAN), along with optimal pumping of such lasers via custom-designed double-clad fluoride fibers.

High power mid infrared operation of the atomic xenon laser

We report high power cw operation of a slab waveguide atomic xenon laser in a spectral region of low atmospheric absorption. Using transverse radio frequency discharge excitation at 49 MHz and a hybrid waveguide-unstable resonator, with a sharp band edge on the reflectivity versus wavelength curve of the laser mirrors, 50 mW was obtained on the 3.869 μm transition and 210 mW on the 3.895 μm line.

Quartz antenna for radio frequency ion source operation

Radio-frequency (rf) driven multicusp ion sources developed at the Lawrence Berkeley National Laboratory use an internal induction coil (antenna) for plasma generation. The copper rf-antenna with a thin layer of porcelain coating, which is presently used, cannot fully satisfy the increasing demands on source cleanliness and antenna lifetime under high power cw or pulsed operation in applications where water cooling is not possible. A quartz antenna has been designed and operated in the multicusp ion source. It has been demonstrated that the overall performance of the new antenna exceeds that of the regular porcelain-coated antenna. It can be operated with a long lifetime in different discharge plasmas. The quartz antenna has also been tested at the Paul Scherrer Institute for cw source operation at rf power higher than 5 kW. Results demonstrated that the antenna can survive under dense plasma discharge operations.

Very low threshold and high power CW operation in1.55 µm gain-coupled DFB lasers with periodically etched quantum wells

The authors demonstrate extremely low threshold and high CW output power in 1.55 µm gain coupled DFB lasers. The structure is an MQW strain compensated active layer with first-order grating etched on the upper wells. The lowest thresholds of 2.5 mA at 20°C and 10 mA at 80°C are obtained using one HR facet coating. With an AR front facet, the CW output is increased up to 40 mW, while the threshold current remains < 10 mA.

Direct imaging of a high-power diode laser cavity using a transparent indium-tin-oxide (ITO) contact

We describe a novel "see-through" indium-tin-oxide contact on the n-side of a high power unstable resonator semiconductor laser (URSL) that allows direct observation of the cavity during high power operation. Under optimized annealing conditions this transparent ITO contact has a low enough specific contact resistivity to permit normal high power CW operation of the URSL and allows the observation of filamentation. This contact scheme is applicable to a wide range of semiconductor lasers and is especially appropriate for high power devices. The same structure can also be used to obtain a 2-D thermal map of the laser cavity.

High-power CW operation of AlGaInP laser-diode array at 640 nm

Visible-emitting high-power laser bars are investigated at an emission wavelength of 640 nm. AlGaInP/GaInP, single tensile-strained quantum well, separate confinement heterostructures are fabricated into one cm long laser bars using a 0.7 fill factor. The low threshold current of the diode, combined with the aggressive heatsinking of a silicon microchannel cooler has resulted in more than 12 W of continuous wave output power.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

150 mW fundamental-transverse-mode operation of 670 nm window laser diode

Fundamental-transverse-mode high-power CW operation over 150 mW has been realized in AlGaInP/GaInP 670-nm window laser diodes. A window structure of Zn-induced-disordered GaInP has been fabricated by solid phase diffusion using ZnO film. A compressively strained double-quantum-well active layer and a multiple quantum barrier (MQB) also have been employed for reduction of threshold current. Stable CW operation beyond 1500 h has been observed under 50 mW at 50 degrees C.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-power cw operation of InGaAs/GaAs surface-emitting lasers with 45° intracavity micro-mirrors

High-power cw operation of horizontal-cavity, monolithic InGaAs/GaAs surface-emitting lasers with all dry etched micro-mirrors has been demonstrated for the first time. The 45° and 90° micro-mirrors of the devices were fabricated by ion-beam etching and reactive ion etching techniques, respectively. Threshold-current densities of less than 500 A/cm2, external differential quantum efficiencies of 10% (0.12 W/A) from the emitting facet, and output powers in excess of 100 mW were achieved from uncoated devices driven under cw operation.

High-power (106 mW) CW operation of transverse-mode stabilised InGaAlP laser diodes with strained In 0.62 Ga 0.38 P active layer

High-power CW operation of transverse-mode stabilised InGaAlP laser diodes has been achieved by using a selectively-buried-ridge waveguide structure with a very thin (150A) active layer. A strained In0.622Ga0.38P active layer was adopted to obtain a sufficient bandgap difference between the active and cladding layers. A maximum light output of 106 mW was obtained from the laser with anti-reflection and high-reflection coatings.

High power cw operation of GaAs/GaAlAs surface-emitting lasers mounted in the junction-up configuration

High power cw operation of horizontal cavity monolithic GaAs/GaAlAs surface-emitting lasers with all dry etched micromirrors in the junction-up configuration has been demonstrated for the first time. The 45° and 90° mirrors of the devices were fabricated by ion beam etching and reactive ion etching techniques, respectively. Typical threshold current densities of less than 360 A/cm2, external differential efficiencies of 22% (0.34 W/A) from the emitting facet, and output powers in excess of 280 mW were achieved under cw operation.

High-temperature operation of high-power InGaAlP visible light laser diodes with an In0.5+δGa0.5−δP active layer

High-power and high-reliable operation of transverse-mode stabilized InGaAlP laser diodes has been achieved by a selectively buried ridge waveguide structure with a thin (0.02 μm) active layer. A composition-shifted In0.5+δGa0.5−δP active layer was employed in order to improve the temperature characteristic. A maximum cw light output power of 54 mW was obtained for the laser with antireflection and high-reflection coatings. A high-power cw operation above 30 mW output power was maintained even at a 60 °C heat-sink temperature. Stable cw operation exceeding 1000 h has been achieved for 20 mW output power at 50 °C.

High-power CW operation of broad area InGaAlP visible light laser diodes

Broad area InGaAlP visible light laser diodes with antireflection and high-reflection coatings have been fabricated. High power cw operation above 300 mW was obtained at 2°C heat-sink temperature. This value corresponded to a light power density of 2.7 MW/cm2. The far field pattern showed a single lobe shape for output power up to 100 mW.

High-power (2.2 W) cw operation of (111)-oriented GaAs/AlGaAs single-quantum-well lasers prepared by molecular-beam epitaxy

High-power (2.2 W) cw operation has been achieved in a (111)-oriented GaAs/AlGaAs graded-index separate-confinement-heterostructure single-quantum-well laser with the 100-μm wide stripe geometry. High differential quantum efficiency of 81% has been obtained up to ∼1.2 W, and high total power-conversion efficiency of 46% has been achieved at 1.5 W.