2.0 W CW, diffraction-limited tapered amplifier with diode injection

The authors have demonstrated an all-semiconductor discrete-element 1.5 mm length tapered-amplifier MOPA (master oscillator power amplifier) emitting up to 2.0 W CW in a diffraction-limited pattern. The tapered single-pass amplifier MOPA exhibits a very high differential efficiency of 72% and a total energy conversion efficiency of 39% at 2.0 W CW output power. The high efficiency of the MOPA is attributed to the tapered amplifier design, which maximises extraction efficiency with a low-power injected beam of 25 mW from a single-mode laser diode. Such an MOPA will have applications where compact, high-efficiency, diffraction-limited sources of radiation are required, such as frequency doubling and free-space communication.<>     

2.0 W CW, diffraction-limited operation of a monolithicallyintegrated master oscillator power amplifier

The authors fabricated a monolithically integrated master oscillator power amplifier, M-MOPA, with a flared power amplifier region which radiates in a single diffraction limited lobe to an output power in excess of 2 W CW. The radiation pattern is stable with increasing drive current. The spectral output of the M-MOPA is a single longitudinal mode with a side-mode suppression ratio greater than 25 dB     

Development of a kW Level-200 GHz Gyrotron FU CW GI with an Internal Quasi-optical Mode Convertor

Development of gyrotrons with an internal mode convertor has started in Research Center for Development of Far-Infrared Region, University of Fukui (FIR FU). As the first gyrotron of such a kind, we have designed and manufactured Gyrotron FU CW GI. It operates at 203 GHz at fundamental cyclotron resonance. We have designed a cavity and a mode convertor under some constraints such as reuse of an electron gun and small diameter of a magnet bore. Designed output power is about 1 kW. We have succeeded in observation of a circular radiation pattern. The maximum observed output power is 0.5 kW for the setting cathode voltage of 20 kV and the beam current of 0.5 A. This success makes gyrotron development in FIR FU to proceed to a new stage.     

Continuously Frequency Tunable High Power Sub-THz Radiation Source—Gyrotron FU CW VI for 600 MHz DNP-NMR Spectroscopy

A high frequency gyrotron with a 15 T superconducting magnet named Gyrotron FU CW VI has achieved continuous frequency tuning through the relatively wide range of 1.5 GHz near 400 GHz. The operation is at the fundamental cyclotron resonance of the TE₀₆ cavity mode with many higher order axial modes. The output power measured at the end of the circular waveguide system ranges from 10 to 50 watts at the low acceleration voltage of 12 kV for beam electrons. The beam current is also low. It is around 250 mA. This gyrotron is designed as a demountable radiation source for the 600 MHz DNP-NMR spectroscopy. The design and operation results of the gyrotron FU CW VI are presented.     

Development of high-power Ka-band and Q-band helix-TWTs

Recent advancements made in millimeter-wave helix-traveling wave tubes (TWTs) at L-3 Communications Electron Technologies (L-3 ETI), Inc. (formerly Electron Dynamic Devices, Inc. and originally Hughes Electron Dynamics Division), in continuous-wave (CW) output power capability and the overall efficiency of Ka-band and Q-band devices are presented. The 8921HP, L-3 ETI's latest high-power communications Ka-band TWT model, demonstrates 250-300-W CW output power and 47% minimum overall efficiency with a two-stage collector over 27.5-31 GHz. Another Ka-band device, the 8922HP, developed for pulsed radar applications over 33.4-36 GHz, produces 230-W minimum output power over the bandwidth with 49% minimum overall efficiency. This device was developed for pulsed operations but has demonstrated CW power-handling capability up to 270 W. In Q-band, the 8925HP, derived from the current production 120-W Q-band helix-TWT (8905HP), significantly extends the CW output power capability, demonstrating 230-W minimum over 43.5-45.5 GHz. The beam focusing is improved in both the Ka-band and the Q-band TWT models, with saturated radio-frequency beam interception well below 1% of the nominal beam current of 95 mA. The devices can be operated in pulsed mode by using the focus electrode to cut off the beam. The electron gun typically requires a focus electrode voltage of -800 to -900 V with respect to cathode for beam cutoff.     

High-Performance Continuous-Wave Operation of $lambda sim {hbox {4.6}}~mu{hbox {m}}$ Quantum-Cascade Lasers Above Room Temperature

We report the high-performance continuous-wave (CW) operation of 10-mum-wide quantum-cascade lasers (QCLs) emitting at lambda ~ 4.6mum, based on the GaInAs-AlInAs material without regrowth, in epilayer-up and -down bonding configurations. The operational characteristics of QCLs such as the maximum average power, peak output power, CW output power, and maximum CW operating temperature are investigated, depending on cavity length. Also, important device parameters, i.e., the waveguide loss, the transparency current density, the modal gain, and the internal quantum efficiency, are calculated from length-dependent results. For a high-reflectivity (HR) coated 4-mm-long cavity with epilayer-up bonding, the highest maximum average output power of 633 mW is measured at 65% duty cycle, with 469 mW still observed at 100%. The laser exhibits the maximum wall-plug efficiencies of 8.6% and 3.1% at 298 K, in pulsed and CW operatons, respectively. From 298 to 393 K, the temperature dependent threshold current density in pulsed operation shows a high characteristic temperature of 200 K. The use of an epilayer-down bonding further improves the device performance. A CW output power of 685 mW at 288 K is achieved for the 4-mm-long cavity. At 298 K, the output power of 590 mW, threshold current density of 1.52 kA/cm², and maximum wall-plug efficiency of 3.73% are obtained under CW mode, operating up to 363 K (90degC). For HR coated 3-mm-long cavities, laser characteristics across the same processed wafer show a good uniformity across the area of 21 cm², giving similar output powers, threshold current densities, and emission wavelengths. The CW beam full-width at half-maximum of far-field patterns are 25deg and 46deg for the parallel and the perpendicular directions, respectively.     

28GHz二次谐波回旋振荡管的自洽非线性计算

中等功率的连续波回旋管在工业领域有着重要的应用前景．本文对工作在28GHz频率的工业应用回旋振荡管进行了自洽非线性计算．结果表明,在二次谐波工作条件下,选取TE02模式,当电压为32kV、电流为6A时,可以获得连续波输出功率-50kW,效率-28％．     

638 nm、532 nm 激光泵浦的连续波翠绿宝石激光器

报道了一种高功率、高光束质量的755 nm连续波翠绿宝石激光器。首先,对比研究了638 nm激光二极管（LDs）和532 nm固体激光器单端泵浦的翠绿宝石激光器。当638 nm LDs作为泵浦源时,得到的连续输出功率、光-光转换效率分别为3.9 W和19.7%。保持其他条件基本不变,将泵浦源换成532 nm激光器,得到的连续输出功率、光-光转换效率分别为2.1 W和10.0%。结果表明利用 638 nm LDs泵浦翠绿宝石可获得更高的激光功率和转换效率。此外,研究了638 nm LDs双端泵浦的翠绿宝石激光器,在755 nm处得到了6.2 W的连续输出功率,相应的光-光转换效率和斜效率分别为16.3%和24.2%,并且连续输出功率为5.0 W时的光束质量M2优于1.47,这是翠绿宝石激光器在近衍射极限下的最高连续输出功率。这种高功率、高光束质量的755 nm翠绿宝石激光器为连续波紫外激光器的研制提供了良好、稳定的基频源。     

All MOCVD grown 850-nm-wavelength refractive-index-guidedsemiconductor-buried vertical-cavity surface-emitting lasers withp/n-InGaP current blocking layers

All metal-organic chemical vapor deposition (MOCVD) grown 850-nm-wavelength refractive-index-guided semiconductor-buried vertical-cavity surface-emitting laser is proposed and their performance is investigated. P/n-InGaP current-blocking region enables both selective regrowth and the formation of refractive-index-guided region which surrounds multiquantum-well active/core regions. We have achieved room temperature CW operation of the new types of vertical-cavity surface-emitting lasers. The minimum threshold current was 9.5 mA with 18 μm square mesa size at 30°C. The device lased at up to 70°C, and the maximum output power exceeds 1 mW at above 30°C. The near field pattern indicates the single-lobed output beam at low bias current     

Efficient Nd:YAG slab longitudinally pumped by diode lasers

An efficient scalable 1.06-μm continuous-wave (CW) Nd:YAG slab laser longitudinally pumped by diode lasers is discussed. The 809-nm diode radiation is focused into every laser channel emerging from the reflection points of the 1.06-μm beam on the coated slab surfaces. A maximum CW TEM₀₀ output power of 675 mW has been obtained at a diode pump power of 2 W resulting in a slope efficiency of 40%     

大功率In(Ga)As/GaAs量子点激光器

利用分子束外延技术和 S- K生长模式 ,系统研究了 In As/Ga As材料体系应变自组装量子点的形成和演化 .研制出激射波长λ≈ 960 nm,条宽 1 0 0μm,腔长 80 0μm的 In( Ga) As/Ga As量子点激光器 :室温连续输出功率大于 3.5W,室温阈值电流密度 2 1 8A/cm2 ,0 .61 W室温连续工作寿命超过 3760小时     

Development of multimegawatt gyrotrons for fusion plasma heating and current drive

High-frequency gyrotrons with high output power are mainly used for microwave heating and current drive in plasmas for thermonuclear fusion. The development of high-power gyrotrons in continuous wave (CW) operation has been in progress for several years in a joint collaboration between different European research centers and an industrial partner. The status of the development of the 140-GHz continuously operating gyrotrons with an output power of 1 MW for the stellarator Wendelstein 7-X will be described. An output power of 890 kW has been achieved with a pulse length of 3 min. limited by the available high-voltage power supply at an electron beam current of 40 A. At a reduced beam current of 27 A , an output power of 540 kW was measured with a pulse length of 939 s. For the next fusion plasma device international thermonuclear experimental reactor, gyrotrons with a higher output power of about 2 MW are desirable. In short-pulse experiments, the feasibility of fabrication of coaxial cavity gyrotrons with an output power up to 2 MW, CW, has been demonstrated, and the information necessary for a technical design has been obtained. An output power of 2.2 MW has been reached in stable operation (without mode competition). At the nominal output power of 1.5 MW an efficiency of 48% could be obtained with single-stage depressed collector. The development of frequency tunable gyrotrons operating in the range from 105 to 140 GHz for stabilization of current driven plasma instabilities in fusion plasma devices (neoclassical tearing modes) is another task in the development of gyrotrons at the Forschungszentrum Karlsruhe.     

Design of a CW 1 THz Gyrotron (Gyrotron Fu Cw III) Using a 20 T Superconducting Magnet

Design of a CW 1 THz gyrotron at second harmonic operation using a 20 T superconducting magnet has been described. The mode competition analysis is employed to investigate operation conditions of second harmonic mode, which is being excited at the frequency ranging from 920 GHz to 1014 GHz. The output power up to 250 watt corresponding to the efficiency of 4.16 percent could be achieved by using an electron beam with accelerating voltage 30 kV and current 200 mA. The important advantage of this gyrotron is that the single mode excitation at second harmonic, and extremely high frequency of the radiation, could be maintained even at high currents. It opens possibility to realize a high power radiation source at 1 THz. Such gyrotron is under construction at FIR Center, University of Fukui.     

Short wavelength (/spl lambda//spl sim/4.3 /spl mu/m) high-performance continuous-wave quantum-cascade lasers

We report continuous-wave (CW) operation of a 4.3-/spl mu/m quantum-cascade laser from 80 K to 313 K. For a high-reflectivity-coated 11-/spl mu/m-wide and 4-mm-long laser, CW output powers of 1.34 W at 80 K and 26 mW at 313 K are achieved. At 298 K, the CW threshold current density of 1.5 kA/cm/sup 2/ is observed with a CW output power of 166 mW and maximum wall-plug efficiency of 1.47%. The CW emission wavelength varies from 4.15 /spl mu/m at 80 K to 4.34 /spl mu/m at 298 K, corresponding to a temperature-tuning rate of 0.87 nm/K. The beam full-width at half-maximum values for the parallel and the perpendicular far-field patterns are 26/spl deg/ and 49/spl deg/ in CW mode, respectively.     

High-power and long-lifetime inGaN blue- violet laser diodes grown by molecular beam epitaxy

InGaN 405 nm multiple quantum well laser diodes grown by molecular beam epitaxy (MBE) with a continuous-wave (CW) lifetime of up to 42 h are reported. The CW threshold current density of the ridge waveguide laser diodes is 3.6 kA/cm² and the slope efficiency for uncoated facets is 0.42 W/A per facet with a maximum CW output power of 45 mW per facet. Statistical variation of CW lifetime with dissipated power is presented for MBE-grown laser diodes from five different wafers.     

Design of a Powerful and Compact THZ Oscillator

According to simulations, a Large Orbit Gyrotron with a 30 keV/1 A electron beam and magnetic field of 5 T can produce CW radiation with output power of 10²?10³ W at the frequencies of 0.4–0.5 THz.     

Single-lobe `Y? coupled laser diode arrays

`Y? Coupled laser arrays have been fabricated with flared waveguides at the output facet to expand the near-field spot and increase the near-field fill factor to greater than 80%. The far-field radiation pattern is predominantly single-lobe, and power outputs of 150mW CW have been obtained with threshold currents as low as 130mA.     

OC-48 capable InGaAsN vertical cavity lasers

A selectively oxidised InGaAsN/GaAs three quantum well vertical cavity laser (VCSEL) demonstrated continuous wave (CW) lasing with a single-mode output power of 0.749 mW at 1266 nm. This is the first reported InGaAsN VCSEL capable of meeting the power and wavelength requirements for both OC-48 SR and OC-48 IR-1 compliant links. The VCSEL uses two low absorption n-type GaAs/AlGaAs distributed Brag reflectors and a tunnel junction to achieve current injection into the active region. A multimode version of the VCSEL had a output power of 1.43 mW at 1.26 μm. CW lasing continued up to temperatures as high as 107°C. The VCSEL material was grown by solid source molecular beam epitaxy with an RF nitrogen plasma source     

高效高功率侧面抽运腔内倍频连续绿光激光器

激光二极管(LD)侧面抽运的内腔倍频激光器技术是实现高功率、高稳定且低成本连续绿光激光器的有效方法。为满足激光彩色显示、激光加工、数据存储、医疗卫生和科研等领域对连续绿光激光器的需求,研制了一台高效、高功率侧面抽运腔内倍频Nd∶YAG/KTP连续绿光激光器。采用优化的平-凹-平三镜折叠腔结构,Ⅱ类相位匹配KTP晶体内腔倍频,当808 nm激光二极管抽运功率约为180 W时,得到最高18.7 W的连续绿光激光输出,对应的光-光转换效率为10.4%。在输出功率15.4 W时测量激光功率稳定性,其功率不稳定度小于0.5%。输出光束平滑,远场为类高斯分布,用刀口法测量了激光器不同输出功率时的光束质量,光束传输因子M2小于7。     

CW laser action in atomic fluorine

We have obtained CW laser action on four transitions in the doublet system of atomic fluorine for the first time. All previously reported laser action was on a pulsed basis only. CW laser radiation was obtained when F2or AgF was used as a fluorine donor in an electron beam pumped helium plasma. A multiline output power of 200 mW was obtained.