Linear and Non-Linear Inserts for Genuinely Wideband Continuous Frequency Tunable Coaxial Gyrotron Cavities

We consider two continuous frequency tunable CW coaxial gyrotron oscillators, one 330 GHz with 3 GHz bandwidth and output power 50 – 400 W for scientific applications and one 30 GHz with 0.4 GHz bandwidth and output power 40 – 140 kW for industrial applications. The continuous tuning of both gyrotrons is achieved by moving the linearly tapered inner conductor in the axial direction in combination with the proper adjustment of the operating magnetic field. We consider also a non-linear tapering, which makes it possible to reduce the length of the insert and to improve efficiency of the device.     

Isotope shifts and accurate wavelengths in Ne II and Ne III

Transition isotope shifts of 3s–3p transitions in Ne II and Ne III are measured in Fourier transform spectra from a hollow-cathode source. Accurate absolute line-center positions of the ²⁰Ne isotope are derived for the purpose of tertiary wavelength standards in the region 2000–5000 ?. A robust statistical treatment is applied, yielding line-position uncertainties that are lower than for the Ar II secondary standards used as references. The influence of Stark shifts on both the new Ne II standards and the Ar II standards is also investigated. In addition, improved wavenumbers of the 3p–3d and 3p–4s transitions are presented, of which 12 in Ne II have been measured for the first time. Electronic supplementary material Supplementary Online Material     

欧姆损耗对太赫兹频段同轴表面波振荡器的影响

为了研究欧姆损耗对太赫兹波段真空电子器件工作特性的影响, 本文推导了2.5维全电磁粒子模拟软件UNIPIC的表面阻抗边界条件, 并采用软件对不同金属材料慢波结构的同轴结构表面波振荡器进行了数值模拟研究, 分析了不同金属材料慢波结构器件的输出功率与电导率的关系, 模拟结果表明: 金属电导率对器件的输出功率有非常大的影响, 对于0.14 THz 同轴表面波振荡器, 铜材料和不锈钢材料慢波结构器件的输出功率分别下降13.4%和63.9%, 起振时间分别延迟0.4 ns 和15 ns.     

Smooth wideband tuning of the operating frequency of a gyrotron

We present the calculation results for the bandwidth of smooth mechanical tuning of the generation frequency in a gyrotron with a coaxial cavity. The tuning is based on moving a cone-shaped coaxial rod along the device axis to vary the eigenfrequencies of the cavity. The use of an internal conductor with an impedance surface allows reducing the thermal load on it. The calculation results show that it is possible to tune the operating frequency of the oscillator by 3–4% at frequencies up to 330 GHz for an output power of about 10 kW in the continuous-wave operation regime. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 1, pp. 63–70, January 2008.     

Table-top KrF amplifier delivering 270 fs output pulses with over 9 W average power at 300 Hz

Applying the combination of a solid-state Ti:Sa laser system and a newly developed wide-aperture, discharge-pumped KrF amplifier, output pulses with over 9 W average power at 300 Hz have been achieved in a single output beam. The frequency-tripled seed pulses of the Ti:Sa system – delivering approximately 10 μJ energy at 248 nm – were amplified to over 30 mJ using a 3-pass off-axis amplification scheme. The optical set-up has been fitted to the amplifier’s parameters, and stored-energy measurements were carried out with different parameters in order to optimize the operational conditions of the device for the highest average power. Received: 10 June 2002 / Published online: 25 September 2002 RID="*" ID="*"Corresponding author. Fax: +49-551/503-599, E-mail: jbekesi@llg.gwdg.de     

Multiwatt optically pumped ammonia laser operation in the 12–13 μm

Design and operating caracteristics of high pulse repetition rate NH₃ laser producing up to 20 W of average output power are described. The NH₃ laser, operating in the 12–13 μm region was optically pumped with a high pulse repetition rate TEA CO₂ laser. Dependences of the NH₃ laser output on the pump energy, ammonia and buffer gas pressures and pulse repetition rate have been studied. The conversion efficiency of up to 16% has been received.     

Development of a 16 kHz repetition rate, 110 W average power copper HyBrID laser

This paper presents the design and performance analysis of an indigenously developed 110 W average output power copper HyBrID laser operating at 16 kHz pulse repetition rate. The laser active medium was confined within a fused silica tube of ∼6 cm diameter and ∼200 cm active length. An in-house developed high-power (∼10 kW) solidstate pulser was used as the electrical excitation source. A simple estimation of deposited electrical power, at the laser head, was carried out and based on it, the laser tube efficiency was found to be 2.9% at 70 W and 2.2% at 110 W laser power levels.     

Experimental studies of a gyroklystron operating in the field of a permanent magnet

We have developed and tested a gyroklystron operating with the second harmonic of the electron cyclotron frequency at a frequency of 32.3 GHz in the field of a permanent magnet. In the two-and three-cavity versions of the gyroklystron, the peak power of the output radiation reached 320 kW with an efficiency of 30%, an amplification coefficient of 20–25 dB, and an operating frequency bandwidth of 0.05%. In the wide-band version of the gyroklystron, the amplification bandwidth was equal to 0.27% for an output power of 200 kW and an amplification coefficient of 13 dB.     

Influence of the iodine vapor pressure on the output characteristics of a UV low-pressure gas-discharge lamp

The influence of the iodine vapor pressure on the output characteristics of a UV lamp pumped by a longitudinal glow discharge is studied. The lamp is filled with a helium-iodine mixture to a pressure of 100–1500 Pa. In the spectral range 320–360 nm, the I₂(D′ → A′) band with a peak at 342 nm prevails, while in the bactericidal range, iodine atomic lines at 183.0 and 206.2 nm dominate. The power of the UV lamp is optimized according to the iodine vapor pressure and working mixture composition by numerical simulation.     

High-power mid-infrared tunable optical parametric oscillator based on 3-mm-thick PPMgCLN

The experimental results of a high-power tunable mid-IR laser are presented. The optical parametric oscillator (OPO) with a 3-mm-thick PPMgCLN crystal was pumped by a 1.064 μm pulse laser. When the pump power of the 1.064 μm laser was 151 W at 10 kHz, and the operating temperature of the PPMgCLN with 5% MgO doping was 100°C, average output power of 23.7 W at 3.91 μm was obtained with a slope efficiency of 18.2% for the idler resonant OPO. The variation of the 3.91 μm output power was about ±4% in 10 min continuous operation. The beam quality factor M ² was less than 2.6. The average output power of 27.4 W at 3.91 μm was also obtained with 151 W pump power and the slope efficiency of 20.9% for the signal resonant OPO by changing the coating parameters of the OPO cavity mirrors. The mid-IR wavelength tunability of 3.7–4.0 μm can be achieved by adjusting the temperature of a 29 μm period PPMgCLN crystal from 200 to 30°C.     

Energy harvesting using multilayer structure based on 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystal

In this paper we fabricated the multilayer structure used as the resonance-based vibration energy-harvesting device based on 0.71Pb(Mg_1/3Nb_2/3)O₃–0.29PbTiO₃ single crystal. The performances of the device including the output voltage and power were studied systematically. Under a cyclic force of 4 N (peak value), a high output power of 4.94 mW and a corresponding peak voltage of 3.14 V were measured at 1.4 kHz with a matching load resistance of 1.0 kΩ. The results demonstrate the potential of the device in energy-harvesting applied to low-power portable electronics and wireless sensors.     

Extracting microwave energy from a cavity by mode conversion at a coupling window

A study is made of the production of high power nanosecond rf pulses by extracting microwave energy from an oversized cavity by means of conversion, at a coupling window, of the high-Q working mode to an auxiliary mode which is strongly coupled to an external load. It is shown that microwave rf pulse compressors with copper storage cavities and energy extraction by mode conversion at a coupling window can provide gains of 5–13 dB with output signal durations of 20–150 ns and peak powers of 5–10 MW in the 3-cm band and 50–100 MW in the 10-cm band. Rf pulses lasting 30 ns with peak powers of 0.5 MW have been obtained experimentally at a frequency of 9.4 GHz with a gain of 9 dB. Zh. Tekh. Fiz. 68, 92–96 (July 1998)     

Short-wavelength emission characteristics of a longitudinal bromine vapor glow discharge in a quartz tube

The output emission characteristics are presented in the spectral range 150–350 nm for a longitudinal bromine vapor glow discharge in a quartz tube (inner diameter 1.4 cm, interelectrode distance 10 cm). Pressure of the working mixtures: P = 0.2–1.0 kPa. The emission spectrum of the lamp based on an He-Br₂ mixture consists of the 163.3 nm and 157.6 nm spectral lines of the bromine atom and a system of molecular bromine bands (170–300 nm). The total power of UV-VUV emission of the lamp based on an He-Br₂ mixture is 5 W max for efficiency <10%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 816–819, November–December, 2007.     

Waveguide bridge as an element for energy extraction from a resonant microwave compressor

We present the results of theoretical analysis of the operation of a waveguide bridge as a device for microwave-energy extraction and the data of experimental studies of 3-cm compressors with energy extraction through the bridge. We determine conditions under which the bridge can be used as an efficient output device capable of doubling the output pulsed power of the compressor. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 3, pp. 216–222, March 2008.     

放电激励重复频率非链式HF激光器

 利用紫外预电离横向放电和气体循环结构建立了一套放电激励重复频率HF激光装置。研究了激光器工作介质SF6/C2H6混合气体放电特性和激光输出特性,获得激光器单次运行的最佳输出参数;通过对激光器重复频率运行时不同气体流速、充电电压与气体总压条件下的放电状态和输出能量的比较,分析了激光器重复频率稳定运行的必要条件。结果表明：所研制的激光器最大单脉冲能量0.6 J,峰值功率3 MW,电光转换效率2.4%;当混合气体工作介质以3.5 m/s的流速循环时,激光器稳定运行的最高工作频率可达50 Hz,脉冲输出能量稳定在0.26 J,平均功率达到13 W。     

AlGaInP visible quantum well lasers for information technology

650 nm-range AlGaInP multi-quantum well (MQW) laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) have been studied and the results are presented in this paper. Threshold current density of broad area contact laser diodes can be as low as 350 A/cm². Laser diodes with buried-ridge strip waveguide structures were made, threshold currents and differential efficiencies are (22–40) mA and (0.2–0.7) mW/mA, respectively. Typical output power for the laser diodes is 5 mW, maximum output power of 15 mW has been obtained. Their operation temperature can be up to 90°C under power of 5 mW. After operating under 90°C and 5 mW for 72 hrs, the average increments for the threshold currents of the lasers at 25°C and the operation currents at 5 mW (at 25°C) are (2–3) mA and (3–5) mA, respectively. Reliability tests showed that no obvious degradation was observed after 1400 hours of CW operation under 50°C and 2.5 mW. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998.     

An all-diode-laser-based, dual-cavity AgGaS2 cw difference-frequency source for the 9–11 μm range

2 ) nonlinear crystal is reported. The device uses a standing-wave dual-resonator scheme to enhance both near-infrared lasers. For 7 mW of 778.2-nm and 275 mW of 842.5-nm input powers, 40 nW of 10.2-μm radiation is generated by a preliminary setup. A μW-level range output power is expected after optimization of the device optical components. This compact tunable source will allow Fabry–Pérot high-resolution Doppler-free spectroscopy of spherical molecules, such as OsO₄ or SF₆, in the 9–11 μm range as an alternative source to frequency-stabilized CO₂ lasers. Received: 17 March 1998     

Mercury-free emitter pumped by a krypton fluoride molecule pulse-periodic barrier discharge

The characteristics of a pulsed-periodic short-barrier-discharge emitter operating at wavelength λ = 248 nm KrF(X-B) are investigated. The operating mixtures of the UV lamp are low-aggressive krypton-sulfur hexafluoride (SF6) mixtures at a total pressure in the range 1–50 kPa and a SF₆ partial pressure of 0.1–0.4 kPa. The spectral characteristics of the plasma are studied, and the 248 nm KrF(X-B) band luminosity is optimized in terms of the operating mixture composition, pump voltage, and pulse repetition rate. The mean power of UV emission from the lateral surface of the cylindrical lamp is estimated.     

Running solid oxide fuel cells on biogas

The feasibility of operating a solid oxide fuel cell on biogas has been studied over a wide compositional range of biogas, using a small tubular solid oxide fuel cell system operating at 850 °C. In addition the response of the SOFC towards waste ammonia has been studied. It is possible to run the SOFC on biogas, even at remarkably low levels of methane, at which conventional heat engines would not work, thus offering a valuable and environmentally friendly use for poor-quality biogas that is currently wasted by detrimental venting to the atmosphere. The power output varies with methane content of the biogas, with maximum power production occurring at 45% methane, corresponding to maximal production of H₂ and CO through internal dry reforming. Direct electrocatalytic oxidation of methane does not contribute to the power output of the cell. For biogas with higher methane contents methane decomposition becomes significant, leading to increased H₂ production, and hence transiently higher power production, and deleterious carbon deposition and thus eventual cell deactivation. SOFCs are tolerant to ammonia, actually utilising the ammonia present in biogas to produce electrical power, at the same time acting as an environmental clean-up device breaking down the ammonia pollutant to N₂ and water, with no formation of any undesirable nitrogen oxides. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

CO<Subscript>2</Subscript> laser oscillating in the range of 16 μm

The ability of a CO₂ laser to oscillate in the range of 16 (14) μm at room temperature was investigated experimentally and theoretically. The output energy per pulse was ~60 mJ at peak power of ~50 kW. It was necessary to minimize not only harmful losses but also useful ones in both channels 00⁰1–02⁰0 and 02⁰0–0110 and to increase the input energy, i.e., the density of free electrons in the discharge, in order to increase the peak power and energy of 16-μm radiation. The highest values of peak power and energy of radiation were reached at different pressures of the active mixture. The rotational bottleneck effect limiting the peak power and energy of oscillation was important at rather low pressures of the active medium. Oscillation at the R12 line is more preferable than that at the P12 line for use as 9.6-μm dumping radiation.