High repetition rate CH4 laser

A 16-m CF₄ laser oscillator has operated at 1 kHz in a cooled static cell. Pump energies required from the low pressure, Q-switched, cw discharge CO₂ laser were as low as 60 J. The laser cavity employed a multiple-pass off-axis path resonator in a ring configuration. CF₄ laser power at 615 cm^–1 and a 1-kHz repetition rate exceeded 300 W.     

An Approach to Linear Scalable DH-PHEMT Model for Millimeterwave Application

This paper describes a scalable small-signal equivalent circuit for 0.25 m gatelength Double Heterojunction delta-doped PHEMTs. The scaling rules for all elements except the pad capacitances and bondwire inductances have been determined. Good agreement is obtained between simulation results and measured results for 2 times 20 m , 2 times 40 m, 2 times 60 m, 2 times 100 m gate width (number of gate fingers times unit gate width) DH PHEMT.     

Efficient vertical-cavity lasers

Recent experimental and theoretical results from strained InGaAs/GaAs quantum-well vertical-cavity surface-emitting lasers indicate that relatively high-power, efficient devices are possible. On 10 m square devices cw output powers of more than 3mW at room temperature and 0.4 mW at 100°C are observed. Broad-area, 100 m diameter devices gave pulsed outputs of over 0.5 W and 60 m diameter devices provided more than 12 mW cw. The device parameters have been modelled and found to be consistent with theoretical predictions. The results generally indicate that considerable device improvements are still possible by reducing internal losses, series resistance and voltage and improving heat sinking. With current internal loss levels 30 cm^–1, three InGaAs quantum-wells have been found to be optimum.     

Efficient multiple-longitudinally diode laser pumped Nd:YAG slab laser

The operation of an eightfold longitudinally diode laser pumped 1.06m cw Nd:YAG slab laser is demonstrated. The 809 nm diode radiation is focused through a dichroic coating into each laser channel starting from the reflection points of the 1.06m beam in the slab crystal. At an absorbed pump power in the crystal of 2830 mW a maximum cw TEM₀₀ output of 1075 mW was achieved with a corresponding slope efficiency of 42.5%.     

Towards slow μ− production via muon catalyzed fusion

Slow ^– production via dd-CF using a two-layer arrangement is investigated. To determine its feasibility, experimental measurements are now in progress using the muonic X-ray detection method. The following experimental steps are being considered: (1) measurement of the number of ^– stopped inside a solid H₂/D₂ layer by detecting p K X-rays, (2) hot d emission detection by placing a secondary target at a distance of 10–30 mm from the layer and by detecting specific delayed X-rays, (3) measurement of the disappearance of d emission as the added D₂ layer is increased, (4) dd-CF measurement by detecting fusion protons, and (5) slow ^– emission detection. Results of the initial test experiment are presented.     

Continuity of type-I intermittency from a measure-theoretical point of view

We study a simple dynamical system which displays a so-called type-I intermittency bifurcation. We determine the Bowen-Ruelle measure and prove that the expectation (g) of any continuous functiong and the Kolmogoroff-Sinai entropyh() are continuous functions of the bifurcation parameter. Therefore the transition is continuous from a measure-theoretical point of view. Those results could be generalized to any similar dynamical system.     

Direction heterolasers based on GaInPAs/InP

Results are presented of investigations of the isoperiodic system GaInPAs/InP and of heterolasers on its basis. Schemes are presented for interpolation of the basic band parameters and of the refractive index of the GaInPAs solid solution, which is isoperiodic with InP. Optimal methods of growing heterostructures based on the solid solution GaInPAs by the method of heterophase epitaxy are determined. The temperature dependence of the threshold current in heterolasers based on the system GaInPAs/InP is investigated in the wavelength range 1–1.7 m. The emitting properties of lasers on this basis are studied. A new type of planar laser is developed, namely a buried mesa-planar laser GaInPaAs/InP heterostructure grown on a p-type substrate and emitting at a wavelength 1.3 m. These lasers are characterized by a low level of threshold current at room temperature (down to 30 mA for the better samples), and linearity of the current-voltage characteristics and of the single-mode lasing regime, when working in the cw mode, is preserved up to appreciable excess above the threshold current.Translated from Trudy Ordena Lenina Fizicheskogo Institute im. P. N. Lebedeva, Vol. 141, pp. 18–45, 1983.     

Far infrared laser frequencies of CH3OD and N2H4

The frequencies of 26 laser lines with wavelengths between 57 and 534 m have been measured in the optically pumped laser gases CH₃OD and N₂H₄. A pair of stabilized cw 12_{CO 2} lasers was used as a frequency standard for the heterodyne frequency measurements. Seven of the 26 lines are new.     

Feasibility of an experiment to determine the branching ratio for the emission of a heavy neutrino after muon capture in3He

The triton energy of the muon capture reaction ³He t+v, where ³ He is the ground state of muonic³He, has been measured in order to investigate a possible heavy v admixture into the flavour with high sensitivity. ³ He has been formed via the pd fusion reaction by stopping ^– in an ionization chamber (IC) filled with an H/D gas mixture of 3% D concentration at a pressure of 161 bar. In a first short experiment 650 triton events were observed yielding an upper limit for the -heavy v mixing strength of 2.3×10^–3 atE _0v=60 MeV.     

Analysis of the effects of doping and barrier design on the small-signal modulation characteristics of long-wavelength multiple quantum well lasers

This theoretical work has modelled the small signal response of InGaAsP and InGaAlAs multiple quantum well (MQW) lasers based on an ambipolar carrier transport model. The MQW parameters such as barrier bandgap, barrier width and the number of quantum wells have been optimized for high-speed modulation. The effect of the p-type doping and the strain of the InGaAs well have also been investigated.For the InGaAsP-based system, the optimization for maximum 3 dB bandwitdth shows that the optimum width is about 5 nm for 1.1 m barriers and 7 nm for 1.2 m barriers. The optimum barrier bandgap wavelength is about 1.1 m for the barrier width of 6 nm, about 1.15 m for 8 nm and 10 nm barriers. The p-doped MQW exhibits a higher modulation bandwidth because of its high differential gain and improved carrier distribution among the MQWs. The compressively strained InGaAs quantum well system has the potential for a higher modulation bandwidth. For the InGaAlAs-based system, the optimization for maximum 3 dB bandwidth shows that the optimum width is about 4 nm for a barrier wavelength of 1.10 m, and 6 nm for 1.2 m. The optimum barrier bandgap wavelength is about 1.1 m for a barrier width of 4 nm, and about 1.2 m for 6, 8 and 10 nm.     

FIR gain measurements in cw laser pumped CH3OD

Direct measurements of small signal and saturated gain in cw laser pumped CH₃OD are reported for three lasing transitions of 57 m, 82 m and 103 m. The 57 m transition has a measured gain of 0.6/m, the strongest gain in methanol reported so far. Moreover small gain saturation of this line makes it to be one of the strongest known cw FIR laser lines.     

Search for right-handed currents in muon decay

We report new limits on right-handed currents, based on precise measurements of the endpoint of the e⁺ spectrum from ⁺ decay. Highly polarized ⁺ from the TRIUMF surface beam were stopped in pure metal foils within either an 1.1-T spin-holding logitudinal field, or a 70-gauss spin-precessing transverse field. Decay e⁺ emitted within 200 mrad of the beam direction were momentum-analyzed to ±0.2%. For the spin-held data, decay via (V-A) currents requires the e⁺ rate to approach zero in the beam direction at the endpoint. Measurement of this rate sets the 90%-confidence limits P />0.9959 and M(W_R)>380 GeV, where W_R is the possible right-handed gauge boson. For the spin-precessed data we independently determine a 90% confidence limit P />0.9918.We are indebted to the entire TRIUMF management and staff for their splendid support of this experiment. In its early stages we benefited from discussion with J. Brewer, R. Cahn, K. Crowe, and W. Wenzel. Rapid commissioning of the polarimeter was made possible by the superb efforts of the LBL support staff. This research was supported in part by the U.S. Department of Energy, Division of Basic Energy Sciences, Office of Energy Research under contracts W-7405-ENG-48 and AC02-ER02289.     

Actively mode-locked 1.3 and 1.55 μm InGaAsP diode lasers

Active mode-locking of uncoated InGaAsP diode lasers having an external diffraction grating cavity was investigated experimentally. A high frequency r.f. signal and short-duration electrical pulses were used to drive the lasers. The pulse duration was measured by an ultrafast streak camera. Pulses as short as 13 ps at 1.3m and 29 ps at 1.55m were generated at a repetition rate of 1 GHz. The reason for obtaining broader pulses from the 1.55m laser which had the same structure as the 1.3m diode laser is explained.Formerly with GEC Hirst Research Centre, Wembley, Middlesex, UK.     

Electrical resistivity and thermoelectric power of amorphous niobium-nickel alloys synthetized by vapour quenching

Thin film samples (10–20 thick) of niobium-nickel alloys in the composition range Nb-5 to 95 at % Ni were vapour quenched by R. F. sputtering onto fused quartz substrates held at a temperature of 450 K. It was found that fully glassy alloys were synthetized in the composition range Nb-30 to 85 at % Ni, 2·5 times larger than reported for splat-quenched alloys. Crystallization temperatures exhibited maxima near the eutectic composition and are comparable to those of splat-quenched materials. At room temperature, the electrical resistivity of these alloys lies between 176–210 cm, and the absolute thermoelectric power S between 2·20–2·52 V/K. On increasing the temperature from 4·2 to 775 K, up to which the amorphous alloys are stable, the resistivity of the alloy with=0·50 decreases by about 1·5%; the value of d/dT progressively increases with increasing Ni content, becoming positive at 0·50dS/dT of all alloys lies between 6–8·5×10^–3V deg^–2. The electrical behaviour of these alloys may be treated in terms of electron scattering in disordered structures assuming the nearly free-electron model, in a manner analogous to Ziman's theory of electronic transport in liquid metals.     

Recent developments in photonic devices for telecommunication applications in Taiwan

We report recent activities and achievements on the development of photonic devices for telecommunication applications. Opto-electronic devices such as high performance 1.55 m complex-coupled InGaAsP-InP distributed feedback (DFB) and 1.3 m uncooled AllnGaAs-InP lasers, the InGaAs-InP p-i-n photodetector on semi-insulating substrate, the 0.98 m InGaAs-GaAs-InGaP pumping laser, and 12-channel laser and detector arrays, are presented. Work on the development of in-house vertical integration for the fabrication of a 1.55 m single frequency transmitter, a 1.3 m multimode transmitter and receiver, and an Er-doped fibre amplifier, and their applications in system trials in the Taiwan National Information Infrastructure network, is described.     

A hollow cathode bismuth ion laser

cw laser oscillations of Bi II at 680.9, 660.0, and 571.9 nm have been achieved for the first time by using a bismuth hollow cathode discharge. In addition, laser oscillations of Bi I at 1.1711 m in the afterglow were observed. The ionic laser lines are excited by Penning ionization. The atomic line is produced by recombination of the bismuth ions and lowenergy electrons in the afterglow.     

Further investigations on ir pumping of CH3OD and CD3OD by a cw CO2 laser

Respectively, 41 and 36 new cw far-infrared lasing lines have been observed using a waveguide resonator in CH₃OD and CD₃OD pumped by a low-pressure CO₂ laser emitting in the 9.4, 10.4 m regular bands and in the 10.8 m hot band. The wavelength range was 46.6 m–1.67 mm in CH₃OD and 53.6 m–1 mm in CD₃OD.     

Frequency measurements of far infrared cw lasing lines in optically pumped CHCl2F

The wavelengths, frequencies, and relative polarizations of 15 FIR cw lasing lines obtained by optically pumping CHCl₂F with a cw CO₂ laser have been measured. The lines are in the wavelength range from 340.3 to 905.4 m and were pumped by P- and R-branch laser lines in the 9 m band of CO₂.Supported in part by a joint grant with the U. S. National Science Foundation grant # INT80-19014 and the Brazilian Consellio Nacional de Pesquisas (CNPq)Contribution of the U. S. Government, not subject to copyright.     

Frequencies and wavelengths from a new, efficient FIR lasing gas: CD2F2

We report for the first time wavelength, relative polarization, and frequency measurements for 47 new cw FIR laser lines in the wavelength region from 120 to 1714 m, all obtained by optically pumping CD₂F₂ with a CO₂ laser. Relative output powers were also measured. For comparison, the 189.8 m line pumped by R_I(34) is nearly five times as efficient as the 118.8 m methyl alcohol line.Contribution of the U.S. Government, not subject to copyright.