Search Results - (Author, Cooperation:J. J. Rocca)

2012-01-28

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0028-0836

1476-4687

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1089-7674

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Physics

Starting with the discovery of x-ray lasers in 1984, laser-created plasmas remained for almost a decade, the only medium in which large amplification of soft-x-ray radiation could be obtained. In this paper the recent first demonstration of large soft-x-ray amplification in a discharge-created plasma column, realized utilizing a fast capillary discharge to collisionally excite the 46.9 nm transition of Ne-like, Ar is reviewed. Results of the parametrization of the Ar IX discharge-pumped amplifier, the study of the dynamics of its plasma column, and the measurement of the time history of the laser pulse are reported. Prospects for laser operation at shorter wavelengths are also discussed. © 1995 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Synchronized trains of 5 ps pulses at two wavelengths were generated in a single-cavity synchronously pumped dye laser containing a mixture of two dyes in a single jet and intracavity spatial masking for frequency selection. The utilization of this dual wavelength dye laser to monitor the relaxation of photoexcited carriers in multiple quantum wells was demonstrated.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The absorption recovery of a photoexcited InGaP epitaxial film 0.4 μm thick was investigated using the pump-probe laser technique and found to have a time constant of 55 ps at room temperature. Measurements done in the temperature range of 300–50 K show the decay of the photoexcited carrier distribution to be dominated by ambipolar diffusion and surface recombination. The measured absorption recovery time constant corresponds to an ambipolar diffusion coefficient D(approximately-greater-than)2.8 cm2/s and a surface recombination velocity of S(approximately-greater-than)4×105 cm/s at room temperature.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report measurements of the transient multimode dynamics of vertical cavity surface emitting lasers excited by short (100–200 ps rise times, 1 ns duration) electrical pulses. Fast changes on the spatial distribution of the output power and strong mode competition are observed. Numerical simulations show that the observed dynamics are due to the partial overlap of the different transverse modes through spatial hole burning. © 1996 American Institute of Physics.

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1077-3118

AIP Digital Archive

Physics

The secondary electron emission coefficient of materials for helium ion bombardment in the energy range 0.5–20 keV was measured for the surface conditions of cathodes in high voltage glow discharges. The materials studied are oxidized aluminum, oxidized magnesium, a molybdenum-aluminum oxide sintered composite, molybdenum, stainless steel, copper, gold, and graphite. Each sample was surface conditioned by operating it as cathode of a helium glow discharge shortly before the electron yield measurement. The results are relevant to the modeling of glow discharges and the design of cold cathode electron guns.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have demonstrated that intense pulsed electron beams can be created by multiplication of lower current electron streams impinging on a high electron yield target. A 17 A electron beam of 1 μs pulse width was generated from a 2.5 A beam bombarding an activated Ag-Mg target 2.5 cm in diameter.

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1077-3118

AIP Digital Archive

Physics

We have measured the electric field distribution in the cathode sheath of an electron beam He glow discharge. Laser saturation spectroscopy was used to determine the quadratic Stark shift produced by the electric field. The experimental results are in good agreement with the calculations of a collisional model of the cathode sheath.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A model of cw argon ion lasers excited by low-energy (50–200 eV) direct current electron beams at current densities between 1 and 50 A/cm2 has been developed. The electron energy distribution in the electron-beam-created plasma is calculated by numerically solving the Boltzmann equation for electrons. Optical gains, powers, and laser efficiences were computed for the 4765-, 4880-, 4965-, and 4658-A(ring) Ar ii transitions for a wide range of discharge conditions. Laser efficiencies comparable to those of a conventional Ar ii laser (∼3×10−4) are predicted for these laser transitions when electron beam excitation is used.

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1089-7550

AIP Digital Archive

Physics

We have measured the electron yields of 7 glow-discharge cathode materials under bombardment by neon and argon ions with energies between 1 and 20 keV. The surfaces of the samples were conditioned by operating the materials as cold cathodes in a high-voltage glow discharge before the electron yield measurement. The materials studied are oxidized magnesium, oxidized aluminum, a molybdenum-aluminum oxide sintered composite, molybdenum, stainless steel, copper, and graphite. The dependence of electron yield on ion velocity was found to be approximately linear for all materials and gases, with the slopes being strongly material dependent. The corresponding glow-discharge current intensities were observed to have a supralinear dependence on the electron yield. The results are relevant to the design and modeling of cold cathode high-voltage glow discharges.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Anisotropic etching of SiO2 has been achieved with a plasma generated by a broad-area low-energy (150–300 eV) electron beam in a He+CF4 atmosphere. Etch rates of up to 330 A(ring)/min for SiO2 and 220 A(ring)/min for Si were obtained. Etching occurred with good uniformity over the entire area exposed to the electron-beam-generated plasma. The fluxes of energetic charged particles to the sample surface are discussed in relation to their possible contribution to the etching process.

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1089-7550

AIP Digital Archive

Physics

We have generated beams with electron current densities of more than 10 mA/cm2 at energies between 150 and 900 eV using a plasma source. This electron source can be operated at background pressures between 0.01 and 0.1 Torr in helium and with the addition of various gases, producing electron beams up to 3.8 cm in diameter. The broad area beam can be used to induce gas phase and surface reactions and has been successfully used to achieve anisotropic etching of SiO2 films in the reactant gas CF4.

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1089-7550

AIP Digital Archive

Physics

The electron temperature in an expanding spark plasma used as active medium in a cadmium-recombination laser was measured using the relative intensities of helium lines originated from levels in local thermodynamic equilibrium. Measurements resolved in space and time show that the electron temperature at the conditions of maximum gain are 1000 and 600 K at 5 and 10 mm of the sparks, respectively. Rapid cooling occurs after the termination of the discharge-current pulse, and the electron temperature reaches values below 1000 K. Subsequently, the electron temperature decrease is slow. The optical gain calculated for the 1.43-μm Cd (I)-recombination-laser transition using the measured electron temperature and particle density values is 3×10−3 cm−1, in good agreement with measurements.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

This article reviews the progress in the development of practical table-top sources of soft x-ray laser radiation. The field is rapidly approaching the stage at which soft x-ray lasers sufficiently compact to fit onto a normal optical table will be routinely utilized in science and technology. This is the result of recent advances in the amplification of soft x-ray radiation in both compact laser-pumped and discharge-pumped devices. The use of excitation mechanisms that take full advantage of new ultrafast high power optical laser drivers and multiple pulse excitation schemes has resulted in the demonstration of saturated soft x-ray amplification at wavelengths as short as 14 nm using several Joule of laser-pump energy. Moreover, several schemes have demonstrated significant gain with only a fraction of a Joule of laser-pump energy. In addition, the demonstration of saturated table-top soft x-ray lasers pumped by very compact capillary discharges has shattered the notion that discharge-created plasmas are insufficiently uniform to allow for soft x-ray amplification, opening a route for the development of efficient, high average power soft x-ray lasers. Recently, a table-top capillary discharge laser operating at 46.9 nm has produced millijoule-level laser pulses at a repetition rate of several Hz, with a corresponding spatially coherent average power per unit bandwidth comparable to that of a beam line at a third generation synchrotron facility. This review summarizes fundamental and technical aspects of table-top soft x-ray lasers based on the generation of population inversions in plasmas, and discusses the present status of development of specific laser systems. © 1999 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We describe the use of a simple spherical aluminum-coated mirror to image the radiation of a distant XUV-emitting plasma in the slit of a vacuum spectrograph. Calculations to determine the optimum position and curvature radius of the mirror as a function of the divergence of the emitted plasma radiation are described. Efficient light collection by the grazing incidence mirror allows calibration of an intensified diode array used as a detector with a low-pressure (10−4 Torr) dc capillary discharge that does not require a complex differential pumping system.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A cold plasma switch scheme with opening and closing capabilities is reported. An externally applied magnetic field causes a low pressure hollow cathode discharge to transition from a low impedance mode sustained by oscillating beam electrons into a virtually collisionless high impedance mode. The impedance of a 10 A discharge was demonstrated to increase by 20 with the application of a field of 0.018 T.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the observation of ultrahigh frequency oscillations of up to 240 GHz in optically gain switched vertical cavity surface emitting lasers. These oscillations are shown to be produced by multimode emission through mode competition (10–30 GHz) or mode beating (above 100 GHz). Although these oscillations are not related to the intrinsic modulation bandwidth, some of them could be mistaken for relaxation oscillations, calling for careful interpretation of the results of this type of experiments. The highest frequencies observed for single mode relaxation oscillations were about 9 GHz in agreement with values of modulation bandwidth reported in the literature. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Nonresonant tunneling rates have been measured in InGaP/InAlP asymmetric double quantum-well structures for which optical phonon assisted tunneling is energetically forbidden. For an initial photoexcited carrier density of 2.4×1011 cm−2, tunneling times of 220, 60, and less than 9 ps have been measured in samples with barrier thickness 4.5, 3.0, and 1.5 nm, respectively. The tunneling times were found to be strongly dependent on carrier density. The measured tunneling times and their dependence on carrier density are compatible with impurity scattering being the dominant mechanism assisting the tunneling.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Polarization switching in gain-guided, vertical-cavity, surface-emitting lasers was studied as a function of the active region temperature. We show that polarization switching occurs even when the active region temperature is kept constant during fast pulse low duty cycle operation. This temperature independent polarization switching phenomenon is explained in terms of a recently developed model. © 1997 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Indirect Γ-L scattering within the well, and real space carrier transfer to the barrier X1c states are shown to significantly affect the carrier dynamics in In0.48Ga0.52P/In0.5Al0.5P multiple quantum wells. When carriers transfer to the indirect states occurs, the carrier dynamics is modified by the slow return of the carriers from the low mobility states to the well. As a result, the absorption recovery time increases by almost an order of magnitude. Carrier transfer to the indirect states also increases the carrier lifetime to values characteristic of indirect recombination. © 1997 American Institute of Physics.

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