摘要:

Amplification by stimulated emission has been observed from an optically pumped nickel vapor on the transitions at 347 and 381 nm. Nickel vapor was produced by direct laser vaporization, and the nickel atoms were optically pumped by a N2laser at 337 nm. The amplification factor at 347 nm reaches a maximum after the amplification factor at 381 nm reaches a maximum. The maximum amplification factors are 1.62 and 1.69, respectively.

ISSN:0003-6951    

DOI:10.1063/1.104065

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Magnesium fluoride coatings ∼170 A˚ thick have been evaporated onto mirror‐quality Be substrates in ultrahigh vacuum and subsequently subjected to 250 keV &agr; particle irradiation at room temperature. Analysis of the irradiated area by medium energy backscattering spectrometry revealed that the irradiation selectively removed fluorine with an initial yield of 2.2 fluorine atoms per incident &agr; particle. A visible degradation in reflectivity, which became progressively more extensive with increasing dose, was observed after an &agr; particle fluence of 1016cm−2. After a total irradiation of 4×1017cm−2less than 20% of the fluorine in the film remained, effectively reducing it to metallic magnesium. The effect of this change on the reflectivity of the surface was catastrophic.

ISSN:0003-6951    

DOI:10.1063/1.104141

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Solitons of different wavelengths are found to exhibit substantial spectral and temporal changes when collisions are centered in erbium‐doped fiber amplifiers. By using two soliton pulse trains, with ∼70‐ps‐wide pulses, spectrally separated by 1.8 A˚, and 106 km of non‐dispersion‐shifted fiber, we observe a spectral and temporal shift of as much as 0.35 A˚ and 55 ps, respectively, for each soliton. Both soliton wavelengths shift the same amount, but in opposite directions and remain undisturbed in terms of shape and amplitude after the collision. This shift may impose limitations on multiple wavelength soliton based communication systems utilizing fiber amplifiers.

ISSN:0003-6951    

DOI:10.1063/1.104044

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Using the refractive index modulation in liquid crystals by an externally applied electric field, we show that common nematic liquid crystals can be used in a Fabry–Perot e´talon to produce an electrically tunable optical filter for use in the infrared region. Using commercial liquid crystals we demonstrate that the wavelength can be tuned over 175 nm using less than 10 V. In our first device the free‐spectral range of the e´talon is about 75 nm with a passband of about 1–2 nm which is determined by the quality of the mirrors that we have used.

ISSN:0003-6951    

DOI:10.1063/1.104045

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The vertical‐cavity surface‐emitting single quantum well laser is examined in terms of the short Fabry–Perot cavity’s effect on optical gain. It is suggested that for this vertical‐ cavity structure the optical gain mechanism is fundamentally altered as compared to the case of the more standard edge‐emitting device with longer cavity lengths. The short cavity and highly reflecting mirrors of the vertical cavity structure lead to an enhanced gain coefficient at fixed carrier densities, due to enhanced spontaneous emission into the Fabry–Perot modes of the optical cavity, and the resultantly reduced spontaneous linewidth.

ISSN:0003-6951    

DOI:10.1063/1.104046

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An optical flip‐flop with two nonlinear e´talons as inverter gates was investigated. The results show that the device works well for a large coupling constant, large detuning (which lead to a high contrast and stable operation), and short feedback delay. Based on calculated results, an optical flip‐flop was constructed by coupling two optical triode switches using a nonlinear e´talon and gradient‐index lenses, and successful operation was demonstrated.

ISSN:0003-6951    

DOI:10.1063/1.104047

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Two new laser transitions are reported for the Er3+ion in YLiF4: in the blue at 469.7 nm and in the green at 560.6 nm. These are pumped with red and near‐infrared laser radiation using nonlinear excitation processes in which more than one upconversion step occurs, yet the threshold pump powers are as low as 10 mW. Single longitudinal mode cw operation was observed at temperatures below 40 K. This is the first report of a blue laser using the Er3+ion, and the first report of an infrared‐pumped blue laser.

ISSN:0003-6951    

DOI:10.1063/1.104048

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present a model for the operation of a particular type of electron beam diode used in the Sandia Recirculating Linear Accelerator system. The critical element of the model is ion emission from the anode aperture, which neutralizes enough beam space charge to permit focusing. Recent experimental results are shown which support the model in several respects.

ISSN:0003-6951    

DOI:10.1063/1.104049

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Diethylgalliumchloride (DEGaCl) adsorption on Si(100) 2×1 and Si(111) 7×7 surfaces is studied by reflection high‐energy electron diffraction and x‐ray photoelectron spectroscopy. DEGaCl adsorbs molecularly on the (100) surface at room temperature, while the Ga—Cl bond dissociates on Si(111). The Si(111) 7×7 structure is greatly disturbed after DEGaCl exposure, indicating a strong interaction between the surface and the adsorbate. The spatial distribution of dangling bonds is thought to be responsible for the differences in the reactivity between the two surfaces. The Ga—ethyl bond dissociates on both Si(100) and (111) surfaces after annealing at 210 °C, and at the same time Cl desorbs from the surfaces. The Cl desorption process is also discussed.

ISSN:0003-6951    

DOI:10.1063/1.104050

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have investigated the effectiveness and failure mechanism of thin tantalum layers as diffusion barriers to copper. 50 nm tantalum films were sputtered onto unpatterned single‐crystal ⟨100⟩ Si wafers and overlaid with 100 nm Cu. Material reactions in these films were followed as a function of annealing temperature byinsituresistance measurements, and characterized by Rutherford backscattering spectroscopy and cross‐section transmission electron microscopy. While pure Cu on Si reacts at 200 °C, the Ta film prevents Cu silicon interaction up to 600 °C. At higher temperatures, reaction of the Si substrate with Ta forms a planar layer of hexagonal TaSi2. Cu rapidly penetrates to the Si substrate, forming &eegr;‘‐Cu3Si precipitates at the Ta‐Si2‐Si interface.

ISSN:0003-6951    

DOI:10.1063/1.104051

出版商:AIP    

年代:1990

数据来源: AIP