摘要:

We report near diffraction-limited laser emission from the conjugated polymer BEH:PPV in a cavity made with two dielectric mirrors providing a high finesse planar cavity. The laser has a sharp intensity threshold, a strong directionality, and a high degree of polarization. These emission characteristics are compared with those of a single polymer layer without optical feedback. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120709

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Both experiment and numerical calculation were performed to study the nonlinear optical (NLO) effects in ferrofluids consisting of magnetic particles suspended in an organic solvent. We show that, in contrast to all the mechanisms responsible for NLO phenomena known so far, the novel NLO effects in ferrofluids in the zero applied field can be explained by the cross coupling between the temperature of the system and the concentration of particles throughthermophoresis, which in turn leads to the spatial distribution of the refractive index. This NLO effect is enhanced by applying a moderate magnetic field whose mechanism is unclear so far. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120710

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present a nondestructive experimental technique for the determination of the lateral distribution of the polar order in second-order nonlinear optical thin films. The sample, which consists of a poled polymer film is scanned through the focus of an infrared laser beam in a second-harmonic generation setup and the second-harmonic intensity is monitored stepwise. In combination with a conventional electro-optic (EO) characterization it is possible to create an EO-coefficient map of the sample. The resolution of this mapping technique can be significantly increased by using high numerical aperture microscope optics for the illumination of the poled polymer. This method, for instance, allows the evaluation of poling inhomogeneities due to high-field poling and field distortions at the edges of poling electrodes. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120711

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate a target for recombination-pumped soft-x-ray lasers, consisting of an equally spaced array of parallel fibers. This target is capable of producing long media of several centimeters, and can also generate high gain due to the initial two-dimensional expansion of the plasma. Numerical simulations show that amplification occurs after the plasma expansion changes from a cylindrical to a slablike one, as a result of collisions with plasma produced from neighboring fibers. Initial gain measurements using graphite-coated fiber array targets reveal Balmer &agr; gain coefficients of4.1 cm−1.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120712

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A theoretical model has been formulated using lumped rate equations to analyze the temperature dependence of theQ-switched (i.e., saturable absorber operated) and gain-switched operation of a quantum-well laser. The results are found to agree with experimental results obtained from AlGaAs quantum-well devices, and show that improvement in the pulse energy inQ-switched and gain-switched lasers can be achieved by optimizing the operating temperature above room temperature. With increasing temperature, the pulse energy increases due to the pulses broadening while the peak power remains approximately constant. The effect is mainly attributed to the decrease of the gain with temperature. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120748

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate experimental results on the generation of sub-Poissonian photon fluxes emanating from an AlGaAs light-emitting diode, which manifest a wide-band (0–100 MHz) noise suppression below the standard quantum limit level despite low current density(∼38 A/cm2)operation at room temperature. The experimental noise power spectrum is well fitted in terms of the theoretical curve estimated with the quantum mechanical Langevin equations. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120713

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The optical gain of wurtziteInxGa1−xN/In0.02Ga0.98NandGaN/AlxGa1−xNquantum well (QW) lasers taking into account many-body effects is investigated. The valence band structures are calculated as a function of strain and well thickness. The inclusion of compressive strain shows better lasing performance because of the increase of the subband energy separation in the valence band. Our theoretical gain spectra ofIn0.15Ga0.85N/In0.02Ga0.98NQW lasers are in good agreement with measured ones reported by Nakamura, IEEE J. Sel. Top. Quantum Electron.3, 712 (1997). It is also shown that there is a universal relation governing the dependence of the band-gap renormalization on the two-dimensional carrier density for GaN-based QW lasers as there is for the infrared III-V systems. ©1998 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.120714

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Most plasmas used in the microelectronics industry are electronegative, i.e., they contain a large number of negative ions. One simple way to characterize the negative-to-positive ion density ratio(n−/n+)in such plasmas is to measure the velocity of ion acoustic waves (IAWs). In this letter, a detailed study of the propagation of IAWs in high-densitySF6magnetoplasmas is given. Results(n−/n+)obtained by way of this technique as functions of different parameters (gas pressure,SF6content inSF6/Armixture, and radial position in the reactor) are compared to those obtained with a more sophisticated technique based on laser photodetachment. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120715

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report a characterization of fullerite surface modification by cumulative laser irradiation. We show that the nano- and mesostructure of the transformed material are related and that they depend on the laser wavelength and fluence. Irradiating the sample at 1064 nm we observe periodic exfoliation of the transformed surface which is composed, on a nanometer scale, of a network of graphitic elongated nanoparticles. Under UV irradiation, the nanostructure is characterized by tangled graphene layers and cone formation is observed on a mesoscopic scale. Our observations show that different destabilization mechanisms ofC60produce coalescence pathways towards different nanostructures and mesoscopic morphologies. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120716

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A direct current (dc) glow discharge—surface interaction process forin situsubstrate surface pretreatment, for the promotion of diamond growth on mirror polished Si(100) is reported. A key step of the pretreatment is a generation of a stable dc-glow discharge between a grounded substrate and a positively biased electrode using aCH4/H2gas mixture. During this stage, no additional gas phase activation by a hot filament is carried out. For subsequent diamond deposition, the dc-glow discharge is switched off and the standard hot filament CVD growth conditions are applied. The nature of the deposits formed by the dc-glow discharge process and after standard diamond deposition conditions, are investigated by Raman spectroscopy and high resolution scanning electron microscopy. It is found that the properties of the films, deposited following the dc-glow discharge pretreatment, strongly depend on the pretreatment conditions: methane concentration, substrate temperature, and pretreatment time. It is suggested that the nature of the diamond precursor formed during the dc-glow discharge pretreatment is similar to that one observed after bias enhanced nucleation process. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120747

出版商:AIP    

年代:1998

数据来源: AIP