摘要:

Self‐pulsations are induced in broad area diode lasers by including an extra layer functioning as a saturable absorber. The absorption of this layer and its coupling to the photon field can be tuned via the layer thickness and its distance to the active layer. In the case of an Al0.13GaAs bulk active layer a GaAs absorber of 4 nm thickness at a distance of 0.2 &mgr;m induces stable oscillations with frequencies of 300–700 MHz in a current range just above the threshold. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115545

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have demonstrated continuous wave operation of 2.7‐&mgr;m InGaAsSb/AlGaAsSb multiquantum‐well diode lasers up to a temperature of 234 K (−39 °C). These devices were grown by molecular‐beam‐epitaxy. They have a tendency to operate in a dominant single mode over well‐defined temperature and current intervals. A comparison of spontaneous emission spectra shows that above threshold, the quasi‐Fermi level is pinned and that most of the carriers are injected into nonlasing states. This effect leads to a rapid decrease of differential efficiency with increasing temperature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115546

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Measurements of the linear (Pockels) electro‐optical coefficient of wurtzite GaN are reported. The values for the electro‐optic coefficientsr33andr31are 1.91±0.35 and 0.57±0.11 pm/V at 633 nm, respectively, in agreement with extrapolations from measured second‐harmonic generation coefficients (&khgr;33(2)=−20±6 pm/V and &khgr;31(2)=10±3 pm/V) suggesting that the dominant contributions are electronic in origin. Measurements were performed using a Mach–Zehnder interferometer with LiNbO3as a reference material. Piezoelectric effects were also observed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115547

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Molybdenum‐doped barium titanate crystals have been grown and characterized. Electron paramagnetic resonance spectroscopy has confirmed the presence of Mo5+centers inreducedcrystals that correlate with a strong optical absorption band at ∼600 nm. Self‐pumped phase‐conjugation and electro‐optic beam‐coupling measurements indicate that the reduced crystals are photorefractive in the visible, as well as the near‐infrared wavelength region. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115548

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the observation of electroluminescence and photoluminescence from microcavity structures containing poly(2,5‐dialkoxy‐p‐phenylene vinylene) (PDAOPV) conjugated polymer emitting regions. Strong spectral narrowing from 112 nm full width half‐maximum to 34 nm in electroluminescence and from 128 to 16 nm in photoluminescence and clear angular dependence of the peak emission wavelength are observed. These are characteristic signatures of the modification of spontaneous emission properties in microcavity structures. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115549

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the generation of terahertz radiation via optical rectification from a poled polymer using femtosecond optical pulses. We have measured the refractive index and power absorption in the terahertz frequency range. The corresponding difference frequency mixing coherence length in the poled polymer (1 mm at 1 THz) is ∼20 times greater than that of LiNbO3(50 &mgr;m at 1 THz). The observed far‐infrared electric field radiated from a 16 &mgr;m thick polymer sample is only 4 times smaller than that from a 1 mm thicky‐cut LiNbO3crystal. We discuss conversion efficiencies for thicker polymer samples. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115550

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

By measuring the beat frequency of adjacent transverse modes it is possible to determine the thermal lensing of end‐pumped laser crystals. Because frequencies are used the method is very precise. Even for very weak thermal lensing the technique can be applied. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115551

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present the temporal and spectral evolution of stimulated emission from In0.2Ga0.8As/GaAs microcavity laser samples at 20 K after femtosecond optical excitation. Both, linewidth and chirp become smaller when the cavity resonance is at shorter wavelengths within the gain spectrum of the quantum well: The linewidth is reduced from &Dgr;&lgr;=0.41 nm at 923 nm, where the threshold is lowest, to &Dgr;&lgr;=0.26 nm at 884 nm. Comparison with a phenomenological model yields linewidth enhancement factors &agr; of 2 and 5 for emission wavelengths of 884 and 925 nm, respectively. A time‐bandwidth product of 0.68 is obtained at the shorter wavelength. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115534

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Radio frequency discharges in Ar/He/Xe gas mixtures have been studied in the range 5–150 MHz, and the importance of the ion sheaths in Xe laser excitation has been recognized. The discharge data have been used to improve the cw Xe laser performance, and efficiencies up to 0.8% observed. Area scaling in the slab geometry has been studied for &agr; discharge excitation at 49 MHz, and multimode cw laser power up to 5.5 W has been observed. High quality beams have been produced at 4.9 W using a hybrid waveguide/unstable resonator. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115535

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The nanostructural formation kinetics in a soft magnetic Fe80Nb6B14alloy have been investigated by means of differential scanning calorimetry, thermogravimetric analysis and transmission electron microscopy. Unlike nanocrystalline Fe–Zr–B soft magnetic alloys, where the nanocrystallite formation is governed mostly by a nucleation and growth mechanism, the nanostructural formation mechanism in the Fe–Nb–B alloy shows a change in the fraction transformed range 0.1–0.2. The first‐ and second‐stage nanostructural formation processes have been described by the nucleation and growth and grain‐growth models, respectively. This two‐stage nature in the nanostructural formation kinetics can be attributed to a high population density of the primary bcc nuclei. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115536

出版商:AIP    

年代:1995

数据来源: AIP