摘要:

Using infrared transmission and Raman spectroscopy, we have studied the optical phonon modes of GaN layers grown on GaAs(001) substrates by molecular beam epitaxy. The crystal structure of the GaN layers ranges from predominantly wurtzite to predominantly zincblende depending on the growth conditions. The transverse and longitudinal optical phonons in cubic GaN are found to be at 552 and 739 cm−1, respectively. These frequencies are slightly shifted with respect to the correspondingA1andE1phonon modes in hexagonal GaN. The frequency shifts, together with Raman scattering selection rules, can be used for identifying the phase composition of GaN. A more distinct fingerprint of the hexagonal phase is provided by the occurrence of theE2phonon modes that are spectrally separated from optical phonon modes in the cubic phase and thus uniquely related to the hexagonal phase. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115208

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photorefractive asymmetric Fabry–Pe´rot quantum‐well structures yield significantly enhanced diffraction during four‐wave mixing by employing the sensitive amplitude and phase control of multiple‐beam interference within the device. We present an Al0.1Ga0.9As/GaAs photorefractive quantum‐well device with a near optimal input diffraction efficiency of 0.36% and an AlAs/GaAs quantum‐well device with an output diffraction efficiency of 200%. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115209

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Biprisms are used as a method of wavefront division with an excimer laser source to holographically write first‐order Bragg gratings in single‐mode optical fibers. Gratings with a period of 556 nm and peak reflectivity of 62% are produced using single pulses from a krypton fluoride (KrF) laser. A comparison is made between grating production with line‐narrowed and nonline narrowed lasers. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115210

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Subwavelength amorphous silicon transmission gratings with a period from 100 to 800 nm and a thickness of 180 nm on silica substrates have been fabricated and studied. For a normal incident light (&lgr;=633 nm), in addition to strong birefringence (as large as 170° in phase difference), it was observed that the transmission of TE (the electric field parallel to the grating finger) wave is significantly different from that of TM (the electric field perpendicular to the grating fingers) wave (as large as 12 dB), and that both polarization and birefringence effects strongly depend on the ratio of grating period to wavelength, having the largest variations at the grating periods around a half of the wavelength. This observation deviates significantly from simple form birefringence theory and effective medium theory. Applications such as polarization selection mirrors for vertical cavity surface emitting lasers and waveplates are discussed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115211

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The magnitude of the gray levels in an image obtained by an acoustric microscope can be exploited to measure the acoustic impedance of a sample with the spatial resolution of the instrument. Theoretical considerations show the functional dependence of the maximal amplitude of specular reflection from material constants, which is confirmed by experiments. It turns out that for these amplitude values the opening angle of the lens plays a minor role. For a quantitative evaluation of the impedance, calibration by a known object material is necessary. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115212

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report on the depth profile of the nonlinear optical susceptibility in ion‐implanted potassium niobate (KNbO3) waveguides using reflected second harmonic generation from wedged samples. After irradiation the waveguide layer exhibits partial loss of its optical nonlinearity that can be recovered to better than 90% of its value of the virgin crystal by subsequent annealing and repoling. We propose microscopic depolarization due to ion implantation to be responsible for the observed decrease of the nonlinear optical susceptibility. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115213

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a theoretical prediction of the threshold current density and the temperature sensitivity of a GaN laser operating in the intrinsic band‐to‐band transition. We calculate the material gain and spontaneous emission spectrum for unintentionally doped bulk GaN under carrier injection. All stimulated and spontaneous emission calculations are compared to those of bulk GaAs. The transparency carrier density of GaN is found to be more than four times that of GaAs, and the momentum matrix element for optical transitions in bulk GaN is estimated to be about one‐third the value in GaAs. In addition, the differential gain is approximately four times smaller in GaN. These differences are attributed to the larger effective masses of the electrons and holes in GaN. The calculated characteristic temperatureT0of the threshold current density for a GaN laser ranges from 185 to 220 K, which agrees well with the recently observed data from optical pumping experiments. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.115214

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A many‐body calculation of the nonlinear optical response of bulk group‐III nitrides is presented. For the example of GaN it is shown that the Coulomb effects contribute significantly to the magnitude and spectral extension, as well as the temperature and carrier density dependences of the optical gain and absorption. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115215

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We discuss an improved mid‐wave infrared diode laser structure based on InAs‐Ga1−xInxSb‐ InAs‐Ga1−xAlxSb Type‐II multiple quantum wells. The proposed design combines strong optical coupling, 2D dispersion for both electrons and holes, suppression of the Auger recombination rate, and excellent electrical and optical confinement. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115216

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have found the cross‐phase modulation (XPM) for cross‐polarized beams to be equal to the self‐phase modulation (SPM) in bulk AlGaAs semiconductor waveguide at photon energies lower than half the band gap. For multiple quantum well (MQW) waveguide the ratio of the cross‐phase modulation coefficient to the self‐phase modulation coefficient is approximately one for the pump polarized perpendicular to the well plane (TM) and one‐half for pump beams in the plane of the wells (TE). ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115217

出版商:AIP    

年代:1995

数据来源: AIP