摘要:

Local intensity fluctuations in a large aperture dye laser have been measured for several solvent viscosities. A decrease on the relative fluctuations amplitude as the solvent viscosity increases is found. From a theoretical approach, we show that the intensity fluctuations follow the same behavior as the molecular polarization orientation driven by the laser field. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121854

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation photon energy(Eexc)to further understand the origin of SE in these structures. Optically pumped SE was observed for excitation photon energies well below that of the absorption edge of the MQWs, indicating the states responsible for the soft absorption edge in these structures can efficiently couple carriers with the gain region. “Mobility edge”-type behavior in the SE peak was observed asEexcwas varied. The effective mobility edge measured in these SE experiments lies ∼110 meV above the main spontaneous emission peak and ∼62 meV above the SE peak. Tuning the excitation energy below the mobility edge was found to be accompanied by a drastic increase in the SE threshold due to a decrease in the effective absorption cross section. The experimental results indicate that the SE peak observed here has the same microscopic origin as the spontaneous emission peak, i.e., radiative recombination of localized states. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121855

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Epitaxial structuring of blue light-emitting molecules,p-phenylene oligomers(p-nP,n=3,4,5,6),was investigated in thin crystals vapor deposited on the (001) surface of a KCl single crystal. Their molecular orientation and morphology changed depending on the molecular length and substrate temperatures during deposition. As the length ofp-nPwas longer and the substrate temperature was lower, the orientation of the molecular axis changed from standing to lying on the KCl surface due to an increase of molecule–substrate interactions.p-terphenyl (3P) hardly adsorbed on the KCl (001) surface, but a portion of the standing molecules stuck along the step edge of KCl and formed a walllike structure. Long needlelike crystals ofp-hexaphenyl (6P) epitaxially grew in two orthogonal KCl [110] directions taking lying orientation even at a higher substrate temperature. In these epitaxial needles, the transition dipoles parallel to the molecular axis gave rise to blue fluorescence sharply polarized along the KCl [110] directions. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121856

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on photon-spin controlled lasing oscillation in GaAs surface-emitting lasers at room temperature. We demonstrate experimentally that the partial electron-spin alignment, created by optically pumping the GaAs laser active media with circularly polarized pulses, drastically changes the polarization state of the lasing output, causing circularly polarized lasing emission. We discuss the laser polarization characteristics in relation to the measured electron-spin relaxation time. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121857

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The interplay of carrier heating effects and transverse variations of the carrier distribution functions has a significant influence on the ultrafast emission dynamics of semiconductor vertical cavity surface emitting lasers. This interplay can lead to dynamic overshooting and oscillations (here at 200 GHz) even for lasing on a single transverse and single longitudinal mode. A simple equivalent model is a cavity containing the gain medium and a saturable absorber. The numerical results can directly be compared with recently published experiments. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121858

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have observed large second-order nonlinear optical response from zinc oxide (ZnO) thin films deposited on sapphire substrates by pulsed laser ablation. By comparing the second harmonic signal generated in a series of ZnO films with different crystallinity and thickness, we conclude that a significant part of the second harmonic signal is generated at the grain boundaries and interfaces. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121859

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An external-cavity tapered diode laser utilizing fiber Bragg grating feedback was designed to oscillate on a single-longitudinal mode. Stable single-longitudinal mode operation was attained at powers as high as 1.35 W. The emission frequency tuned smoothly with current over the cavity’s free spectral range of 6 GHz. The power in the lasing mode was >30 dB above the background amplified spontaneous emission and the side-mode suppression ratio was >15 dB. No deterioration in the beam quality was measurable up to the highest output power. The coupling efficiency into a Gaussian resonator mode was >65&percent; up to 1.35 W. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121860

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Optical temperature sensing using upconversion fluorescence emission inEr3+/Yb3+-codopedGa2S3:La2O3chalcogenide glass excited at 1.06 &mgr;m is reported. Temperature measurements in the region of 20–225 °C with a resolution of approximately 0.5 °C using excitation powers of a few tens of milliwatts were obtained. The temperature sensing mechanism is independent of variations in the excitation intensity, possible fluctuations of transmission, and utilizes a simple signal detection and processing system. The results also revealed that the glass host material plays an important role in the performance of the sensing system. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121861

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe a method for interferometric distance measurements in the presence of phase noise. The method is based on the beating between white light and a reference beam that travel along the same path through the interferometer. Since both the reference and the white light suffer the same phase noise, the envelope of the high frequency fringes is not affected by the noise. By measuring the signal variance, we recover the envelope while averaging out the high frequency fringes. We demonstrate the usefulness of the method for surface profilometers. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121862

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Second harmonic generation is investigated in aZnSe/ZnS0.22Se0.78waveguide grown by metal organic vapor phase epitaxy on (001) GaAs substrate. Phase matching is achieved by a first order periodic modulation of the nonlinear susceptibility&khgr;(2)within the waveguide structure. The modulation is generated by a focused ion beam implantation technique, resulting in a well confined damage of the crystalline structure. The observed phase matching wavelengths corresponding to various modulation periods between 1.6 and 1.9 &mgr;m agree with those predicted by calculations. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121863

出版商:AIP    

年代:1998

数据来源: AIP