摘要:

We report on an experimental technique for investigating the intensity profile in distributed feedback fiber lasers. By scanning along the laser length and monitoring the side green fluorescence, the intensity distribution in the laser can be inferred. With this approach, we experimentally verify the sharply peaked intensity distribution predicted for &lgr;/4 phase‐shifted distributed feedback lasers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116994

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Eu2+ions were incorporated in SiO2and Al2O3–SiO2glasses using a sol‐gel process of Si(OC2H5)4, Al(OC4H9sec)3, and EuCl36H2O. Glasses incorporated with the Eu2+ions showed the emission with peak at ∼22000 cm−1due to 4f 6 5d→4f 7(8S7/2) transition of the Eu2+ions. 1Al2O3⋅99SiO2(mol %) glass had an intense emission, 250 times larger than that of 100SiO2glass. The covalency of the Eu–O bonds is decreased by the Al3+ions. We concluded that this weak covalency causes the offset of the excited 4f 6 5dlevel to be small, resulting in an increase in the probability of the radiative relaxation from the 4f 6 5dto 4f 7(8S7/2) level. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116995

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It has been shown that the blue photoluminescence (PL) of porous silicon (PS) can be obtained simply from postanodization illumination by white light without any oxidation processes. The PS samples were formed on 5–6 &OHgr; cmp‐type (100) Si wafers. The anodization was carried out in an ethanoic HF solution at a current density of 50 mA/cm2for 5 min in the dark. After the anodization, the samples were illuminated under the open‐circuit condition by a 500 W tungsten lamp for several minutes. The PL measurements of prepared PS samples were carried out in vacuum. With increasing the postanodization illumination time, the PL band exhibited a continuous shift from red to blue. During this blue shift, fourier transform infrared spectra did not show any signs of the growth of the surface oxide. In addition, the emission energy dependence of the PL decay time for each PL band behaved in accordance with a universal curve. These results strongly suggest that there is an oxide‐free mechanism in the PL emission from PS throughout the visible range. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116996

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Heterodyne interferometers using two‐wave mixing in photorefractive cubic crystals for ultrasound detection on rough surfaces are demonstrated. The speckled scattered beam from a rough surface sample interferes with a planar coherent pump beam inside a photorefractive crystal. A thirdfrequency‐shiftedbeam is used to read the grating. The diffracted readout beam and the transmitted signal beam are wavefront matched, resulting in an optimal heterodyne interference signal. The signal to noise ratio for the two commonly used crystallographic configurations with cubic crystals,G∥⟨110⟩∥ andG∥⟨001⟩, whereGis the grating wave vector, are investigated. Very good sensitivity is demonstrated for the detection of small amplitude ultrasonic surface displacements. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116997

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A means of reproducibly fabricating stable cw lasers in rare‐earth‐doped Ti:LiNbO3has been demonstrated through judicious choice of waveguide orientation. Z‐propagating waveguides have been fabricated in Nd‐ and Er‐diffused Ti:LiNbO3and room‐temperature laser operation with greatly reduced photorefractive instability has been obtained. The reduced photorefractive damage susceptibility in this waveguide configuration has led to the realization of a 980 nm pumped laser in Er:Ti:LiNbO3, with a threshold of 10.5 mW of absorbed pump power and a slope efficiency of 8.5%. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116998

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Mach–Zehnder interferometry was used to measure the Pockels effect in a poled electro‐optic polymer thin film with a coplanar electrode structure. The beam at the sample arm of the Mach–Zehnder interferometer passed through a polymer thin film which had been spin‐coated on top of a clear gap between two electrodes patterned on an optical substrate. This unique optical geometry enabled the Pockels coefficients of the poled electro‐optic polymer film in the directions of the ordinary and the extraordinary optic axes to be determined independently. As an example, the tensor ratior33/r13for a stilbene‐dye‐doped polyimide guest/host polymer film was determined experimentally; the ratio turned out to be 4.6, which was higher than the value of 3 predicted by the thermodynamic model. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116999

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Hemicyanine‐doped silica film was fabricated by sol–gel technique. Time evolution of structural changes in hemicyanine and their influence on the second‐order optical nonlinearity were investigated through UV‐visible absorption and second‐harmonic generation (SHG) measurements. We found that the conversion of protonated hemicyanine to monomeric and aggregated hemicyanine occurred within 4 h after film deposition. During this period of time the SHG signal continued to rise and finally reached the maximum. The growth of optical nonlinearity was mainly due to deprotonation of hemicyanine molecules. Blueshift of the absorption peaks for both aggregate and monomer were found during the drying of the film. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117000

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have used polyvinylcarbazole, PVK, in combination with poly(p‐phenylene vinylene), PPV and a green‐emitting, soluble derivative, poly(4,4′‐diphenylene diphenylvinylene) or briefly PDPV, to fabricate triple‐layer light‐emitting diodes PPV/PVK/PDPV/metal, with indium tin oxide as the anode. We report luminances in excess of 1300 cd/m2with Al cathodes, turn‐on voltages of ∼8 V in structures 300 nm thick, and internal efficiencies in the range 0.4%–0.8% for Al and Ca cathodes; at least ten times higher than for single‐layer PDPV devices. Quantum efficiencies for Ca or Al electrodes are only a factor 1.5 different. The improvements over single‐layer PDPV devices are considered to be due to better hole injection by PPV and to the formation of a hole barrier at the PPV/PVK interface, which forces a better balance of the electron and hole currents. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117001

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have investigated metallic photonic crystals built around a layer‐by‐layer geometry. Two different crystal structures (face‐centered‐tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7–8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117002

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Visibly transparent near‐UV dye (Exalite 377E)‐doped silica in the form of parallelepiped were prepared by the low‐temperature sol‐gel process. The laser output performance of dye‐doped sol‐gel silica samples pumped by a short pulse (1 ns) N2laser at 337 nm was reported. With a grating as the wavelength selection element, the laser was tuned from 367 to 387 nm with a laser linewidth of 2 nm. Using a resonator cavity consisting of two flat mirrors, the sol‐gel laser showed a slope efficiency of 34.7% and a pump energy threshold of 20 &mgr;J. The variation of sol‐gel laser energy output as a function of the number of pulses under repetitive N2laser excitation was investigated. The laser output energy decreased initially with the number of shots. The output energy recovered to its original intensity after a ten minute interruption in pumping. In this way, the dye‐doped samples showed no signs of long term degradation after being irradiated at 337 nm for tens of thousand shots. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117109

出版商:AIP    

年代:1996

数据来源: AIP