摘要:

A hyperlinear increase of radiative quantum efficiencies of poly(para-phenylene)-type ladderpolymer in the blue–green region as a function of subpicosecond excitation intensity is reported. The light emission in the range from 485 to 495 nm undergoes a change from linear behavior to a second order response; the two regimes are separated by a distinct threshold of 3.1mJ/cm2.Above this threshold, investigation by femtosecond excitation–correlation measurements indicate that the hyperlinear blue emission is associated with a characteristic excitonic depopulation of 2 ps. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120118

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A thinEr2O3layer grown on a Si surface by vapor doping of Er exhibits intense photoluminescence in the green and red regions excited by laser beams in the 800 nm and 450–490 nm ranges. These intense light emissions take place via resonant two or one step photoexcitations of the4flevels inEr3+ions. Our sample fabrication procedure is integrated circuit compatible and producesEr2O3layers of excellent homogeneity and quality as demonstrated in the optical measurements. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120119

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate frequency stabilization of widely tunable erbium–ytterbium microlasers in the wavelength interval between 1540 and 1550 nm by locking the oscillators to nine different absorption lines of13C2H2,spaced by approximately 150 GHz. Frequency stability is evaluated by measuring the two-sample Allan variance of the heterodyne beat-note signal between two identical lasers. The square root of the Allan variance is7×10−10for integration times between10−3and102 s.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120120

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the femtosecond impulsive excitation of coherent phonons in alkali metal-doped fullerenes. These excitations appear as small oscillations of the reflectivity(&Dgr;R/R∼10−7)produced by the pump in an optical pump-probe experiment. The observed phonons include previously unobserved highly damped modes near 150cm−1as well as long-livedAg(1)modes near 490cm−1.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120121

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Planar and channel optical waveguides were fabricated in Cu dopedKTiOPO4(KTP) substrates usingRb+:K+ion exchange process and annealing process. The effective refractive indices were measured using them-line method and the refractive index profiles of these waveguides were calculated using the inverse WKB method. For waveguides in Cu:KTP substrates the difference of diffusion depthdand index change&Dgr;nat thez−andz+surfaces can hardly be observed. This observation is different from KTP. Compared with undoped KTP substrates the diffusion depthdat thez−surfaces is larger, whereas the index change&Dgr;nis smaller. At thez+surfaces bothdand&Dgr;nare larger. The light induced effective index changes in Cu doped KTP channel waveguides were measured at 0.476, 0.488, 0.514, 0.6328, and 0.83 &mgr;m wavelengths. No changes were observed at the power flow of1×108 W/m2,revealing that Cu ion does not play an important role in photorefractive effect of KTP crystals. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120122

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Room-temperature visible luminescence fromPr3+ions embedded in germaniumsulfide glass hosts is reported along with edge luminescence from these hosts. The important role of energy transfer processes between the host and Pr ions is demonstrated experimentally through the dependencies of photoluminescence on excitation wavelength, temperature, and polarization. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120549

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Optical heterodyne conversion, or photomixing, occurs in an epitaxial low-temperature-grown GaAs layer with voltage-biased metal electrodes on which two laser beams are focused with their frequencies offset by a desired difference frequency. Difference-frequency power couples out of the photomixer through a log-spiral antenna at THz frequencies. Pumping such a device with the maximum optical power of ∼90 mW at 77 K led to a measured output power of 0.2 &mgr;W at 2.5 THz, approximately twice the maximum output power of a photomixer operated near 300 K. Photomixers that were operated above the maximum optical power were destroyed, often because of a thermally induced fracture in the GaAs substrate. The fracture seemed to occur at high pump power when the temperature of the photomixer active area was elevated by roughly 110 K, independent of the bath temperature. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120445

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new approach to produce structured optical materials is described. The method relies on the capability of growing eutectic crystals of wide optical band gap materials by directional solidification procedures. The laser float zone technique was used to produce ordered arrays of alternate lamellae with thickness of the order of microns of erbium doped CaZrO3and calcia stabilized zirconia single crystals. The later, having a higher refractive index, exhibited planar waveguiding effects as it has been proved experimentally. The possibility of producing waveguides from eutectic crystals promises the fabrication of hundreds of planar waveguides integrated into a crystal grown at a speed of several tenths of cm/h. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120200

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The enhanced transmission efficiency of chemically etched near-field optical fiber probes makes it possible to greatly increase the scanning speed of near-field optical microscopes. This increase in system bandwidth allows sub-diffraction limit imaging of samples at video rates. We demonstrate image acquisition at 10 frames/s, rate-limited by mechanical resonances in our scanner. It is demonstrated that the optical signal to noise ratio is large enough for megahertz single pixel acquisition rates. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120123

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thin films of 4-cyano-4’-pentylbiphenyl (5CB) liquid crystal have been fabricated by pulsed laser deposition. The suitability of different lasers (ArF, KrF and CO2)has been investigated over a range of fluence using visible-UV and infrared absorption and optical microscopy to characterise the films. High performance liquid chromatography (HPLC) and matrix assisted laser desorption ionization mass spectroscopy (MALDI-MS) were used to assess the extent of decomposition of the films. The results suggest that the CO2laser acts as a quasi-steady heat source, while for ArF laser irradiation severe photodecomposition is observed. However, use of the KrF laser allows the production of excellent quality submicron films, showing properties similar to the 5CB target with only slight photodecomposition. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120124

出版商:AIP    

年代:1997

数据来源: AIP