摘要:

We report the observation of midinfrared super radiant pulses emitted from molecular gases pumped by a narrow-band, continuously tunable infrared optical parametric oscillator. Molecules pumped either into a vibrational combination band or a vibrational overtone state decay by means of super radiant emission to a lower vibrationally excited state. Emission was observed inN2Oat 4.5 and 8 &mgr;m, and inC2H2at 13.6 &mgr;m and 15.7 &mgr;m. Pulse energies as high as 0.5 mJ and pulse widths as short as 7 ns make this an excellent technique for the production of intense midinfrared light. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118818

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe in this letter a novel approach to obtain a tunable midinfrared (mid-IR) laser output. By applying quasiphase-matched difference frequency generation in a periodically domain inverted LiNbO3crystal placed inside aCr3+:LiSAF laser cavity, more than 50 mW of mid-IR output was generated using only 1.8 watts of red diode or dye laser pumping. Wavelength tuning of the mid-IR signals from 3.3 to 4.2 &mgr;m was demonstrated by tuning only the wavelength of theCr3+:LiSAF emission, without the need to reorient the LiNbO3crystal for domain period adjustment. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118820

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The Maxwell–Garnett class of effective medium model applies if a representative cell can be found whose polarization vanishes upon insertion in the effective medium. For an anisotropic composite with randomly distributed ellipsoidal particles aligned along the principal axis, this leads to electrostatic restraints on the shape of such cells. It is shown that the cell boundary must have different depolarization factors to the inclusion within the cell. Practice is to equate them. A new physically correct ellipsometric modeling routine still with only two fitting parameters is demonstrated. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118821

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A wide bandpass x-ray polarizer for photon energies near 8358 eV(LIIIabsorption edge of erbium) has been grown using molecular beam epitaxy. The results illustrate a general approach to preparing graded-lattice diffracting optical components. The active optical element is an 8-&mgr;m-thick single crystal film ofIn0.51Ga0.49Sbgrown on a GaAs (001) substrate. The alloy was chosen to ensure maximum linear polarization for the (006) Bragg reflection at the target energy. The polarizer reflectivity has a full width at half-maximum of 27 eV in a fixed geometry with an angle of 90° between the incident and diffracted beams. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118822

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Polymeric passive TE/TM polarization converters are fabricated based on an adiabatic following in twisted optic–axis waveguides. Waveguides are formed by a reactive ion etching, and the optic axis of the waveguide is twisted by 90° with specially designed poling electrodes. Both TE and TM modes confined in the waveguides are converted to their counterparts by following the twisted ordinary and extraordinary axes, respectively. Conversion efficiency better than 20 dB and polarization-dependent loss less than 0.5 dB are obtained. The device provides wavelength insensitive operations and has large fabrication tolerances. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118823

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the observation of optically pumped lasing in ZnO at room temperature. Thin films of ZnO were grown by plasma-enhanced molecular beam epitaxy on (0001) sapphire substrates. Laser cavities formed by cleaving were found to lase at a threshold excitation intensity of 240kW cm−2. We believe these results demonstrate the high quality of ZnO epilayers grown by molecular beam epitaxy while clearly demonstrating the viability of ZnO based light emitting devices. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118824

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on thin-film microstrip lines (TFMSLs) fabricated on low-resistivity Si with polymerized cyclotene as the dielectric between signal and ground conductor, all on top of the wafer. Electro-optic high-frequency characterization of the TFMSLs reveals negligible modal dispersion up to the highest frequencies of 1.0 THz. In spite of the high substrate conductivity, the attenuation is low(⩽1 dB/mm at 100 GHz). Over the full frequency range, it is dominated by conductor losses and not by absorption in the dielectric. With these dispersion and attenuation properties, TFMSLs are an attractive alternative to coplanar waveguides, with the additional advantage of immunity against substrate absorption and radiation losses. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118849

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new method for measuring the space charge distribution in polymer insulators has been developed. This frequency method is based on the thermoacoustic signal which propagates into the insulator when a chopped laser beam is modulated in intensity and focused on the surface of the sample. This method has been used for measuring space charge distribution in a polyethyleneterephtalate sample. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118825

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A magnetic force has been used to control a partially magnetized atomic force microscope cantilever in ultrahigh vacuum in order to investigate tip-surface interactions. It is shown that forces applied by an oscillating tip can drastically affect the measured response of the lever. In particular the oscillating force influences the measured tip-surface adhesion and can be treated as a simple addition to the static applied force in breaking adhesive bonds. Qualitative differences in force spectroscopy measurements due to the amplitude of the driving oscillation of the lever are presented and an alternative nonintrusive technique introduced. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.118826

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The observation of Barkhausen current spikes during the recording of volume phase holograms in potassium lithium tantalate niobate is reported on. These spikes are due to the ferroelectric domain reversal induced by photorefractive space charge fields. Both “small” (1 nA) and “large” (100 nA) spikes are observed, which correspond to micro and macro domain reversal, respectively. The diffraction efficiency can change as much as 50&percent; during a single macrodomain switching. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118827

出版商:AIP    

年代:1997

数据来源: AIP