摘要:

A new species of self‐organized light‐induced scattering, appearing only in bulk periodically poled lithium niobate, is reported. Clearly defined diffracted beams develop on exposure to 532 nm light from a frequency‐doubled,Q‐switched, and mode‐locked Nd:YAG laser. The structure thus created also diffracts light at 1064 nm. The effect is strongly dependent on temperature, the polarization state of the light, and the period of domain reversal. It exhibits a sharply defined nonlinear threshold at which the far‐field pattern of the diffracted light evolves rapidly. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114578

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present time domain impulse scattering measurements of freely propagating terahertz radiation measured with subpicosecond resolution. This fast time response corresponds to a usable bandwidth of over 1 THz. Measured scattered fields from thin wire targets agree well with the calculated scattering for the early and late time response in both the time and frequency domains. Realistic ranging from scale model aircraft is demonstrated. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114579

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A multiwavelength laser system designed for precise and efficient tissue ablation under water was realized by simultaneously coupling radiation of a holmium:YAG laser, emitting at a wavelength of 2.12 &mgr;m and an erbium: YSGG laser at 2.79 &mgr;m into the same zirconium fluoride (ZrF4) fiber. The beam paths of the two lasers were collinearly combined taking advantage of the dispersion of an Infrasil prism. Fast video flash photographs and laser induced pressure transients simultaneously recorded with a PVDF pressure transducer were used to study the dynamics of bubble formation at the submerged fiber tip. The bubble size and the bubble lifetime were determined as a function of the wavelength and the delay time between the two different laser pulses. The results indicate that the combination of 2 and 3 &mgr;m radiation takes specific advantage of both wavelengths and strongly enhances the ablation efficiency of tissue under water. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114580

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ultrafast absorption studies on free‐standing porous silicon films have been carried out at room temperature to investigate the carrier dynamics and the luminescence mechanism. Ultraviolet and visible excitations were used on an as‐prepared sample and two annealed samples. Transient absorption curves of UV pumped, as‐prepared samples contain a fast decay (&tgr;f) of 0.8±0.2 ps and a slower decay of ≳30 ps. &tgr;fis found to be shorter for both the 500 °C annealed sample with UV excitation and for the as‐prepared sample with visible excitation. The faster decay rates suggest that the subpicosecond component of the transient absorption may be due to carrier thermalization rather than core‐to‐surface state excitation transfer. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114755

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have used laser‐micromachined alumina substrates to build a three‐dimensional photonic band‐gap crystal. The rod‐based structure has a three‐dimensional full photonic band gap between 90 and 100 GHz. The high resistivity of alumina results in a typical attenuation rate of 15 dB per unit cell within the band gap. By removing material, we have built defects which can be used as millimeter‐wave cavity structures. The resulting quality (Q) factors of the millimeter‐wave cavity structures were as high as 1000 with a peak transmission of 10 dB below the incident signal. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114756

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Upon the combination of double refraction and diffraction effects, a new kind of polarization device is proposed, which is made of the birefringent plate with the grooves of a sawtooth profile on its surface. This device may separate an incident light beam into two polarized beams spatially with a high extinction ratio and large beam‐splitting angle, moreover it has a sheet form, large aperture, and low cost, thus being suitable for practical use. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114757

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Third‐order nonlinear optical response of a cadmium texaphyrin solution at 532 nm was measured using time‐resolved degenerate four‐wave mixing with picosecond pulses. The molecules of cadmium texaphyrin exhibit a large optical nonlinearity, which arises from the excited‐state population. The dynamics of the nonlinear optical response show an evident fluence dependence. The temporal response is characterized by three components, a slower, a faster, and a fastest, which are attributed to populations of the first triplet excited state, the first singlet excited state, and the higher singlet excited state, respectively. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114758

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Wavelength‐shifted GaAs/AlGaAs Fabry–Pe´rot ridge waveguide lasers were fabricated by vacancy‐enhanced quantum well disordering using dielectric cap annealing. 500 &mgr;m long and 4 &mgr;m wide Fabry–Pe´rot lasers with emission wavelengths selectively shifted by 20 nm were integrated with unshifted lasers on the same chip, characterized and further compared with lasers fabricated from as‐grown material. These investigations showed that the absorption edge of a single‐quantum well double heterostructure can be selectively blueshifted after epitaxial growth without compromising diode laser performance. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114759

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Near‐field probes have been developed, based on standard, i.e., commercially available, Si cantilever probes for scanning force microscopy (SFM), which directly convert the optical near‐field signal into an electrical signal using Schottky contacts. With these optoelectronic probes it is possible to realize very compact near‐field microscopes. The probes are inserted into a SFM and measure the topography and the optical near‐field signal simultaneously. The qualitative analysis of the light‐sensitive areas of the probes and the detection of the optical near field is described. Finally, subwavelength resolution is demonstrated when a polished glass surface is investigated. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114760

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have observed midinfrared emission due to intersubband transitions in a coupled quantum wells structure. The excitation process involves optical pumping of the carriers from the ground subband into the third subband and a generation of a population in the third subband. The luminescence is produced by a radiative transition of the photoexcited carriers from the third to the second subband, followed by a fast relaxation into the ground subband due to a resonance LO‐phonon assisted relaxation process. The emission signal persists from low temperatures up to room temperature with a maximum efficiency at 190 K. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114761

出版商:AIP    

年代:1995

数据来源: AIP