摘要:

Near‐field photodetection optical microscopy (NPOM) is a fundamentally new approach to near‐field optical microscopy. This scanning probe technique uses a nanometer‐scale photodiode detector which absorbs optical power directly as it is scanned in the near field of an illuminated sample surface. We have applied NPOM to measure the visible absorption spectrum of dye molecules embedded in a single 300 nm polystyrene sphere. The near‐field absorption spectrum is obtained by measuring the NPOM probe photocurrent while the wavelength of the illumination pump beam is scanned from 450 to 800 nm. Peaks are identified at 567, 608, and 657 nm in the near‐field spectrum of the single‐dyed polystyrene sphere. These peak positions are in good agreement with far‐field absorption measurements performed on many dyed polystyrene spheres. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117403

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Performance degradation in liquid crystal cells was studied by analyzing the time evolution of optical and integrated current vs voltage hysteresis curves as test cells were subjected to a dc bias. We find evidence for permanent increases in liquid crystal mobile ion populations, the primary cause of device performance degradation, and suggest this permanent increase is due to selective adsorption by the alignment layers of ions of a single charge sign combined with the presence of a neutral ionizable species in the liquid crystal. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117404

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A microscopic theory for vertical‐cavity surface‐emitting lasers (VCSELs) with quantum‐well active layers is applied to study the transient gain dynamics, nonequilibrium carrier effects and the influence of the laser design. We investigate how the laser response on femtosecond pulse excitation can be controlled in terms of (i) excitation conditions of the VCSEL, (ii) the mirror design, which allows to change the cavity quality and the resonance frequency, and (iii) the number and position of active semiconductor quantum‐wells. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117405

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It was demonstrated that the third‐order optical nonlinearity of polymer films could be reversibly controlled by the photochromic conversion and followingJ‐aggregate formation of spiropyran embedded in an inert polymer matrix. Patterns consisting of areas with high and low third‐order nonlinear optical activities were prepared by imagewise exposure of the photochromic films followed by thermal treatment to form thermally stableJaggregates of photoinduced merocyanine in the exposed area. This system could be useful in developing new unconventional optical devices based on optical nonlinearities, including new types of spatial light modulators. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117406

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A novel all‐optical light modulation has been proposed based on photoinduced changes of an imaginary part of complex refractive index in guided wave geometry. Very fast and repeated modulation of a reading beam (reflected intensity) was demonstrated at the incident angle corresponding to a sharp guided wave resonance using phthalocyanine‐doped poly(vinyl alcohol) film as a photoresponsive layer and a nanosecond pulsed laser as a writing beam. Such responses were mainly due to the formation and decay of excited triplet phthalocyanine. The rise and fall time was markedly improved as compared with previous systems based on photothermal changes of the refractive index. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117407

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a systematic investigation of the operation conditions of photoconductive switches fabricated on LT‐GaAs as sources of THz pulses. We find a pronounced dependence of the THz pulse intensities and spectra on bias voltage and excitation density, which can be explained in terms of carrier dynamics and screening of the electric bias field. This study provides guidelines for the selection of the optimal operation parameters to obtain short THz pulses with a given geometry of the photoconductive switch. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117408

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The electro‐optic properties of single crystal films ofN‐(4‐nitrophenyl)‐L‐prolinol (NPP) were evaluated. The direct coating technique was used to form the electrodes on the surface of the single‐crystal film samples. The ac voltage and lock‐in technique were used to measure the electro‐optic coefficients. The electro‐optic effects for different orientation of electrodes on a single‐crystal film sample were measured. The dependence of the field induced birefringence on the orientation of electric field with respect to the charge transfer axis was evaluated. The results show that for NPP |n3xr12−n3yr22|=340 pm/V andr12=65 pm/V. The results are promising for various application in electro‐optics involving appropriate device geometries. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117409

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on a high‐reflectivity (up to 670%) wide‐bandwidth (up to 230 MHz) phase‐conjugate mirror formed using backward‐four‐wave mixing with continuous‐wave pump beams in a 2‐mm potassium vapor cell. The reflectivities and bandwidths are significantly larger than have been measured previously, and the bandwidth is ten times greater than is predicted theoretically. The reflectivity‐bandwidth product is more than an order of magnitude improvement over those previously achieved with other continuous‐wave phase‐conjugate systems. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117410

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Steady‐state and transient responses of a nonintentionally doped GaN photodetector are investigated. The kinetics of the photoresponse demonstrate the existence of deep levels in the gap, acting as recombination centers with an acceptor character. The photoresponse displays two competing processes: a bimolecular recombination, dominating at high optical power range, and a monomolecular recombination involving long response times. The observed persistent photoconductivity and the huge photoconductive gain are due to the small electron capture cross section and a much faster hole capture rate. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117411

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The combustion of H2gas with N2O gas was investigated in order to rapidly heat substrate to a high temperature. A transient thermometry with a 100‐nm‐thick Cr film as a temperature sensor formed on quartz substrate was used to measure temperature change at the surface. The gas combustion was induced by heating a W filament. It propagated with a velocity higher than 100 m/s throughout a chamber for an initial total gas pressure of 500 Torr ([H2]/[N2O]=1). The sample surface is heated to 800 °C for an initial substrate temperature at 300 °C. The full heating time width at half maximum was 4.5 ms. This letter shows a possibility of millisecond‐order rapid thermal treatment. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117412

出版商:AIP    

年代:1996

数据来源: AIP