摘要:

We show that UV Raman spectroscopy is eminently well suited for thein situinvestigation of samples at high temperatures. Using sapphire as a test material, we have recorded Raman spectra from ambient temperature to 1700 K using different excitation wavelengths, both in the visible and near UV region of the spectrum. These spectra show that, because of the very rapid decrease of blackbody radiation in the short wavelength region, Raman spectra recorded in the near UV region of the spectrum are free from the blackbody radiation background, which typically hampers experiments in the visible. With 266 nm exciting radiation, we observe no thermal background even at 1700 K. We foresee that the method will become a powerful tool forin situinvestigations of high-temperature materials. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121437

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Al-free active-region diode lasers grown by low-pressure, metal-organic chemical vapor deposition and emitting at &lgr;=805 nm have been optimized for high continuous wave output power. The 1-mm-long devices consisting of anInGaAsP/In0.5Ga0.5P/In0.5(Ga0.5Al0.5)0.5Plaser structure have a threshold-current density,Jth,of 310A/cm2and relatively high values for the characteristic temperatures of the threshold current,T0(135 K), and differential quantum efficiency,T1(900 K). Lasers with 10&percent;/90&percent; coatings and a 100-&mgr;m-wide stripe provide a maximum cw output power of 6.1 W at a heatsink temperature of 10 °C. The devices fail due to catastrophic optical mirror damage (COMD), where the internal power density,P¯COMD,is 17.4MW/cm2;that is, twice that for conventionally facet-coated, 810 nm emitting, AlGaAs active-region diode lasers. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120628

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A quantum-well infrared photodetector (QWIP) based on the corrugated light-coupling scheme has been fabricated and tested for remote temperature sensing. The QWIP consists of two stacks of multiple quantum wells (MQWs), each sensitive in one of the atmospheric infrared transmission windows and each with a separate readout circuit. High optical coupling efficiency is obtained in both wavelength ranges, demonstrating the use of the corrugated structure for two-color detection. By monitoring the ratio of the photocurrent generated simultaneously in each MQW stack, the temperature of the object emitting the radiation can be determined, regardless of its emissivity and the geometrical factors. This temperature sensing ability is tested by using a blackbody radiator with precision temperature control as the target. The agreement between the measured and the preset temperatures indicates that the corrugated QWIP is capable of precision thermometric measurements. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120629

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Micromachined wavelength tunable vertical cavity lasers are attractive for applications ranging from wavelength division multiplexing to spectroscopy. An improved tunable structure that incorporates a partial anti-reflection coating to increase coupling between the air gap and the semiconductor cavity, and a more flexible micromachine process that enables independent optimization of the central reflector region and deformable membrane structure are described. This combination of structural and process modifications enables decoupling the tradeoffs between wavelength tuning rate and threshold current, as well as the tradeoffs between top mirror reflectance and tuning voltage. With these improved approaches, a 2.5 pair dielectric distributed Bragg reflector hybrid membrane top mirror produced singlemode devices with a 23 nm wavelength tuning range and multi-transverse-mode devices with a 30 nm wavelength tuning range. Threshold current, differential quantum efficiency, and lasing mode are characterized as a function of membrane bias. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120630

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We fabricated hydrogenated amorphous silicon carbide(a-Si1-XCX:H)films by the plasma-enhanced chemical vapor deposition technique using organic compound xylene(C8H10)as the carbon source, which was initially attempted by W. A. Nevin H. Yamagishi, M. Yamaguchi, and Y. Tawada, Nature368, 529 (1994). Here we used different preparation conditions from those authors to produce xylene-baseda-Si1-XCX:Hfilms, and a different light emission behavior of the films has been observed at room temperature. The light emission wavelength can be shifted from 630 nm to 450 nm by changing the optical band gap(Eopt)of the films from 2.3 eV to 3.5 eV, nearly covering the whole visible light range, which was never reported previously. Fourier transform infrared spectra showed that the configuration of the material was a combination of organic aromatic rings and inorganic SiC networks. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120631

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Temperature propagation near the critical point of a classical fluid is investigated theoretically. The governing equations of thermal energy transfer near the critical point are introduced and a linear analysis is carried out. The dispersion relation between the angular frequency and the wave number is obtained and the wave characteristics are discussed. The effect of gravitational acceleration on the temperature wave propagation is made clear. Through this analysis, the following results were obtained; (1) The propagation speed of temperature waves is&ggr;/(&rgr;0&kgr;T),where &ggr;,&rgr;0,and&kgr;Tare, respectively, the ratio of specific heats, the density, and the isothermal compressibility, with or without gravity if the wavelength is larger than10−3.(2) The amplitude of wave increases with time in the antigravitational direction and decreases in the gravitational direction but the decay time is long if the wave number is small. (3) Waves decay quickly if the wave number is larger than104.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120632

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The output radiation of a dc to ac radiation converter is characterized. A relativistic ionization front passing through a capacitor array of periodd=1cm produces short pulses of tunable radiation between 39 and 84 GHz with a gas pressure between 0 and 30 mT. The frequency spectra of the produced pulses are discrete and exhibit full widths at half maximum between 12&percent; and 28&percent;, consistent with the expected width for six cycles’ pulses. An upper bound of 750 ps (detection bandwidth limited) is placed on the pulse widths. These are the shortest pulses produced by a source of coherent radiation in this frequency range. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120633

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A novel, nonequilibrium, high-pressure, direct current discharge, the microhollow cathode discharge, has been found to be an intense source of xenon and argon excimer radiation peaking at wavelengths of 170 and 130 nm, respectively. In argon discharges with a 100 &mgr;m diam hollow cathode, the intensity of the excimer radiation increased by a factor of 5 over the pressure range from 100 to 800 mbar. In xenon discharges, the intensity at 170 nm increased by two orders of magnitude when the pressure was raised from 250 mbar to 1 bar. Sustaining voltages were 200 V for argon and 400 V for xenon discharges, at current levels on the order of mA. The resistive current–voltage characteristics of the microdischarges indicate the possibility to form arrays for direct current, flat panel excimer lamps. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120634

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A feedback mechanism based on fuzzy logic has been applied to operate a combined atomic force microscope (AFM)/scanning tunneling microscope (STM), which is able to measure the resonance frequency shift&Dgr;fof the cantilever-type spring and the mean tunneling currentI¯tsimultaneously. Using a decision making logic, the microscope can be scanned over a heterogeneous surface without tip crash. On the conductive parts of the sample, the STM mode is preferred, whereas the noncontact (nc)-AFM mode is used on the poorly conductive parts of the surface. The transition from the STM mode to nc-AFM mode is performed smoothly with the fuzzy logic feedback. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120635

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The annihilation of mobile protons in thinSiO2films by capture of ultraviolet-excited electrons has been analyzed for temperatures between 77 and 500 K. We observe a strong increase in proton annihilation with increasing temperature, and derive an activation energy for electron capture of about 0.2 eV. Based on quantum chemical[(OH)3Si]2&sngbnd;O&sngbnd;H+cluster calculations, we suggest photoexcitation of electrons from excited vibrational states of the ground electronic (valence band) state to a nearby excited electronic (SiO2gap) state. It is argued that the latter excitation can result inH0formation at elevated temperatures. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121447

出版商:AIP    

年代:1998

数据来源: AIP