摘要:

A digital software‐controlled back‐off system for probe lamp dc signal nullification has been designed and incorporated into a laser flash photolysis spectrometer. This method takes advantage of modern high‐speed operational amplifiers already employed in the detection circuitry and the dedicated small computer that runs the spectrometer. The determination ofI0, necessary for absorbance calculations, is inherent in the method.

ISSN:0034-6748    

DOI:10.1063/1.1139359

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A thermally assisted laser‐induced fluorescence (LIF) detection system is developed to measure two‐dimensional spatial profiles of number density of alkali atoms seeded in an open‐cycle MHD generator, especially in the boundary layer on channel electrodes. The spatial resolution of this system is evaluated to be 1.3 mm. To assess the system, the LIF intensity from Na atoms used as a seed tracer is measured in a laminar air‐acetylene flame. The detected spatial profiles of the intensity show good agreement with those of the number density of sodium atoms measured by the spectral line absorption method. The LIF intensity near the surface of a cooled metal piece placed in the acetylene flame is also measured with this system as a preliminary experiment for applying it to the boundary layer on MHD channel electrodes.

ISSN:0034-6748    

DOI:10.1063/1.1139360

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

An automated laser light scattering system which uses a single detector to measure both classical and dynamic light scattering from soot particles in flames was designed, fabricated, and tested. Measurements of classical and dynamic light scattering along with extinction for a premixed methane/oxygen flame are presented, as a function of position in the flame. It is demonstrated that by introducing a theoretical relationship between the real and imaginary parts of the complex index of refraction, the optical properties of Rayleigh size soot particles can be directly inferred from suchinsitumeasurements. The sensitivity of the inferred quantities to the measured parameters is assessed. Soot particles sizes, number densities and optical properties were simultaneously inferred. The potential for determining theinsiturefractive indices of soot has been demonstrated.

ISSN:0034-6748    

DOI:10.1063/1.1139361

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

In order to acquire real‐time transient alkali data on coal‐derived gaseous fuel and combustion streams often at low ppb levels, an extractive, total (vapor and particle‐bound) sodium and potassium monitor has been designed, constructed, and tested. This fiber‐optic alkali monitor (FOAM) utilizes state‐of‐the‐art fiber‐optic light transfer, a novel light‐filtering background correction method, and high sensitivity photodiode signal detection. The sample enters the monitor’s high‐temperature flame, which supplies energy to both decompose and excite the sample. The flame then emits light at the characteristic wavelengths of sodium and potassium. The resulting emissions are transferred by the fiber‐optic bundle to the detection system, where the signal is filtered, background corrected, and transferred to the data system. The FOAM has advantages over previous instrumentation in being rugged, portable, and compact. Laboratory testing of the FOAM has been completed. The FOAM was determined to be highly sensitive (mid‐ppt detection limits) with a wide linear dynamic range (four orders of magnitude). The results of field monitoring of alkali levels in the exhaust stream of a pressurized combustor using the FOAM indicated that the monitor was capable of real‐time, fast tracking of transient alkali behavior in a high‐temperature/high‐pressure process stream.

ISSN:0034-6748    

DOI:10.1063/1.1139362

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A fiber‐optic pressure sensor is described which uses a diaphragm to modulate the mirror separation of a Fabry–Perot cavity (the sensing cavity). A multimode optical fiber delivers broadband light to the sensing cavity and returns the spectrally modulated light which the cavity reflects. The sensor’s output spectrum is analyzed using a tunable Fabry–Perot cavity (the reference cavity) to determine the mismatch in the mirror separations of the two cavities. An electronic servo control uses this result to cause the mirror separation of the reference cavity to equal that of the sensing cavity. The displacement of the pressure‐sensing diaphragm is then obtained by measuring the capacitance of the reference cavity’s metal‐coated mirrors. Relative to other fiber‐optic sensors, an important advantage of this instrument is its high immunity to the effects of variations in both the transmissivity of the fiber link and the wavelength of the optical source.

ISSN:0034-6748    

DOI:10.1063/1.1139363

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A wideband fiber‐optic system for the measurement of ac high voltages is presented. The system is based on a capacitively coupled Pockels cell which works as a passive voltage sensor. The lower frequency limit is a few Hz and the upper is 150–230 MHz depending on the application. Other system characteristics are excellent electrical noise suppression, large voltage range, high input impedance, and ability to perform differential measurements separated from ground potential. Furthermore, the low cost, rugged design, and ease of operation make it suitable for measurements in a variety of high‐voltage applications.

ISSN:0034-6748    

DOI:10.1063/1.1139364

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

This paper describes two opto‐electronic processes useful for measuring curvature radii of optical components. The two methods start from the fact that, within the geometrical optics approximation, a pencil of rays can be marked electronically and thus located during its propagation through the optical system. The two methods have proved to be useful for accurately measuring plano‐cylindrical lens curvature radius.

ISSN:0034-6748    

DOI:10.1063/1.1139365

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A versatile and compact fiber‐optic system for Raman scattering and photoluminescence is described. This optical fiber system was used for inelastic light‐scattering experiments at temperatures down toT=0.35 K and dc magnetic fields toB=30 T. We believe this is the first observation of Raman scattering in either of these environments, both of which are normally inaccessible with optical Dewars. The portable head has a 1‐cm o.d. and permits measurements longitudinal and transverse to the applied magnetic field. Observation of spin‐flip Raman scattering from donor bound magnetic polarons in (Cd, Mn)Se demonstrates this system at the extremes of both magnetic field and temperature.

ISSN:0034-6748    

DOI:10.1063/1.1139366

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The construction of a photoelastic modulator is described which is intended to push the long wavelength limit of infrared circular dichroism measurements down to about 300 cm−1(33 &mgr;m). A simple electronic circuit has been designed to drive the device. The performance of the modulator is evaluated by transmission and calibration spectra.

ISSN:0034-6748    

DOI:10.1063/1.1139656

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A device capable of measuring small displacements and vibrations of a moving body is presented. A small mirror, firmly attached to the object under investigation, deflects a pair of laser beams onto two distinct photodetectors. From the examination of the output signals, it is possible to have separate information on the rotational and translational movements of a surface.

ISSN:0034-6748    

DOI:10.1063/1.1139367

出版商:AIP    

年代:1987

数据来源: AIP