摘要:

We have developed a novel simple technique for a wide gain laser narrow line selection and tuning using classical interferometric selectors (Fabry–Perot interferometer, interference wedge). Its most important advantage is that selection and tuning need only one thick interferometer instead of a combination of a thin (5 &mgr;m) and a thick (∼100 &mgr;m) one as in the conventional approach. This makes tuning much simpler without having to synchronize two tuning elements and the system as a whole essentially cheaper. The computer simulation and the experimental test have shown that the proposed technique is highly competitive compared with traditional interferometers with thicknesses of 30–70 &mgr;m. It assures a spectral resolution of less than ∼0.01 nm and tuning in the wide region (≥100 nm), in particular, it completely covers the spectrum of the dye solution and that of the Ti:Al2O3crystal. Besides enlarging the tuning region, the linewidth is narrowed and the spectral purity of emission is increased. Using a qualitative interferometer with transmission close to unity a high efficiency can be reached. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146968

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present an analysis of the Fabry–Pe´rot response to a phase‐modulated light in the reflection mode, by considering the general problem of the lock‐in detection at thepth harmonics of the rf modulating frequency. Suitable frequency modulation conditions for servo‐locking purposes are obtained and the values of modulation index which maximize the sensitivity for the first, third, and fifth harmonics are found. Moreover, we investigate the effects of the residual amplitude modulation introduced by the electro‐optic frequency modulator, the presence of laser amplitude and frequency noise, and the dependence of the achievable closed‐loop frequency fluctuation spectrum on the modulation index and detection noise. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146982

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This article describes a new, direct way to measure the time evolution of single light pulses in the subnanosecond region using time‐of‐flight analysis. The light pulse is coupled into a set of 40 optical fibers of increasing length arranged in an array. The output of the fiber array is imaged onto a fast gated optical imager (gatewidth 100 ps) coupled to a CCD camera (12 bit). The intensified part of the pulse of each fiber corresponds to the intensity of the light pulse at a different time due to the different transmission time of each fiber. Additional, two‐dimensional (2D) spatial resolution is possible if image guides are used instead of fibers. The temporal resolution is limited by the gatewidth of the detector. The difference in length between the longest and the shortest fiber determines the total period of time displayed by the system (1 ns). The pulse characteristics of a recently developed short‐pulse Raman‐excimer laser are analyzed as an example of an application. Laser parameters like pulse length, energy stability, and jitter are measured with the fiber array. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146983

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Vehicles that are required to travel off‐road in arid and semiarid conditions can be exposed to high levels of airborne particles. The airborne material, typically sand, can be detrimental to the performance of air‐breathing engines and other mechanisms. The U. S. Army, for instance, has experienced the influence of airborne desert dust during testing of equipment at Yuma Proving Ground, and during critical operations at other desert locations. To enhance testing of equipment under loading of airborne desert dust, a laser‐based nephelometer has been constructed which provides the real‐time measurement of dust mass per unit volume. The instrument is sensitive and provides a linear response to dust concentration levels from 0.01 to above 25 g/m3. Important is that: (1) the light scattering technique is independent of particle size distribution in the sampling volume; and (2) the instrument is rugged to allow for mounting and operation on vehicles traveling off‐road in the desert environment. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146984

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have investigated the feasibility of widening the bandpath of the Bragg–Fresnel optical element through the use of ion implantation. The focusing properties of Bragg–Fresnel lenses (BFLs) were studied as a function of the implantation dose and energy. An enhancement of the focus intensity of up to 15% was found, which is less than expected. Due to the complicated scattering of the low energy ions inside the micrometer‐ and submicrometer‐sized crystal features that make up the BFL relief, the implantation technology destroys the peripheral zones of the BFL more than it increases the intensity in the focus. Nevertheless we believe that high energy implantation can be successfully used to modify the BFL reflectivity, especially in the case of nearly backscattering reflection. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146985

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A high resolution x‐ray video camera has been developed for Synchrotron radiation x‐ray microimaging applications. The image from an x‐ray converter screen is optically coupled to a charge coupled device. A linespread function of 10 &mgr;m full width at half‐maximum has been observed. This concept may be extended to the resolution range of 1–100 &mgr;m. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146986

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A highly automatic system with a three‐angle rotation mechanism has been designed and constructed to measure several thousand permanent magnet blocks. The system’s main features include its high speed, highly automatic measurement, and the ease with which the different size magnet blocks can be installed and removed. This system provides precise and accurate measurements of the three orthogonal magnetic moment components to accurately characterize each block, as deemed necessary to assess the field quality of undulators and wigglers. A three‐angle in rotation mechanism, together with a simple mathematical algorithm is used to measure and analyze the magnetic moments of the magnet block. The system includes the Helmholtz coil pair, block holder, the three‐degree rotation mechanism, and the control and data acquisition system. A power train system consists of one motor coupled with a nonmagnetic stainless steel for 360° rotation and two motors individually coupled with two groups of nonmagnetic time belts for rotation angles of 0°, 180°, 0°, and 90°. The control system uses a microcomputer together with a stepping motor control card and a digital fluxmeter connected by the general purpose interface bus. The measurement speed of this system is 40 blocks per h. One reference magnet was measured, with those results verifying the long term precision of the order of 0.04% for the easy component and 0.02° for two minor components. The coil‐pair geometry factor is calibrated via the voltage‐field reciprocity principle, indicating that the system absolute accuracy is around 0.43%. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146987

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present an apparatus which is capable of small‐angle x‐ray scattering studies of polymer deformation at strain rates ranging from 49.6 &mgr;m/s to less than 0.033 &mgr;m/s and temperatures ranging from room (≊22 °C) to 120 °C. The system also includes a load cell for measuring the force applied to the sample and a symmetric stretching system to keep the sample centered in the x‐ray beam. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146969

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe a crossed electron beam‐atomic beam apparatus which utilizes a pulsed electron gun and field free drift tube to obtain time‐of‐flight (TOF) spectra of electrons scattered from atoms and molecules. This apparatus was constructed for the purpose of obtaining inelastic‐to‐elastic differential cross‐section (DCS) ratios in the energy range extending from threshold to several eV above the threshold of the inelastic channel. The TOF approach eliminates the need for complicated calibration procedures required when using conventional electrostatic electron energy‐loss spectroscopy (EELS) at these low energies. The characteristics of the apparatus will be given, along with representative TOF spectra from carbon monoxide. From those spectra we obtained DCS ratios at 90° scattering angle for excitation of thea3&Pgr; state of CO, in the impact energy range of 6–15 eV. These ratios were measured with uncertainties as small as ±4%, which represents a substantial improvement over previous measurements in this energy range. This demonstrates the feasibility of using the TOF technique to measure DCS ratios which in turn can serve as secondary standards to normalize other inelastic DCSs obtained from measurements with EELS. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146970

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe the experimental setup at Centro Ato´mico Bariloche for the measurement of doubly differential electron distributions, in energy and angle of emission, induced by atomic collisions. We present detailed information about the performance of the equipment including a discussion of instrumental effects that could have affected the measured spectra. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146971

出版商:AIP    

年代:1996

数据来源: AIP