摘要:

A beam profile sensor for use in an automatic alignment and power stabilization system for a multikilowatt CO2laser is described. An inexpensive pyroelectric array is used in conjunction with a diamond machined rotating wand, to provide on‐line samples of the laser beam. Interface circuits utilize the multiple outputs derived from the detector array for precise monitoring and control of the laser’s output radiation. Data from a 5‐kW CO2laser are presented to characterize the response of this new beam profile sensor to major perturbations in the optical cavity and lasing gas chemistry. The device has demonstrated exceptional performance in the maintenance of both mode quality and optical power level.

ISSN:0034-6748    

DOI:10.1063/1.1143295

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The construction of a differential optical absorption spectrometer (DOAS) is described. The instrument was designed for making automated measurements, with relatively high detection sensitivities, of important tropospheric trace gases, and with the ability to operate in rugged environments without frequent attention. Major innovative features of the instrument include a retroreflector to fold the light path, a diode array detector, and computer‐controlled operation of the entire instrument package. The advantages of these modifications with respect to previously reported designs are discussed in detail. This DOAS has been employed since 1989 to measure NO3(1 ppt), NO2(0.6 ppb), HONO, O3, and CH2O (0.8 ppb), where the mixing ratios in parentheses indicate the detection limits over a 5 km path length and 4 min integration time, for the species where these could be determined.

ISSN:0034-6748    

DOI:10.1063/1.1143296

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Signals acquired with a laser fluorosensor are composed of the fluorescence of the object and noises. The average ofnsignals theoretically has the signal‐to‐noise ratio (S/N) which is &sqrt;ntimes higher than theS/Nof the single signal, provided that the fluorescence remains constant from signal to signal and that the noises are independent of each other. In practice, the sources of noise in the signals are often correlated with each other, leading toS/Nimprovement below the theoretical one. In this paper a procedure is proposed and applied in a laser fluorosensor to obtain betterS/N. It is shown that the average signal can have betterS/Nif the signals with the correlated noises are selectively discarded by averaging many signals. This procedure can be advanced for improvingS/Nof any multi sample averager.

ISSN:0034-6748    

DOI:10.1063/1.1143297

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A new‐type disk antenna has been developed to search for continuous gravitational waves emitted from millisecond and submillisecond pulsars. The antenna not only has a wide tunable range of the eigenfrequency that covers down to almost half of the original frequency of the quadrupole mode, but also is easily tuned to an objective frequency with an accuracy of 4×10−5at 4.2 K. The mechanical quality factor has reached 3.0×107at 4.2 K in an antenna made of Al5056.

ISSN:0034-6748    

DOI:10.1063/1.1143298

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A general method for determining true acoustic‐mode linewidths from Brillouin scattering data is presented. The method is specifically applied to diamond anvil cell experiments to obtain accurate hypersonic attenuation data at high pressure. This work was motivated by the noticeable lack of acoustic attenuation data at high pressure in the literature and by our own attempts to obtain relaxation data from Brillouin experiments in the diamond anvil cell. A detailed discussion of both instrumental and finite aperture contributions to the measured acoustic‐mode linewidth is given, as well as specific algorithms for calculating these effects. Fits to Brillouin scattering spectra obtained at high pressures in different organic liquids are shown. Finally, a discussion is given of experimental details for obtaining accurate Brillouin linewidths in high‐pressure diamond anvil cell experiments.

ISSN:0034-6748    

DOI:10.1063/1.1143299

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A compact, normal incidence vacuum ultraviolet (VUV) fluorescence spectrometer for use with both electron and photon excitation in the energy range of 15–40 eV was built and tested. This 1‐m concave grating spectrometer is described together with the performance of its microchannel plate‐charge coupled device detector system. Results of the calibration of the system at the SURF‐II synchrotron light source at the National Institute of Standards and Technology are given. Initial results of experiments using both photon and electron excitation are also presented.

ISSN:0034-6748    

DOI:10.1063/1.1143300

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A beamline has been established at the National Synchrotron Light Source to perform angle‐resolved photoemission experiments on magnetic surfaces with spin sensitivity. The system has two novel features: it uses a miniature electron‐spin polarization analyzer and it also uses synchrotron radiation from an undulator rather than a bending magnet.

ISSN:0034-6748    

DOI:10.1063/1.1143301

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In order to improve the sensitivity of photothermal deflection spectroscopy, we propose a double pass method, in which a pump beam is passed twice through the sample using a total reflector set behind the sample. A one‐dimensional theoretical analysis of this method is developed and is verified by the measurement results of Si and InP wafers. Also, it is shown theoretically and experimentally that this method can determine lower optical absorption coefficients than conventional ones.

ISSN:0034-6748    

DOI:10.1063/1.1143302

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Since atomic force microscopy (AFM) is capable of imaging nonconducting surfaces, the technique holds great promises for high‐resolution imaging of biological specimens. A disadvantage of most AFMs is the fact that the relatively large sample surface has to be scanned multiple times to pinpoint a specific biological object of interest. Here an AFM is presented which has an incorporated inverted optical microscope. The optical image from the optical microscope is not obscured by the cantilever. Using aXYstage to move the sample, an object is selected with the optical microscope and an AFM image of the selected object can be obtained. AFM images of chromosomes and K562 cells show the potential of the microscope. The microscope further enables a direct comparison between optically observed features and topological information obtained from AFM images.

ISSN:0034-6748    

DOI:10.1063/1.1143303

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Fabrication of a variety of ultrasmall tunneling structures is presented for possible applications in single electronics. Two main structures are described: (i) arrays of nanometer‐scale metal dots and (ii) single and multiple linear tunnel junctions formed by overlapping lines. Very large, uniform particle arrays were fabricated by electron‐beam lithography (EBL) with particle diameters as small as 25 nm. The advantage of our dot array system is its high degree of uniformity and very small junction size coupled with the use of isolated particles to reduce stray capacitance effects. Single and multiple linear tunnel junctions were fabricated by EBL using single‐layer resist and angled evaporations. Our fabrication technique differs from previous ones in its ability to create very small tunnel junctions without the need for multilayer resist systems or precise knowledge of the angle of evaporation.

ISSN:0034-6748    

DOI:10.1063/1.1143304

出版商:AIP    

年代:1992

数据来源: AIP