摘要:

An investigation of the use of mass‐loaded piezoelectric accelerometers for active damping of highQ, mechanical, vibration isolation suspensions is reported. The transfer function and noise of the accelerometer are modeled, and the predicted noise compared with measurements. A servo which damps the normal modes of a two‐stage suspension by sensing the acceleration of, and feeding back to, the intermediate mass is then modeled. The rms and ‘‘high frequency’’ closed loop motions of the isolated mass are calculated. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146656

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Time‐resolved electron‐beam diagnostics have been developed for use with free‐electron lasers (FELs) and associated electron sources, based on the techniques of secondary electron emission and optical transition radiation (OTR). The 32‐channel OTR detector forms part of a high‐resolution (0.18%) electron spectrometer with a time resolution of 50 ns. Variable‐magnification optics allow the spectrometer to view single‐macropulse spectra with widths in the range of 0.2%–7%; wider spectra are taken with several momentum settings. Design criteria for the spectrometer are presented, and experience of operating with the diagnostics over a range of FEL physics experiments is summarized. The spectrometer is used, in conjunction with optical diagnostics, in studies at FELIX of efficiency enhancement, pulse chirping, and stepped‐undulator operation. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146835

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In permanent magnet undulators, dimensional variations in the magnet blocks are responsible for displacing the magnets from their ideal positions. These displacements, which can be characterized in terms of the periodicity of the arrangement of the magnets, perturb the undulator field. It is shown that the deviations in the undulator field can be reduced to the desired level by adding two cost factors, based on the uniformity in periodicity, in the cost function used in the simulated annealing technique to determine the placement of the magnet blocks. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146647

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Calculable synchrotron radiation (SR) from BESSY dipole magnets has been used by PTB for radiometry from the visible to the soft x‐ray region with very low uncertainties for many years. The use of wavelength shifter (WLS) radiation bears the potential of extending the usable spectral range for radiometry with calculable SR to higher photon energies. Initial investigations on the feasibility of this approach have been performed: an energy dispersive high‐purity germanium detector (HPGe) was used to characterize the radiation of the new BESSY WLS with a magnetic field ofB=3.2 T. The HPGe detector has previously been calibrated and so the absolute spectral photon flux could be determined. The measured spectral photon flux was then compared to calculations and good agreement was found in the order of ±5%. Although this is to our knowledge the best agreement demonstrated so far for an absolute comparison of measured WLS radiation to calculations, further improvements are needed for a future radiometric use of WLS radiation. This will be discussed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146836

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have developed a new gas purifier for ArF excimer lasers that can remove all the impurities from degraded ArF excimer laser gas. We found that cooled activated charcoal at temperatures below −50 °C effectively removes CF4, which is the preponderant impurity generated in ArF excimer laser gas mixtures. We also demonstrated that the new gas purifier can regenerate the ArF excimer laser gas up to its initial purity level after about 1×109shots of operation. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146837

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a new and simple fiber‐optic backreflectance method for precise short distance measurement using a single‐mode fiber and cw laser. The method is based on the intensity sensing of focused backreflectance laser emission, and the spatial location of three specific points: the focal point of the focusing optical element and two object points. The optical fiber is used in a multifunctional regime where it serves simultaneously as a point light source, an object for projecting, and a point receiver that is highly sensitive to spatial displacements of the focused backreflectance emission. The experimental and analytical investigations conducted demonstrate the usefulness of the method for distance measurement with submicron (about 370 nm) and millimeter accuracies in the near and far distance region, respectively, for a mirror target 1 m away. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146838

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A Fourier transform (FT) apparatus specially dedicated to photoluminescence measurements in the near infrared has been assembled. The details of the experimental setup and a comparison with a conventional dispersive apparatus are discussed. Advantages of the FT approach for photoluminescence measurements as well as warnings about limitations and artifacts are illustrated. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146839

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A design of a photoacoustic (PA) cell for dynamic measurements in liquid samples with nanosecond time resolution is presented. The design is based on a layered scheme of laser‐induced sound excitation and detection. A theoretical basis for the use of the cell in dynamic PA diagnostics and in pulsed acoustic spectroscopy is given. The cell parameters which determine its performance in both applications are established, and ways of cell optimization are discussed. The validity of the theoretical description was proven in a set of calibration experiments. The functioning of the cell as a PA‐diagnostics device was tested on a model photochemical system (the quenching of the triplet state of benzophenone by 2,5‐dimethyl‐2,4‐hexadiene). With a slight modification the cell was used for pulsed broadband acoustic spectroscopy to probe the structural relaxation in formic acid in the frequency range of 2–20 MHz. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146840

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The general characteristics and spectrometric features of a high resolution four‐crystal reflection x‐ray monochromator with wavelength analysis installed at the HASYLAB beam lineLat DESY are presented. The monochromator is part of a spectrometer developed to calibrate x‐ray absorption edge spectra in the energy range of 6–36 keV with a relative uncertainty &Dgr;E/Efrom 10−5to 10−6. This requires an extremely effective suppression of harmonics and also a negligible instrumental influence in order to obtain almost intrinsic spectra. As the results show, the monochromator fulfills the requirements, including very high stability. An example of the calibration procedure for the copperKedge is given as well as a comparison of the remeasured absorption edge energies with the previously tabulated data. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146657

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A point‐focusing small angle x‐ray scattering (SAXS) camera using a doubly curved monochromator of a W/Si multilayer has been designed, constructed, and tested. The two radii of curvature of the monochromator are 20 400 and 7.6 mm. The reflectivity of its first‐order Bragg reflection for CuK&agr; radiation was calculated to be 0.82, being comparable to that (0.81) of its total reflection. By only 10 s x‐ray exposure, scattering from a high‐density polyethylene film was detected on an imaging plate (IP). A rotating‐anode x‐ray generator operated at 40 kV and 30 mA was used. Diffraction from rat‐tail collagen has shown that the optical arrangement gives the Bragg spacing up to, at least, 30 nm for CuK&agr; radiation. Combined with IPs, the camera may permit us to carry out time‐resolved SAXS measurements for phase behaviors of liquid crystals, lipids, polymer alloys, etc., on conventional x‐ray generators available in laboratories. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146841

出版商:AIP    

年代:1996

数据来源: AIP