摘要:

Since the discovery of photosensitivity in optical fibers there has been great interest in the fabrication of Bragg gratings within the core of a fiber. The ability to inscribe intracore Bragg gratings in these photosensitive fibers has revolutionized the field of telecommunications and optical fiber based sensor technology. Over the last few years, the number of researchers investigating fundamental, as well as application aspects of these gratings has increased dramatically. This article reviews the technology of Bragg gratings in optical fibers. It introduces the phenomenon of photosensitivity in optical fibers, examines the properties of Bragg gratings, and presents some of the important developments in devices and applications. The most common fabrication techniques (interferometric, phase mask, and point by point) are examined in detail with reference to the advantages and the disadvantages in utilizing them for inscribing Bragg gratings. Reflectivity, bandwidth, temperature, and strain sensitivity of the Bragg reflectors are examined and novel and special Bragg grating structures such as chirped gratings, blazed gratings, phase-shifted gratings, and superimposed multiple gratings are discussed. A formalism for calculating the spectral response of Bragg grating structures is described. Finally, devices and applications for telecommunication and fiber-optic sensors are described, and the impact of this technology on the future of the above areas is discussed. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148392

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the design of a long wavelength extension to the free electron laser for infrared experiments. A parallel plate is inserted in the resonator to reduce diffraction losses. It will be shown that with a 10 mm gap waveguide, single transverse mode operation can be expected over a wavelength range from 300 down to 40 &mgr;m, allowing pulses as short as a few optical cycles to be produced. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148393

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The potential use of a free electron laser (FEL) amplifier as a diagnostic tool for relativistic electron beams is investigated. It is in fact shown that a simple relation exists between electron bunch length, energy spread, and the gain of a FEL resonant amplification. It is also discussed how the beam qualities can be derived from an actual experimental configuration. Finally, the possibility of combining the present methods to other techniques, like nondestructive diagnosis with short undulators, is also analyzed. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148394

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article reports on the results of free electron laser (FEL) power transmission measurements through chalcogenide fibers. The FEL power transmission was tested by two types of chalcogenaide NSEG fibers, a normal fiber and a tapered fiber, made by varying the drawing speed from 2 to 17 cm/min. As a result, the tapered NSEG fiber is able to transmit 5–7 &mgr;m FEL power with a 10 MW/micropulse without surface damage. Tapered NSEG fibers are useful, therefore, for power transmission to narrow spaces such as the slide glass between the stage and the objective lens in a microscope. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148395

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel scheme combining interferometer and refractometer for simultaneous plasma density and plasma density gradient measurements is described. The scheme employs a ribbon laser beam obtained from one-dimensional laser beam expansion by a pair of cylindrical lenses. This beam shape allows measurements at several spatial locations simultaneously. The beam deflection measurements give additional important information on the spatial distribution of plasma density gradient in the direction perpendicular to the major axis of the expanded beam. Fast pin photodiodes are used as light detectors for temporal resolution better than 1 ns. The high power (700 mW) of the argon ion laser allows 0.1° phase resolution and simultaneously 0.1 mrad refractional deflection angle resolution. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148396

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new digital correlator was developed. The one-bit-clipped digital correlator used so far is simple and sensitive enough to detect one photon. The clipping circuits, however, tend to distort the temporal characteristics. In order to alleviate the distortion, we extended the clipping points of counters and multipliers to two bits and three bits, respectively. The novel correlator has the dynamic range ten times wider than that of one-bit-clipped correlator. Here we report the 130 channel correlator that uses seven chips of field programmable gate array. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148391

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel atmospheric temperature programmed desorption-mass spectrometer (TPD-MS) device based on supersonic molecular beams (SMB) is demonstrated. The coupling between SMB and TPD-MS enables one to obtain highly sensitive TPD measurements with very fast time response (less than 1 s), that makes it possible to distinguish between desorptions from energetically neighboring sites. Quantitative adsorption measurements of adsorbing gas and vapors could be easily done. High detection sensitivity of 4 ng/s forH2O16and 100 pg/s forH2O18is achieved. The high sensitivity TPD measurements are demonstrated by the ability to monitor simultaneous physical adsorption of nitrogen, oxygen, and water on various sites on carbon fibers at room temperature. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148397

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A double-beam Ti:sapphire laser photolysis system has been constructed for measurements of the subpicosecond transient absorption spectra by a pump-probe method. Although the spectroscopic characteristics tested for the practical availability are satisfactory enough, the transient absorption spectrum thus obtained exhibits an artificial time-dependent spectral change owing to the group velocity dispersion of the probing light pulse. Hence, its wavelength-dependent arrival time to the sample cell is determined utilizing the optical Kerr effect induced in carbon tetrachloride and the true transient absorption spectrum (the corrected spectrum) at a given delay-line setting is calculated by a microcomputer using a great number of uncorrected transient absorption spectra obtained at different delay-line settings. Interestingly, the corrected singlet-singlet absorption band (bandCwith a lifetime of 0.8 ps) obtained for the lowest excited singlet state of 9-nitroanthracene in cyclohexane really shifts with time. This can be interpreted in terms of the wide wavelength-range superposition of bandCand an absorption band which increases and then decreases with rise and decay times of 0.8 and 1.8 ps, respectively; the latter band is ascribed to the absorption of 9-nitrite (or its precursor) or that of a higher excited triplet state of 9-nitroanthracene. By 400 nm biphotonic excitation of the neat solvents (cyclohexane andn-heptane), furthermore, population of their higher excited singlet states with a very short lifetime of 0.4 ps can be seen. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148398

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The design of a synchrotron x-ray liquid surface spectrometer at beamline X19C at the National Synchrotron Light Source is described. This spectrometer is capable of performing the full range of x-ray surface scattering techniques. A few examples of measurements made using this spectrometer are presented, including studies of organic monolayers on the surface of water and of the structure of strongly fluctuating oil–microemulsion interfaces. The measurements discussed illustrate the accuracy, resolution, and capabilities of the spectrometer. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148399

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A compact 60 kV Mott polarimeter has been constructed, tested, and calibrated especially for the local analysis of surface and two-dimension magnetism by means of electron spectroscopy with spin resolution. The use of construction combining spherical accelerating field with the absence of retarding potential after electron scattering provides low sensitivity of the polarimeter to movements of the analyzed electron beam and changes in its diameter. Special silicon surface-barrier detectors with large electron-optical acceptance provide efficiency∈(≡Seff2×I/I0)about≈2.5×10−4.The unique fast electronics allow to work with maximum count rate of detected electrons up to5×106 counts/s.As a result, there is the possibility to calibrate the polarimeter (to calculate the effective Sherman functionSeff) by extrapolation of the measured asymmetry to the high level of discrimination. This instrument is compact, fully UHV compatible and may be used in other fields of solid state physics, atomic physics, and physics of high energies. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148400

出版商:AIP    

年代:1997

数据来源: AIP