摘要:

A new measurement system has been developed for two-photon spectroscopy in solids with a combination of synchrotron radiation and laser. This system is based on a time-gated photon counting technique to observe luminescence signals induced by two-photon excitation. It is demonstrated that this technique enables us to achieve a high sensitivity and a good signal-to-noise ratio because it is a kind of zero method. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148874

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A digital control system has been developed for the iodine stabilized He–Ne laser. The system is based on a digital signal processor and a general purpose microprocessor. The hardware is briefly described. The algorithms used for laser frequency locking are presented and new methods which are made possible by this system are discussed. An improved way of locking the laser to the fifth or seventh harmonic of the modulation frequency has been implemented digitally. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148875

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new array calorimeter detector has been developed and was used to measure the spatial profile of a KrF laser with 300 J energy and a 267 mm diameter in near field. The detector contains 441(21×21)calorimeters. A tantalum foil is used as the absorber. The boiling of liquid nitrogen is used as the reference temperature of the thermocouples, as it is both insulating and stable. Thus, it is the basis of the physical measurement in the sub-&mgr;V–mV level with a multithermocouple detector. The response of the tantalum foil is linear in the range of fluence from30 mJ/cm2to1.1 J/cm2.The experimental results show that the spatial profile of the KrF laser pumped by two side electron beams is saddle shaped with a valley at the center and one peak at each side of the center on the coaxial line of electron beams in the near field. With a decrease of the laser’s gas pressure, the distribution become more even rather than flat. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148876

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A simultaneous time and frequency-resolved photoluminescence setup based upon the concept of sum-frequency generation has been developed using the parallel collection capabilities of a liquid nitrogen cooled, high quantum efficiency charge coupled device (CCD) detector. This up conversion system can provide excellent time resolution (down to∼100 fs), when the detector is used in the single channel mode, with large dynamic range. When the CCD detector is used in its full capacity (1024 channels), wide spectral range as well as temporal information are obtained simultaneously from the up-converted signal, thus providing important information on the dynamics of various emission peaks which can occur simultaneously. Together with this, an efficient method for generation of high repetition rate, low energy infrared light between 1.44 and 1.62 &mgr;m is described. The technique uses difference frequency mixing of the fundamental wavelength of a mode-locked Nd:yttrium aluminum garnet laser and the output of a synchronously pumped Rhodamine 640 dye laser in a 10 mm long lithium triborate crystal. This source was then used to performed cw and time-resolved up-conversion photoluminescence measurements on a 1.54 &mgr;m emitting InGaAsP epitaxial layer. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148877

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We characterize an x-ray spectrometer in the wavelength range 10–70 Å. The instrument has been designed for the study of the soft x-ray emission from plasmas generated with intense sub-ps laser pulses. It uses a flat field reflection grating with 2400 lines per mm as dispersing element and an x-ray charged coupled device (CCD) as detector. The sensitivity of the spectrometer and CCD detector has been absolutely calibrated by means of a ns-laser generated gold plasma of well known x-ray conversion efficiency. The calibration procedure is explained in detail. Finally, we present examples of spectra emitted by a sub-ps laser plasma. From the spectra follows a resolving power of 150–350 and a low conversion efficiency into the second diffraction order of the flat field grating of only a few &percent;. The measured frequency averaged total conversion of laser energy into x-ray energy emitted into2&pgr;is in the range of2.4×10−4up to6.2×10−3depending on the material of the solid targets. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148878

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A high-pressure fiber-optic light-scattering spectrometer has been constructed forin situobservation of molecular dissolution/association as well as the polymerization process in supercritical fluids. Single (or multiple) fiber-optic probes, each comprised of a single optical fiber (or multiple optical fibers) and a graded index microlens, are used to transmit the incident laser beam and to receive the scattered light as well as the transmitted light from the high pressure cell. The direct immersion in the scattering medium of the fiber-optic probes makes the spectrometer more compact and more flexible with an easier alignment process. With the miniaturization and flexibility, our high-pressure light-scattering cell can be transported and adapted in combination with other physical techniques, such as synchrotron small angle x-ray scattering which requires a different set of windows (e.g., made of diamond) suitable for x-ray transmissions. This spectrometer has been successfully used for thein situstudy of the molecular association behavior of a diblock copolymer of 1,1-dihydroperfluorooctylacrylate and vinyl acetate in supercritical carbon dioxide under pressures up to 552 bar. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148879

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A novel hybrid interferometer stabilization scheme used for wavelength shift measurement, such as for in-fiber Bragg grating-based sensors, is described. This scheme combines the advantages of the long term optical imbalance stability offered by the locking system used and a comparative insensitivity to vibration-induced noise at frequencies up to 200 Hz, achieved with the use of a so-called “detection-and-compensation” scheme. By including an additional reference beam and the hybrid interferometer stabilization scheme, the vibration-induced fluctuation in the signal can be reduced by about 20 dB, and the value of the phase variation can be reduced by a factor of 20. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148880

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We proposed a method to estimate the point-spread function from the power cepstrum of the penumbral image in this paper. It is used as a preprocessing step before deconvolution. Both computer simulations and experimental results for real x-ray imaging demonstrated the potential of the method for practical applications. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148881

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have fabricated and characterized the performance of a monolithic Ge Bragg–Laue phase retarder capable of simultaneously producing both right- and left-handed circularly polarized x rays. The energy range of operation of the phase retarder is between 50 and 100 keV making it well suited to the measurement of spin-dependent Compton profiles within the impulse approximation, primarily because of the increased momentum resolution and larger Compton scattering cross section available at these higher incident energies. Although the phase retarder was optimized for operation at 86 keV, it can produce highly circularly polarized x rays over a substantial energy range. The performance of the phase retarder was tested via magnetic Compton scattering measurements on an Fe sample at the undulator A of the Advanced Photon Source. It was found to perform well in terms of flux and degree of circular polarization thereby greatly reducing the data collection times required for this inherently weak scattering process. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148882

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe a simple method for creating multiple optical tweezers from a single laser beam using diffractive optical elements. As a demonstration of this technique, we have implemented a4×4square array of optical tweezers—the hexadeca tweezer. Not only will diffractively generated optical tweezers facilitate many new experiments in pure and applied physics, but they also will be useful for fabricating nanocomposite materials and devices, including photonic bandgap materials and optical circuit elements. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148883

出版商:AIP    

年代:1998

数据来源: AIP