摘要:

This paper presents a design for a Fabry–Perot optical frequency reference resonator which utilizes the high dimensional stability of cryogenically cooled sapphire. We show that cryogenic sapphire cavities can achieve substantial improvements in frequency stability compared with room‐temperature cavities. The design of a laser stabilization system based on such a resonator is discussed. Estimates of fundamental and practical limitations on the frequency stability of such a system suggest that a fractional frequency stability of 10−16over integration times from 10 to 104s is possible. The fundamental limits to stability from quantum shot noise, radiation pressure fluctuations, and thermal noise are overwhelmed by practical limits which arise due to mechanical, thermal, and optical effects. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145629

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A method for obtaining very high electro‐optic switching rates is demonstrated and employed for cavity dumping of a synchronously pumped mode‐locked dye laser. The intracavity light switch consists of a Pockels cell and a thin‐film polarizer. A synchronous, field‐effect transistor‐switch based generator delivers, at 10 MHz repetition rate, 15‐ns pulses with an amplitude of 300 V required for operating the Pockels cell. High electrical efficiency is obtained by connecting the Pockels cell via a resonant line. Dispersion of the high‐voltage pulse shuttling on the line is minimized by using phase compensation networks at its ends. From the optical pulse circulating in the laser cavity at 80 MHz, an adjustable fraction is dumped out on every eighth round trip. Intermediate pulses are suppressed by about 1:100. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145630

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This paper deals with the specifications and the possibilities of a novel highly sensitive optical absorption spectroscopy method. It consists of a cascaded arc as an extremely bright broadband light source with a high resolution spectrometer as a detector. Its interest for a continuous quantitative monitoring of the densities of waste atoms and molecules in the atmosphere is investigated. To this end, theoretical considerations are given with respect to the detection limits and the resolution necessary for selective spectrochemical analysis. In the first measurements with the setup, on a laboratory argon‐hydrogen plasma, the versatility and sensitivity of the technique for measuring low species densities is demonstrated. Densities of the sublevels of the argon first excited state, the four Ar(3p54s) metastable and resonant substates, were measured simultaneously in one measuring sequence. The data were analyzed using an efficient line of sight integration technique. The densities of these substates are of the order of 1017m−3in a plasma with a pressure of 40 Pa. For the atomic hydrogen H(n=2) state, densities of the order of 1014m−3over a length of about 2 cm could be measured, representing a detection limit of approximately 2×1012m−2. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145631

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This paper describes an experimental setup for spectroscopy measurements based on the digital processing of samples obtained by digitizing the signal pulse as it appears at the output of a proper conditioning circuit. The system shares with conventional pulse‐height analysis systems the connection to the detector and the preamplifier, but differs from them as it uses an antialiasing filter and a digitizer instead of a shaper and a multichannel analyzer. The implemented algorithm maximizes the signal‐to‐noise ratio in the estimate of the amplitude of the signal pulse and represents the digital counterpart of the optimum analog processor stated by the theory of the optimum filtering. The system is able to synthesize the best possible filter through the on line measurement of the noises actually present in the experiment, thus leading to the best resolution and allowing a total flexibility in adapting to changeable noise conditions. The performance of the digital system in terms of resolution is investigated and its count rate capability is mentioned. In particular, an improvement in energy resolution of more than 10% has been experimentally achieved with respect to conventional systems based on analog circuitry. All the components of the system are described and, as an example of application, the energy spectrum of241Am is acquired and reported. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145632

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We studied the possibility of soft x‐ray microscopy using unoccupied &pgr;*‐character molecular orbits of bases in DNA and RNA. We estimated the photoabsorption cross section of benzene molecule using the atomic base model. Discussion is extended to the case of nuclear acid bases caused by excitation of the 1selectron to the &pgr;* orbit under assumption of the similar electronic transition with the benzene case and found that for the photon energy used in this study it is three times larger than that for the photoionization of the 1selectron at the water window region. We concluded that an image of DNA or RNA in wet biological cells may be observed with good contrast using this proposed method. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145633

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A double‐focusing small‐angle x‐ray scattering camera has been installed at the European Synchrotron Radiation Facility. The camera uses a low‐&bgr; undulator as insertion device. Stable operation has been demonstrated at 13 keV. A beam size at the sample position in the range of 100–200 &mgr;m and a flux in excess of 1010Ph/s have been obtained. The camera allows to resolve the first order of collagen (67 nm). ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1146450

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Groundstation antennas located in Western Australia have been used as elements in the Southern Hemisphere very long baseline interferometry (VLBI) experiment. These commercial antennas of 27.5 and 15 m diameter provide a very economical improvement to the imaging capability of this array and the practice of using such antennas can be extended to other sites in the Southern Hemisphere in preparation for the forthcoming space‐VLBI experiments. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145634

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Theoretical and experimental investigations for a new design of an ultrashort pulsed laser activated electron gun for time resolved surface analysis are described. In addition, a novel electron detection and image analysis system, as it applies specifically to time resolved reflection high‐energy electron diffraction in the multiple‐shot operation, are reviewed. Special attention is directed to minimize the photoelectron transit‐time spread from the electron gun, in spite of an unusually long focal length and a small convergence angle of the pulsed electron beam. Both requirements are necessary to use the electron gun for diffraction techniques. The design value for the temporal resolution in the synchroscan operation is 1.3 ps. Based on a thorough theoretical investigation, a new electron gun has been designed, constructed, and tested. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146036

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new type of relativistic electron acceleration facility is being developed by the Laser Science Research Group at The Institute of Physical and Chemical Research. It utilizes laser‐induced photoelectrons accelerated by a compact DISKTRON electrostatic accelerator, which makes it possible to generate a controllable bright short‐pulsed electron beam up to the energy of 1 MeV with a low emittance (<2×10−5mrad) and high current density (∼500 A/cm2) without any guiding field. The characteristics of the entire facility and some of the key components are described in detail. The experimental results which confirm the possibilities of increasing quantum efficiency of metal photocathodes by geometric alteration are reported. Observation of laser undulator effects in the visible wavelength was demonstrated in the facility. The coming use of the system includes a far‐infrared/submillimeter free‐electron laser using a microwiggler and generation of extreme ultraviolet radiation by the laser undulator. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146037

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Characteristics and application of a nozzle‐beam‐type microwave radical source are described. This source generates microwave plasma in a space between a nozzle and a skimmer for exciting a processing gas. Long‐lived metastable nitrogen molecules effective for film growth processes are observed clearly in this source.p‐type doping of ZnSe films was achieved by employing this source with N2plasma which was installed in a molecular‐beam epitaxy system. A net acceptor concentration of 5.4×1017cm−3was obtained byC–Vmeasurements with lower microwave power of 50 W and lower gas flow of 0.06 sccm compared to conventional rf plasma sources. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146517

出版商:AIP    

年代:1995

数据来源: AIP