摘要:

Excited by the frequency doubled optically compressed 10‐ps pulses from a cw mode‐locked Nd:YAG laser, the amplified output from a GaAs photoconductive device was used to drive a synchronously operated Photochron IIA streak camera at 300‐MHz sweep rates. A temporal jitter of ±6 ps was measured which was limited by the driving laser pulse width and amplitude stability.

ISSN:0034-6748    

DOI:10.1063/1.1139093

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We describe a new type of electric probe which is capable of measuring the time‐resolved current density profile of a stable, reproducible, high‐energy (>4‐MeV) high‐current (>1‐kA) electron beam. The sensing element of this probe is an open‐ended but capped‐off 50‐&OHgr; coaxial line constructed of graphite. The graphite sensor is 4.3 mm in diameter, 6 cm long, and is range thin to the primary beam electrons. The probe produces a signal proportional to the intercepted beam current. When the sensor is scanned radially through the beam during repeated pulses, a curve of signal versus depth of insertion is produced from which the radial current density profile can be determined. Measurements are presented of the profile of the electron beam from the Experimental Test Accelerator (4.5 MeV, 10 kA) at Lawrence Livermore National Laboratory. Good agreement is shown between measurements made with this probe and the beam radius as predicted by transport codes. The advantage of the electric probe lies in its ruggedness, simplicity, inherent fast rise time, and low cost. In contrast to other systems it requires no radiation shielding, water cooling, or auxiliary support equipment to operate in an intense beam environment.

ISSN:0034-6748    

DOI:10.1063/1.1139094

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A self‐integrating magnetic‐loop device having a rise time of less than 175 ps has been developed to monitor the temporal behavior of the current and position associated with an electron beam. Beam current and centroid position are measured with a 2‐GHz bandwidth by combining the output of these loops with two 0°/180° hybrids. The improved monitors are essentially free of self‐resonances and spurious responses at bandwidths extended to 2 GHz. The probes are economical and easy to produce in volume for a wide range of applications.

ISSN:0034-6748    

DOI:10.1063/1.1139095

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

It is possible to generate high‐power microwave pulses with fast rise time by using resonant cavities to obtain power gain from pulse compression. In the usual case, especially when normal‐conducting cavities are used, the principal output pulse from a pulse‐compression device is preceded by a precursor signal that may be only 40 dB below the main pulse. For some applications this large a prepulse is unacceptable. We have developed a prototype normal‐conducting,x‐band, pulse‐compression cavity in which the prepulse is suppressed by more than 70 dB. When this cavity is driven by a 20‐kW source, output pulses with 200‐kW peak power, 5‐ns pulse width, and sub‐nanosecond rise time can be obtained. We have also built ans‐band cavity that has produced pulses of 5‐ns width, 200‐MW peak power, and under 3‐ns rise time. Thes‐band cavity is typically driven at 5–10 MW and has a prepulse that can be more than 80 dB below the peak of the main pulse.

ISSN:0034-6748    

DOI:10.1063/1.1139096

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

One method of generating short, high‐power microwave pulses is to store rf energy in a resonant cavity over a relatively long fill time and extract it rapidly. With this pulse compression technique power gain roughly equal to the ratio of fill time to extraction time can be obtained. During the filling of a resonant cavity some of the energy is lost in heating the cavity walls, and some will generally be reflected at the input coupling of the cavity. In this paper, we discuss the time dependence of the stored energy and related quantities and the way in which it depends on the coupling of the source to the cavity.

ISSN:0034-6748    

DOI:10.1063/1.1139097

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new type of sub‐keV x‐ray (0.1–1.2 keV) spectrometer diode array time‐resolved transmission grating spectrometer (DATTS) with a fast time response (≤270 ps) has been developed to measure transient soft x‐ray spectra from laser‐produced plasmas. DATTS, the combination of the transmission grating (TG) and fast biplanar diodes, offers many advantages over the conventional x‐ray diagnostics. Among the advantages are flexibility of the energy windows, fast time response, large dynamic range, and the capability of measuring absolute x‐ray energy. All of these measurements have not been possible with a single diagnostic. The performance of the DATTS was compared with the data taken with the x‐ray diode system, showing excellent agreement in the sub‐keV x‐ray energy range.

ISSN:0034-6748    

DOI:10.1063/1.1139098

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

This paper describes a dual‐beam, tunable diode laser (TDL) spectrometer built for gas‐phase vibrational spectroscopy studies. It employs a commercially available cryogenic cooler and control electronics and can incorporate Pb‐salt diode lasers with operating wavelengths from 7 to 12 &mgr;m. The instrument optics have been largely assembled using inexpensive reflecting components. An IBM personal computer with enhanced graphics and high‐speed data‐acquisition unit permits dual‐channel sweep averaging (normally done with expensive, commercial hard‐wired units) as well as on‐line spectral line parameter calculations. Such an arrangement puts this type of laser spectroscopy capability within reach of undergraduate physics and chemistry programs.

ISSN:0034-6748    

DOI:10.1063/1.1139099

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We developed a frequency‐domain fluorometer which operates from 4 to 2000 MHz. The modulated excitation is provided by the harmonic content of a laser pulse train (3.76 MHz, 5 ps) from a synchronously pumped and cavity dumped dye laser. The phase angle and modulation of the emission are measured with a microchannel‐plate photomultiplier (PMT). Cross‐correlation detection is performed outside the PMT. The high‐frequency signals for cross correlation were obtained by multiplication of the output from a 500‐MHz frequency synthesizer. The performance was verified in several ways, including measurement of known time delays and examination of standard fluorophores. The detector displayed no detectable color effect, with the 300–600‐nm difference being less than 5 ps. The precision of the measurements is adequate to detect differences of 20 ps for decay times of 500 ps. A correlation time of 53 ps was found for indole in water at 20 °C. The shortest correlation time we measured was 15 ps for indole in methanol/water (75/25) at 40 °C. Also, the 2‐GHz data reveal the time‐dependent ((t)1/2) terms found in the presence of collisional quenching. The degree of random error is about 0.3° of phase and 0.005 in modulation throughout the frequency range.

ISSN:0034-6748    

DOI:10.1063/1.1139215

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A spectrometer for measuring spontaneous Raman scattering in gaseous samples at pressures below 100 Pa (0.75 Torr) with nanosecond time resolution is presented. The apparatus was developed for studying intramolecular vibrational energy distributions in infrared multiphoton excited molecules and makes it possible to study the anti‐Stokes Raman scattering from isolated molecules at pressures down to 14 Pa (110 mTorr). To achieve high sensitivity and time resolution simultaneously, spectral resolution (1 nm) is sacrificed. Because of the low level of the signals, the measurements are completely computer controlled. A detailed description of the apparatus, including the multichannel data‐acquisition hardware and computer interface, is given.

ISSN:0034-6748    

DOI:10.1063/1.1139100

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We describe the design of two telescope pointing systems for remote optical sensing of the stratosphere from a balloon‐borne gondola. The telescope pointing accuracy is ±0.02° in elevation, from a gondola which has static and dynamic tilts up to ±3°. Each system consists of a telescope, an elevation control subsystem, and a pitch‐stabilized single‐axis reference platform. The Mark I unit has performed successfully on each of its two balloon flights, for a total of over 16 h in the stratosphere; the Mark II unit is currently under construction. The single‐axis platform is referenced to a rate‐integrating gyroscope and an inclinometer for high‐ and low‐frequency pitch‐angle variations, respectively. The Mark I platform is supported by ball bearings, driven by a brush‐contact torque motor, and is subject to a small, permanent pitch angle error which depends directly on the gyro drift rate. The Mark II platform uses flex‐pivot supports, a brushless motor, and for even a relatively large gyro drift rate, is designed to asymptotically approach zero angular offset error.

ISSN:0034-6748    

DOI:10.1063/1.1139101

出版商:AIP    

年代:1986

数据来源: AIP