摘要:

In this article, we review progress in the development of high peak-power ultrafast lasers, and discuss in detail the design issues which determine the performance of these systems. Presently, lasers capable of generating terawatt peak powers with unprecedented short pulse duration can now be built on a single optical table in a small-scale laboratory, while large-scale lasers can generate peak power of over a petawatt. This progress is made possible by the use of the chirped-pulse amplification technique, combined with the use of broad-bandwidth laser materials such as Ti:sapphire, and the development of techniques for generating and propagating very short (10–30 fs) duration light pulses. We also briefly summarize some of the new scientific advances made possible by this technology, such as the generation of coherent femtosecond x-ray pulses, and the generation of MeV-energy electron beams and high-energy ions. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148795

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A high resolution reflectivity diffractometer (HRRD) has been recently commissioned on Station 2.3 at the SRS, Daresbury Laboratory. Using the instrument which is x-ray wavelength tunable, the characterization of the interface structure in an ion-assisted deposited Co/Cu multilayer has been carried out. In order to improve the electron density contrast of the sample, we have used an x-ray energy near the Cu Kedge of 8.989 keV. By scanning the normal (specular), near normal (off specular), and parallel axes (transverse) of the surface, we have obtained useful reflectivity intensity data. By applying simulations to the data, we have determined a total roughness (rms) of6.0±0.5 Åwith a significant contribution from correlated interfacial roughness(4.2±0.2 Å).Other detailed structural information obtained has successfully demonstrated that the commissioned instrument is a viable tool for reflectivity studies. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148754

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This work designs and implements an inexpensive and simple double-crystal monochromator, which yields a high performance at a bending magnet x-ray beamline. A primary feature of the proposed monochromator is that the offset between the incident and monochromatic exit of the x-ray beam can be adjusted to cover a wide energy range with a shortX–Ytraveling stroke. Such a short range ofX–Ystrokes can reduce the monochromator’s overall size and, also, increase the stability of motions. Meanwhile, in this monochromator, instead of using a complicated hardware linkage mechanism, a software program is developed to effectively control theX–Ystage for positioning the second crystal in a fixed exit configuration, alleviating mechanic motion errors to maintain the parallelism of the two crystals. The entire software control mechanical linkage offers a relatively inexpensive and simple assembly monochromator that is more flexible than the commercially available one. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148755

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Operating a laser diode in an extended cavity which provides frequency-selective feedback is a very effective method of reducing the laser’s linewidth and improving its tunability. We have developed an extremely simple laser of this type, built from inexpensive commercial components with only a few minor modifications. A 780 nm laser built to this design has an output power of 80 mW, a linewidth of 350 kHz, and it has been continuously locked to a Doppler-free rubidium transition for several days. ©1998 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1148756

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A low cost, high performance single pulse switch-out system based on the high speed Pockels cell shutter, is presented. The circuit uses commonly available fast transistor transistor logic circuit elements for control logic and chains of bipolar junction transistors 2N2222A connected in avalanche mode for high-voltage switching of the Pockels cell. The system provides high contrast ratio pulses free from amplitude and timing jitter, and has been tested for more than 50 000 000 shots. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148757

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The present work is devoted to the experimental measurements and calculations of thermo-optical and dielectric constants of four commonly used dielectric polar and nonpolar laser dye solvents; toluene, chloroform, carbon disulphide, and benzene. Using a modified high precision laser Mach–Zehnder interferometric technique the refractive indexnand its thermal coefficientdn/dTwere measured at two different laser wavelengths (514.5 and 632.8 nm). The measured experimental data ofnanddn/dTwere used in determining about 16 important physical constants and related parameters. On the other hand, the density and molar refraction as a function of temperature for the four solvents are calculated. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148758

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

To simulate a phase-modulated interferometer, a novel electrical signal generator has been demonstrated. There are two phase-locked loop (PLL) circuits used in our system to process the phase signal. The first PLL is adopted as a voltage-controlled phase shifter, and the second PLL is used to amplify the phase signal to get a phase shift with a dynamic range over±16&pgr; rad.This system can be further modulated with sinusoidal, sawtooth, and triangular wave forms for interferometric signal detection. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148759

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new optical oscilloscope has been developed on the basis of the image-converter tube camera technology. Optical or electrical pulses in single or repetitive mode can be tested. When single pulse without time dependence on the sweep circuit is tested, an optical-fiber delay unit is adopted to ensure the pulse is captured. The optical oscilloscope works at a fixed frequency while repetitive pulses of any frequency less than 20 GHz were tested. A newly designed photocathode optical oscilloscope tube, control circuits, and a linear charge-coupled device readout system have been incorporated into the optical oscilloscope. Experimental results show that the temporal resolution of the optical oscilloscope is better than 5 ps, the spectral response range is 380–850 nm, and the single pulse can be captured with the probability of 100&percent;. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148760

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe a novel electro-optic double-modulation (DM) sampling technique for ultrafast transient spectroscopy, which is characterized by a superior signal-to-noise ratio compared to that of a regular single-modulation technique. DM is achieved by a combined effect of a radio-frequency modulation, which eliminates most of the low-frequency noise, and an audio-frequency modulation, which makes use of a high-performance, low-frequency lock-in amplifier. The DM sensitivity is comparable to that of the more sophisticated schemes involving electrical mixing and theA–Bnoise reduction method. We show that the DM technique offers superior performance in two-beam transient pump-and-probe correlation measurements compared to the regular single frequency modulation technique and is an ideal scheme for three-beam picosecond correlation measurements. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148792

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Using a dual chopping scheme where both the pump beam and the probe beam are chopped, we show that it is possible to perform photoreflectance spectroscopy with a broadband white light source as the pump beam instead of a laser source. We show that although the signal strength is reduced by a factor of1/&pgr;in the dual chopping scheme, it nevertheless has several advantages. A white light pump beam provides a wide range of excitation energy values, enabling one to characterize semiconductors of different band gaps spread over a wide energy range with a single modulation source. In the case of semiconductor heterostructures, simultaneous as well as selective excitation of different interfaces can be achieved easily. This technique is not plagued by the problem of background due to luminescence often encountered in low-temperature photoreflectance measurements. In this article, we present the details of this technique and demonstrate its usefulness by applying it to selected semiconductor heterostructure samples. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148761

出版商:AIP    

年代:1998

数据来源: AIP