摘要:

We observe that 266 nm laser pulses of 30 ps duration and fluence near 10 J/cm2causes reproducible surface sputtering and etching of crystalline sapphire in air. The etching rate for the initial ten pulses is relatively slow, 0.04 &mgr;m/pulse, producing a smooth surface of the etched area and a broad‐angle plume emission. After some 20 pulses, the etching rate is dramatically faster, 0.5 &mgr;m/pulse, producing a rough etched surface and a plume composed of broad‐angle emission as well as a narrow perpendicular jet emission. Micron‐sized depressions can be made on the sapphire with no visible damage or cracking to the surroundings.

ISSN:0003-6951    

DOI:10.1063/1.102100

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The polarization dependence of the optical input energy required to switch an inhomogeneously pumped bistable laser diode is studied at various input signal wavelengths. Polarization‐independent switching is achieved for input pulse wavelengths 30–40 nm shorter than the lasing wavelength of the bistable laser diode, whereas input pulse wavelengths close to the lasing wavelength result in a strong polarization dependence. A simple theory explains the observed behavior.

ISSN:0003-6951    

DOI:10.1063/1.102101

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A scanning optical profilometer is described which overcomes some of the limitations of existing interferometric profilometers. Two laser beams are incident on the sample ensuring common path operation. One beam forms a tightly focused sample probe spot and the other remains collimated, acting as a large‐area, common path reference beam. Our configuration allows the relative size of the two beams to be varied both arbitrarily and independently, thus guaranteeing an accurate absolute phase measurement. Preliminary results demonstrating the operation of the system are presented.

ISSN:0003-6951    

DOI:10.1063/1.102102

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Thermal characteristics of a split‐disk amplifier system with 50 mm diam aperture were measured by a Schlieren method with a ball stopper of 88 &mgr;m diam under repetitively pulsed operation for a pump loading of up to 1 kW(1 kJ/ Hz). The thermal beam divergence reached 100 &mgr;rad at an average input power of 200 W(1 kJ/0.2 Hz) under 300l/min(0.73 m/s) N2gas flow. The thermal limitations of this amplifier system are discussed under repetitive operation.

ISSN:0003-6951    

DOI:10.1063/1.102103

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A new asymmetric dual quantum well laser diode with a segmented contact is proposed. With inhomogeneous current injection, the lasing wavelength can be changed quasi‐continuously over 22 nm, which is much wider than any tuning range previously reported. To achieve such wide‐range tuning, it is found to be essential that the length of the cavity and each segment (and the mirror reflectivity) of the laser diode should be within an optimized range. In the asymmetric dual quantum well laser diode structure used in the present experiment, in particular, the cavity length should be such that light of a shorter wavelength lases under homogeneous excitation.

ISSN:0003-6951    

DOI:10.1063/1.102104

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Pure in‐phase‐mode operation is obtained from 20/21‐element AlGaAs/GaAs antiguided arrays grown by two‐step metalorganic chemical vapor deposition. Oscillation of out‐of‐phase modes is substantially suppressed by a built‐in spatial filter: two sets of noncollinear antiguides separated by a 50‐&mgr;m‐long laterally unguided region, corresponding to the half‐Talbot distance. Design considerations for 20‐ vs 10‐element arrays are discussed. Diffraction‐limited‐beam operation (i.e., 0.8° lobewidth) is obtained to 1.5×threshold (90 mW, both facets). Beams with 1.3° lobewidth (1.6×diffraction limit) are obtained at 3×threshold and 300 mW (both facets). Devices with optimized facet coatings operate in a single, 1.5°‐wide lobe (i.e., 1.8×diffraction limit) at 330 mW front‐facet emitted power. The main lobe contains 80–87% of the total power.

ISSN:0003-6951    

DOI:10.1063/1.102105

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A low‐temperature (≊400 °C) plasma‐enhanced chemical vapor deposition process has been developed to grow diamond films for optical coatings application. Films with fine grains (≤3000 A˚) have been obtained by controlling diamond nucleation. The surface roughness of the films is on the order of 50–200 A˚. The optical transparency of the films is over 60% in the range 0.6–2 &mgr;m wavelength, which is comparable to that of Type IIa natural diamond. Using a block‐on ring tribotester, it is found that the diamond films adhere well to quartz substrates.

ISSN:0003-6951    

DOI:10.1063/1.102106

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We report experimental results from a first‐of‐a‐kind ultrasonic transducer that generates a beam with a Bessel function profile. Using a technique of nonuniform poling, an axially symmetric Bessel function pattern is ‘‘polarized into’’ a piezoelectric ceramic element. The resulting circular‐disk transducer has the usual full‐plating electrode configuration, but produces an ultrasonic beam with a radial displacement profile approximating that of the Bessel functionJ0(r), both in amplitude and in phase. The radiation field of a 1‐in.‐diam, 2.25 MHz Bessel transducer mapped out with a point probe shows good agreement with calculated results using a Gauss‐Hermite model. Bessel transducers are of particular interest in attempts to achieve ‘‘diffractionless’’ beams.

ISSN:0003-6951    

DOI:10.1063/1.102107

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The propagation of a relativistic sheet electron beam through a spatially periodic magnetic field (wiggler) has been studied experimentally. The wiggler serves two purposes; it provides beam focusing as well as the magnetostatic pump for the free‐electron laser (FEL) interaction. Experiments conducted to study sheet beam generation and propagation in a short‐period (1 cm) planar wiggler are presented. A 500 keV, 7 A sheet electron beam was propagated through a 3.2 mm waveguide with negligible losses due to intercepted current. In addition, the first observation of wiggler‐induced radiation was obtained from the sheet beam FEL in a short‐period wiggler oscillator configuration.

ISSN:0003-6951    

DOI:10.1063/1.102108

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The fuel areal density &rgr;Rmeasurement of imploded plastic hollow shell targets by use of a neutron activation technique is reported. Silicon was doped as an activatable tracer into a hollow shell of tritium‐contained deuterated polymer(CDTSi). This target was imploded by 0.53 &mgr;m Nd:glass laser light and the induced radioactivity of28Al was measured with a &bgr;‐&ggr; coincidence counting system. The collection efficiency was calibrated by the use of radioactive tracer24Na and was verified by comparing the estimated &rgr;Rwith that simultaneously measured by a knock‐on method.

ISSN:0003-6951    

DOI:10.1063/1.102109

出版商:AIP    

年代:1989

数据来源: AIP