Use Of Absorbers Research Articles

Dynamic behavior and applications of a three-contact vertical-cavity surface-emitting laser

We have developed a novel three-contact vertical-cavity surface-emitting laser (VCSEL) with an intracavity absorber for use in high-speed data communications. We demonstrate two distinct designs for our VCSEL and discuss the device physics underlying the behaviors of the two designs. Furthermore, we demonstrate a wide range of applications for these VCSELs, including optical intensity modulation, phase and amplitude modulation of a microwave optical subcarrier, optical bistability, self-pulsation, and optical disk readout.

Oxygen absorber for use in food preservation — comprises active carbon material and oxygen-absorbing layer comprising thermoplastic resin and oxygen-absorbing agent (Eng): SUMITOMO CHEM CO LTD 94.12.27 94JP-324483 D13 E36 F09 J01 (96.07.10) A23L 3/3436 95.12.27 95EP-120580 R(DE FR GB IT)

Oxygen absorber for use in food preservation — comprises active carbon material and oxygen-absorbing layer comprising thermoplastic resin and oxygen-absorbing agent (Eng): SUMITOMO CHEM CO LTD 94.12.27 94JP-324483 D13 E36 F09 J01 (96.07.10) A23L 3/3436 95.12.27 95EP-120580 R(DE FR GB IT)

A perfectly matched anisotropic absorber for use as an absorbing boundary condition

An alternative formulation of the "perfectly matched layer" mesh truncation scheme is introduced. The present scheme is based on using a layer of diagonally anisotropic material to absorb outgoing waves from the computation domain. The material properties can be chosen such that the interface between the absorbing material and free space is reflection-less for all frequencies, polarizations, and angles of incidence. This approach does not involve a modification of Maxwell's equations and is easy to implement in codes that allow the use of anisotropic material properties.

Design of wideband Jaumann radar absorbers with optimum oblique incidence performance

The authors consider the criteria for the optimum design of multilayer, wideband Jaumann radar absorbers for use at oblique incidence. If optimum performance for only one incident polarisation is required and the spacer permittivity is small, the oblique incidence and normal incidence optimum designs are simply related. The more general case of optimum performance for both polarisations simultaneously is investigated using an optimisation technique based on a genetic algorithm and examples of designs are presented.

X-ray masks with tungsten absorbers for use in the LIGA process

X-ray masks with tungsten absorbers have been made for the LIGA process by sputter deposition of tungsten and subtractive patterning through reactive ion etching with CF 4 and SF 6. Sputtering was optimised in order to minimise stress and the anisotropy of stress in tungsten layers. Absorbers with critical dimensions as small as 0.5 μm and thicknesses of 2.5 μm have been achieved. With tungsten absorbers, 2.2 μm in thickness, templates for electroplating, more than 20 μm in thickness, have been fabricated from PMMA.

A New Filter Material for Measuring Soil Suction

Abstract The filter paper method for determining soil suction has been in use for many years and owes its attraction to its simplicity. A major drawback of the method is that the suction range over which it can be applied is limited by the moisture sensitivity of the filter paper or absorbent used. By convention, filter paper has been adopted for use in the method, but other absorbents may well be more suitable, increasing the sensitivity of the method and extending the suction range over which the method may usefully be applied. In this paper the desirable attributes of absorbents for use in determining soil suctions are outlined, and the suitability of a nonconventional absorbent material is assessed. It was found that this material had enhanced sensitivity over the middle suction range.

An energy saving device for flat plate solar energy collectors

Describes an optical element consisting of three specularly reflecting surfaces and an IR reflecting surface facing towards the absorber for use in flat plate solar energy collector. By incorporating a panel of such optical elements in between the absorber and the window of the flat plate solar energy collector, the radiation and convection heat losses are reduced. The design aspects and merits of the optical element are discussed. The concentration factor, radiation trapping capacity and transmission efficiency of the device are computed and presented in the graphical form. The radiation trapping capacity of the device is shown to be better than that of the optical valve with two specularly reflecting surfaces.

Shock absorber arrangement for mounting delicate equipment and shock absorber for use in the arrangement

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The damping of structural vibration by thin gas films

A theoretical and experimental investigation of the processes by which thin layers of gas trapped between surfaces of a structure may contribute to damping of structural vibrations is described. Effects of gas compressibility, inertia and thermal conductivity are allowed for in the theory. Particular attention is given to the variation of damping with gas pressure and layer thickness. The aim of the investigation was to provide results of use in the design of vibration absorbers for use in pressurized gas environments, as well as to contribute to a better understanding of the behaviour of pre-existing gas layers in structures.

Absolute reference calorimeter for measuring high power laser pulses

A calorimeter for making absolute energy measurements of high power laser pulses is described. The calorimeter, based on volume absorption in a solid, is calibrated electrically and requires no window or vacuum environment. An error analysis is included giving the systematic and random errors of the instrument for a laser measurement. Briefly, the following performance is typical of the 32-mm x 32-mm aperture calorimeter: range 0.4-15-J; random error +/-0.2% (one standard deviation); systematic error +/-2.3%; and an upper operational limit of 3 J/cm(2). Most of the volume absorber documentation is applicable for 1.06 microm; however, the calorimeter should be useful from the near ir through the visible. Absorbers for use with CO(2) lasers in the 9-11-microm range are also discussed.

The planning of treatment of gynaecological cancer with combined intracavitary and external beam irradiation.

Abstract The planning of treatment for patients with gynaecological cancer undergoing combined intracavitary and external beam irradiation at the Royal Marsden Hospital is described. The purpose of the external beam irradiation is to increase the dose to the parametria and pelvic nodes since these tissues are generally too far from the intracavitary 137Cs sources to receive a tumoricidal dose. The treatment policy and problems of dosimetry are discussed. The main problem is to combine the two modes of radiotherapy so as to ensure an adequate dose to the required regions and to afford protection to previously irradiated areas. The method of computing the dose distribution from the intracavitary 137Cs sources is described and also how this distribution is used to design protective absorbers for use with the external beam therapy. Different shapes of absorbers are required for cobalt units and linear accelerators because of the different beam characteristics. The way in which these are designed for individua...

Saturation of infrared absorption in gaseous molecular systems

Saturable absorbers for use in the infrared, consisting of molecular gases, are considered. A basic objective of the study is the understanding and prediction of saturation behavior. A model for the absorber is developed. Features considered include 1) strong interaction between the absorbing pair of vibrational-rotational levels and numerous neighboring levels; 2) spatial diffusion of molecules; 3) temperature gradients; 4) distortion of optical beams by the saturable absorber; 5) inhomogeneous broadening of absorbing transitions; 6) effects of geometry of the absorption cell. The model is intended to be quite general in its applicability, but is particularly considered in relation to absorption of CO 2 laser radiation by sulfur hexafluoride. The equations arising from the absorber model are complex, but under suitable assumptions can be simplified. Experiments have been performed to determine the values of the relevant parameters for SF 6 absorbers. These values are inserted into the general absorber model and the resulting equations solved by digital computation. The theoretical saturation behavior thus obtained is in reasonably good agreement with saturation behavior observed in experiments with SF 6 .

An Analysis of Saturable Absorbers

This paper contains an analysis of the behavior of saturable filters, based on models with simple energy level structures. In this analysis, the effects of possible excited state absorption at the irradiating wavelength are considered and are shown to give rise to a nonsaturable component of the absorption coefficient. Expressions for the steady-state transmission of an optically thick saturable absorber, and for the temporal response of an optically thin absorber, are derived. The question of homogeneous vs inhomogeneous broadening of the absorption line is discussed, and it is suggested that spectral hole burning may occur in a thermally broadened line at a sufficiently high irradiance level. The desirable features of a saturable absorber for use in a Q-switched laser system are briefly described, and it is shown how the usual rate equations for a laser system may be amended to include the effects of an intracavity saturable filter.

Paper 17: Development of the Dimpled Sheet Shock Absorber for Use in a Nuclear Reactor

Paper 17: Development of the Dimpled Sheet Shock Absorber for Use in a Nuclear Reactor