Gaussian Power Distribution Research Articles

Transmission and holographic properties of radiation-colored NaCl crystals

The behavior of color center layers under light exposure and the formation of holographic gratings in heavily electron colored NaCl crystals were studied. For exposure the 488-nm argon laser line having a Gaussian power distribution was used. The dynamic transmission of the layer was observed to be dependent on the surface exposed, e.g., back or front. Besides F centers, the heavily colored samples contained a remarkable amount of aggregate, whose dissociation gives a rapid increase in the optical density in the beginning of the exposure. In addition, a noise-type variation was observed in the powers of the transmitted and diffracted beams during the writing process of the holographic grating. This is explained with the help of the dynamic transmission behavior. Finally, stability, selectivity, and diffraction efficiency of the holographic gratings are discussed.

Development of a FIR interferometer for ATF: Part II—System design

Because of the highly elliptical cross section of the Advanced Toroidal Facility (ATF) plasma, a large number of interferometer channels are required to determine the radial density profile by Abel inversion. A 15-channel system is being developed using a single fan-shaped beam through the plasma and observing the phase shift across the profile with a 15-element detector array. The laser output at 119 μ will be transmitted about 10 m from the laser to the plasma device via an oversized dielectric waveguide. A surface grating will be used to redistribute the Gaussian power distribution to a sinc-type distribution. The beam will then be expanded in one dimension and focused through the plasma. It will then be combined with the local oscillator and focused on the detector array. Commercial Schottky diodes mounted in corner cube reflectors will be used as mixers. The entire system will be controlled by computer including the lasers and the data-acquisition system. Research supported by the Office of Fusion Energy, U.S. DOE, under Contract No. DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.

Efficient generation of surface acoustic waves by thermoelasticity

Short laser pulses were used for generating surface acoustic waves (SAW’s) on optically opaque solids via the thermoelastic effect. The spatial and temporal shapes of the laser pulses were either a spot or a line of variable total width δ=2a with a Gaussian power distribution. Maximal efficiency is obtained when a=vRτ(vR: Rayleigh velocity, 2τ: total laser-pulse length). This condition is caused by interference effects between the individual frequency components radiating from the area of the thermoelastic source. If the intensity of the laser beam were 100% modulated at a given frequency, maximal efficiency would occur if kR=(2)1/2/a (kR: wave vector of the SAW’s).

A Loss Model for Parabolic-Profile Fiber Splices

In the past, measurement results of splice loss of optical fibers have corresponded poorly to existing theory, which assumes a uniform power distribution across the cone of radiation defined by the local numerical aperture. In this paper, a model is developed in which a Gaussian power distribution across the local numerical aperture is assumed. Transmission through a splice at each point on the transmitting core is found to depend on the ratio of receiving to transmitting numerical aperture at that point. Numerical integration of these “point” transmission functions over core areas of interest yields both splice loss and the additional loss that occurs in a long fiber following the splice. This model cannot be theoretically rigorous, since it is inconsistent with boundary conditions required by the laws of light propagation. However, it has been found to predict splice loss under varying conditions with much greater accuracy than existing theory. The model has the further virtue of being able to calculate how variations in many intrinsic and extrinsic splice parameters combine to produce an overall splice loss.