Contra-directional two-beam coupling by use of a single input beam in an iron-doped lithium niobate multimode fiber.

Experimental results are presented for 1,800 contra-directional two-beam coupling (TBC) measurements in a single crystal fiber of LiNbO8:Fe using a single incident beam and its Fresnel reflection off the back surface of the fiber. To our knowledge, this is the first time that volume gratings have been written in a fiber using this beam coupling geometry. At small f-numbers, the TBC efficiency has been predicted to decrease in bulk LiNbO3:Fe due to the erasure of the weak gratings by the dark conductivity. We present experimental results validating the published theory and show experimentally that confinement of the interfering beams in a fiber geometry overcomes this limitation.

Spectroscopic properties of Cr(4+):Lu(3)Al(5)O(12).

We report on the near-infrared absorption, emission, and lifetime data of Cr(4+):Lu(3)Al(5)O(12) (Cr:LAG) and compare the results with the known laser material Cr(4+)-doped Y(3)Al(5)O(12) (Cr:YAG). Lu(3)Al(5)O(12) has a smaller unit cell than Y(3)Al(5)O(12), and this feature is reflected in its spectroscopic properties. The low-temperature luminescence spectrum is shifted by 85 cm(-1) to higher energy compared with Cr:YAG. The luminescence lifetime of Cr:LAG at 10 K is 28.7 micros (Cr:YAG, 30.6 micros) and at 300 K is 4.3 micros (Cr:YAG, 3.5 micros). From these lifetimes we postulate that the quantum efficiency in Cr:LAG is higher than in Cr:YAG. We discuss the potential of Cr:LAG as a tunable near-infrared laser.

Effects of tensile stress on the R lines of Cr(3+) in a sapphire fiber.

We have investigated the spectroscopic properties of a crystalline sapphire fiber unintentionally doped with Cr(3+). We find that tensile stress produces blue shifts of the R lines and changes in their radiative lifetimes and integrated intensities that can be correlated to stress-induced changes of the crystal-field parameters.

The in vitro and in vivo photoreactivity of bilirubin: I. Laser-defined wavelength dependence.

Monochromatic light was provided by a continuous wave Argon ion laser. We chose to study the in vitro effects of light at 457.9, 465.8, 476.5, 488.0, 501.7, and 514.5 nm as representative of a reasonably evenly spaced sampling across the blue-green spectrum. The in vivo experiments were conducted at 457.9, 476.5, 488.0, and 514.5 nm. In vitro light at 488.0 nm appeared to be more effective than the others studied. After 24 h of irradiance, the in vivo decline in serum bilirubin concentration produced by light at 488.0 nm was one-and-one-half, two, and four times as effective as light at 457.9, 476.5 and 514.5 nm, respectively. By 48 h of exposure, the declines produced by light at 457.9 nm and 488.0 nm are significantly superior to that at 476.5 nm and 514.5 nm, but they do not differ from one another.

Variable birefringent beam splitter.

A sapphire disk is used as a variable birefringent beam splitter for the linearly polarized pump beam in an oscillator-amplifier dye laser system. Rotation of the disk varies the extent of retardation. The induced elliptical polarization results in a variable back surface reflectance between approximately 0.02-0.15 for the green spectral region. Reflectances are measured on two disks with different thicknesses and compared with an approximate model describing the reflectance as a function of angle of rotation of the disk.

Spin-lattice relaxation in the excited (4)S(3/2) state of Er(3+) in LaF(3).

We have employed a purely optical method to measure spin-lattice relaxation in the lower excited (4)S(3/2) state of Er(3+) in LaF(3) at helium temperatures. Above 3 K the relaxation is dominated by an Orbach process through the upper (4)S(3/2) state. Below 3 K the relaxation is caused by some residual mechanism that obscures the Kramers-Van Vleck direct process. By relating the Orbach relaxation measurements to the homogeneous broadening of the upper (4)S(3/2) level, we determine values of the transition rates between the upper and lower (4)S(3/2) states.

Photoacoustic measurement of absolute quantum efficiencies in solids.

We have developed a simple new technique for measuring absolute radiative quantum efficiencies of fluorescing ions in solids that can be applied to systems exhibiting concentration quenching of the fluorescence. The technique requires measurement of the photoacoustic signal and fluorescent lifetime as a function of ion concentration. Application of this method to the upper laser level of Nd(3+) in ED2 glass yields a value for the quantum efficiency somewhat smaller than that found in previous estimates and measurements.

Radiative spectral transfer in ruby.

The first direct observation of radiative spectral transfer within an inhomogeneously broadened line (the R(1) line of ruby) is reported. As opposed to nonradiative transfer, the temperature dependence of the radiative process is consistent with exponential, in agreement with recent predictions. A temperature-independent, resonant process is also directly observed. The implication of these results for the concept of microscopic strain broadening is discussed.

Pulsed dye laser applied to modulated spectroscopy magnetic circular dichroism.

A tunable jet-stream dye laser pumped by a cavity-dumped argon laser has been synchronized to a photoelastic modulator to measure magnetic circular dichroism. Gated signal amplification takes advantage of the laser's pulsed operation to detect weak dichroic signals. Comparative data show that the dye laser and gated amplification give a SNR better than that obtained with the previously used lamp, monochromator, and lockin detector. Other applications of the dye laser and gated amplification are discussed.

Independence of hand preference and sex-linked genetic effects on spatial performance.

The paper-and-pencil spatial performance of right- and left-handed high school students was compared separately for 1236 males and 1241 females. Handedness differences in favor of right-handed subjects were found among males only. Analysis of data for a subgroup of 555 subjects indicated that handedness and sex-linked genetic effects acted independently and additively on spatial performance.

Sex-linked major-gene influences on selected types of spatial performance.

Four paper-and-pencil spatial tests, measuring two- and three-dimesional spatial visualization and spatial orientation, were administered to 2508 Caucasian high-school students. Sibling correlations and within-sex score distributions were examined for the influence of a major sex-linked gene. Sex-linked influences were most clear on the test of two-dimensional visualization and on an average of the standard scores on all the tests. For those tests best fitting the genetic model, estimates of the frequency of the recessive gene (contributing to good performance) we-re near 0.45. There was evidence of incomplete dominance in females. Environmental or non-sex-linked genetic factors influenced spatial performance but did not systematically improve performance with age.

On the Empirical Relation Between Spatial Ability and Sex Differences in Other Aspects of Cognitive Performance.

The hypothesis that sex differences in field independence and mental arithmetic can be accounted for by sex differences in spatial ability was supported for a group of 46 female and 35 male undergraduates. Sex-typing does not appear to be strongly related to spatial ability for either sex. There is a possibility of the existence of a field-independence trait independent of spatial ability, particularly among females; however, if such a trait does exist there do not appear to be significant sex differences with respect to it. Factor analysis indicates that tests of spatial ability, field independence, and mental arithmetic emerge together in a spatial ability factor. Sex differences in the factor structure of nine measures, most of which typically display sex differences (spatial ability, field independence, mental arithmetic, vocabulary, verbal and nonverbal creativity, femininity, and achievement motivation) were largely the result of differences with respect to a spatial factor.