Continuous Absorption Band Research Articles

Effects of gamma-irradiation on the characteristics of a ruby laser

An increase in the absorption cross section responsible for optical pumping of a ruby laser occurs as a result of γ-irradiation. As single crystal ruby is irradiated with Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> γ-rays, the usual absorption bands which exist between 200 and 550 mμ change from four distinct bands to one continuous absorption band. Similar work on sapphire, the host crystal for ruby, indicates that the majority of this increased absorption is experienced by the Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+++</sup> ion in ruby. Thermoluminescence data are presented showing that electron traps with activation energies of about 0.64 and 0.78 eV are formed in ruby as a result of γ-irradiation. These traps remain in the crystal until it is annealed at about 800°C. It is found that the threshold energy for laser action increases in relation to the amount of irradiation. This effect is also manifested as a decrease in the luminescence of the R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> line after γ-irradiation. A model has been devised to explain the changes in Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+++</sup> ions due to γ-irradiation and to show how this affects laser action. Theoretical curves are presented indicating how the energy output vs. energy input varies with the amount of γ-irradiation. These data show a definite increase in threshold energy, and at higher pump energies they suggest the possibility of higher efficiencies than possible before irradiation. These theoretical results are supported by experimental data.

Absolute Intensities of the Discrete and Continuous Absorption Bands of Oxygen Gas at 1.26 and 1.065 μ and the Radiative Lifetime of the 1Δg State of Oxygen

Laboratory measurements have been made of the absolute intensities of the discrete-line absorption band at 1.26 μ, and of the continuous bands at 1.26 and 1.065 μ in oxygen gas at pressures up to 4.3 atm. It has been shown that discrete and continuous absorptions are quite independent features, the one being a measure of the intrinsic transition probability in isolated molecules, the other of its enhancement in collision complexes. In the former the lines show significant pressure broadening, but the integral molecular absorption coefficients are constant; in the latter they are proportional to pressure and continuous absorption dominates in the 1.26-μ region at about ½ atm oxygen pressure. The radiative half-life of isolated 1Δg oxygen molecules is estimated to be 45 min, and the effect of gas pressure on the rate of decay has been predicted.

O 2 Vibration Relaxation in Oxygen-Argon Mixtures

This paper and the one following [M. Camac and A. Vaughan, J. Chem. Phys. 34, 459 (1961)] discuss the use of a new experi-mental technique for the determination of O2 vibration and dissociation rates. The concentration of O2 in the ground vibrational state can be inferred from measurements of ultraviolet light transmission at 1470 A. O2 has a strong continuous absorption band in this vacuum ultraviolet region. The vibrational relaxation rate of O2 in shock-heated O2-Ar mixtures was obtained from 1200 °K to 7000 °K. For Ar-O2 collisions, the measured relaxation time t, can be fit by the Landau-Teller theory [L. Landau and E. Teller, Physik. Z. Sowjetunion 10, 34 (1936)] 1/τv = nC1T1/6[1−exp(−2228T)]exp(−(C/T)1/3), where n is the number of particles/cc and T is the temperature in °K. C1 = 1.2×10−7 cc/particle∼sec-(K)1/6 and C = 1.04×107 (±30%)°K. The observed vibrational relaxation time for O2-O2 collisions is 5.0±0.5 times faster than that for O2-Ar collisions. The experimental results are compared to the theoretical predictions of Schwartz and Herzfeld [R. N. Schwartz, Z. I. Slawsky, and K. F. Herzfeld, J. Chem. Phys. 20, 1591 (1952); R. N. Schwartz and K. F. Herzfeld, ibid. 22, 767 (1954)]. At the lower temperatures, the O2-O2 rates given by Blackman [V. H. Blackman, J. Fluid Mech. 1, 61 (1956)] have a different temperature dependence than the O2-Ar rates obtained in this experiment.

Spectrum of Venus in the Violet and Near-Ultraviolet

Recent observations of the spectrum of the planet Venus, with spectrographs of low and high dispersion at the Georgetown College Observatory, show that a wide, continuous absorption band is present in the violet and near-ultraviolet. The band begins near wavelength 4500 A and extends to the short-wavelength limit of our spectrograms near 3800 A. It is similar in structure to the strong absorption, reported by others, for gaseous nitrogen tetroxide.

Absorption Spectrum of NaNO3 Exposed to Ionizing Radiation

The changes produced by ionizing radiation in the absorption spectrum of NaNO3 crystals are in the main caused by two effects: the conversion of NO3— ions into NO2— ions with an absorption band, which has its peak at 345 mμ and shows a characteristic structure when observed at low temperature; and the production of color centers with a continuous absorption band with peak at 335 mμ. The formation of the color centers is assumed to be connected with the presence in the lattice of NO2— ions, although no precise model can be proposed for these centers. The color center band can be bleached by ultraviolet light even at — 190°C; at room temperature it is partially destroyed by the ionizing radiation which is able to produce the centers, while this is not the case with respect to the NO2— ions. Therefore the NO2— band is relatively much stronger in crystals exposed to the ionizing radiation at higher temperatures, for instance in the pile, while in crystals x-rayed at — 190°C the color center band prevails.

Continuous Absorption Band of Rubidium in the Presence of Foreign Gases

A NEW absorption band has been observed, with a Hilger E1 glass spectrograph, on the shorter wavelength side of the second member of the rubidium principal series, in the presence of neon, helium, hydrogen or nitrogen. The position of the band depends on the nature of the foreign gas admitted into the absorption tube, which was kept at around 250° C. A pressure of a few centimetres of mercury of the foreign gas was sufficient to make the band appear distinctly. Fig. 1 is a sample spectrum taken when neon gas was present in the absorption tube of rubidium vapour, and Fig. 2 the corresponding microphotometer curve.

Ultraviolet Absorption of Heavy Water Vapor

The absorption spectrum of the vapor of normal and heavy water has been examined in the ultraviolet down to 1450A. The long wave-length limit of the continuous absorption band is shifted towards shorter wave-lengths in the case of heavy water. Comparison with theory is made.

Absorption Bands of Iodine Vapour at High Temperatures

I HAVE investigated the absorption of iodine vapour in a tube of 26 cm. length at temperatures above 800° C. over the region 2900–5000 A. and have observed the appearance of a continuous absorption band with a sharp limit at 3425 A. on the long wave side. With increasing temperature the intensity of this band increases and at 900° C. a new absorption band appears with the long wave limit at 3252 A. At about 1050° C. both bands extending from 3425 A. to 3000 A. change in appearance, showing on the continuous background many close bands. These are extremely diffuse and it was impossible to decide whether they are genuine band heads or due to fluctuations of intensity in the continuous spectrum.

Societies and Academies

Societies and Academies