Irwin Schneider

Intensity‐dependent upconversion efficiencies of Er3+ ions in heavy‐metal fluoride glass

The upconversion of infrared radiation to shorter wavelengths by Er3+ ions in heavy‐metal fluoride glasses, some doped with Yb3+, has been studied over a wide intensity range and for various excitation wavelengths. The upconversion efficiency measured at room temperature varies linearly or quadratically with intensity and saturates at 100 W/cm2 or higher, depending on emission wavelength. For 4 mol % ErF3 in BaF2/ThF4, the 4I11/2 to 4I15/2 transition is over 10% efficient for 400 W/cm2 of absorbed 1.5‐μm power, i.e., for 4I15/2 to 4I13/2 excitation. A rate equation model and Judd–Ofelt analysis of data for the glasses doped with just Er3+ provide an understanding of the upconversion process while yielding values for Er3+ energy‐transfer rates and excited‐state populations. These results could be used to develop glasses for lasing and as infrared optical detectors.The upconversion of infrared radiation to shorter wavelengths by Er3+ ions in heavy‐metal fluoride glasses, some doped with Yb3+, has been studied over a wide intensity range and for various excitation wavelengths. The upconversion efficiency measured at room temperature varies linearly or quadratically with intensity and saturates at 100 W/cm2 or higher, depending on emission wavelength. For 4 mol % ErF3 in BaF2/ThF4, the 4I11/2 to 4I15/2 transition is over 10% efficient for 400 W/cm2 of absorbed 1.5‐μm power, i.e., for 4I15/2 to 4I13/2 excitation. A rate equation model and Judd–Ofelt analysis of data for the glasses doped with just Er3+ provide an understanding of the upconversion process while yielding values for Er3+ energy‐transfer rates and excited‐state populations. These results could be used to develop glasses for lasing and as infrared optical detectors.

Continuous-wave laser action of (F 2 + )A centers in sodium-doped KCl crystals

Broadly tunable laser action is reported for the (F2+)A center in sodium-doped, additively colored KCl. The laser is continuously tunable from about 1.62 to 1.91 μm, has a continuous-wave threshold of under 10-mW absorbed power, and can be stored for at least limited periods at room temperature without losing its lasing capability.

Dichroic absorption of m centers as a basis for optical information storage.

The rotational properties of M centers in alkali halides are investigated as a possible basis for storing information. Measurements using a NaF matrix indicate that high storage density, high writing efficiency, thermal stability, and nondestructive readout are attainable in a practical situation at room temperature or lower. However, temperatures below 300 K are necessary for fatigue-free operation in the present material.

Information Storage Using the Anisotropy of Color Centers in Alkali Halide Crystals

Color centers exhibit certain unusual properties which potentially might prove useful for information storage purposes.i One is the relative ease with which they can often be created or destroyed with ordinary light. Binary information could simply be related to the presence or absence of a color center with its associated absorption bands. However, to be a practical alternative for present day storage techniques, the photochemical conversion processes should at least be completely reversible and be capable of an optical readout which does not affect the stored information. Unfortunately, these conditions severely limit the actual number of centers which can be used. This situation can be improved by using a somewhat different technique which makes use of the anisotropic properties of color centers. Instead of changing the concentration of a center, this technique would involve optically altering its orientation in the crystal. The stored information is now related to the dichroic absorption of the center. This note illustrates how this technique might be applied to the MA center in sodium doped KCl.3 The MA center in a crystal like KCl consists of a pair of nearest neighbor F centers lying next to an Na+ impurity (see Fig. 1). An F center is simply an electron trapped at a negative ion vacancy.

Tunable, continuous-wave laser action using (F 2 + )A centers in lithium-doped KCl

Continuous-wave, broadly tunable laser action is reported for an (F2+)A center in lithium-doped KC1. The laser is continuously tunable from about 2.00 to 2.50 microm, is highly efficient, has a low threshold for absorbed power, and retains its laser capability after several weeks of storage at room temperature.

Fiber-optic near-infrared reflectance sensor for detection of organics in soils

A near infrared fiber-optic chemical sensor system using reflectance spectroscopic measurements has been assembled. This system was evaluated and found attractive for remote detection of organics in soils over distances of at least 30 meters.<<ETX>>

Extinction technique for optical storage using anisotropic color centers in alkali halides

An extinction technique is described for obtaining high‐contrast images while effectively increasing sensitivity in photodichroic alkali halide crystals.

Photodynamics and stability of laser active (F+2)A centers

In additively colored KCl : Li crystals, the (F+2)A color center laser operates through a photodynamic equilibrium in which UV excitation generates a partial conversion of (F2)A centers to (F+2)A. Evidence is presented which shows that continuous UV exposure is necessary to sustain laser action because of the neutralization of (F+2)A centers which occurs through the capture of F′A center electrons. The bleaching of FA centers results directly from absorption of the 1.3‐μm pump radiation. Since the absorption is extremely weak, only modest UV intensities are needed for intense cw laser operation.

Additive and electrolytic coloration of NaF

It is shown that well‐characterized F and M centers can be introduced into NaF crystals by both additive and electrolytic coloring techniques. This success is attributed primarily to a substantial elimination of hydroxyl‐ion contamination.

Sodium and lithium MA centers in KCl

Abstract Results on the reorientation of the sodium MA center at various temperatures is presented and discussed. Evidence is also given for the existence of the lithium MA center.