W. M. Yen

Composition dependence of Nd3+ homogeneous linewidths in glasses

Optical homogeneous linewidths of the 4F3/2–4I9/2 transition of Nd3+ in oxide and fluoride based glasses are measured for host composition ranging from simple binary to multicomponent glasses. Homogeneous linewidths at 300 K exhibit a broad range of values, varying by approximately a factor of 4. The ratio of homogenous to inhomogeneous linewidth also varies over a broad range, from 0.16 for a sodium barium borate glass to 1.86 for a rubidium phosphate glass. In addition, the homogeneous linewidth is inversely dependent to the ∼2.5 power of the velocity of sound from host to host. This dependence is not predicted by existing theories of the line broadening process.

Measurements of excited‐state absorption in Ce3+ : YAG

We have investigated Ce3+ : Y3Al5O12 (YAG) as a model system for a 5d‐4f solid‐state tunable laser. This system has been chosen since YAG has been extensively studied as a laser host and good quality crystals are readily available. Despite providing apparently adequate conditions to achieve stimulated emission, we were unable to detect laser action in Ce3+ : YAG. We find, however, strong excited‐state absorption in this material at the wavelengths of its fluorescence and we report on this excited‐state absorption (ESA) here. This self‐absorption may explain the failure of all attempts to obtain stimulated emission in this material and has serious implications for any attempt to develop a 5d4fn−1‐4fn laser.

Photoacoustic measurement of the ruby quantum efficiency

We have measured the radiative quantum efficiency (QE) of the ruby fluorescence using a novel photoacoustic technique. The technique requires the measurement of the phase of the photoacoustic signal as a function of chopping frequency, and is applicable to systems with a simple decay scheme and a sufficiently long fluorescence lifetime. The measured value QE=0.900.05 is consistent with several previous optical measurements.

On the adequacy of one‐dimensional treatments of the photoacoustic effect

It is demonstrated both theoretically and experimentally that the one‐dimensional theories of the photoacoustic effect in solids are still applicable when the heat flow is three dimensional, provided that the thermal diffusion length in the gas is much less than the radius of the sample chamber.

Photoacoustic theory including energy migration

All theories of the photoacoustic effect to date have assumed that heat is deposited in the sample only where light is absorbed, i.e., that no spatial migration of the energy occurs. We present here an extension of the standard Rosencwaig‐Gersho photoacoustic theory, taking into account the possibility of spatial energy migration. Also included in the theory are the effects of surface quenching, i.e., the possibility that excitations near the surface of the sample decay more efficiently than excitations in the bulk. By comparing the experimentally determined chopping frequency dependence of the photoacoustic signal to that predicted by the theory, it should be possible to determine the diffusion constant for energy migration.

Effect of thermal contact resistance on the photoacoustic signal

We show both theoretically and experimentally that under essentially all conditions of experimental interest, the thermal contact resistance between sample and gas plays a negligible role in photoacoustic spectroscopy of solids.

Laser action in PrF3

The 3P0‐3H6(1) transition of Pr in PrF3 was observed to undergo laser action under direct pulsed excitation at low temperature with a high conversion efficiency. Comparison with such behavior in other types of material is made and the usefulness of this stimulated emission behavior as a spectroscopic tool in characterizing concentrated materials is discussed. The parameters describing threshold conditions, linewidths, and energy conversion are measured and compared to theory.

Magnetic Circular Dichroism in Antiferromagnetic MnF2

The magnetic circular dichroism (MCD) properties of antiferromagnetic MnF2 in the 4T1(4G) region have been studied. We show that MCD is a useful technique in furthering our understanding of the spectra of these materials, particularly when complex assisted transitions are involved. Out of the complex band absorption, only a weak electric dipole feature at 18 536 cm−1 and the one‐magnon sideband region exhibit magnetic circular dichroism. We present conclusive evidence that the weak electric dipole transition is a two‐magnon sideband of the pure electronic line E2 in this manifold. The position and temperature dependence are in good agreement with other two magnon experimental data. The MCD splitting also yields an effective g factor for the two‐magnon sideband which is in good agreement with existing data. We conclude that this three‐center excitation is caused by a zone‐center exciton plus two X2 zone‐edge magnons. Fitting the observed MCD signal from the one‐magnon sideband region to a calculated line s...

Tricritical behavior in randomly disordered Fe1−xCl2 : Cdx

We have determined the magnetic phase diagrams of Fe1−xCl2 : Cdx (x=0, 0.09, 0.11, 0.17, 0.24). Below the tricritical temperature Tc the antiferroparamagnetic mixed phase is easily detectable because it strongly scatters visible light. This light scattering allowed us to map the first order phase boundaries up to Tc. Above Tc the optical density of the 426.8 nm absorption line changes at the continuous phase transition. Well defined tricritical and Neel temperatures were observed in each sample. Randomly quenched disorder introduced by the cadmium impurities reduced Tn and Tc but did not destroy the tricritical behavior. We present phase diagrams for each of the doped samples and plot Tn, Tc, and Hc (the critical field) as functions of Cd concentration.

Investigation of resonant energy transfer for LaF3:Pr3+

The problem of resonant energy transfer (RET) is addressed for diluted rare-earth and transition-metal ions in a solid. Such processes involve the redistribution of excitation among sites with degenerate states. A new spectroscopic double selection technique is presented which is capable of detecting RET for inhomogeneously broadened multilevel systems. The method has been applied to LaF3:Pr3+ for concentrations from 5 to 80 at.%. The experiments indicate that no significant RET occurs in this system. Reasons for this result are discussed, and other interesting materials to which this technique may be applied are mentioned.