New PbSnTe heterojunction laser diode structures with improved performance

Several recent advances in the state-of-the-art of lead tin telluride double heterojunction laser diodes are summarized. Continuous Wave operation to 120 K and pulsed operation to 166 K with single, lowest order transverse mode emission to in excess of four times threshold at 80 K were achieved in buried stripe lasers fabricated by liquid phase epitaxy in the lattice-matched system, lead-tin telluride-lead telluride selenide. At the same time, liquid phase epitaxy was used to produce PbSnTe distributed feedback lasers with much broader continuous single mode tuning ranges than are available from Fabry-Perot lasers. The physics and philosophy behind these advances is as important as the structures and performance of the specific devices embodying the advances, particularly since structures are continually being evolved and the performance continues to be improved

The effect of permeate flux on membrane fouling during microfiltration of oily water

Critical and threshold flux concepts were recently developed to distinguish no fouling, slow fouling and rapid fouling regimes. Membrane fouling behavior is expected to vary with respect to the imposed flux relative to the critical and threshold flux values. However, crossflow fouling tests are often performed independent of critical and threshold flux determinations. In this study, constant flux fouling experiments were performed in connection with critical and threshold flux determination. Fouling behavior was examined in the context of critical and threshold flux. A poly(vinylidene fluoride) microfiltration membrane was challenged with various oil-in-water emulsions. The critical and threshold flux values were estimated using the flux-stepping technique. Constant flux crossflow fouling tests were performed at selected fluxes below and above the critical and threshold fluxes. Below the critical flux, mass transfer resistance remained constant at the clean membrane value. Above the critical flux but below the threshold flux, mass transfer resistance approached a steady state resistance, RB, which was determined from the linear regression of flux-stepping experiments. Above the threshold flux, a three-stage transmembrane pressure (TMP) was observed, consisting of: (1) an initial gradual increase, (2) a TMP jump stage, and (3) a pseudo-steady state. The pseudo-steady state TMP corresponded to the estimated critical pressure of the oil layer