Molecular beam epitaxy-grown separate confinement buried heterostructure PbEuSeTe-PbTe diode lasers

Separate confinement buried heterostructure (SCBH) tunable PbEuSeTe-PbTe diode lasers were fabricated by molecular beam epitaxy for the first time. Continuous wave (CW) operating temperature of 215 K was realized, which is the highest CW operating temperature ever reported for lead-chalcogenide diode lasers. Preliminary results show a significant improvement in threshold current and emission power. Exceptionally low threshold currents of 2.5 mA at 120 K, 76 mA at 180 K, and 252 mA at 200 K were measured. The temperature tuning range of the SCBH diode laser spans between 6.49 /spl mu/m at 20 K to 4.19 /spl mu/m at 215 K.     

Geomechanical Substantiation and Development of Technology of Methane Extraction from Coal Seams in the Regime of Cavitation Using the Rock-Mass Energy

The geomechanical substantiation is presented for a new technology of intensifying the methane extraction from coal seams. This technology meets requirements of resource saving and ecological safety. The experimentally established criteria of strength and regularities of coal failure in changing the type of the stress state were used.     

Physical principles of prediction and prevention of gas-dynamic phenomena

Summary We have given some results above of laboratory and field research on the structures and mechanical and physical-chemical properties of coals from burst-prone and burst-free seams, as well as results of studies of the movement of gas in coal seams, carried out at the Skochinskii Mining Institute over the last 15 years. In attacking the problem of prediction and prevention of gas-dynamic phenomena, we must jointly pursue methods from rock mechanics, physical chemistry, underground hydraulics, geology, and geophysics—the theoretical foundations of mining science. A knowledge of the physical and physical-chemical properties of a medium and its laws of motion in gas-dynamic phenomena will enable us to develop the most efficient methods of predicting and preventing such phenomena in coal pits. Skochinskii Mining Institute, Moscow. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 5, pp. 7–24, September–October, 1967.     

Electrical conduction in polyimide between 20 and 350° C

Although conduction in polyimides at elevated temperatures has been widely reported, measurements at ordinary device temperatures have been less well documented. Quantitatively reproducible low field conduction measurements on two device-grade polyimides (PMDA-ODA, BTDA-ODA/MPDA) in the temperature range of 20–350° C and under dry conditions are reported. Aluminum—polyimide—aluminum capacitors are prepared by spin coating an aluminized silicon wafer with between two and four coats of polyimide (prebake at 135° C for 10 min between coats). Samples are cured in dry nitrogen at 400° C for 45 min. Final thickness ranged between 3.3 and 6.6 μm. To permit rapid equilibration of moisture between the film and ambient, the upper electrode is patterned into multiple 25 μm stripes with 5 μ spaces for a total area of 5.1 cm². After a bake-out at 120° C under dry air and subsequent equilibration in a dry ambient at the test temperature, a voltage step is applied to the sample and the current versus time is recorded for 16,000 sec (the charging current). The sample is then shorted, and the discharging current is recorded. Below 100° C, both charging and discharging currents are dominated by a reversible polarization that follows a power law (approximately t^−0.8). Isochronal plots of the polarization current reveal a linear dependence on the applied voltage for fields in the range 10⁴–10⁵ V/cm. The polarization current is nearly independent of temperature and is well modeled by the Lewis molecular dipole theory of polarization. Above 150° C, the current is increasingly dominated by a relatively constant transport current, defined as the difference between charging and discharging currents. This current is ohmic over the field range examined, and shows a complex, activated temperature dependence. For PMDA-ODA the transport current has an activation energy (E _a ) of 0.5 eV below 175° C and 1.5 eV above that temperature. For BTDA-ODA/MPDA the E_a is 0.6 up to 250° C and 2.1 eV above. This corresponds to a resistivity of 9 × 10¹⁸ Ω-@#@ cm at 23° C and 3.5 × 10¹⁴ Ω-cm at 200° C for PMDA-ODA and 5 × 10¹⁹ Ω-cm at 23° C and 5.6 × 10¹³ Ω-cm at 300° C for BTDA-ODA/MPDA. This work demonstrates that the low temperature behavior of polyimide cannot be extrapolated from high temperature measurements. Work sponsored in part by E. I. DuPont de Nemours & Co., Inc.     

Laser-induced damage in deuterated potassium dihydrogen phosphate

Laser-induced pinpoint bulk damage of deuterated potassium dihydrogen phosphate at 351 nm is shown to depend on the propagation direction relative to the crystallographic axes and on growth temperature in addition to the previously reported dependence on continuous filtration. Pulse-length scaling is also consistent with earlier reports. The leading hypothesis for the cause of pinpoint damage is absorbing nanoparticle impurities, and our results are consistent with but not conclusive for that model. Advances in technology have led to greatly improved damage resistance.