Supporting evidence of the unusual insulating behavior in the low-temperature normal-state resistivity of underdoped La2−xSrxCuO4

Low-temperature anisotropic normal-state resistivity is measured in La_2–xSr_xCuO₄ single crystals by suppressing the superconductivity with a 61-T pulsed magnetic field. The logarithmic temperature dependence of both ab and c first reported in Phys. Rev. Lett.75, 4662 (1995) is observed in a much cleaner x=0.08 sample, as well as in samples with x=0.15 which is near optimum doping, but slighly underdoped. This extension of the original observation suggests that the unusual insulating behavior is a generic property of the low-temperature normal-state of underdoped La_2–xSr_xCuO₄ once superconductivity is suppressed.     

Ultrashort laser: Lasing in MBE GaAs layer with perpendicular-to-film optical excitation and emission

Lasing was observed in a 4.5 μm thick GaAs MBE-grown heterostructure (0.2 μm Al0.42Ga0.58As, 4.1 μm GaAs, 0.21 μm AlGaAs). The laser was driven by pulses from a mode-locked Ar laser (514.5 nm) with a maximum of 20 W peak power in 100 ps long pulses focused to 25 μm. The lasing occured along the pump axis within a cavity defined by the coated AlGaAs surfaces.     

Inexpensive, pulsed, tunable ir dye laser pumped by a flashlamp-driven dye laser

A flashlamp-driven dye laser with a 250-ns, 10-mrad divergence, 2-mm-diam beam at 620 nm is used to pump an ir dye laser. The ir laser pulses are tunable from 700 to 900 nm with spectral widths of less than 1 A. Peak ir powers of 100 W have been obtained with a 5-k W pump power.