Lasing from Semiconductor Quantum Rods in a Cylindrical Microcavity

For transient ellipsometry, the sample is placed between crossed polarizers at an angle of 54 between the sample normal and the laser beam. A laser diode at a wavelength k = 905 nm is employed and the residual birefringence of the sam- ple is compensated by a crystal compensator. The transmission through the el- lipsometry setup is measured in response to a step function of the electric field applied to the sample with a rise time of ~100 ls. The two-wave mixing is measured in a standard geometry (29) with the two beams having external angles of 30 and 60 to the sample normal and beam ra- tio 1:1. The laser source is a Kr ion laser at a wavelength of 647 nm. The time transients are measured by opening a shutter for both beams with a switching time of about 150 ls. After the measurements, the gratings are erased by a larg- er, non-Bragg matched erasing beam. In the beam fanning experiments, the same setup as in the two-wave mixing is used except only one beam is present. The angle of the beam to the sample normal is 60 and the applied electric field is inverted compared to two-wave mixing to enhance the fanning. Additionally, an aperture is placed in the beam path 50 cm behind the sample, which clips only 5 % of the unperturbed beam.