Volume 91, Issue 1, 01 January 2002
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Coherent response of a biased double-well superlattice subjected to an ultrashort interband excitation91(2002); http://dx.doi.org/10.1063/1.1421043View Description Hide Description
The temporal evolution of electrons in a biased double-well superlattice, subjected to an ultrashort interband excitation, is theoretically examined. Both the temporal oscillations of the induced current and the evolution of the photoexcitedelectron concentration are considered for different parameters of the structure subjected to a δ-pulse excitation. Due to the mixing of the Wannier–Stark-ladder branches, the induced response depends on the applied bias voltage in a complicated way. In particular, long-time beats appear in the vicinities of intra- and inter-cell anti-crossings of the energy spectrum. These dependencies are examined within the framework of the Kane model, invoking the parabolic approximation for electron and heavy hole states. Numerical calculations of the carrier coherent dynamics are performed for the case of a δ-pulse excitation and with a phenomenologically introduced damping factor.
91(2002); http://dx.doi.org/10.1063/1.1419266View Description Hide Description
We have investigated the effects of gamma-rayirradiation on the optical properties of visible strained multi-quantum-well lasers. It was observed that the power emission from the laser fell progressively and the wavelength linewidth increased with increase of irradiation. The laser emission properties recovered as the duration of the subsequent dc current increased. The far-field beam emission divergence was reduced after irradiation. We propose that these irradiationeffects may be caused by structural changes in the strained thin layers, due to an atomic displacement and migration between layers and due to changes in the degree of strain. This affects the layer’s atomic composition, which changes the band-gaps’ energy levels and the indexes of refraction, and as a result, the carrier and optical confinements, respectively.
Cr:Er:Tm:Ho:yttrium aluminum garnet laser exhibiting dual wavelength lasing at 2.1 and 2.9 μm: Spectroscopy and laser performance91(2002); http://dx.doi.org/10.1063/1.1419211View Description Hide Description
Over 1.0 J of 2.1 μm laser energy and over 0.5 J of 2.9 μm laser energy have been demonstrated in a single flashlamp pumped solid state laser material, specifically Cr:Er:Tm:Ho:YAG. Flashlamp pumped laser operation of Ho:YAG at 2.1 μm and Er:YAG at 2.9 μm in various host materials is well known. We have developed an innovative laser system that operates at each of these wavelengths independently or simultaneously in a single solid state laser material with performance comparable to single wavelength systems Er:YAG and Cr:Tm:Ho:YAG. Variation of the flashlamp pump pulse length provides a method to discriminate between lasing at 2.1 and 2.9 μm. This effect results from energy transfer, the short lifetime of the upper lasing manifold in Er, the manifold, and the relatively long upper laser level lifetime in Ho, the manifold. This simple tuning method of achieving two widely separated wavelengths without the use of optical tuning elements has potential applications in remote sensing and medical lasers.
91(2002); http://dx.doi.org/10.1063/1.1423397View Description Hide Description
The ultrafast time dependence of the energy absorption of covalent solids upon excitation with femtosecond laser pulses is theoretically analyzed. We use a microscopic theory to describe laser induced structural changes and their influence on the electronic properties. We show that from the time evolution of the energy absorbed by the system important information on the electronic and atomic structure during ultrafast phase transitions can be gained. Our results reflect how structural changes affect the capability of the system to absorb external energy.