Intersubband absorption energy shifts in 3-level system for asymmetric quantum well terahertz emitters

Intersubband absorption energy shifts in 3-level system stemming from depolarization and excitonlike effects are investigated. Analytically, the expressions we derive present good explanations to the conventional 2-level results and bare potential transition energy results; and numerical results show that they are more exact than the previous studies to describe the 3-level system depolarization and excitonlike shift (DES) character especially for higher carrier density (more than 8 x 10(11) cm(-2)). One interesting detail we find is that the "large blue" DES becomes "slight redshift" in the low doping limit (less than 1.9 x 10(11) cm(-2)), which may be neglected by the previous studies of intersubband transitions. Temperature character of DES in the step well structure is also numerically studied. Finally the above are applied to calculate asymmetric step quantum well structures. The two main functional aspects of terahertz (THz) emitters are discussed and several basic optimizing conditions are considered. By adjusting the well geometry parameters and material composition systematically, some optimized structures which satisfy all of the six conditions are recommended in tables. These optimizations may provide useful references to the design of 3-level-based optically pumping THz emitters.

Blue-shift photoluminescence from porous InAlAs

A porous InAlAs structure was first obtained by electrochemical etching. Nano-pore arrays were formed when the In0.52Al0.48As membrane was anodized at constant voltages in an HF aqueous solution. These self-assembled structures showed evident blue-shift photoluminescence emissions. While a quantum size effect alone underestimates the blue-shift energy for a sample with a relatively large average pore wall thickness, a novel effect caused by the asymmetric etching is proposed to account for this phenomenon. The results inferred from the x-ray double crystal diffraction are in good agreement with the experimental data.

Selecting ionization path by dynamic stark shift with strong laser pulse

Multiphoton ionization of NO via intermediate Rydberg states with ultra-short laser pulses is investigated with time-resolved photoelectron spectroscopy in combination with fermosecond pump-probe technology. The Rydberg states of NO, which are characterized by obvious ac-Stark shift in ultra-strong laser field, can be tuned in resonance to ionize NO molecule at one's will with identical laser pulses, i.e., one can 'select' resonance path to ionization. The results shown in this Letter demonstrate that the states holding notable dynamic Stark shift provide us another dimension to chemical control with strong laser field. (C) 2003 Elsevier Science B.V. All rights reserved.