Carbon fiber reinforced polymer (CFRP) composites are increasingly used in aerospace applications due to its superior mechanical properties and reduced weight. Adhesive bonding is commonly used to join the composite parts since it is capable of joining incompatible or dissimilar components. However, insufficient adhesive or contamination in the adhesive bonds might occur and pose as threats to the integrity of the plane during service. It is thus important to look for suitable nondestructive testing (NDT) techniques to detect and characterize the sub-surface defects within the CFRP composites. Some of the common NDT techniques include ultrasonic techniques and thermography. In this work, we report the use of the abovementioned techniques for improved interpretation of the results.
Theoretical and experimental investigation of 980nm quantum well ridge waveguide lasers suitable for pumping Er<SUP>3+</SUP> doped fiber amplifiers are carried out. The valence hole subbands, the TE and TM mode optical gains, and the radiative current density of the In<SUB>0.2</SUB>Ga<SUB>0.8</SUB>As/GaAs/GaAs strained quantum well lasing at 980 nm have been investigated using a 6 by 6 Hamiltonian model. A very low threshold current density is predicted. These theoretical results would be useful for the design and further performance improvements of the ternary InGaAs and quaternary InAlGaAs strained QW laser diodes. Mesa, stripe geometry and ridge waveguide three quantum wells lasers have fabricated from a graded index separate confinement heterostructure grown by molecule beam epitaxy. For a 4 micrometers wide and 1000micrometers long ridge waveguide laser, a cw threshold current of 12.5mA, the threshold current density of 313A/cm<SUP>2</SUP>, an external quantum efficiency of 0.31mW/mA and power slope efficiency of 0.37mW/mA per facet were obtained.
A series of theoretical investigations of the quaternary InAlGaAs material system are carried out. The electronic band structures, the density-of-states, the optical gain spectra and the radiative current density have been investigated based on the Hamiltonian derived using the k.p method. We investigated the dependence of the optical gain and transparent current density on the well width, barrier height, and strain using a numerical approach with high accuracy. By varying the well width, mole fraction in the well material and the Al mole fraction in the barrier the effects of quantum confinement and compressive strain are examined. Furthermore, we demonstrate that a reduction of the well width offers improved modal gain over all radiative current densities. Two different material systems, InAlGaAs on InP and GaAs substrates, strained and unstrained, are examined, respectively. Our results suggest that a suitable combination of well width and barrier height should be selected in improving the TE mode optical gain in InAlGaAs single QW. A very low transparent threshold current density 35 A/cm<SUP>2</SUP> of (formula available in paper) strained quantum well laser is predicted. These theoretical results would be useful for design and further performance improvement of the quaternary InAlGaAs strained QW laser diodes.