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.
Laser beam shaping is a widely used technique in many application areas, such as material processing, lithography, optical data storage, and medical procedures. In most cases a laser beam shaping system consists of conventional lenses with curved surfaces. However these lenses are bulky and their fabrication precisions are limited. In this work, we design and fabricate a lens for laser beam shaping using nanostructures. The lens is designed with traditional geometrical optical methods, using energy conservation and optical coordinate transformation algorithms. But instead of using curved surfaces to implement the lens design, we realize the designs with dielectric nanostructures. The lens is then fabricated using electron beam lithography to achieve a high precision. The fabricated lens has very low profile and is capable of fine tuning laser beams. The lens is then experimentally tested. In the experimental setup a laser beam is directed into a multimode fiber and the irradiance of the output beam irradiance profile is measured. Then the lens is placed in front of the multimode fiber and the outcome beam irradiance profile is measured again to test the effects of our laser beam shaping lens.
High power fiber lasers are proposed to be a better candidate than conventional solid-state lasers for industries such
as precision engineering since they are more compact and easier to operate. However, the beam quality generally
degrades when one scales up the output power of the fiber laser.
One can improve the output beam quality by altering the phase of the laser beam at the exit surface, and a promising
method to do so is by integrating specially designed nano-structures at the laser facets. In fact, this method was recently
demonstrated – by integrating gold concentric ring grating structures to the facet of a quantum cascade laser, one
observes significant improvement in the beam quality. Nevertheless, to improve the beam quality of high power fiber
lasers using the method mentioned above, the material of the nano-structures must be able to withstand high laser fluence
in the range of J/cm<sup>2</sup>.
In this work, we investigated the laser-induced damage threshold (LIDT) values of a suitable material for high
intensity fiber laser applications. Consequently, we demonstrated that the shortlisted material and the fabricated nanostructures
can withstand laser fluence exceeding 1.0 J/cm<sup>2</sup>.