Wavefront shaping: A versatile tool to conquer multiple scattering in multidisciplinary fields

Optical techniques offer a wide variety of applications as light-matter interactions provide extremely sensitive mechanisms to probe or treat target media.Most of these implementations rely on the usage of ballistic or quasi-ballistic photons to achieve high spatial resolution.However,the inherent scattering nature of light in biological tissues or tissue-like scattering media constitutes a critical obstacle that has restricted the penetration depth of non-scattered photons and hence limited the implementation of most optical techniques for wider applications.In addition,the components of an optical system are usually designed and manufactured for a fixed function or performance.Recent advances in wavefront shaping have demonstrated that scattering-or component-induced phase distortions can be compensated by optimizing the wavefront of the input light pattern through iteration or by conjugating the transmission matrix of the scattering medium.

Real-time porosity reduction during metal directed energy deposition using a pulse laser

Porosity is a challenging issue in additive manufacturing and is detrimental to the quality of the additively manufactured products.In this study,a real-time porosity reduction technique was developed by incorporating a pulse laser into a laser metal powder directed energy deposition(DED)system.The incorporated pulse laser can accelerate fluid flow within the melt pool and facilitate the escape of pores before complete solidification.It achieves this real-time porosity reduction by inducing accelerated and turbulent Marangoni flow,ultrasonic waves,and shock waves into the melt pool.The uniqueness and advantages of the proposed technique include the following:(1)For a laser metal powder DED process,this study proposed a noncontact,nondestructive,and real-time porosity reduction technique at the melt pool level.(2)It was experimentally and numerically validated that the developed technique did not alter the geometry and the grain structure of the manufactured Ti-6Al-4V samples.(3)Because the porosity reduction is accomplished at the melt pool level,its application is not limited by the size,shape,or complexity of the printing target.(4)The developed technique can be readily incorporated into the existing DED systems without any modification of the original tool-path design.The experimental results showed that the pore volume fraction decreased from 0.132%to 0.005%,no pores larger than 6×10^(4)μm^(3) were observed,and a 91%reduction in the total pore number was achieved when the pulse laser energy reached 11.5 mJ.