We present an overview of the different processes that can result from focusing an ultrafast laser light in the femtosecond–nanosecond time regime on a host of materials, e.g., metals, semiconductors, and insulators. We summarize the physical processes and surface and bulk applications and highlight how femtosecond lasers can be used to process various materials. Throughout this paper, we will show the advantages and disadvantages of using ultrafast lasers compared with lasers that operate in other regimes and demonstrate their potential for the ultrafast processing of materials and structures.

Ultrafast laser processing of materials: a review

Scale-up criteria of laser ablation in the liquid phase with nanosecond pulses is studied for efficient generation of pure ceramic nanoparticles in an aqueous environment. Besides high laser fluence and low height of the applied liquid layer, specific pulse overlap and defined laser repetition rate are required for significant enhancement in nanoparticle productivity. The ablation rate increases by 350% by reducing the liquid film from 8 mm to 2.5 mm owing to reduced absorption and scattering of the incident laser beam by previously ablated nanoparticles. The controlled interpulse distance yields a further increase in material removal rate by another 300% compared to machining in the pulse overlap mode. The residual cavitation bubble from the previous laser pulse and the dispersed nanoparticle interaction with the following laser pulse and optimized temperature gradient in the lattice of the target are assumed to alter productivity. This hypothesis is confirmed by varying the repetition rate with equal la...

Gram Scale Synthesis of Pure Ceramic Nanoparticles by Laser Ablation in Liquid

Laser Beam MicroMachining (LBMM) – A review

The defects and subsurface damages induced by crystal growth and micro/nano-machining have a significant impact on the functional performance of machined products. Raman spectroscopy is an efficient, powerful, and non-destructive testing method to characterize these defects and subsurface damages. This paper aims to review the fundamentals and applications of Raman spectroscopy on the characterization of defects and subsurface damages in micro/nano-machining. Firstly, the principle and several critical parameters (such as penetration depth, laser spot size, and so on) involved in the Raman characterization are introduced. Then, the mechanism of Raman spectroscopy for detection of defects and subsurface damages is discussed. The Raman spectroscopy characterization of semiconductor materials’ stacking faults, phase transformation, and residual stress in micro/nano-machining is discussed in detail. Identification and characterization of phase transformation and stacking faults for Si and SiC is feasible using the information of new Raman bands. Based on the Raman band position shift and Raman intensity ratio, Raman spectroscopy can be used to quantitatively calculate the residual stress and the thickness of the subsurface damage layer of semiconductor materials. The Tip-Enhanced Raman Spectroscopy (TERS) technique is helpful to dramatically enhance the Raman scattering signal at weak damages and it is considered as a promising research field.

Bryan S. Irwin

Papers

Femtosecond versus nanosecond laser machining: comparison of induced stresses and structural changes in silicon wafers