The behaviour of sapphire under intense two-colour excitation by picosecond laser

Ultrashort pulse lasers are evidencing their benefits in the processing of transparent materials. Sapphire is one of the most attractive engineering materials today. It is hard and, therefore, difficult to machine mechanically to the required shape. Laser dicing is one of the promising techniques for sapphire separation. Two-pulse two-colour irradiation was applied to initiate free-shape cutting of the material. Two collinear laser beams with wavelengths of 1064 and 355 nm, pulse duration of 10 ps and inter-pulse delay of 0.1 ns were combined to induce intra-volume modifications (directional cracks) in sapphire for wafer separation. The photon energy of both beams is well below the band gap, and various channels of the multi-photon excitation were involved in the process. Significant enhancement in the modification area was experimentally observed when intensities of focused infrared and ultraviolet beams were within narrow ranges. We discuss the resonant laser–sapphire interaction mechanisms, leading to up to four times higher excitation of the material involving multiple photons and energetic levels of intrinsic defects in the band-gap. The energy level schemes of colour centres involved in two-step multi-photon absorption in sapphire under intensive laser irradiation have been prepared.

Nanoscale optical pulse limiter enabled by refractory metallic quantum wells

The past several decades have witnessed rapid development of high-intensity, ultrashort pulse lasers, enabling deeper laboratory investigation of nonlinear optics, plasma physics, and quantum science and technology than previously possible. Naturally, with their increasing use, the risk of accidental damage to optical detection systems rises commensurately. Thus, various optical limiting mechanisms and devices have been proposed. However, restricted by the weak optical nonlinearity of natural materials, state-of-the-art optical limiters rely on bulk liquid or solid media, operating in the transmission mode. Device miniaturization becomes complicated with these designs while maintaining superior integrability and controllability. Here, we demonstrate a reflection-mode pulse limiter (sub–100 nm) using nanoscale refractory films made of Al2O3/TiN/Al2O3 metallic quantum wells (MQWs), which provide large and ultrafast Kerr-type optical nonlinearities due to the quantum size effect of the MQW. Functional multilayers consisting of these MQWs could find important applications in nanophotonics, nonlinear optics, and meta-optics.

Formation of Oxide Layers with Femtosecond Laser on Steel Surfaces for Color Marking

With the appearance of ultrashort pulse lasers, the researchers have begun working on various laser marking technology. Atmospheric heating and ablation of a surface induce laser coloration of metal surfaces. However, their application is still problematic today in the industry. With the appearance of femtosecond pulse lasers, a new concept became available for color marking. This concept is based on the formation of laser-induced periodic surface structures (LIPSS) on metal surfaces. The purpose of this article is to summarize the literature of laser color marking with ultrashort pulse lasers.

Implementation of a phase plate for the generation of homogeneous focal-spot intensity distributions at the high-energy short-pulse laser facility PHELIX

We propose and demonstrate the use of random phase plates (RPPs) for high-energy sub-picosecond lasers. Contrarily to previous work related to nanosecond lasers, an RPP poses technical challenges with ultrashort-pulse lasers. Here, we implement the RPP near the beginning of the amplifier and image-relay it throughout the laser amplifier. With this, we obtain a uniform intensity distribution in the focus over an area 1600 times the diffraction limit. This method shows no significant drawbacks for the laser and it has been implemented at the PHELIX laser facility where it is now available for users.

Ultrafast laser pulse (115 fs) generation by using direct bandgap ultrasmall 2D GaTe quantum dots

Mode-locked ultrashort-pulse lasers are obtained by using direct bandgap GaTe quantum dots as a new saturable absorber. The pulse duration obtained is 115 fs.