A laser (Light Amplification by Stimulated Emission of Radiation) is a light source that generates highly coherent, directional, and monochromatic electromagnetic radiation. Unlike conventional light sources, laser light can be concentrated into a very small area, enabling extremely high energy and power densities.

The unique characteristics of laser light make it possible to precisely control the interaction between light and matter. By adjusting parameters such as (i) wavelength, (ii) pulse duration, (iii) pulse energy, (iv) repetition rate, and (v) beam size, laser irradiation can induce a wide range of physical and chemical phenomena in materials.

When a laser beam is focused using an optical lens, the beam diameter decreases and the optical energy is concentrated into a small focal spot. As a result, the laser intensity increases dramatically at the focal region.

Depending on the laser intensity and material properties, different light–matter interactions can occur:

"Laser irradiation → Energy absorption → Excitation → Heating → Melting / Vaporization / Plasma formation"

At relatively low intensities, the absorbed laser energy primarily causes thermal heating, which can lead to melting, phase transformation, or structural modification.

As the laser intensity increases, the material can undergo rapid vaporization and ionization, resulting in the formation of a plasma plume. At sufficiently high intensities, nonlinear optical processes such as multiphoton absorption can also become important, particularly when using ultrashort laser pulses.

The interaction between a focused laser beam and a material is governed by the balance between energy deposition, heat transfer, material removal, and plasma dynamics. Therefore, controlling the laser parameters provides a powerful way to engineer material surfaces and structures across multiple length scales.

In particular, ultrafast lasers, with pulse durations ranging from picoseconds to femtoseconds, can deposit energy into a material on timescales shorter than or comparable to characteristic energy-transfer processes. This enables highly localized and precise material processing with reduced thermal diffusion.

"Laser → Focused Energy → Light–Matter Interaction → Material Transformation"

This fundamental principle forms the basis of many laser-based technologies, including surface texturing, micromachining, laser-induced graphene, ablation, thin-film processing, additive manufacturing, and advanced materials synthesis.

Konkuk University, Seoul Campus

Department of Mechanical Engineering

Laser & Energy Transport Laboratory

Engineering Building (Office), #A1317

New Engineering Building (Laboratory), #404