Fast Acoustic Light Sculpting for On‐Demand Maskless Lithography

Abstract

Light interference is the primary enabler of a number of optical maskless techniques for the large‐scale processing of materials at the nanoscale. However, methods controlling interference phenomena can be limited in speed, ease of implementation, or the selection of pattern designs. Here, an optofluidic system that employs acoustic standing waves in a liquid to produce complex interference patterns at sub‐microsecond temporal resolution, faster than the pulse‐to‐pulse period of many commercial laser systems, is presented. By controlling the frequency of the acoustic waves and the motion of a translation stage, additive and subtractive direct‐writing of tailored patterns over cm 2 areas with sub‐wavelength uniformity in periodicity and scalable spatial resolution, down to the nanometric range, are demonstrated. Such on‐the‐fly dynamic control of light enhances throughput and design flexibility of optical maskless lithography, helping to expand its application portfolio to areas as important as plasmonics, electronics, or metamaterials.

Dynamic Multifocus Laser Writing with Acousto‐Optofluidics

“…In this case, there is an inherent transition time until the acoustic standing wave reaches a new steady‐state. For water, it has been measured to be about 600 ms, which corresponds to a frequency of ≈1.7 kHz . While lower than before, this speed it is still significantly higher than most state‐of‐the‐art active multifocus generators.…”

Acoustically-shaped laser: a machining tool for Industry 4.0

“…The application of sinusoidal signals to the piezoelectric pair generates vibrations in the liquid. Propagation of these acoustic waves along the X-and Y-axes can be described by solving the damped acoustic wave equation with appropriate boundary conditions [33], [34]. On resonance, standing acoustic and, hence, density waves are present in the cavity at resonant frequencies given by the following equation:…”

“…To shed light on this point, we must first determine how the stationary acoustic waves alter the refractive index of the liquid. On resonance, the induced vibrations cause a periodic modulation of the density of the liquid, which, according to the Lorentz-Lorenz model, translates into a periodic refractive index that can be calculated with [33]:…”

“…where 0 is the static refractive index of the liquid and Δn the peak of the induced variations. The latter depends on both the amplitude and frequency of the driving signals [32], [33]. Based on Equation 2, we can anticipate that the cavity behaves as an oscillating periodic grating capable of diffracting the incident light.…”

“…We recently proved that rapid (in the sub-microsecond timescale) both-beam parallelisation (up to 35 beams) and the generation of complex and tuneable light patterns can be achieved through the interaction of laser and acoustic waves in a liquid [32], [33]. Our technology, acousto-optofluidics (AOF), enables high-throughput material processing without suffering from the problems (damage, pixellation, and speed) of conventional methods.…”