# Multi-photon lithography

Written by Grant England AP225, Fall 2011

## Introduction

Wikipedia stub: [1]

Diagram of fundamentals of multiphoton lithography (Maruo, S. and Fourkas, J. (2008), Recent progress in multiphoton microfabrication. Laser & Photonics Reviews, 2: 100–111. doi: 10.1002/lpor.200710039)

Multiphoton lithography involves any process which requires more than one photon for photochemical activation. Since the reaction (usually photopolymerization requires more than one photon to be present in the same location in order for it to occur, the probability of this occurring is only large enough near the focal point of a scanning laser beam which is used to three-dimensionally write the material. Also, for this to happen at an arbitrary volume in the photoresist, the material must be optically transparent to the laser light used for illumination. The schematic on the right shows the principles of multiphoton lithography where the material is transparent at $f=\nu$, but absorbing at $f=\frac{\nu}{2}$.

## Large Area Patterning Using Multiphoton Lithography

Methods for large area patterning using multiphoton lithography have been developed by using conformal phase masks [2], but these are currently limited to periodic structures such as 3D Photonic crystals, and cannot produce structures with arbitrary geometries, such as those shown in the figure.

Example structures which can be created using multiphoton lithography (Maruo, S. and Fourkas, J. (2008), Recent progress in multiphoton microfabrication. Laser & Photonics Reviews, 2: 100–111. doi: 10.1002/lpor.200710039)