# Digital Holography Using Harmonic Generation from Solids for Reconstruction of Subwavelength Nanostructures

## TL;DR

This paper introduces a new method combining digital holography and harmonic generation to reconstruct nanostructures with high precision.

## Contribution

The novel approach combines digital holography with solid-state harmonic generation for subwavelength nanostructure reconstruction.

## Key findings

- The method can distinguish silicon gratings with sub-400 nm pitch and nanometer-scale critical dimension changes.
- The technique is applicable to all high-harmonic-emitting materials and can achieve higher resolution with higher-order harmonics.

## Abstract

Digital holographic
microscopy (DHM) is a successful technique
frequently used to assess the phase in imaging experiments. Combining
DHM with nonlinear generation opens the possibility of measuring phases
in nonlinear processes such as high-harmonic generation and characterizing
nanostructures with an increased sensitivity. In this paper, we demonstrate
that the combination of DHM and harmonic generation from solids can
be used to reliably perform 3D reconstructions of samples and also
investigate structural parameters of subwavelength periodic structures
with improved accuracy. We were able to discriminate gratings etched
in silicon, with only a few tens of nanometers change in critical
dimension, down to a pitch of 400 nm, which is well below the wavelength
of the near-infrared (NIR) probing laser source. This technique can
in principle be used with all high-harmonic-emitting materials and
is expected to reach even larger gains in resolution by probing higher-order
harmonics. These results pave the way for sensing of subwavelength
structures via nonlinear light generation, for instance, in the semiconductor
industry.