Acquisition of Multi-Modal Images of Structural Modifications in Glass with Programmable LED-Array-Based Illumination

Ryo Sugimoto,Wataru Watanabe,Ryoji Maruyama

doi:10.3390/app9061136

Abstract

Ultrashort laser pulses can induce structural modifications in bulk glass, leading to refractive index change and scattering damage. As bright-field, dark-field, and phase imaging each provide complementary information about laser-induced structures, it is often desired to use multiple observations simultaneously. As described herein, we present the acquisition of bright-field, dark-field, and differential phase-contrast images of structural modifications induced in glass by femtosecond laser pulses with an LED array microscope. The contrast of refractive index change can be enhanced by differential phase-contrast images. We also report on the simultaneous acquisition of bright-field and dark-field images of structural modifications in a glass with LED-array-based Rheinberg illumination. A single-shot color image is separated to obtain bright field and dark field images simultaneously. We provide an experimental demonstration on multi-modal imaging of structural modifications in a glass with an LED array microscope using temporally-coded illumination and color-coded illumination.

Highlights

In the 1990s, Davis et al demonstrated that femtosecond laser pulses are useful to induce refractive index change within bulk glasses [1]
From the bright field image, the dark field image, and the differential phase-contrast (DPC) images, structural changes in the glass were observed field image, the dark field image, and the DPC images, structural changes in the glass were observed by changing the illumination pattern of the LED array
Structural change induced inside BK7 glass using a femtosecond laser was observed using the LED array microscope

Summary

Introduction

In the 1990s, Davis et al demonstrated that femtosecond laser pulses are useful to induce refractive index change within bulk glasses [1]. For applications to femtosecond laser micromachining, investigation of the morphology and discrimination of structural changes is important [11]. Researchers check their written structures with optical microscopes under different illumination configurations in a daily and routine manner. In dark-field imaging, an aperture stop is placed at the condenser diaphragm to ensure that the illumination NA is larger than the collection NA. Conventional optical microscopy such as phase-contrast microscopy and differential interference contrast (DIC) microscopy can enhance contrast in refractive index change. Phase-contrast microscopy is useful for the observation of refractive index change in the glass to enhance the

Methods

Results

Conclusion